electricity booklet igcse 1.0

IGCSE Electricity booklet

Light bulb photo by Joyce Cheng, KGV

Name________________________

Physics Teacher___________________________

KGV IGCSE Electricity page 1

6/96/9/10

28 Specification – Edexcel IGCSE in Science (Double Award) (4SC0) –

Issue 1 – September 2008 © Edexcel Limited 2008

1.23 use the relationship between orbital speed, orbital radius and time period:

orbital speed = 2× π ×orbital radius time period v = 2× π × r T

1.24 describe how the orbit of a comet differs from that of a planet

1.25 recall that the solar system is part of the Milky Way galaxy

– describe a galaxy as a large collection of billions of stars

– state that the universe is a large collection of billions of galaxies.

Section 2: Electricity

a) Units

b) Mains electricity

c) Energy and potential difference in circuits

d) Electric charge

a) Units

Students will be assessed on their ability to:

2.1 use the following units: ampere (A), coulomb (C), joule (J), ohm (Ω), second (s), volt (V), watt (W).

b) Mains electricity


2.2 recall the hazards of electricity including frayed cables, long cables, damaged plugs, water around sockets, and pushing metal objects into sockets

2.3 describe the uses of insulation, double insulation, earthing, fuses and circuit breakers in a range of domestic appliances

2.4 know some of the different ways in which electrical heating is used in a variety of domestic contexts

2.5 understand that a current in a resistor results in the electrical transfer of energy and an increase in temperature

2.6 recall and use the relationship:

power = current × voltage

P = I × V

and apply the relationship to the selection of appropriate fuses


Specification – Edexcel IGCSE in Science (Double Award) (4SC0) – Issue 1 – September 2008 © Edexcel Limited 2008

29

2.7 use the relationship between energy transferred, current, voltage and time:

energy transferred = current × voltage × time

E = I × V × t

2.8 recall that mains electricity is alternating current (a.c.) and understand the difference between this and the direct current (d.c.) supplied by a cell or battery.

c) Energy and potential difference in circuits


2.9 explain why a series or parallel circuit is more appropriate for particular applications, including domestic lighting

2.10 understand that the current in a series circuit depends on the applied voltage and the number and nature of other components

2.11 describe how current varies with voltage in wires, resistors, metal filament lamps and diodes, and how this can be investigated experimentally

2.12 describe the qualitative effect of changing resistance on the current in a circuit

2.13 describe the qualitative variation of resistance of LDRs with illumination and of thermistors with temperature

2.14 know that lamps and LEDs can be used to indicate the presence of a current in a circuit

2.15 recall and use the relationship between voltage, current and resistance:

voltage = current × resistance

V = I × R

2.16 understand that current is the rate of flow of charge

2.17 recall and use the relationship between charge, current and time:

charge = current × time

Q = I × t

2.18 identify common materials which are electrical conductors or insulators, including metals and plastics

2.19 recall that electric current in solid metallic conductors is a flow of negatively charged electrons.


Electricity Equations


Specification – Edexcel IGCSE in Science (Double Award) (4SC0) – Issue 1 – September 2008 © Edexcel Limited 2008

55

Appendix 3: Electrical circuit symbols

Description Symbol Description Symbol conductors crossing with no connection

heater

junction of conductors thermistor

open switch light-dependent resistor (LDR)

closed switch relay

open push switch diode

closed push switch light-emitting diode (LED)

cell lamp

battery of cells loudspeaker

power supply or

(d.c.)

(a.c.)

microphone

transformer electric bell

ammeter A earth or ground

milliammeter mA motor M

voltmeter V generator G

fixed resistor fuse/circuit breaker

variable resistor

1752sb250608:\LT\PD\IGCSE\IGCSE Science_Dble Awd (4SC0).doc.1-62/1


Use the text book “Physics for You” to carry out these experiments The experiments are in the PINK BOXES in the textbook 31.1 Draw a circuit diagram of the circuit you built On the diagram draw arrows to show the direction of current flow. 31.2 Build this circuit, try various materials in the gap and complete the table

Conductors Insulators

31.3 Draw a diagram of your circuit with the copper wire connected. Use your diagram to explain why the lamp goes out


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31.4 Build the circuit in 31.4 Draw the circuit diagram. What do we call circuits of this type? 31.5 Connect the ammeter into your circuit Record the current: Current = ________A 31.6 What do you notice as you move the ammeter? As the ammeter moves around ……. 31.7 When I unscrew one lamp the other lamp ……. Draw a circuit diagram to explain why this happens.


31.8 Build this circuit. What do you notice about the brightness of the lamps? 31.9 What is an advantage of a parallel circuit? 31.10 Copy the circuit diagram. By each ammeter record the current. Can you spot a simple mathematical link? 31.11 Make the circuits at the bottom of page 257. What do you notice about the brightness of the bulbs?



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Electricity Lesson 3

Investigating Voltage

Build each of the following circuits. For each one record the readings on the voltmeters.

Label the bulbs in the diagram as bright, dim or normal. Take the bulb in circuit 1 as normal.

Circuit 1

Circuit 2

V

V

V

V

Circuit 3

Circuit 4

V V

V


Circuit 5

Circuit 6

V

V

V

V

V

V

Circuit 7

Circuit 8 Invent and draw your own circuit

V

V

V


Voltmeters and voltage 1. Voltage is a measure of the e.……………... carried by each C……………………….. of charge 2. A voltmeter measures the ……………………….. in electrical energy ………………………two points on the circuit. 3. A voltmeter must always be connected in …………………… 4. What is the energy given to the following charges when passing through the cells: (a) 20 C passing through 6 V …………………………………………………………………………………………..………… (b) 6 C passing through 200 V …………………………………………………………………………………………..………… (c) 100 C passing through 100 mV …………………………………………………………………………………………..………… 7. Complete the following diagram to show a voltmeter connected to measure the voltage drop across the resistor.


http://images.google.com.hk/imgres?imgurl=http://faq.f650.com/FAQs/Photos/ElecPhotos/VoltmeterVolts.jpg&imgrefurl=http://faq.f650.com/FAQs/VoltageRectifierFAQ.htm&h=800&w=600&sz=50&tbnid=ECZNCJKdU8ifeM:&tbnh=142&tbnw=106&hl=en&start=6&prev=/images%3Fq%3Dvoltmeter%26svnum%3D10%26hl%3Den%26lr%3D

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8. If the battery has an output voltage of 6 V what is voltage across each of the four identical lamps shown in the circuit? ………………………………………………. 8. If the battery has an output voltage of 6 V what is voltage across each of the three identical lamps shown in the circuit? ………………………………………………. 9. If the battery has an output voltage of 6 V what is voltage across each of the four identical lamps shown in the circuit? ………………………………………………. 10. What is the energy delivered by: (a) a current of 2 A flowing for 20 s from a 12 V supply ………………………………………………..……………. (b) a current of 1.5 A flowing for 2 m from a 6 V supply …………………………………………………..……………. (c) a current of 0.5 A flowing for 20 s from a 20 V supply ………………………………………………..………………. (d) a current of 2 mA flowing for 2 hrs from a 200 V supply ……………………………………………….………………….

2



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THE MEASUREMENT OF RESISTANCE - OHM’S LAW Before you start the experiment read through the instructions carefully. PURPOSE OF THE EXPERIMENT The aim of this experiment is to help you investigate how the current through a piece of wire is affected by the voltage between its ends.

YOU WILL NEED 1 metre of constantan wire (28SWG) fixed to a metre rule, a variable voltage dc power supply (0 - 6v), a dc ammeter (0 - 1A), a dc voltmeter (0 - 6V), two crocodile clips and 5 leads. WHAT TO DO Set up the circuit shown in the diagram, switch on and adjust the power supply so that the ammeter reads 0.1 A. Record the voltage reading. Repeat this for SIX other values of current and voltage. Do not use currents of more than 0.5A. MEASUREMENTS TO MAKE Ammeter reading = A Voltmeter reading = V

Record your results in a table. Make a third column in the table by dividing the voltage readings by the current readings (V/I) for each result. This ratio is called the RESISTANCE of the wire. FURTHER THINGS TO DO Write up your experiment and plot a graph of voltage on the y axis against current on the x axis. QUESTIONS 1. Did the resistance of your piece of wire stay the same throughout the experiment? 2. Why was the current kept to les than 0.5A? 3. What is the resistance of 50cm of the same wire? 4. Why would constantan not be a good material for making connecting leads? 5. How accurately can you read your voltmeter and ammeter?

1.56

V0.32

A

Electricity lesson 5 KGV IGCSE Electricity page 15

Resistance is futile...

1. What is the resistance of a wire when a) A voltage of 10V causes a current of 2A to flow b) A voltage of 10V causes a current of 1A to flow c) A voltage of 120V causes a current of 0.5 A to flow

2. What current will flow when a) 12 V is applied across a 4Ω resistor b) 4.5 V is applied across a 9Ω resistor c) 240 V is applied across 480Ω resistor

3. What voltage must be applied across a component if a) it has a resistance of 4Ω and a current of 1A is required b) it has a resistance of 10Ω and a current of 2A is required c) a current of 4A is required and the resistance is 960Ω

4. Underline the correct word or phrase in each sentence

a) As the temperature of a light-bulb increases its resistance will increase/decrease/stay the same.

b) As the temperature of a thermistor increases its resistance will increase/decrease/stay the same.

c) As the light intensity falling on a Light Dependent Resistor (LDR) increases its resistance will increase/decrease/stay the same.


Electricity lessons 5 & 6

Ohm’s Law and Resistance 1. If a piece of wire with a high resistance is connected in series with a torch bulb in a circuit what happens to the brightness of the bulb? 2. Write down an equation version to show Ohm’s Law. 3. A piece of wire connected to a 6V cell has a current of 1.5A flowing through it. What is the resistance of the wire? 4. A wire with a resistance of 10 Ω is connected to a 12 V supply. What is the current flowing through it? 5. What is the voltage difference across a piece of wire of resistance 100 Ω with a current of 20 mA flowing through it? (remember 1000mA = 1A) 6. What happens to the resistance of a piece of wire when it is heated? 7. Complete the following graphs. (a) is a metal wire at a constant temperature obeying Ohm’s law and (b) is a light bulb

voltage

current

(b)

voltage (a)

current


THE RESISTANCE OF A THERMISTOR Before starting the experiment, read through the instructions carefully.

PURPOSE OF THE EXPERIMENT The aim of the experiment is to investigate how the resistance of a thermistor changes with temperature. YOU WILL NEED A thermistor connected to leads which have been insulated with silicone jelly, a variable voltage do power supply (0 -12V), a milliammeter (0 - 100mA), a d.c voltmeter (0 -12v), a beaker of water, a thermometer (0 -100o C), a bunsen burner tripod, gauze and mat. (A 6v battery pack can replace the power supply but then a variable resistor would also be needed). A set of connecting leads. WHAT TO DO Set up the circuit shown in the diagram and place the thermistor in the beaker of water at room temperature. Measure the temperature of the water, the current shown by the milliammeter and the voltage shown by the voltmeter. Heat the water and record readings of temperature, current and voltage roughly every 10o C. MEASUREMENTS TO MAKE For each value of temperature taken: Temperature of water (and thermistor) Ammeter reading (I) Voltmeter reading (V) CALCULATIONS Work out the resistance of the thermistor for each temperature value (V/I) and record them in your table. Plot a graph of resistance (Y axis) against temperature (X axis) FURTHER. WORK If possible use your thermistor to estimate the following temperatures: (a) inside a fridge (b) body temperature

mA

V

thermistor


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This is an optional practical - your teacher may ask you not to do this one.

THE SALT METER BEFORE STARTING THE EXPERIMENT READ THROUGH THE INSTRUCTIONS CAREFULLY AIM The aim of this experiment is to find the concentration of the sample of salty water.

0-12 V DC

WHAT TO DO Set up the circuit shown in the diagram below. Dissolve 50g of salt in 1 litre of water, put some of it in the small beaker and pass a current through it. Adjust your power supply until the current flowing through the solution gives a current through the solution of no more than 100 mA.

86

mA d.c

Record the current and concentration (50g/litre). Repeat the experiment for seven other weaker concentrations. Plot a graph of current against concentration. Now measure the current through the sample of salty water provided and use your graph to find its concentration. Write up your experiment carefully, mentioning any problems that you had, where you think errors might have occurred and including any ideas for improving the experiment. Why do you think that the current should be kept to a low value?


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This is an optional practical - your teacher may ask you not to do this one.

DCP Marking Criterion

Results Table Not at all

0 Partial

1 Complete

2 The results are presented in a table

The table has correct headings

The headings also contain units

Significant figures are reasonable

Graph

The right kind of graph (line graph) has been plotted

The axes are correctly labelled

The graph is carefully plotted

An appropriate line of best fit is added

Optional (your teacher may not ask you to do these)

A value has been correctly read from the graph

Uncertainty bars have been added



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ELECTRICITY QUESTIONS . 1. In the circuit in Fig.1 which lamps light when the

switch is closed? 2. In the circuit in Fig.2 which lamps

light when: (a) S1 is closed (b) S2 is closed (c) both switches are closed

3. What is the name of the particles that carry the

current in solids? 4. A charge of 20C passes a point in a circuit in 5s.

What current is flowing? 5. A current of 3A flows for 15s. What charge has

passed by? 6. In the circuits shown what are the readings on the

ammeters and voltmeters. (Assume that one cell has a voltage of 1.5V and gives a current of 0.2A when connected to one bulb.

7. Which circuit will run the battery down slowest? 8. (a) Which circuit would be the best one for wiring

Christmas tree lights. (b) Why?

9. A fire taking 8A, a kettle taking 4.5A and a stereo

taking 1A are all plugged into one adaptor and then into a plug with a 13A fuse. What might happen?

10. A stereo takes 1A from the mains when running properly. What fuse would you use in

the plug 1A or 2A? Why? 11. Write down: (a) two things that you SHOULD do to ensure electrical safety in a house

and (b) two things that you SHOULDN’T do.

Figure 2

R Q

P

S2

S1

S T

Figure 1

A2 V4

V5

A3

A4Circuit B

A1 V1

V2 V3

Circuit A

Electricity lesson 9 KGV IGCSE Electricity page 22


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Physics word search – Electricity 1 Try and find these words: Amp Battery Capacitor Cathode Cell Circuit Conduct Connect Coulomb Current Diode Electricity Electron Ion Lamp LDR LED Ohm Resistance Short Spark Static Switch Voltage This is quite a difficult word search. Some of the words go across, some up or down and some are diagonal.

S P A R K W A T T Y N C

C I R C U I T C P R O A

Q R C I T A T S T E I P

E L E C T R I C I T Y A

C C M S O N U P E T C C

O H O H I D E L K A C I

U C S N N S E R T B E T

L T L O N C T H R D L O

O I C A T E O A O U L R

M W P R M D C I N E C O

B S O M E P D T D C H P

P N E G A T L O V M E J


Electricity past IGCSE Questions


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*N26263A0420*

1. A student connects a series circuit as shown.

(a) (i) The switch is closed. Name two components in the circuit, other than the lamp, which affect the size of the current.

1 .............................................................................................................................

2 .............................................................................................................................(2)

(ii) The current is 0.40 A. Calculate the charge that flows during a time of 20 s.

................................................................................................................................

................................................................................................................................

Charge = ................................C(2)

(b) You are asked to connect a second lamp so that each lamp can be switched on and off independently. Show, by drawing on the circuit above, how this can be done.

(2)

lamp

A

Q2

(Total 6 marks)


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*H28030A0624*

3. A circuit contains a resistor R, a thermistor and a buzzer connected to a cell as shown. The circuit can be used as a simple fire alarm.

(a) (i) Complete the sentence.

When temperature increases, the resistance of a

thermistor ....................................... .(1)

(ii) What happens to the current in the circuit when the temperature increases?

................................................................................................................................(1)

(b) (i) State the equation which relates voltage, current and resistance.

................................................................................................................................(1)

(ii) When temperature increases, does the voltage across R stay the same, increase or decrease?

................................................................................................................................(1)

(iii) Explain your answer.

................................................................................................................................

................................................................................................................................(2)

R


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(c) The buzzer starts to sound when the voltage across R is a particular value. Add a voltmeter to the circuit diagram to show how this voltage is measured.

(1)

QUESTION 3 IS ON THE NEXT PAGE

Q2

(Total 7 marks)


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4. The diagram shows a 9 V battery.

(a) The battery contains six cells connected in series.

Calculate the voltage of each cell.

.......................................................................................................................................

Voltage = .............................. V(1)

(b) Complete the sentence.

Current is the rate of flow of ........................................................................................(1)

(c) The battery supplies an average current of 0.20 A for 3.0 hours. Use the equation

energy transferred = current × voltage × time

to calculate how much energy the battery transfers during this time and give its unit.

.......................................................................................................................................

.......................................................................................................................................

Energy = ..................................(3)

(d) Describe the nature of an electric current in a metal wire.

.......................................................................................................................................

.......................................................................................................................................(2)


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(e) The battery is described as a 9 V d.c. supply. State what the letters d.c. stand for.

.......................................................................................................................................(1)

(f) State two differences between a mains supply and the supply from the battery.

1 ....................................................................................................................................

2 ....................................................................................................................................(2) Q6

(Total 10 marks)


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5. A student connects a light dependent resistor (LDR) to a battery.

(a) The current in the LDR is 0.050 A and its resistance is 90Ω in the dark.

(i) State the equation which relates current, resistance and voltage.

................................................................................................................................

................................................................................................................................(1)

(ii) Calculate the voltage across the LDR. Show your working and give the unit.

................................................................................................................................

................................................................................................................................

Voltage = ..................................................(2)

(b) The LDR is moved to a position in the light.

Choose words from the box to complete the table. You may use each word once, more than once or not at all.

decrease increase stay the same

Effect on … It will …

the resistance of the LDR

the current in the LDR

(2) Q3

(Total 5 marks)


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to switch and mains electricity supply

100 W lamp

lampholder and stand black plastic tube

V

mA

LDRfilament

distance, d

2. A student investigates the light received at different distances d from a 100 W lamp. The diagram shows the 100 W lamp and the circuit which he uses to measure the light. His circuit contains a light dependent resistor (LDR), a voltmeter and a milliammeter.

(a) Suggest a safety precaution which the student needs to take.

.......................................................................................................................................

.......................................................................................................................................(1)

(b) Most of the light which reaches the LDR comes from the filament.

Explain why very little light reaches the LDR from other sources.

.......................................................................................................................................

.......................................................................................................................................

.......................................................................................................................................(2)

(c) (i) What can the student use to measure the distance d from the filament to the LDR?

................................................................................................................................(1)

(ii) What problem will he have in measuring the distance d?

................................................................................................................................

................................................................................................................................(1)

(iii) How can he overcome this problem?

................................................................................................................................

................................................................................................................................(1)


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(d) (i) What is the reading in volts on this voltmeter?

Reading = ............................ V (1)

(ii) What is the reading in milliamps on this milliammeter?

Reading = ......................... mA (1)

(iii) Use the equation

resistance = voltagecurrent

to calculate the resistance in ohms of the LDR which will give these readings.

Give your answer to two significant figures. 1 A = 1000 mA

................................................................................................................................

................................................................................................................................

Resistance = ........................ Ω (2)

(iv) Explain why it is not justified to give the answer to more than two significant figures.

................................................................................................................................

................................................................................................................................

................................................................................................................................(2)

67 8

67 8


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(e) Another student carries out a similar experiment with a different lamp.

This is her table of results.

Distance d Resistance of LDR

40 690

50 1100

60 1600

70 2100

80 2800

90 3500

(i) What should she have included in this table?

................................................................................................................................(1)

(ii) What conclusion can she come to on the basis of these results?

................................................................................................................................

................................................................................................................................

................................................................................................................................(2) Q2

(Total 15 marks)


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4. The diagram shows a rheostat (variable resistor) together with its circuit symbol.

The slider can be moved. When the distance L is changed, the resistance of the rheostat is changed. The maximum value of L is 19 cm.

A student investigates how the current I in the rheostat depends on the length L.

(a) In the space below draw a circuit diagram for this investigation.

(2)

(b) (i) State one extra item of equipment, not shown on your diagram, that the student would need.

................................................................................................................................(1)

(ii) Describe how this investigation would be carried out.

................................................................................................................................

................................................................................................................................

................................................................................................................................

................................................................................................................................(3)

slider

L


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(c) During the investigation, the ammeter reading was as shown below.

Record this reading.

Current = ................................... A(1)

(d) During the investigation the student recorded the following results.

(i) Put these results in a table with column headings and units.

(3)

19, 0.11 10, 0.17 7, 0.24

5, 0.33 6, 0.14 16, 0.12

A0

0.10.2 0.3

0.4

0.5


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(ii) Using the grid plot a graph of current against length. Label the axes.

(3)

(iii) Circle the anomalous (unexpected) result.(1)

(iv) Draw the best-fit curve for the remaining points.(1)

(v) Suggest a reason for the anomalous result.

................................................................................................................................

................................................................................................................................

................................................................................................................................(1)

...............................

.......................................................................................


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(e) Suggest why the student did not use a value of 2 cm for L during the investigation.

.......................................................................................................................................

.......................................................................................................................................

.......................................................................................................................................(1)

TOTAL FOR PAPER: 50 MARKS

END

Q4

(Total 17 marks)


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3. A student designed a small electric heater. The diagram shows how he used his heater.

(a) Suggest the purpose of the polystyrene pellets.

.......................................................................................................................................

.......................................................................................................................................(1)

(b) The student measured the temperature of the water in the small beaker using a thermometer.

What should be done to the water before measuring its temperature?

.......................................................................................................................................

.......................................................................................................................................(1)

open switch

battery of cells

meter X

meter Y

variable resistor

plastic beaker

electric heater

polystyrene pellets

small beaker

water


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(c) The student then closed the switch and noted the readings on meters X and Y.

(i) Each diagram shows a meter. What is the numerical reading on each meter?

Reading = .............................. Reading = .............................. (1) (1)

(ii) Name meter X.

................................................................................................................................(1)

(iii) Name meter Y.

................................................................................................................................(1)

(iv) After 5 minutes he opened the switch and measured the new temperature of the water.

The diagrams show two thermometers. What is the reading on each thermometer and what is the difference between the readings?

Reading = .............. °C Reading = .............. °C Difference = .............. °C(2)

QUESTION 3 CONTINUES ON THE NEXT PAGE

30

20

10

30

20

10

40

45 6

meter X6

7 8

meter Y


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(d) The student repeated the experiment several times. Each time he used an identical mass of water at the same starting temperature. He adjusted the variable resistor to give different values of current and voltage before heating the water for five minutes.

He expected to find that the temperature increase is proportional to the power. Suggest and explain two experimental reasons why this did not happen.

1 ....................................................................................................................................

.......................................................................................................................................

.......................................................................................................................................(2)

2 ....................................................................................................................................

.......................................................................................................................................

.......................................................................................................................................(2) Q3

(Total 12 marks)


electricity booklet igcse 1.0

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