using electricity - lesmahagow high · web view= voltage in volts (v) i = current in amps (a)...

The Ultimate Collection of Physics Problems - Using Electricity

CONTENTS PAGE

SECTION 1 - FROM THE WALL SOCKET 2

SECTION 2 - ALTERNATING AND DIRECT CURRENT 4

Current, Charge and Time 4

SECTION 3- RESISTANCE 6

Voltage, Current and Resistance 6

Power, Energy and Time 8

Power , Current and Voltage 10

Power and Resistance 13

Section 3 Miscellaneous Questions 15

SECTION 4 - USEFUL CIRCUITS 18

Series Circuits 18

Parallel Circuits 20

Resistance in Series 22

Resistance in Parallel 23

Combination Circuits 25

Section 4 Miscellaneous Questions 27

SECTION 5 - BEHIND THE WALL 29

SECTION 6 - MOVEMENT FROM ELECTRICITY 31

USING ELECTRICITY REVISION QUESTIONS 32

General Level 32

Credit Level 35

APPENDIX (I) DATA SHEET 41

APPENDIX (II) ANSWERS TO NUMERICAL PROBLEMS. 42

©GMV Science. Photocopiable only by the purchasing institution. 1


Section 1 - From the Wall Socket

The wordsearch below tests your knowledge and understanding of the main ideas covered in the section.Work out the answers to questions 1-10 and then find them in the wordsearch below.

N E U T R A L E H B X T Q Z D TB A T H R O O M A Z A G C E X JP F G P J B E E I R D H T M T GL R T M T U F Y E R T A O O H NA W X E L H D M E M L H L K G IS B A B L C R Y N U E V B M E ST N J T N E R E S J G S Z D R AI O W N E D V N E R H C U D I CC F O O R R I I A A E I O F F LT U F I R E K V S U M K W L N AJ J A D L B V U T I D P O K S TG H V B I Z D L B Z O U B O I EE K U A K A E V I L K N T S C MC O W O L L E Y D N A N E E R GD O D N U O S D N A T H G I L UH I N Q T O P P I N W L U H X M



Wordsearch Questions

1. The mains supplies electrical energy to a television. This energy is converted into two other forms of energy. What are they?

2. A household appliance with power rating 12 000 W.

3. The colour of the neutral wire in a plug.

4. The following symbol was found on the rating plate of a hairdryer

(a) What does this symbol mean?

(b) What must the outer casing of the hairdryer be made of?

5. The rating plate for a radio is shown below.

(a) What size of fuse should be fitted in the plug of the radio?

(b) Which wire is missing in the flex of the radio?

6. Which component in the plug of an appliance breaks the circuit if the current gets too high?

7. A washing machine has three wires in the flex connecting it to the plug.

(a) Which wire, under normal circumstances, does not carry electricity?

(b) To what part of the machine is this wire normally connected?

8. The human body can conduct electricity. What substance can improve this conductivity?

9. Which room in the house has no electrical sockets?

10. To which pin in a plug is the earth wire connected?


model no. RF 230A.C 230 V 50 Hz6 W


Section 2 - Alternating and Direct Current

Current, Charge and Time

In this section you can use the equation:

also written as

where Q = charge in coulombs (C) I = current in amperes (A) t = time in seconds (s).

1. Find the missing values in the following table.

Charge (C) Current (A) Time (s)

(a) 5 30

(b) 0·005 3 600

(c) 3 1·5

(d) 27·6 2·3

(e) 1 800 60

(f) 94 10

2. A bulb draws a current of 1 A. How much charge flows through it in 60 seconds?

3. 756 C of charge flow though an electric heater in 180 seconds. What is the current in the heater?

4. A hairdryer operates with a current of 5 A. How much time would it take for 6 000 C to pass through the hairdryer?

5.


12V

charge = current x time

Q = It


A current of 2·1 A flows through an electric shaver for 5 minutes. How much charge flows in this time?

6. A 60 W bulb is switched on for 30 minutes. If 450 C pass through it in this time, what is the current flowing in the bulb?

7. A ‘surround sound’ speaker system on a TV draws a current of 0·6 A. In an average day 6 480 C of charge flows through the speaker system. For how long is the TV switched on each day?

8. An electric kettle has a label on it as shown below.

MODEL No. 5510 - 01capacity 1·7 litres

9·2 A /220 - 240 V 2·2 kW

After the kettle is switched on it automatically switches off when the water in it has boiled. On one occasion 1 656 C passed through the kettle before it switched off. Use the information given to work out how long the water took to boil?

9. An electric fire is rated at 2·875 kW, 230 V, 12·5 A. How much charge will flow through this fire in a period of 2 hours 20 minutes?

10. One day an electric iron was switched on from 1·45 p.m. until 3·15 p.m. What current was drawn by the iron if 2·484 x 104 C passed through it in this time?



Section 3 - Resistance

Voltage, Current and Resistance


also written as:

where V = voltage in volts (V) I = current in amps (A)R = resistance in ohms ().


Voltage (V) Current (A) Resistance ()

(a) 15 35

(b) 0·2 1 000

(c) 230 125

(d) 24 550

(e) 120 12

(f) 6 6·25 x 10-3

2. Look at the following circuits and calculate the supply voltage in each case:

(a) (b) (c)


Helpful Hint.Many appliances run from mains voltage which is 230 V ac.

Useful units for electricity are:1 A = 0·000 001 A = 1 x 10-6 A1 mA = 0·001 A = 1 x 10-3 A

50 mA

480

VsVs Vs

2·56 A10 A

250 5

voltage = current x resistance

V = IR


3. Look at the following circuits and calculate the current in each case:

(a) 24 V (b) 12 V (c) 48 V

4. Look at the following circuits and calculate the unknown resistance in each case:

(a) 24 V (b) 12 V (c) 48 V

5. Calculate the resistance of a lamp if the current through it is 10 mA when operated by a 24 V supply.

6. A power drill is operated at mains voltage and has a resistance of 1·5 k. Calculate the current through the drill.

7. The maximum current an electric motor can safely handle is 10 mA and it has a resistance of 360 . Calculate its safe operating voltage.

8. A cooker draws a maximum current of 28·75 A and has a resistance of 8 . At what voltage should it operate?

9. Hairdryers work from the mains voltage and can have currents of up to 15 mA flowing through them. Calculate the resistance of the hairdryer.

10. Overhead cables have resistance of 25 k. If the voltage across the cables is 4 000 V calculate the current through them.


I550 50 12

I I

660 A25 mA 30 A

R RR


Power, Energy and Time


also written as

where P = power in watts (W)E = energy in joules (J) t = time in seconds (s).


Power (W) Energy (J) Time (s)

(a) 1 500 30

(b) 180 000 36 000

(c) 100 600

(d) 1 200 2

(e) 3 000 120 000

(f) 2·5 25

2. How long will it take for a 60 W bulb to use 720 J of electrical energy?

3. A bulb uses 45 000 J of energy in 300 seconds. What is its power rating?

4. A 50 W immersion heater is switched on for 80 seconds. How much electrical energy passes through it in this time?

5.Calculate the power rating of an electric sewing machine which uses 4 560 J of energy in 8 minutes.


P = Et

power = energy time


6. A 1 200 W hairdryer is switched on for 20 minutes. How much electrical energy does it use?

7. For how many minutes must a 600 W shaver be switched on in order to use 540 000 J of electrical energy?

8. An electric fire uses 5·22 MJ of electrical energy in half an hour. Calculate the power rating of the fire.(1 MJ = 1 x 106 J = 1 000 000 J )

9. How long will it take a 1·4 kW paint stripper to use 1·68 MJ of electrical energy?

10. A microwave oven is on for twenty minutes each day. If it uses 7·98 MJ of electrical energy in one week, what is its power rating?



Power, Current and Voltage


also written as

where: P = power in watts (W)I = current in amps (A)V = voltage in volts (V).

Helpful HintThe voltage of the mains is 230 V ac.


Power (W) Current (A) Voltage (V)

(a) 2·5 12

(b) 0·6 9

(c) 1·5 x 103 230

(d) 36 12

(e) 0·624 2·6 x 10-3

(f) 1·5 0·25

2. A car battery supplies a voltage of 12 V. One headlamp bulb draws a current of 3 A. What is the power rating of this bulb?

3. An electric shower has a power rating of 12 W and draws a current of 0·11 A. What voltage is required to operate the shower?


power = current x voltage

P = IV


4. What current flows through a 230 V, 60 W household lamp when it is operating at the correct voltage?

5. Calculate the power rating of an electric drill which draws a current of 3 A when connected to the mains.

6. What would be the reading on the ammeter in the circuit shown?

7. The following information was found on the rating plate of a food processor:

Calculate the current flowing in the food processor.

8. A fridge has a power rating of 160 W. When it is plugged into the mains what current will it draw?

9. A radio has a power rating of 6 W and draws a current of 0·5 A when operating normally.

(a) What voltage does this radio need?

(b) How many 1·5 V batteries would be needed to operate the radio?

10. The circuit shows a heating element (resistor) operating correctly.

What is the voltage of the supply?

11. A torch bulb draws a current of 500 mA. It has a power rating of 1·75 W. What voltage is required to light the bulb to its correct brightness?


BL300360 W

230 V 50/60 Hzmade in the U.K

A

12 V

24 W

I = 4·2 A1 kW


12. An electric locomotive on the East Coast line gets its electricity from the overhead cables which supply 25 kV a.c. The locomotive has a top speed of 140 mph and it operates at 4·7 MW. Calculate the current flowing to the locomotive.

13. A helium - neon laser emits red light and has many uses in medicine. The laser uses the 230 V mains supply and has a power rating of 5 mW. What current flows in the laser?

14. The current flowing in an electric keyboard is measured as 800 mA. What voltage is required to operate the keyboard if it has a power rating of 7·2 W?

15. An electric fire has three heating elements which can be switched on and off independently. Each element has a power of 1·3 kW and is controlled by a switch on the side of the fire.

(a) Calculate the current drawn from the socket when one heating element is switched on.

(b) What is the maximum current that the fire could draw?



Power and Resistance

Helpful HintBy combining the formulae:

we have alternative forms of the formula for power.

i.e. P = I (IR) and P = (V/R) V

P = I 2 R P = V2/R

Use these alternative forms of ‘power formulae’ in the following questions.1.

Calculate the power rating of a lawn mower which has a resistance of 70·5 and draws a current of 2·5 amps.

2. What power is dissipated in the element of a toaster if it has a resistance of 64 and draws a current of 3·75 amps?

3. Find the power rating of a television given that it operates at mains voltage and has a resistance of 480 .

4. What would be the power rating of an iron if it operates at mains voltage and has a resistance of 45 ?

5. Calculate the power rating of a hedge trimmer given that it draws a current of 1·67 A and has a resistance of 144 .

6. Calculate the power rating of a Karaoke machine if it has a resistance of 5 760 and operates at mains voltage.

7. How much power is dissipated in curling tongs if they draw a current of 1·05 A and have a resistance of 230 while operating from the mains?


P = I V and V = I R


8. A microwave oven has a resistance of 68 and works properly from a mains supply. What is the power rating for such an oven?

9.Find the power rating of a Hoover designed with a resistance of 110 when operating at mains voltage.

10. What current is drawn from the supply by a transistor radio if it has a power rating of 3 W and a resistance of 12 ?

11. Find the resistance of a table lamp which has a power rating of 115 W and draws a current of 0·5 A.

12. An alarm clock is driven by a domestic supply voltage of 230 V. What is its resistance if it has a power rating of 2 W?

13. Calculate the total resistance of an electric fire if it operates safely at 230 V and uses electrical energy at a rate of 750 W.

14. Calculate the voltage of a car alarm which has a power rating of 3 W and resistance of 50 .

15. Find the power rating of an electric food mixer if it operates at mains voltage and has a resistance of 400 .



Section 3 Miscellaneous Questions

1. The following circuit is set up in a laboratory.

The bulb is switched on for 3 minutes and the voltmeter and ammeter readings remain as shown in the diagram.

(a) What is the power rating of the bulb?

(b) Calculate the resistance of the bulb.

(c) How much electrical energy is supplied to the bulb in the 3 minutes?

(d) How much charge passes through the bulb in the 3 minutes?

2. The resistor in the following circuit has a power rating of 0·09 W.

(a) What reading would you expect to find on the ammeter?

(b) What reading would you expect to find on the voltmeter?

(c) How long would it take for 5·4 joules of electrical energy to be supplied to the resistor?

(d) How much charge passes through the resistor in 1 minute?


3 A

12 V

A

V

10 k

Type KE 180 Serie 2

230 V 50 - 60 Hz

2·2 kW


3. Some students decide to measure the resistance of a torch bulb and each set up a circuit to do this. The circuits are shown below.

(a) Which circuit has been set up correctly? Explain your answer.

(b) Use the following results to plot a graph of voltage against current and hence or otherwise find the resistance of the torch bulb.

Current (A) Voltage (V)

0·5 5

0·8 8

1·1 11

1·4 14

1·7 17

4. The rating plate on an electric kettle is shown below.

(a) Calculate the current flowing in the kettle.

(b) What is the resistance of the heating element in the kettle?


A

V

AV

Circuit 1 Circuit 2


5. A vacuum cleaner connected to the mains draws a current of 3·1 A.

(a) What is the power rating of the vacuum cleaner?

(b) What is the resistance of this appliance?

6. An iron rated at 11 kW draws a current of 4·6 A. One day 8 280 C of charge passed through the iron.

(a) How long was the iron in use?

(b) How much electrical energy was supplied in this time?

7. A bulb in a laboratory operates with a current of 2 A. During an experiment 1 200 C of charge flow through the bulb, supplying it with 14 400 J of electrical energy.

(a) How long did this experiment last?

(b) What was the power rating of the bulb?

8. The power rating of an electric fire is 3 kW and it draws a current of 12·5 A. One afternoon the fire used up 8·1 MJ of electrical energy.

(a) For how long was the fire switched on?

(b) How much charge passed through the fire in this time?

9. An electrical appliance has a power rating of 2·4 kW. If 432 000 J of electrical energy are supplied to the appliance by 1 800 C of charge, calculate the current drawn by the appliance.

10. The following label is attached to a hairdryer.

Type 4533

1·44 kW

230 V / 6 A

Calculate the amount of electrical energy supplied to the hairdryer by 4 320 C of charge.


B


Section 4 - Useful Circuits

Series Circuits

Helpful HintThe rules for series circuits are:

1. the current is the same at all points in the circuit2. the voltage of the source is shared amongst the components in the circuit.

1. Two identical 2·5 V bulbs are connected to a supply as shown. What is the voltage of the supply?

2. Four identical resistors are connected across a 12 V supply as shown in the diagram. What is the voltage across each of the resistors?

3. A simple circuit with a bulb and resistor in series is shown below.

(a) If the bulb is operating at its correct voltage and power rating what is the voltageacross the resistor R?

(b) The current in the bulb is 3 A. What current flows in the resistor?


D

12 V

36 V

2·5 V

C

R

2·5 V

A

12 V, 36 W


4. Two resistors are connected in series to a supply as shown in the diagram.

(a) The current in the 200 resistor is 0·05 A. What is the current in the other resistor?

(b) The voltage across the 100 resistor is 5 V. What is the voltage across the200 resistor?

5. A rheostat is used as a dimmer switch in a simple series circuit as shown.

The rheostat is adjusted until the bulb is shining brightly. The voltage across the bulb is 13·8 V and the current through the rheostat at this setting is 1·7 A.

(a) Calculate the voltage across the rheostat.

(b) What is the current flowing in the bulb?


15 V

14 V

100 200


Parallel Circuits

Helpful HintThe rules for parallel circuits are:

1. the voltage is the same across all the components in parallel.2. the current from the supply is shared amongst the different branches of the

circuit.

1. Two resistors are connected in parallel to a 12 V battery.

(a) What is the voltage across R1?

(b) What is the voltage across R2?

(c) What size of current is drawn from the battery?

2. Two identical bulbs and a resistor are connected in parallel to a 6 V supply.

(a) What is the voltage across L2 ?

(b) A current of 1·8 A flows through each of the bulbs. What is the current flowing through the resistor?

3. An electric fire has three elements which can be switched on and off independently. The elements are connected in parallel to the mains supply. Each element draws a current of 0·3 A when switched on.

(a) What is the voltage across the middle element?

(b) What is the total current flowing from the supply when two of the elementsare switched on?

(c) What is the maximum current drawnfrom the mains by the fire?


R2

12 V

R1

L1

L2

R1

6 V

230 V

0·2 A

0·3 A

4 A


4. The headlamps and side lights in a car are connected in parallel. The diagram below shows how they are connected. The side lights (L1 & L2) may be switched on by themselves using switch S1. The headlights (H1 & H2) are switched on by switch S2

and only come on if the sidelights are already on.

(a) What is the voltage across the sidelight L1?

(b) What is the voltage across the headlight H2?

(c) Each sidelight draws a current of 3 A from the car battery. What is the total current drawn from the battery when S1 only is closed?

(d) Each headlight draws a current of 5 A from the car battery. What is the total current drawn from the battery when S1 and S2 are closed?

5. A hairdryer contains a motor and heating elements (resistors). The hairdryer shown below has three heat settings- cold, warm and hot. The circuit diagram shows how these settings are achieved using switches A, B and C.

The motor draws a current of 3 A from the mains and the heating elements draw a current of 2 A each from the mains.(a) Which switches must be closed to make the hairdryer blow warm air?

(b) What current is drawn from the mains when the hairdryer blows warm air?

(c) Which switches must be closed to make the hairdryer blow hot air?

(d) What current is drawn from the mains when the hairdryer blows hot air?

(e) What is the minimum current drawn from the mains when the hairdryer is on?

(f) What is the voltage across the motor?


S2

CBA

H1 H2230 V M

12 V

S1

L1L2 H2H1


Resistance in Series


where Rs = total resistance of a series circuit or series section of a circuit ().

1. Three resistors R1, R2 and R3 are arranged in series as shown in the diagram below.

Find the missing values in the table.

R1 () R2 () R3 () Rs ()

(a) 5 000 490 85

(b) 80 300 25

(c) 800 2 000 200

(d) 700 300 1 400

(e) 140 100 550

(f) 225 85 390

2. Calculate the total resistance of the following circuit.

3. The resistance of the following circuit is 8·8 k. Calculate the resistance of R.

Resistance in Parallel


R1

800

950

R2

5 k

R

R3

3·2

6·3

Rs = R1 + R2 + R3 +......


In this section you can use the equation1 1 1 1 Rp R1 R2 R3

where Rp = total resistance of a parallel circuit or parallel section of a circuit ().

1. Calculate the total resistance of each of the following circuits:

(a) (b) (c)

(d) (e) (f)

(g) (h) (i)


20

100

20

150

120

120

400

1 600

300

80

80

600

80

120

800

2 400

150

300

+= + ....+


2. Calculate the total resistance of each of the following circuits:

(a) (b) (c)

(d) (e) (f)

3. The total resistance of the circuit below is 80 . Calculate the resistance of R.

4. The total resistance of the following circuit is 112·5 . Calculate the resistance of resistor A.

5. The total resistance of the following circuit is 240 . Calculate the resistance of resistor X


600

600

600

1·2 k600

600

R

300

1 200

280 k

220

A

3 k

1 232

900

560 k

X

560 k

3 k

3 k

3 k

900

600

300

600

200

60


Combination Circuits

1. Calculate the total resistance in each of the following networks:

(a) (b)

(c) (d)

(e) (f)


10 20

20 40

60

10 10 10

10

15

30

15

30

10

10

100

1 800

100 10

5

5 10

Helpful HintRs = R1 + R2 + R3 +...... ( for a series section of a circuit)

1 = 1 + 1 + 1 +...... (for a parallel section of a circuit)Rp R1 R2 R3


2. The following circuit shows part of a car lighting system.

Calculate the resistance between points:

(a) X and Y

(b) Y and Z

(c) X and Z.

3. Calculate the resistance of the network of resistors shown below.

4. Which network of resistors has the lowest total resistance?

Network A Network B

5. A school technician has different resistors to use in building house wiring models.

He has two 10 resistors, two 50 resistors and two 100 resistors.How can these resistors be combined to produce a total resistance of:

(a) 260 (b) 300 (c) 30 (d) 35 ?

Section 4 Miscellaneous Questions


250

250

560

560 Y ZX

80 40

60

80 120

90

90

90

15

90

15

10 100 100 50 50 10


1. Bulbs B1, B2 and B3 are all identical. What is the voltage across bulb B2 and bulb B3?

2. Look at the circuit shown and find:

(a) the voltage across R2

(b) the current through R1.

3. In the following circuit the bulbs are identical. Find:

(a) the voltage across each bulb

(b) the current through each bulb.


B3

8 V

16 V

12 V

12 V

24 V

R2R3

R1

I = 2 A

I = 0·9 A

36 V

B1

B2


4. In the following circuit all the resistors are identical. Find:

(a) the voltage across each resistor

(b) the current through each resistor.

5. Daral has a selection of resistors and has to combine them in some way to obtain a total resistance of 60 .He has two 5 , two 20 and two 90 resistors.He sets up three different networks as shown below. Which one is correct?

Network 2

Network 3


D

5

C

5

A B

20

90

24 V

3 A

90

20 20

20

20

90

90 5

Network 1


Section 5 - Behind the Wall


also written as

where E = energy in kilowatt hours (kWh)P = power in kilowatts (kW) t = time in hours (h).

Helpful Hint

Since the joule is such a small unit of energy electricity boards use the unit kilowatt hour to measure how much electricity has been used.

1 kWh = 1 000 W x 3 600 s1 kWh = 3 600 000 J

(1 kWh is often called a ‘unit’ of electricity )

1. How many kilowatt hours of energy does a 3 kW electric fire use when it is switched on for 4 hours?

2. A 4 kW immersion heater is left on for 2 hours to heat water for a bath.

(a) How many kilowatt hours of energy does it use?

(b) How many joules of energy does it use?

3. How many units of energy will a 100 W security light use if it is left on overnight for 8 hours?

4. A 35 kW electric fire is left on full power for 4 hours.

(a) How many units of electricity did the fire use?

(b) If each unit of electricity costs 7·4 p calculate the total cost of running the fire for4 hours.


E = Pt

energy = power x time


5. How long would it take a 1·6 kW fridge to use 8 kWh of energy?

6. A 360 W food processor used 0·072 kWh of energy. For how many minutes was it working?

7. An electric iron uses 0·3 kWh of electricity when left on for 15 minutes. What is the power rating of the iron?

8. A 2 kW hot water urn is left on full power for 30 minutes.

(a) How many kilowatt hours of energy does it use in this time?

(b) What did this electricity cost if each unit costs 7·4 p?

9. How much more expensive would it be to run a 4·5 kW heater for 15 minutes than a 60 W bulb for 10 hours if each unit of electricity costs 7·4 p?

10. The electricity board issue a bill every three months. The bill shows the electricity meter reading at the beginning and end of this period and the total number of units used. The cost per unit of electricity is given along with the standing charge for use of the electricity board’s facilities. An exert from an electricity bill is given below.

Meter Reading Detail of charges

Present Previous

49211 48347 domestic cost per unit 7·4 p

standing charge £10·73

(a) How many units of electricity were used?

(b) What was the total cost of this bill?

(c) How many joules of electricity were used?

(d) Why do you think that electricity companies measure the amount of electricity used in kilowatt hours rather than joules?



Section 6 - Movement from ElectricityThe questions and wordsearch below revise the main ideas in this section.Copy and complete the passage then find the missing words in the wordsearch.

An...............is created when current flows in a wire wrapped around an iron bar. The...............and...............are two devices which use electromagnets.

When a current carrying wire is placed in a magnetic...............it experiences a ................ The electric.................. uses this principle to rotate a coil of wire in a magnetic field. Current flows into this coil of wire through ...............which make contact with a rotating commutator.

The ...............is a split ring of metal which changes the direction of current in the wire at every half turn.

Large commercial motors use ............... for the brushes because it is soft enough to prevent wearing of the commutator. They also use electromagnets rather than .................... magnets as this is a cheaper, lighter and more compact way of producing a magnetic field.

B W P C O M S H L E X L E R YC C M U K R O T L L R O T O MI A E L E C T R I C B E L L NR R L P E R R T I U N C R O FM B E T R I I B O G Z I N E NY O F O R E L A A R C E T R YJ N O C O R B M O B N O S F YO I R O T O O D E A R S I I SE E M N A R M I M T T E P E HL N A O T I A R O O L H L D EE O G C U L E C R D T S I A SN P E R M A N E N T O U N A YT L A F M E A R T C B R U S TE E C R O F L I D E O B E M IR O T I C O E Y A L U M M O C



Using Electricity Revision Questions

General Level

1. Clare has set up a circuit, as shown below, in order to switch on a bulb.

She wants to measure the voltage across the bulb and the current through it.

(a) What should Clare use in order to measure the voltage across the bulb?

(b) What should be used to measure the current in the bulb?

(c) Redraw the circuit to show the correct positions of these meters.

2. Look at the following circuits:

(a) Calculate the voltage across the 12 resistor.

(b) Calculate the current through the 100 resistor.

(c) What is the value of resistor R?

3. An electric kettle operates at mains voltage drawing a current of 9 A.

(a) What is the value of mains voltage?

(b) What is the power rating of the kettle?

(c) How much electrical energy is supplied to this kettle each second?

(d) How much electrical energy would the kettle use if it was switched on for 3 minutes?


0·3 A 12 100

2 V 6 V

R0·015 A


4. For each of the following circuits what should be the reading on the ammeter and voltmeter?

(a) (b)

(c)

5. Calculate the power rating of each of the following electrical appliances.

(a) An electric shaver which draws a current of 2 A from the mains supply.

(b) An electric fire which uses 5 400 000 J of energy in 30 minutes.

(c) A lamp which operates on the mains voltage drawing a current of 0·26 A.

(d) A hairdryer which uses 1 080 000 J of electrical energy in 15 minutes.


A05 A

05 A05 A

V

2·5 V 3·6 V

A

10 20

V1·2 V

V

A 0·2 A

1·5 V


6. The labels for two electrical appliances are shown below but one important piece of information is missing from each label.

(a) Suggest suitable values for the operating voltage of a kettle and the power rating of a lamp.

The flexes for these appliances are shown below:

(b) Complete the following table for flex A.

Colour of insulation

Name of wire

brown

green and yellow

blue

(c) What is the purpose of the green and yellow wire in flex A?

(d) Which flex belongs to the lamp? Explain your answer.

(e) Both the kettle and the lamp are fitted with a 3 A fuse. Which appliance fails to operate? Explain your answer and suggest a solution.

7. Explain how each of the following situations could result in an accident.

(a) Eight appliances are connected to one socket using adapters.

(b) An electricity socket is fitted in the bathroom.

(c) A 13 A fuse is fitted to an alarm clock/radio.


Model No. 5510capacity 17 litres..............V, 50 Hz

2 000 W BEEB approved

Model No. 50736

230 V a.c50 Hz

.....................W

KettleLamp

bluegreen & yellowbrown

bluebrown

Flex A

Flex B


Credit Level

1. A lamp is connected in parallel with a resistor as shown below. The bulb is a 12 V, 36 W bulb.

(a) Calculate the current through the bulb when it is operating at its correct voltage.

(b) What is the resistance of the bulb?

(c) Calculate the current through the resistor.

(d) Calculate the total current drawn from the supply.

2. The rating plate from a hand blender is shown below.

Electronic model no. 3456230 V 50 Hz

1 500 W

(a) Calculate the current drawn by the blender.

(b) Calculate the resistance of the blender.

(c) Explain the significance of the symbol on the rating plate.

The blender has to be charged up before use. It is charged for 5 hours and the average charging current is 10 mA.

(d) Calculate the charge stored.


12 V

6


3. Paul is always being accused of wasting electricity because he has nearly every electrical appliance switched on at once in his room.His stereo, CD player, television, lamp and computer are all connected to the mains via an adapter as shown below.

(a) What kind of circuit is this?

(b) What simple test could you carry out to prove this?

(c) Calculate the total resistance of the circuit when all appliances are on.

(d) Calculate the current drawn from the mains when all the appliances are on.

(e) What is the power rating of the computer?

(f) How many units of energy are used when the computer is on for 6 hours?

(g) If a unit of electricity is 7·4p how much does it cost to run the computer for this length of time?

(h) The lamp is usually on for 5 hours a day. How much money is saved:

(i) per day?(ii) per week?

if the lamp is switched off.


hairdryerR = 500

TVR = 480

lampR = 400

computerR = 2 k

stereoR = 2·2 k

mainsvoltage


4. Junior Spark tries his hand at some DIY electrics in and around his new home.He designs two circuits. Circuit 1 is a model for a room light and Circuit 2 is a model for toy car lights.

His designs are shown below.

Sidelights 12 V , 24 W Headlights 12 V , 36 W

Look at the circuits and answer the following questions.

(a) Describe the function of the variable resistor in circuit 1.

(b) The variable resistor can be set at any resistance between 10 and 10 k. Use this range to calculate the minimum and maximum current that could flow through the bulb.

(c) In circuit 2, which switches must be closed to switch on the head lights?

(d) What size of current is drawn from the battery when all the lights in circuit 2 are

on?

(e) What is the advantage of having the sidelights and the headlights connected in parallel instead of in series with one another?


24 V

R = 900

S2 S3

L1 L2H1 H2S1

Circuit 1

Circuit 2


5. A typical toaster design consists of two heating elements arranged in parallel as shown below.

Calculate the power rating of the toaster.

6. Look at the circuit below and answer the following questions:

(a) Calculate the resistance of the circuit when switch S is open.

(b) What is the reading on the ammeter when switch S is open?

(c) What is the reading on the voltmeter when switch S is open?

(d) Calculate the resistance of the circuit when switch S is closed.

7. Consider the following circuit.

(a) What is the total resistance of this circuit?

(b) Calculate the reading on the ammeter.

(c) What is the voltage across the 90 resistor?8. The following circuit was set up in a classroom.


0·04A

80

Vs

80 230 V

V

AS10

90

60

A

20

9 V

40

6 V

20


(a) What is the current through the bulb?

(b) Calculate the voltmeter reading.

(c) What should the reading on the ammeter be?

(d) Calculate the voltage across the 100 resistor.

(e) What is the voltage across the 300 resistor?

(f) What is the voltage across PQ?

(g) Calculate the supply voltage, Vs.

9. A basic design for an electric bell is shown below.

Explain how the bell operates.


VA

0·03A100

300

P Q0·25 W


10. A d.c. electric motor was built using the following design:

(a) Name the parts of the motor labelled X, Y and Z.

(b) Explain how the d.c. motor operates.

(c) Why is carbon used in commercial motors as the material for component X?

(d) Explain how the magnetic field is produced in larger commercial motors.

(e) How could component Y be improved, from this simple design, for use in large scale motors.



Appendix (i) Data SheetSpeed of light in materials Speed of sound in materialsMaterial Speed in m/s Material Speed in m/sAir 3 x 108 Aluminium 5 200Carbon dioxide 3 x 108 Air 340Diamond 12 x 108 Bone 4 100Glass 20 x 108 Carbon dioxide 270Glycerol 2.1 x 108 Glycerol 1 900Water 23 x 108 Muscle 1 600

Steel 5 200Gravitational field strengths Tissue 1 500

Gravitational field strength on the surface in N/kg

Water 1 500

Earth 10 Specific heat capacity of materialsJupiter 26 Material Specific heat

capacity in J/kgoCMars 4Mercury 4 Alcohol 2 350Moon 16 Aluminium 902Neptune 12 Copper 386Saturn 11 Glass 500Sun 270 Glycerol 2 400Venus 9 Ice 2 100Uranus 117 Lead 128Pluto 42 Silica 1 033

Water 4 180Steel 500

Specific latent heat of fusion of materialsMaterial Specific latent heat of

fusion in J/kgMelting and boiling points of materialsMaterial Melting

point in oCBoiling point in oC Alcohol 099 x 105

Aluminium 395 x 105 Alcohol -98 65Carbon dioxide 180 x 105 Aluminium 660 2470Copper 205 x 105 Copper 1 077 2 567Glycerol 181 x 105 Glycerol 18 290Lead 025 x 105 Lead 328 1 737Water 334 x 105 Turpentine -10 156

SI Prefixes and Multiplication FactorsSpecific latent heat of vaporisation of materials

Prefix Symbol Factor

|Material Sp.l.ht vap(J/kg) giga G 1 000 000 000=109

Alcohol 112 x 105 mega M 1 000 000 =106

Carbon dioxide 377 x 105 kilo k 1 000 =103

Glycerol 830 x 105 milli m 0001 =10-3

Turpentine 290 x 105 micro 0000 001 =10-6

Water 226 x 105 nano n 0000 000 001=10-9



Appendix (ii) Answers to Numerical Problems.Section 2-A.C.& D.C.Current, Charge & Time (p.4)1.(a) 150 C(b) 18 C(c) 2 s(d) 12 s(e) 30 A(f) 94 A2. 60 C3. 42 A4. 1 200 s5. 630 C6. 025 A7.(a) 10 800 s8. 180 s9. 105 000 C10. 46 A

Section 3 - ResistanceVoltage, Current & Resistance(p.6)1.(a) 525 V(b) 200 V(c) 184 A(d) 004 A(e) 10 (f) 960 2. (a) 50 V(b) 640 V(c) 24 V3. (a) 2 A(b) 024 A(c) 009 A4.(a) 960 (b) 400 000 (c) 72 727 5. 2 400 6. 015 A7. 36 V8. 230 V9. 15 333 10. 016 A

Power, Energy & Time (p.8)1.(a) 50 W(b) 5 W(c) 60 000 J

(d) 2 400 J(e) 40 s1.(f) 10 s2. 12 s3. 150 W4. 4 000 J5. 95 W6. 1 440 000 J7. 15 minutes8. 2 900 W9. 1 200 s10. 950 W

Power, Current & Voltage(p.10)1.(a) 30 W(b) 54 W(c) 652 A(d) 3 A(e) 240 V(f) 6 V2. 36 W3. 10909 V4. 026 A5. 690 W6. 2 A7. 157 A8. 070 A9. (a) 12 V(b) 810. 23810 V11. 35 V12. 188 A13. 217 x 10-5 A14. 9 V15. (a) 565 A(b) 1696 A

Power and Resistance(p.13)1. 44063 W2. 900 W3. 11021 W4. 1 17556 W5. 40160 W6. 918 W7. 25358 W 8. 77794 W9. 48091 W10. 05 A11. 460 12. 26 450 13. 7053 14. 1225 V15. 13225 W

Section 3 Misc. Questions(p.15)1. (a) 36 W(b) 4 (c) 6 480 J(d) 540 C2. (a) 3 mA(b) 30 V(c) 60 s(d) 018 C3.(a) circuit 2 (b) 10 4. (a) 957 A(b) 24 5. (a) 713 W(b) 7419 6. (a) 1 800 s(b) 198 x 106 J 7. (a) 600 s(b) 24 W8. (a) 2 700 s(b) 33 750 C9. 10 A10. 1 036 800 J

Section 4 - Useful CircuitsSeries Circuits(p18)1. 5 V2. 3 V3. (a) 24 V(b) 3 A4. (a) 005 A(b) 10 V5. (a) 02 V(b) 17 A

Parallel Circuits (p.20)1.(a) 12 V(b) 12 V(c) 05 A2. (a) 6 V(b) 04 A



3. (a) 230 V(b) 06 A(c) 09 A4. (a) 12 V(b) 12 V(c) 6 A(d) 16 A5. (a) A & B(b) 5 A(c) A, B & C(d) 7 A(e) 3 A(f) 230 V

Resistance in Series Circuits(p.22)1.(a) 5575 (b) 405 (c) 3000 (d) 400 (e) 310 (f) 80 2. 9 000 3. 1 550

Resistance in Parallel Circuits (p.23)1. (a) 40 (b) 10 (c) 60 (d) 48 (e) 60 (f) 320 (g) 200 (h) 100 (i) 600 2.(a) 200 (b) 1 k(c) 240 (d) 140 k(e) 100 (f) 32143 3. 140 4. 225 5. 360

Combination Circuits (p.25)1.(a) 20 (b) 70 (c) 25

(d) 20 (e) 55 (f) 225 2. (a) 125 (b) 280 (c) 405 3. 27429 4. network B5.(a) 100 100 50 10

(b) 100 100 50 50

(c) 50 10

50 10(d)

50 10

50

Section 4 Misc. Questions(p.27)1. 4 V2. (a) 8 V(b) 2 A3. (a) 24 V(b) 03 A4. (a) 12 V (b) 15 A5. network 3

Section 5 - Behind the WallKilowatt hour(p.29)1. 12 kWh2. (a) 8 kWh(b) 288 x 107 J3. 08 units4. (a) 14 units (b) £1045. 5 hours6. 12 minutes7. 12 kW8. (a) 1 kWh(b) 74 p9. 39 p10. (a) 864 units(b) £7467(c) 3.11 x 109 J Revision Questions

General Level(p32)2.(a) 36 V(b) 002 A(c) 400 3.(a) 230 V(b) 2 070 W(c) 2 070 J(d) 372 600 J4.(a) 15 A 25 V(b) 012 A 24 V(c) 02 A 15 V

5.(a) 460 W(b) 3 000 W(c) 598 W(d) 1 200 W6.(a) kettle - 230 V lamp ~ 60 W

Credit Level(p.36)1. (a) 3 A(b) 4 (c) 2 A(d) 5 A2.(a) 652 A(b) 3527 (d) 180 C3.(c) 13266 (d) 173 A(e) 2645 W(f) 016 units(g) 1 p(h)(i) 489 p (ii) 3425 p4.(b) 22x10-3 A, 003 A(d) 10 A5. 1 3225 W6.(a) 30 (b) 02 A(c) 4 V(d) 25 7.(a) 36 (b) 025 A(c) 9 V8.(a) 004 A(b) 625 A(c) 001 A



(d) 3 V(e) 3 V(f) 3 V(g) 925 V


using electricity - lesmahagow high · web view= voltage in volts (v) i = current in amps (a)...

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