measurement - · pdf filemeasurement measurement of length length can be measured by, ......

Measurement

Measurement of length

Length can be measured by,

A metre stick (straight lines)

An opisometer (small curved lines)

A trundle wheel (large curved lines)

A vernier callipers (diameters and small

widths)

Length is measured in mm, cm, m, km.

Experiment: To measure the length of a curved

line

Roll the wheel of an opisometer back to

the pointer.

Place the pointer at the start of the

line.

Roll it carefully along the line, to the

end.

Now place the pointer on the zero of a

metre stick and roll it backwards until

the wheel stops at the pointer.

The reading on the metre stick is the

length of the line.

Measurement of area;Area is how much ground

something covers. Area is measured in area

mm2, cm2, m2, km2.

Experiment: To find the area of your hand

Place your hand, fingers together,

on squared paper.

Draw its outline on the page.

Count all of the squares which are completely inside or more than ½ inside the outline of your hand.

Discount any squares which are less than ½ inside the outline of your hand.

Multiply this number by the area of

one square. This is the area of your

hand.

Measurement of volume;Volume is the amount

of space occupied by an object. Volume is

measured in mm3, cm3, m3.

Experiment: To measure the volume of a regular

rectangular block

Measure the length, width and

height of the block.

Multiply the measurements together.

Experiment: To find the volume of an irregular

object (a stone)

Method 1

Add water to a graduated cylinder as

shown.

Gently slide in the stone.

The water level rises by 25 cm3.

The volume of the stone is 25 cm3.

Method 2

Fill the overflow can to the point of

overflowing.

Lower the stone gently into the

water (use a thread).

The stone will displace its own volume of water.

The water which collects in the

graduated cylinder is the volume of

the stone.

Density

The mass of an object is the amount of

matter in it.

The density of an object is the mass of

1cm3 of it. The unit of density is

g/cm3 (grams per cm3).

)volume(cm

mass(g)Density

3

Mandatory experiment: To find the density of a

regular rectangular block

Find the mass of the block with an

electronic balance.

Find the volume by multiplying

l x b x h.

)volume(cm

mass(g)Density

3

Mandatory experiment: To density of an

irregular shaped object, such as a stone.

Find the mass of the stone with an

electronic balance.

Find the volume with an overflow can or

graduated cylinder (see chapter 37).

)volume(cm

mass(g)Density

3

Mandatory experiment: To find the density of a

liquid (water)

Find the volume of the water by

reading the side of the graduated

cylinder.

To find the mass of the water make

two measurements, (i) Get the mass

of the graduated cylinder. (ii) Get

the mass of the graduated cylinder

and the water.

)volume(cm

mass(g)Density

3

Flotation - an object will float in water if its

density is less than that of water (1 g/cm3) and

will sink if its density is greater than the density

of water.

Over flow can

Graduated

cylinder

Before After

65

cm3 40

cm3

Stone

10.5g

Block

10.5g

10.5g

peed, Velocity and Acceleration 1. Speed is the distance travelled by an object

per unit time. This can be written

mathematically as,

taken Time

travelled DistanceSpeed

Example: If a man walks 4 km in 1 hour,

what is his average speed, in m/s?

Answer:

1.11m/s3600s

4000mSpeed

To use the speed formula, it is sometimes

useful to consider the triangle below.

If you want to ‘find the distance travelled’, cover the ‘D’ and the answer is S x T.

Speed, Velocity and Acceleration

. Speed is the distance travelled by

an object per unit time. This

If you want to ‘find the time taken’ for a journey, cover ‘T’ and the

answer is D/T.

2. Velocity is the speed in a given direction.

30 km/hr would be the speed of a car.

30 km/hr due south would be its velocity.

3. Acceleration is the change in velocity per

second. This can be written mathematically as,

taken Time

velocity in ChangeonAccelerati

Example: The velocity of a car changes from 30

km/hr to 60 km/hr in 5 seconds, what is its

acceleration?

Answer:

6km/hr/s5

30

5

3060onAccelerati

Pressure The pressure exerted by an object is the force (in

Newtons) which it exerts on 1m2.

Mathematically, this maybe written as:

(Pa)] Pascal[unit Area

ForcePressure

The connection between pressure and force

If you press down on the flat

end of a thumb-tack with your finger, applying a

certain force, you will experience no discomfort.

If, however, you press, on the same thumb-tack,

at the pointed end, with the same force as before

you will feel considerable pain.

Why does the same force, applied to the same

object, have such different results?

The force, in the first case, is spread over a larger

area than in the second case and therefore is not

as keenly felt.

Pressure exerted by a liquid

Liquids exert pressure.

This pressure increases with depth.

The pressure in a liquid is the same

in all directions.

Atmospheric pressure

Above us we have 15 km of air pressing down

on the surface of the earth. This air, like a

liquid, exerts a pressure which is called

atmospheric pressure.

To demonstrate atmospheric pressure –

Method 1

Atmospheric pressure

Glass of water

Cardboard

Fill a glass to the rim with water.

Cover it with a cardboard.

Hold the cardboard in place and turn the

glass upside down.

The water remains in the glass and the

cardboard stays in place.

Explanation; the pressure of the

atmosphere, acting upwards, holds the

water in the glass by pressing the

cardboard upwards. This demonstrates

that atmospheric pressure acts upwards as

well as downwards.

Method 2 – The crushed can experiment

Heat a small volume of water in a tin can

until it starts to boil.

As soon as steam is seen leaving the can,

remove the heat and seal the can with a

stopper.

Allow the can to sit on a bench to cool.

As it cools, the steam in the can

condenses to water and a vacuum is

created.

The creation of this vacuum means the can

will be crushed by the atmospheric

pressure.

Measuring atmospheric pressure

The pressure of the atmosphere is measured

with a barometer. There are two main types

of barometer, a mercury barometer and an

aneroid barometer.

What can we tell from atmospheric pressure?

1. Predict the weather – high atmospheric

pressure means fine, calm, sunny

weather, with no winds. Low pressure

means unsettled, windy, wet weather.

Lines joining points on a map with similar

atmospheric pressure are called isobars.

If the isobars are close together the

winds will be strong.

2. Measure altitude (height above sea level)

– The higher you go above sea level the

lower is the atmospheric pressure. An

altimeter is a barometer which is

adapted for making measurements of

height-above-ground.

S T

D

x

Heat

Force, Work and Power

A force is anything which changes the velocity

or shape of an object. Forces are measured in

Newtons (N). There are different kinds of

forces – push, pull, friction, electric,

magnetic.

Forces always occur in pairs.

Example 1: When a balloon is released, the

air shoots out the back with a certain force

and the balloon travels in the opposite

direction with an equal but opposite force.

Example 2: When a gun is discharged, the

bullet flies in one direction and the gun

moves in the opposite direction with an equal

force.

Friction is the force which opposes the motion

between two objects in contact.

Examples of friction:

1. If you rub two pieces of sand paper

together, there will be a very large

force of friction between them.

2. The friction between rubber soles

on your shoes and the ground gives

you grip and stops you slipping.

Preventing friction

To prevent or reduce friction we put

lubricant between the two surfaces in

contact. Grease and oil are common

lubricants.

Advantages of friction

The force of fiction between your

shoes and the ground, prevent you

from slipping.

Friction helps tyres to grip the

road.

Friction generates heat when you

rub your hands together.

Disadvantages of friction

Shoes wear out.

Tyres wear out.

Machine parts wear out.

Friction burns from a rope.

Experiment: To investigate the force of friction

Set up the apparatus as shown.

Fix sand paper to the base of the

block and onto the bench surface.

Pull the block along the bench

surface with the spring balance.

Read the force applied to the block

from the side of the Newton-meter.

Repeat the experiment but use no

sand paper.

Repeat the experiment with oil

between the block and the bench.

You should find that the force

needed to move the block is greatest

for the sand paper because of the

large force of friction and smallest

for the oil.

Work is done when a force moves an object.

Work is measured in joules (J).

Work = Force (N) x Distance (m)

Example 1:

If a man uses a force of 300 N to move a wheel

barrow a distance of 100 m, what work has the

man done?

Answer;

Work = 300 N x 100 m =

30,000 J

Power is the rate at which work is done. It is

measured in J/s (joules per second), or Watts.

taken(s) Time

done(J) WorkPower

Example; A man lifts a 200 N object from the floor to

a table which is 750 cm above the ground, in 0.5

seconds. What is his power?

Answer:

Work done = (200)(0.75) = 150 J

Power = 150J/0.5s = 300 W

Mandatory experiment: To investigate Hooke’s law of

spiral springs


Measure the length of the spring and pan

before any weights are added.

Now add a weight to the pan.

Measure the extension of the spring with

the metre stick.

Repeat the procedure by adding more

weights and recording the extension each

time.

Record your results in a table, as shown.

Weight

(N)

Extensi

on (cm)

Now draw a graph of Extension versus weight placed on the spring.

The graph should look like this,

The graph is a straight line

through (0,0). This means that the extension is directly proportional to the force applied to it.

Note; When recording the force

on the spring, you multiply the

mass by 9.8 e.g. 200g (0.2kg)

should be recorded as 0.2 x 9.8 = 1.960 N.

Pull Newton-meter Block

Bench top

20 N

Weights

Pan

Spring

Metre

stick

0 0

Weight on the spring

(N)

Extension

A lever is a rigid body which is free to rotate

about a fixed point called the fulcrum.

Everyday examples of levers

The Centre of Gravity (cog) is the point

through which all of the weight of a body

appears to act. This is usually its balancing

point.

Experiment: To find the centre of gravity of an

irregular piece of cardboard

Hang the cardboard from a pin on

a stand, so that it can swing

freely.

Attach a string with a weight as

shown on the diagram below.

Draw a line behind the string to

mark its position.

Move the cardboard to a new

position and repeat the procedure.

The centre of gravity is where the

two lines cross.

Equilibrium and the stability of objects

When an object is balanced and not moving it is

said to be in equilibrium. There are three states

of equilibrium,

Stable equilibrium – An object is in stable

equilibrium if moving it raises its centre of

gravity.

Stable equilbrium

Unstable equilibrium

Neutral equilibrium

Unstable equilibrium – An object is in

unstable equilibrium if moving it lowers its

centre of gravity.

Neutral equilibrium – An object is in

neutral equilibrium if moving it has no

effect on the centre of gravity.

Objects in stable equilibrium will have a wide

base and a low centre of gravity. When designing

objects this fact must be kept in mind.

The law of the lever - When a lever is balanced the

sum of the clockwise moments* is equal to the sum of

the anti-clockwise moments.

*The moment of a force = (Force) x (perpendicular

distance from the force to the fulcrum).

Example 1: Is the metre stick below balanced?

Answer:

Left-hand side (anticlockwise) Right-hand side

moments 12 moments 12

0.3m40N 0.4m30N

DistanceForce Moment Distance Force Moments

Since the moments are equal on both sides, the lever

is balanced.

Example 2: Where on the metre stick must the

weight, 20 N, be placed if it is balanced?

Answer:

Left-hand side Right-hand side

cmm 303.0

20

6x

20x moments 6

(20N)(x) )(15N)(0.4m

DistanceForce Moment Distance Force Moments

Load

Fulcrum

LLoad

Fulcrum

Effort

Wheel barrow Weight

Pin

Centre of

gravity

? 40

cm | | | | | | | | | | | |

| | | | | | | | |

15

N

20

N

30

cm

40

cm | | | | | | | | | | |

| | | | | | | | | |

30 40

Light is a form of energy. We can say this because it can be

made to do work.

Solar cells produce electricity from sunlight.

Plants make food energy from sunlight in

photosynthesis.

Luminous objects are those which give out their own light, e.g.

the sun gives out its own light.

Non-luminous objects do not give out their own light but only

reflect light, e.g. the moon reflects light from the sun.

Mandatory experiment; To show that light travels in straight

lines.

3 Cardboards with holes screen

Line up three pieces of cardboard so that the holes in the

middle of the cardboards are in a straight line.

Turn on the ray box.

As long as the holes in the cardboards are in a straight line

light will shine on the screen.

This shows that light travels in a straight line.

Experiment : To show how shadows are formed.


The ray box emits a beam of light.

Part of the beam hits the object and is stopped.

Part of the beam hits the screen.

Where the beam is stopped, a shadow is left on the

screen, the shape of the object.

Important shadows

When the moon comes between the earth and the

sun, a shadow of the moon falls on the earth. This is

called a solar eclipse (because the sun’s light is

blocked out).

When the earth comes between the sun and the

moon, a shadow of the earth falls across the moon.

This called a lunar eclipse.

Dispersion is the name given to the splitting of white light into

its seven colours.

Example1: When sunlight passes through a shower of rain the

seven colours separate out from each other to give a rainbow

effect.

Experiment: To produce a spectrum of white light.


A beam of light hits the glass prism.

As it passes through the glass the colours in the light

are dispersed (scattered).

The screen should show a rainbow effect.

The colours of the white light are red, orange,

yellow, green, blue, indigo and violet (Richard of York

gave battle in vain).

Refraction is the bending of a light beam, from its original

pathway, as it passes from one medium into another (from air

to water or from water to air).

Experiment To show refraction of light.



When the beam hits the glass block, it passes through,

but it changes direction, and exits the block at a

different angle.

This change in direction is due to the refraction of the

light beam.

Importance of refraction

In lenses, mirages, rainbow effect, extra daylight each day.

Mandatory experiment: To show that light can be reflected.



Place a small mirror in front of the beam.

The direction of the beam will change.

The light beam has been reflected.

Important uses of reflection of light

1. Periscopes are used to see over tall objects.

2. Reflective mirrors in cars.

3. Shaving and make-up mirrors.

4. Microscopes.

5. Security mirrors.

Object

Ray box Screen

Light

beam

Prism of

glass

Screen

Ray

box

Refracted

beam

Glass block

Light

beam Ray

box

Mirror Light beam

Ray

box

Ray box

Sound is a form of energy

How do we hear sounds?

When a sound is made (hammer hitting a nail) the

air molecules start to vibrate.

These vibrations are passed from molecule to

molecule until they reach your outer ear.

The outer ear acts as a funnel and directs these

vibrations to the eardrum.

Once the eardrum starts vibrating, a signal is sent

to the brain and the sound is registered.

Experiment: To show that sound is a form of energy.

Hold the foam ball near the speaker of a stereo

system when it is playing loud music.

The ball should move because of the sound

vibrations.

If sound can move objects then it is able to do

work.

This makes it a form of energy.

How fast does it travel?

Sound travels at a speed of

340 metres per second (in air)

1400 m/s in water

5,000 m/s in concrete.

Speed of light = 300,000,000 m/s.

Question: If an observer hears the sound of thunder three

seconds after he sees the flash of lightening, how far is the

lightening from the observer?

Answer:

away. km 1.02 istrhunder The

1020m3340Distance

TimeSpeedDistanceTime

DistanceSpeed

An echo is a reflected sound.

Experiment: To show that sound needs a to travel through a medium

Start the alarm bell ringing on the clock.

Turn on the suction pump.

The air is sucked out of the bell jar.

A vacuum has been created.

The alarm bell can still be seen to be working but no

sound will be heard.

Ultrasound waves (sound of very high frequency) are used in

various instruments to locate objects or places. A machine sends

out a burst of ultrasound waves and times how long it takes for the

sound to bounce off an object and return.

In medicine, ultrasound machines are used to ‘see’ inside

the body and look at organs or even a baby in the womb.

Fishing vessels use ultrasound to locate the seabed and

shoals of fish.

Doctors use ultrasound waves to smash kidney stones so

that they can be passed without the need for surgery.

Loudness of sound

The decibel (dB ) is the unit used to compare the loudness of

sounds. Jet plane (120dB), lawnmower(80dB), talk (50dB).

Speakers Foam ball on a light string

To vacuum

Alarm

clock

Bell

Magnetism

A magnet is a metal which attracts other pieces

of metal.

Only three metals can be made into

magnets, or will be attracted by

magnets. These metals are nickel

(Ni), iron (Fe), copper (cu). In fact,

most magnets are mixtures of these

metals.

The first magnets were magnetic

rock called lodestone, used as far

back as 500 b.c.

Magnets have two poles, a north and

a south pole.

Like poles repel,Unlike poles attract.

Magentic field – is an area around a

magnet where a magnet exerts an

influence.

Experiment: To show the magnetic field of a bar

magnet (method 1)

Place a bar magnet on a bench.

Cover it with a sheet of paper.

Sprinkle iron filings over the sheet.

The filings will line up along the

magnetic field lines.

The magnetic field of the magnet

has become ‘visible’ (see diagram).

Experiment: To show the magnetic field of a bar

magnet (method 2)

Place a magnet on a sheet of paper.

Place a number of plotting compasses

near the magnet so that the pointers

follow each other as shown below.

Mark the positions of the dots with

a pen.

Mark the positions of the dots with

a pen.

Remove the plotting compasses and

join the dots to form one of the

field lines.

Repeat this procedure several times

to construct more field lines.

Experiment: To investigate the behaviour of

magnets.

Suspend a magnet from a piece of

light thread, so that it can swing

freely.

Bring another magnet close to this.

If two north poles are brought near

each other, the magnets repel.

Same result, with two south poles.

If a south pole is brought a near a

north pole, the magnets will attract.

Uses of magnets

In speakers.

Fridge doors.

Electric motors.

Earth’s magnetic field

The earth behaves like a large bar magnet,

with two poles, one at the north and one at

the south. The south pole of this imaginary

magnet is in the northern hemisphere and the

north pole is in the southern hemisphere. This

is why the north pole of all compasses point to

the north.

Storing magnets

Magnets are stored in pairs, with

opposite poles together.

Two pieces of iron are placed at

either end, as keepers. These close

the magnetic fields and so preserve

the magnetism.

A piece of cardboard is place

between the magnets as a spacer.

Static electricity

Static electricity is electric charge which is

stationary. This kind of charge usually builds

up on plastic materials and fabrics. Since

they are insulators they don’t allow electricity

to flow through them.

Static charge builds up on materials when

they are rubbed together.

Electrons are knocked off one material and

onto the other.

When a material loses electrons it becomes

positive.

When it gains electrons it becomes

negatively charged.

When polythene is rubbed with a cloth it

becomes negatively charged.

When Perspex is rubbed with a cloth it

becomes positively charged.

Earthing

When a large electric charge builds up on an

object, it must be allowed to flow into the

earth, to make the object safe for us to

touch.

The charge will discharge itself, often with

violent consequences. The most dramatic

example of this is lightening. The charge on

the thunder clouds builds up to an intolerable

level.

Eventually, it will discharge into another cloud

(sheet lightening) or into the ground (fork

lightening).

Many structures and buildings are provided

with lightening conductors to avoid damage by

lightening strikes.

Experiment: To show the presence of static

electricity.

Rub a plastic biro with a cloth. It can

pick up small pieces of paper.

Rub an inflated balloon against your

clothes. It becomes charged and will

stick to the paint on walls and to your

clothes.

Hold a charged biro near a thin

stream of water from a tap. The

water will move towards the biro

because water has tiny charges.

Sheet of paper

N

Mag

Current electricity

An electric current is a flow of electric charge.

To understand the behaviour of electricity we will look

at a simple circuit.

When the switch is closed, electricity flows from the

cell and the bulb lights. When the switch is open, as

in the diagram above, no current flows from the cell.

There are number of quantities which you must know

to talk about electrical circuits.

Voltage (symbol is V) is the pushing power of the

power supply. It is measured in volts (V).

Current (symbol is I) is the flow of electrical charge.

It is measured in amps (A).

Resistance (symbol is R) is the ability of a substance to

resist, or slow down, the flow of electricity through a

circuit.

Ohms law states that at constant temperature the

voltage (V) is always proportional to the current (I) in a

circuit i.e. V = I.R

Electrical Power = V.I

To show the heating effect of electric

current

Close the switch and allow current

to flow through the circuit for a

few minutes.

Hold a thermometer against the

bulb.

The increase in temperature

registered on the thermometer

shows that heat has been produced

in the circuit.

To show the magnetic effect of an electric

current

Set up a circuit as above with the

switch open.

Bring a compass near any part of

the circuit wiring.

Nothing happens.

Now close the switch.

The needle of the compass will be

seen to deflect.

This happens because the all

electrical circuits are magnetic

when carrying current.

To show the chemical effect of an electric

current

Set up the apparatus as shown

below.

When electric current is flowing in

the circuit the water molecules are

broken up and form hydrogen and

oxygen gases.

Hydrogen collects at the negative

electrode.

Oxygen collects at the positive

electrode and is only ½ the volume

of the hydrogen gas.

Bulbs in series

When the bulbs are connected in series,

The more bulbs which are connected

the dimmer the light given out by each

one. This is because the voltage of the

battery has to be divided amongst a

greater number of bulbs.

If you disconnect one, all the lights

will go out.

Bulbs in parallel

When bulbs are connected in parallel as

shown below,

All the bulbs will shine equally brightly

and there will be no dimming effect if

you add more bulbs. This because all

bulbs have the same voltage across

them.

If you disconnect one bulb, the

others remain lighting. For this

reason, parallel circuits are used in

lighting circuits in our homes.

Mandatory experiment: To distinguish

between conductors and insulators


Connect a variety of substances across

the wires at ‘x’.

If the bulb lights,the substance is a

conductor, if not, the substance is an

insulator.

- +

Bulb

Switch

Cell (power supply) - +

Bulb

Switch

Cell (power supply)

- +

Bulb

Cell (power supply)

x

Mandatory experiment: To verify Ohm’s Law

Set up the apparatus as shown in the

diagram.

Record the current flowing through the resistor by reading the ammeter.

Record the voltage across the coil by reading the voltmeter.

Adjust the variable resistor to give a new

voltage across the resistor.

Record this new voltage.

Record the current reading from the

ammeter.

Repeat this procedure for several different

values of voltage and current.

Make a table of your values.

Plot a graph of Voltage versus Current.

A straight line through (0,0) proves that the

voltage is proportional to the current.

If you divide V by I you should get the same

value for R each time.

Electricity in the home

There are two types of current electricity;

Alternating current (a.c.)

Changes its direction of flow, constantly.

The electrical supply to your home, provided

by the ESB, is alternating.

The supply is called a 50 Hz (50 hertz)

supply. This means that the direction of

the current changes 50 times every

second.

Direct current (d.c.)

This type of current flows in the same

direction all the time.

The power supplied by a battery is direct

current.

Advantages of alternating current over direct

current

The ESB can transport it over long

distances without losing power.

It can be converted to d.c. easily when

needed for appliances in the home.

Electricity is supplied to your home by two

cables;

The live cable (brown colour) and

The neutral (blue colour).

A third type of cable is found in household

circuits;

The earth wire (green and yellow)

which is connected to the ground via

a galvanised rod outside the house.

This is a safety cable attached to all

major circuits and to appliances with

metal bodies.

Safety measures in the home

1. Fuses

A fuse is a thin metal wire housed in a

ceramic container. In the event of a fault

developing and too large a current flowing,

the fuse wire melts preventing any major

damage or fire. When using a fuse a number

of precautions must be observed,

The fuse must be of the correct rating.

The fuse rating is the maximum

current that the fuse can carry

without melting.

The fuse must be in the live side of the

circuit for safety.

2. Earthing

An additional measure must be taken to

safeguard a user. All electrical

appliances, which have exposed metal

parts should be made safe to touch

even if a fault develops inside them.

This is achieved by earthing, i.e. by

providing a wire (green and yellow)

which connects the metal parts to a

metal plate or rod, sunk deeply in the

soil.

Some electrical appliances are

manufactured with an all-plastic outer

casing and do not require an earth

connection.

Wiring a plug

The live (brown) is connected to the

fuse on the right- hand side.

The neutral (blue) is connected to

the pin on the left-hand side.

The earth (green and yellow) is

connected to the top pin. This is also

the longest pin.

The earth pin, being the longest,

opens the holes of the socket and

only then can the other pins be

inserted. This ensures that the

earth, and safety pin, is always first

to be connected.

The units of electrical power

Electrical power is given by the following

equation:

seconds in time

joulesin done workPower

The unit of power is the watt (W).

The ESB calculates the electrical power used

by your home in kilowatt hours (kWh).

A kilowatt hour is the electrical energy used

by a 1kW appliance which has been running for

one hour.

Example;

(i) Calculate the number of units of electrical

power used by a 3 kW electrical heater over 4

hours of use.

(ii) If one unit of electrical energy costs 15c,

how much will the heater cost to run, over the

four hours?

Answer;

(i) Number of units used = (3kW)(4h)

= 12 kWh = 12 units

(ii) Cost = (12)(15) = 180c = €1.80

Example;

Calculate the cost of running a 50W television

set for 10 hours.

Answer;

Number of units used = (0.05 kW)(10)

Voltag

e

Variable

resistor

Resistor

Voltmeter Ammeter

A V

Sand

Fuse

wire

Metal

caps

Current

Mandatory experiment: To verify Ohm’s Law

Set up the apparatus as shown in the

diagram.

Record the current flowing through the resistor by reading the ammeter.

Record the voltage across the coil by reading the voltmeter.

Adjust the variable resistor to give a new

voltage across the resistor.

Record this new voltage.

Record the current reading from the

ammeter.

Repeat this procedure for several different

values of voltage and current.

Make a table of your values.

Plot a graph of Voltage versus Current.

A straight line through (0,0) proves that the

voltage is proportional to the current.

If you divide V by I you should get the same

value for R each time.

Electricity in the home

There are two types of current electricity;

Alternating current (a.c.)

Changes its direction of flow, constantly.

The electrical supply to your home, provided

by the ESB, is alternating.

The supply is called a 50 Hz (50 hertz)

supply. This means that the direction of

the current changes 50 times every

second.

Direct current (d.c.)

This type of current flows in the same

direction all the time.

The power supplied by a battery is direct

current.

Advantages of alternating current over direct

current

The ESB can transport it over long

distances without losing power.

It can be converted to d.c. easily when

needed for appliances in the home.

Electricity is supplied to your home by two

cables;

The live cable (brown colour) and

The neutral (blue colour).

A third type of cable is found in household

circuits;

The earth wire (green and yellow)

which is connected to the ground via

a galvanised rod outside the house.

This is a safety cable attached to all

major circuits and to appliances with

metal bodies.

Safety measures in the home

1. Fuses

A fuse is a thin metal wire housed in a

ceramic container. In the event of a fault

developing and too large a current flowing,

the fuse wire melts preventing any major

damage or fire. When using a fuse a number

of precautions must be observed,

The fuse must be of the correct rating.

The fuse rating is the maximum

current that the fuse can carry

without melting.

The fuse must be in the live side of the

circuit for safety.

3. Earthing

An additional measure must be taken to

safeguard a user. All electrical

appliances, which have exposed metal

parts should be made safe to touch

even if a fault develops inside them.

This is achieved by earthing, i.e. by

providing a wire (green and yellow)

which connects the metal parts to a

metal plate or rod, sunk deeply in the

soil.

Some electrical appliances are

manufactured with an all-plastic outer

casing and do not require an earth

connection.

Wiring a plug

The live (brown) is connected to the

fuse on the right- hand side.

The neutral (blue) is connected to

the pin on the left-hand side.

The earth (green and yellow) is

connected to the top pin. This is also

the longest pin.

The earth pin, being the longest,

opens the holes of the socket and

only then can the other pins be

inserted. This ensures that the

earth, and safety pin, is always first

to be connected.

The units of electrical power

Electrical power is given by the following

equation:

seconds in time

joulesin done workPower

The unit of power is the watt (W).

The ESB calculates the electrical power used

by your home in kilowatt hours (kWh).

A kilowatt hour is the electrical energy used

by a 1kW appliance which has been running for

one hour.

Example;

(i) Calculate the number of units of electrical

power used by a 3 kW electrical heater over 4

hours of use.

(ii) If one unit of electrical energy costs 15c,

how much will the heater cost to run, over the

four hours?

Answer;

(i) Number of units used = (3kW)(4h)

= 12 kWh = 12 units

(ii) Cost = (12)(15) = 180c = €1.80

Example;

Calculate the cost of running a 50W television

set for 10 hours.

Answer;

Number of units used = (0.05 kW)(10)

Voltag

e

Variable

resistor

Resistor

Voltmeter Ammeter

A V

Sand

Fuse

wire

Metal

caps

Current

Experiment; To show the action of a fuse


Close the switch.

A current flows through the thin fuse wire.

Gradually increase the current delivered by

the power source.

At some point, the fuse wire will get red

hot and break.

This illustrates the operation of a fuse.

Electronic devices

Diodes

A diode is a device which will allow current to

flow in only one direction through it. A diode

looks like this,

but in a circuit it is represented by the

symbol shown below.

A diode can be connected in a circuit in two

ways, forward bias or reverse bias.

Experiment: To show the action of a diode in

(i) Forward bias

Set up the circuit as shown.

Close the switch.

The light bulb will light.

The diode is in forward bias and since the current always flows from

the + to the – terminal, current will

flow through in the direction of the

arrow.

(ii) Reverse bias


Close the switch.

The light bulb will not light.

The diode is in reverse bias and allows

current through only in the direction of

the arrow.

But the current from the battery is going

in the opposite direction and cannot pass

through the diode.

Uses of diodes

To control the direction of current

in electronic devices.

To change alternating current to

direct current.

Light Emitting Diodes (LED)

A LED is a diode which gives out light when

current passes through it. A LED looks like

this,

but in a circuit it is represented by the

symbol shown below.

Experiment: To show the action of a LED


Close the switch.

The LED is in forward bias and since the current always flows from the + to the

– terminal, current will flow through in

the direction of the arrow.

The LED will give out light.

The 330Ω resistor is placed in the circuit

to protect the LED against a large

current.

Light Dependent Resistor (LDR)

A LDR is a resistor in which the resistance

decreases when the light intensity increases.

This means that more current is allowed to

flow through the LDR in bright light

conditions.

Experiment: To show the action of an LDR


Shine light on the LDR.

The bulb will get brighter.

An increase in current flowing in the

circuit will also be seen on the

ammeter.

Remove the light on the LDR and the

current reading on the ammeter will

fall again.

The brightness of the bulb will

decrease.

Variable power source

12 V

Fuse wire Switch

+

+

+

330

ΩΩ

LDR

Bulb A

Energy

Energy is the ability to do work. There are

many different forms of energy. Energy is

measured in joules (J).

Forms of energy

Potential energy (P.E.) – This is the energy

which an object has because of its

mechanical condition or position above

ground e.g. a coiled spring or a hammer

held above ground.

Kinetic energy (K.E.) – This is the energy

which a moving object has.

Heat energy – Heat is a form of energy

because it causes things to move e.g. hot

air balloon.

Light energy – Light is a form of energy

because it causes things to move and it

does work e.g. solar cells produce

electricity to work appliances.

Sound energy – sound can cause things to

move e.g. feel the vibrations near a

speaker of a stereo.

Electrical energy – Electricity can cause

things to move or do work e.g. electrical

motor.

Chemical energy – This the energy stored in

chemicals petrol or food.

Nuclear energy – This is the energy stored

in the nucleus of an atom.

The law of conservation of energy states that

energy cannot be created or destroyed but

changed from one form into another.

Examples of energy conversion

Light bulb – electrical energy is converted

into light and heat energy.

Radio – converts electrical to sound energy.

Energy loss in the home

Energy is lost from your home in different

ways. The main areas where heat is lost are,

floors, walls, roof, windows, draughts.

Methods of preventing heat loss

Glass fibre on the attic floor.

Lagging the hot water tank.

Air cavity in walls.

Draught excluders on doors and

windows.

Double glazing on windows.

Energy supplies

Non-renewable sources – once used they gone

forever e.g. coal, oil, gas, turf. These are

referred to as fossil fuels. They are costly to

extract and transport, cause pollution, and

there is only 300 years (at present usage) of

known reserves left.

Renewable resources – are constantly being

replaced by nature. The main sources of

renewable energy are,

Solar - Solar panels turn sunlight

into electricity.

Hydro-electric energy – Dams hold

back water and stored potential

energy is released as kinetic energy

to turn the turbine and produce

electricity.

Wind energy – Wind mills are used to

produce electricity.

Wave energy – The movement of

large floats are used to produce

electricity.

Geothermal – The temperature of the

earth’s crust is used to heat water

to steam and produce electricity.

Biomass – Some quick-growing plants

are used to produce alcohol and

methane gas.

Solar energy

The sun is our primary source of

energy.

Plants absorb light for making food

(photosynthesis).

Animals eat plants and obtain food energy

from digesting the food made in

photosynthesis.

The fossil fuels which run our cars,

trucks, trains, planes, factories, homes

etc. are formed from a build up of

hundreds of millions of years of decaying

plants and animals. The energy released

when burn these fuels is a result of

photosynthesis that happened millions of

years ago.

All of our heat energy, electrical energy,

kinetic energy, food energy comes,

either directly or indirectly, from the

sun.

The warmth of the sun drives the winds on

which wind generators depend

Nuclear energy

Nuclear energy is the energy stored

in the nucleus of an atom.

When the nucleus of an atom

disintegrates, a vast amount of

energy is released.

An uncontrolled release results in a

devastating nuclear explosion.

But controlled nuclear breakdown in a

reactor, results in huge energy

release which can be harnessed and

used to produce electricity.

Advantages of nuclear energy

In medicine, to kill cancer cells.

Sterilise food (kills bacteria).

Produce electricity.

Will not run out.

Disadvantages of nuclear energy

Waste produced by the nuclear

industry is very dangerous.

There is always a danger of

explosion.

Experiment: To compare the insulating ability of

different materials

Place two beakers of boiling water on a

bench. One is insulated the other is not.

Take the temperature in each after 10

minutes.

The water in the insulated beaker should

be much warmer.

This because the insulation holds in the

heat.

Try this experiment again but with a

different insulating material and see which

is best.

Experiment: To convert mechanical energy to

heat energy and sound energy.

Drill into a piece of timber with an electric

drill (mechanical energy).

After 1 minute, remove the drill and touch

a thermometer off the tip of the drill.

The temperature shoots up, showing that

heat energy has been produced.

The noise made by the drill shows that

sound energy is also produced.

Experiment: To convert chemical energy to heat

energy

Light a candle.

Hold a thermometer near the flame.

Record the temperature change.

The heat produced is due to the chemical

energy in the wax being converted to

heat.

Beaker of

water

Thermomete

rs

Polystyrene

foam

Mandatory experiment: To convert chemical

energy to electrical energy to heat energy

Close the switch and allow current to

flow through the circuit for a few

minutes.

Hold a thermometer against the bulb.

The increase in temperature

registered on the thermometer shows

that heat has been produced in the

circuit.

The energy conversions which have

occurred are,

Chemical energy (in the battery) to

electrical energy (in the circuit).

Electrical energy (in the circuit) to

heat energy (in the bulb).

Mandatory experiment: To convert electrical

energy to magnetic energy to kinetic energy

Close the switch and allow current to

flow through the circuit.

The electric current in the circuit is

converted to magnetic energy, as the

wires in the circuit are now magnetic.

The magnetic energy of the wires is

converted to kinetic energy when the

compass needle moves.

Mandatory experiment: To convert light energy

to electrical energy to kinetic energy

The light hits the solar cell and is

converted to electrical energy.

The electrical energy is then

converted to kinetic when the

propeller turns.

- +

Bulb

Switch

Cell (power supply)

Compass

- +

Switch

Cell (power supply)

Light

Solar cell

Heat

Heat is a form of energy. The unit of heat

energy is the joule (J).

There are three methods of moving heat from

place to place.

1. Conduction – this is the transfer of

heat from one place to another,

through a solid, without the

particles, of the solid, moving out of

position.

2. Convection – this is the movement of

heat, through a liquid or gas, by the

upward movement of heated

particles.

3. Radiation – this is the movement of

heat, by invisible rays, from a hot

object without the need for a

medium to pass through.

An insulator – is a substance which will not

allow heat to pass through it easily.

Examples of conduction:

Metal pots

Cooking pots are made of metal because they

are good conductors and will allow food,

placed in them, to heat-up.

A poker

A poker can get extremely hot if the end is

left in the fire. The heat will travel out by

conduction to the handle.

Examples of convection:

Electric kettle

The element is placed at the bottom of a

kettle. As the water is heated, the heated

particles rise by convection and cooler ones

take their place. In this way, all of the

water will be heated.

Electric immersion heater

This works in a similar way to a kettle.

Convection heaters

These are usually called radiators, but this is not a good name for them, as they heat a

room, mostly, by convection.

Examples of radiation:

Solar energy

Energy from the sun travels through space to

the earth by radiation. There is no medium

just a vacuum.

All hot objects

All hot objects radiate heat, in all directions.

If you put your hand over a lighted candle

you will feel great. This is heat by

convection.

If you put your hands around a candle you

will also feel heat. This is radiated heat and

it is not as much as the convected heat.

Examples of insulators:

Fibre glass wool – used for attic

insulation.

Polystyrene – used for burger boxes,

pizza boxes (keeping food hot).

Polystyrene board – used for wall

insulation to prevent heat being lost from

the walls of a house.

Wool clothing – wool is a good insulator

and prevents us from losing body heat.

The effects of heating

When solids, liquids and gases are heated they

expand. The only exception to this rule is water,

between 40 and 00C. W

Mandatory experiment: To compare the

conductivity of various metals


A thumbtack is attached with wax

to each of four metal strips with

wax.

A Bunsen flame is placed at ‘x’ and

the four strips are heated evenly.

The thumbtack which falls first

indicates the best conductor.

Mandatory experiment: To show that water is a

poor conductor.

Fill a test tube with water.

Hold the test tube at the bottom

and heat the mouth with a Bunsen

burner.

The water at the mouth of the

test tube will be boiling but you

will still be able to hold the

bottom of the tube.

This is because the water is a

poor conductor.

Mandatory experiment: To show convection in

water

Heat the water as shown.

The hot water rises as a convection

current and the dye goes with it.

The dye makes the current visible.

Mandatory experiment: To show convection in a

gas

The candle creates an updraft

(convection current) of hot air.

The hot air rises and leaves through

the chimney on the left.

Cold air is drawn in from outside,

through the chimney on the right, to

replace it.

Wooden

ring

Metals

x

Box with glass front

Smoke

Candle

Bunsen

Dy

e

Coloured

water

rises

Mandatory experiment: To show heat transfer

by radiation

Place two thermometers equal

distances from a candle, as shown

above.

Thermometer 1 shows a small increase in temperature. This is due

to radiated heat only.

Thermometer 2 shows a large increase in temperature. This due to

radiated heat and convection.

Solids, liquids and gases expand when they are

heated. The following experiments are used to

demonstrate this fact.

Mandatory experiment: To show that solids

expand when heated.

Put the ball through the hoop, to

check that it fits through the hoop.

Heat the ball for 30 seconds with a

Bunsen burner.

Try to fit the ball through now.

It cannot be done.

Mandatory experiment: To show that liquids

expand when heated

Heat the flask as shown.

Since the flask is already full, any

expansion of the water will be seen

as the water rises up the tube.

The water level in the tube will fall

if the flask is cooled.

Mandatory experiment: To show that gases

expand when heated

Heat the flask as shown.

The air in the flask will expand.

The expanded air has only one

escape route, out through the top of

the tube.

If the tube is held under the water,

the expanded air can be seen

bubbling out.

If the flask is allowed to cool, the

air in the flask will contract and

water will be sucked into the flask.

Candle

Thermometer 2

Thermometer 1

Flask

filled

with

water Heat

Heat the flask

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