Physics Summary- Electrical Energy in the Home

1. Society has become increasingly dependent on electricity over the last 200 years.

1.1.1 Discuss how the main sources of electrical energy have changed over time.

The main sources of electrical energy before used to be wood, coal, gas and oils, however due to the development of technology, many renewable and efficient resources came about and have become the more common use of electrical energy today.

1.1.2 Assess some of the impacts of changes in, and increased access to sources of energy for a community.

Throughout the past decade, pollution has risen all over the world resulting in climate change. Also the source of coal, the main electricity provider, is decreasing day by day. This raised awareness in the government, which has led to public policies reforming and encouraging the use of renewable resources such as Solar Power, Wind power, Hydro Power etc. Due to this, the community now has an increased access to these energy sources which has had a positive impact financially and also environmentally.

1.1.3 Discuss some of the ways in which electricity can be provided in remote areas.

Electricity can be provided in remote areas such as large scale electricity production, diesel generators, solar power, wind power and electricity storage. These energy sources are highly effective in providing electricity in remote areas, so long as they can afford it and have the geographical location and condition to maintain it. Most of them are low cost and environmentally friendly and sustainable which further simplifies their use in remote areas.

1.2.1 Identify data sources, gather, process and analyse secondary information about the differing views of Volta and Galvani about animal and chemical electricity and discuss whether their differing views contributed to increased understanding of electricity.

Luigi Galvani observed when a skinned dead frog’s leg twitched violently when touched by a metal knife in a circuit. From this he drew the conclusion that animals have the ability to produce electricity as this electricity lurks in their nerves and brain. However Volta disagreed and said the electricity only occurred because two metals were joined in the circuit. This led him to develop the first electric battery and voltaic pile.

2. One of the main advantages of electricity is that it can be moved with comparative ease from one place to another through electric circuits.

2.1.1 Describe the behaviour of electrostatic charges and the properties of the fields associated with them.

Electric charges push or pull each other therefore forces exist between them as force field. Any charge in electric field region will experience a force. Charges are protons and electrons and only electron move as part of an object.

2.1.2 Define the unit of electric charge as coulomb.

Coulomb is the unit of electric charge

2.1.3 Define the electric field as a field of force with field strength equal to the force per unit charge at that point: E= F/Q.

The electric field is a field of force with field strength equal to the force per unit at that point. E=F/Q ie. Electric field strength = force/charge whereby force is measure in Newtons per Coulomb.

2.1.4 Define electric current as the rate at which charge flows (coulombs/second or amperes) under the influence of an electric field.

Electric current is the rate at which charge flows under the influence of an electric field. This is measures in coulombs/second or amperes.

2.1.5 Identify that current can either be direct with the net flow of charge carriers moving in one direction or alternating with the charge carriers moving backwards and forward periodically.

Current can be direct with the net flow of charge carriers moving in one direction or alternating with the charge carriers moving backwards and forwards periodically.

2.1.6 Describe electric potential difference (voltage) between 2 points as the change in potential energy per unit charge moving from one point to another (joules/coulomb or volts).

Electric potential difference is equal to the change in potential energy per unit charge moving through the potential difference. Potential difference is also known as voltage. Voltage is therefore measured in joules/coulomb or volts.

2.1.7 Discuss how potential difference changes at different points around a DC circuit.

The potential difference across the power supply is equal to the sum of the potential difference across the resistors in a series circuit. Same goes for the potential difference in a parallel circuit as the potential difference is the same across the power supply.

2.1.8 Identify the differences between conductors and insulators.

Between positive and negative points

Between 2 positive points

Between charged parallel plates

Conductors are materials which contain charge carriers and allow particles to move through them whilst insulators are materials containing no charge carriers and don’t allow movement of charged particles.

2.1.9 Define resistors as the ratio of voltage to current for a particular conductor.

Resistance is the ratio of voltage to current for a particular conductor. R=V/I

2.1.10 Describe qualitatively how each of the following affects the movement of electricity through a conductor: length, cross-sectional area, temperature, material.

Length- the longer the wire, the greater the chance of collision, thus greater resistance.

Cross-sectional area- the smaller the cross-sectional area the greater the chance of collision between electrons, thus greater the resistance.

Temperature- The higher the temperature the greater the resistance as great heat causes collision between the free-moving electrons.

Material- Materials with lower resistance are better conductors as opposed to materials with higher resistance.

2.2.1 Present diagrammatic information to describe the electric field strength and direction: between charged parallel plates, about and between a positive and negative point charge.

2.2.2 Solve problems and analyse information using: E = F/Q

1. What force would a charge of 8.0x10-8C experience in a field strength 4.0x108N/C

3.2N

2. A charge of 3.6x10-1C experienced a force of 1.08N in an electric field. What was the magnitude of the field at that point?

3.0 N/C

3. A charged sphere experienced a force of 2.56x10-2N in an electric field of strength 1.6x108 N/C. What was the charge on the sphere?

1.56x10-10

2.2.3 Plan, choose equipment for and perform a first-hand investigation to gather data and use the available evidence to show the relationship between voltage across and current in a DC circuit.

Aim- To observe the relationship between voltage and current.

Method- 1. Set up electric circuit as such: Connect a switch, ammeter and light bulb and series circuit to the transformer and voltage parallel to the light bulb.

2. Observe and record the voltage and current each time the energy is turned up a notch.

2.2.4 Solve problems and analyse information applying: R =V/I.

1. What is the resistance when voltage is 8V and current is 2A?

4 ohms.

2. What is the current when resistance in 20 Ohms and voltage is 70V?

35 Amps.

3. What is the voltage when resistance is 1200 Ohms and current is 0.2A?

240 Volts.

2.2.6 Gather and process secondary information to identify materials that are commonly used as conductors to provide household electricity.

Copper- is mainly used as it has little resistance and does not carry high currents therefore is safer to use for large amount of electricity conductivity.

Silver- occasionally used in some high quality electronic equipment due to its high conductivity. It is not used widely due to its high price.

Aluminium- not as good a conductor as silver or copper but is used in wires as overhead power line distribution because of its light weight.

3. Series and Parallel circuits serve different purposes in households.

3.1.1 Identify the difference between series and parallel circuits

Series circuit is when components in a circuit are arranged one after the other in the same circuit. Parallel circuits are circuits in which the current has two or more paths to follow.

3.1.2 Compare parallel and series circuits in terms of voltage across circuits and current through them.

Series Circuit Parallel CircuitCircuit connected end to end with only one Closed circuit which has the current divide

possible path. into 2 or more pathways.Each resistor carries the same value. Each resistor in a parallel circuit has its own

value. Each resistor in series has its own voltage drop and the sum of the voltage drops equals the voltage supplied.

Each resistor in parallel has the same voltage drop regardless of theresistor value and the voltage drop in each parallel resistor equals the voltage supplied.

3.1.3 Identify uses of ammeters and voltmeters.

Ammeters are used to measure current in amps and has negligible resistance whilst volt meters measures potential difference in volts and has internal resistance.

3.1.4 Explain why ammeters and volt meters are connected differently in a circuit.

Ammeters are placed in series circuits because they measure the rate at which the charge flows which does not decrease as it passes through a resistor. Voltmeters are placed parallel to the component which we are required to measure the potential difference across because the volt meter measures the difference in potential energy.

3.1.5 Explain why there are different circuits for lighting, heating and other appliances in a house.

There are different circuits for different household appliances because:

a) Each circuit is designed to carry a certain maximum current and it varies amongst the circuits based on the requirements for individual appliances.

b) The amount of current that passes through also influences the wires needed. For example more current requires larger wires so the resistance decreases, which decreases the heat generated.

c) Separate circuits are used to decrease the chance of short circuits.

3.2.1 Plan, choose equipment or resources for and perform first-hand investigations to gather data and use available evidence to compare measurements of current and voltage in series and parallel circuits in computer simulations or hands-on equipment

Set up the following and record the current and voltage through each:

3.2.2 Plan, choose equipment or resources and perform a first-hand investigation to construct simple model household circuits using electrical components.

4. The amount of power is related to the rate at which energy is transformed.

4.1.1 Explain that power is the rate at which energy is transformed from one form to another.

Power is the rate at which energy is transformed from one form to another or the rate at which energy is supplied to a device.

4.1.2 Identify the relationship between power, potential difference and current.

Power = Current x Voltage

P=IV

4.1.3 Identify that total amount of energy used depends on the length of time the current is flowing and can be calculated using: Energy = VIt

The total amount of energy used is dependent on the length of time for which the current is flowing and can be calculated by using the formula:

Energy = Voltage x Current x Time

E=VIt

4.1.4 Explain why kilowatt-hour is used to measure electrical energy consumption rather than the joule.

Kilowatt-hour is used as a means to measure electricity rather than joule as a joule is a very small amount of energy and since electricity is used in large amount, the standard of measurement is kilowatt-hour. Kilowatt-hour is the amount of energy used by a one kilowatt device in one hour.

Energy in Kilo hours = power in kilowatts x time in hours

W=Pt

4.2.1 Perform a first-hand investigation, gather information and use available evidence to demonstrate the relationship between current, voltage and power for a model 6V to 12V electric heating coil.

Aim- To design, make and test a 6V to 12V heating coil which will raise 200mL of water from room temperature to boiling point in approximately 10 minutes.

Method- 1. Place 200mL of water from the tap into a beaker and measure its temperature.

2. Obtain the length of the resistance wire and make a coil suitable for heating the water in your beaker.

3. Suspend the coil so it is immersed in the water. Do not let it touch the sides of the beaker.

4. Use the power supply and the variable resistor to set the current to the required value.

5. Test your coil by heating 200mL of water and measuring the time taken to raise the temperature to boiling point.

6. Record Results.

Results:

Temperature of waterRise in temperature of the waterEnergy required to raise temperature of water to 100oCPower to raise temperature in 10 minutesCurrentResistance of coilResistance per cm of resistance wireLength of resistance wire requiredTime taken to raise temperature of water

4.2.2 Solve problems and analyse information using: P=VI and Energy = VIt.

1. A 12 V lamp used a current of 3.0A. What was the power of the lamp? 36 Watts

2. What power would be neededto pass a current of 4.0A through a resistor marked 5.0 Ohms? 80 Watts

3. In 5 minutes an appliance uses 2.7 x 103Joules of energy. If the current passing through it was 2.0A what was its resistance? 2.25 Ohms

5. Electric currents also produce magnetic fields and these fields are used in different devices in the home.

5.1.1 Describe the behaviour of magnetic poles of bar magnets when they are brought close together.

When opposite poles are brought together they attract whilst when the same poles are brought together they repel.

5.1.2 Define the direction of a magnetic field at a point as the direction of force on a very small north magnetic pole when placed at that point.

The direction of a magnetic field at a point is determined by calculating the direction of force on a very small north magnetic pole when placed at that point e.g. compass.

5.1.3 Describe the magnetic field around pairs of magnetic poles.

5.1.4 Describe the production of a magnetic field by an electric current in a straight current carrying conductor and describe how the right hand grip rule can determine the direction of current and field lines.

When a current is passed through a conductor, a magnetic field is created around it. This can be determined using the right hand rule. Point the right hand thumb in the direction of the current and the direction of the fingers in the direction of the magnetic field.

5.1.5 Compare the nature and generation of magnetic fields by solenoids and a bar magnet.

Solenoid is a coil or helix of wire as a tube In and around the solenoid the magnetic field is added together leaving too an

intensified field The polarity can be determined using the right hand rule- thumb points north and

fingers wrap in direction of conventional current flow Electro magnets are solenoid with iron bar through the middle which leads to a

stronger magnetic field This is because the iron bar becomes a temporary magnet and magnetic fields add

together.

5.2.1 Plan, choose equipment or resources for, and perform a first-hand investigation to build an electromagnet.

Aim- To build an electromagnet and doing so, comparing the strength of iron bars in an electromagnet.

Method- 1. Create an electric magnet by wrapping a solenoid of wire around the pen.

2. Connect the power and pick up paper clips (record).

3. Insert various iron bars and pick up more paper clips (record).

Results-

Large Iron bar Medium Iron Small Iron bar Pen

barAmount of paper clips picked up

12 4 0 0

5.2.2 Perform a first-hand investigation to observe magnetic fields by mapping lines of force: – around a bar magnet – surrounding a straight DC, current-carrying conductor – a solenoid – present information using ⊗ and • to show the direction of a current and direction of a magnetic field.

Around a magnet-

Aim- To use a compass to map the magnetic field surrounding a bar magnet.

Method-

1. Place a sheet of paper on a horizontal surface2. Use compass to find the North and South direction and mark this direction at the

centre of paper3. Place the bar magnet on the paper along with North and South lines marked on the

paper with the north pole of the magnet pointing north.4. Mark on the paper the outline of the magnet and label the poles N and S.5. Place a compass at a point near the North Pole of the magnet. Mark with 2 points

the position taken up by the compass needle.6. Move the compass to a new position so that the position of the compass needle

follows from the previous position. 7. Continue this way until you reach the south pole of the magnet.8. Draw a continuous curve through the points you have marked on the paper.9. Mark with arrows the direction of the magnetic field at several points along your

line.10. Repeat 5 times starting from different positions of the compass.

Magnetic Field produced by a current-

Aim- To map the magnetic field surrounding a long straight wire carrying an electric current.

Method-

1. Set up the apparatus as such: Switch, cardboard with compasses and ammeter connected in series.

2. Connect the power supply such that the conventional current flows downwards through the wire.

3. Adjust the voltage of the power supply and the variable resistance as needed.4. Place the compass about 5cm from the wire.5. Switch on the current and mark the positions of the ends of the compass on the

cardboard.6. Repeat steps 6-9 from the previous prac.7. Reverse the direction of the current and observe what happens to the compass

needle.

Magnetic field of a solenoid carrying a current-

Aim- To map the magnetic field surrounding a solenoid

Method-

1. Connect the apparatus as shown: Iron core wrapped with solenoid connected in series with battery, switch, ammeter and resistor.

2. Note the direction of the conventional current through the solenoid.3. Map the magnetic field around the solenoid using the same method mentioned in

previous practicals.4. Reverse the direction of the current through the solenoid. Note what happens to the

direction of the magnetic field.

6. Safety devices are important in household circuits.

6.1.1 Discuss the dangers of an electric shock from both a 240V AC mains supply and various DC voltages from appliances on the muscles of the body.

Effect of DC voltages- Muscle contraction

Effect of AC voltages:

6.1.2 Describe the functions of circuit breakers, fuses, earthing, double insulation and other safety devices in the home.

Double insulation- Insulators restrict current flow and prevent short circuits. Double insulators are used to protect the user in case the inner insulator fails.

Fuses- Prevent overloading of household circuits. Prevents wires from heating up excessively which, if it does so, causes fires.

Circuit breakers- Preventative as when the current escalates, an electromagnet within it breaks the circuit. It can also be reset.

Earth wire- Provides protection to the occupants from electric shocks when using appliances.

Residual Current Device- detects any leakage of current to the earth either through your body or through some other conductor and switches off the current very quickly before it reaches a harmful level.