Topic 2

QUESTIONSHEET 1

(a) 3 A / 2 1 1

= 1.5 A 1 1

(b) 6 V 1 1

= 6 / 1.5 1 1

= 4 W 1 1

TOTAL / 6

QUESTIONSHEET 2

(a) 5 W + 10 W 1 1

= 15 W 1 1

(b) I = V / R 1 1

= 3 / 15 1 1

= 0.2 A 1 1

Units are essential in calculations. Sometimes examination questions give a blank space for the answer followed by the unit. Sometimes no unit is given and you are expected to supply it. It is a common mistake to leave the units out altogether – don’t get into this bad habit.

TOTAL / 5

QUESTIONSHEET 3

(a)

symbols correct 1 1

2 W and 4 W resistors in parallel 1 1

5 W resistor in series 1 1

(b) resistance of parallel resistors given by

1 1

so total resistance = + 5 = W 1 1

= 0.95 A 1 1

For parallel resistors, it is sometimes easier to use the expression Product / Sum for the total resistance.

i.e. here we get 2 × 4 / (2 + 4) = 8 / 6 = 4/3 W

TOTAL / 9

QUESTIONSHEET 4

(a) (i) Power of lamp is 6 W 1 1

when used on 12 V 1 1

(ii) 6 W = 6 J/s 1 1

5 minutes = 300 s 1 1

energy transferred = 300 ´ 6 1 1

= 1800 J 1 1

(b) (i) I = P / V = 6 / 12 1 1

= 0.5 A 1 1

(ii) R = V / I = 12 / 0.5 1 1

= 24 W 1 1

24 V shared between 2 lamps / pd across each lamp is 12 V 1

Power is the rate of transferring electrical energy into other forms – in this case, heat and light. A 6 W lamp transfers 6 Joules of electrical energy into heat & light each second, since 1 W = 1 J/s.

The formula P = I / V is one you need to know.

TOTAL / 12

QUESTIONSHEET 5

(a) (i) 0.6 ´ 10/20 1 1

= 0.3 A 1 1

(ii) 0.6 + 0.3 1 1

= 0.9 A 1 1

(b) V = I R 1 1

0.6 ´ 10 or 0.3 ´ 20 1 1

= 6 V 1 1

Current is inversely proportional to the resistance as long as the pd is constant. So half the current flows through the resistor that is twice as big.

TOTAL / 7

QUESTIONSHEET 6

(a) 1 1

R = 5 W 1 1

(b) 10 + 5 1 1

= 15 W 1 1

= 0.4 A 1 1

current through parallel resistors = 0.2 A 1

In many questions, the value of the parallel resistors is the same. In this case, the total resistance is half the value of one.

TOTAL / 7

QUESTIONSHEET 7

(a) (i) 2 + 5 + 10 1 1

= 17 W 1 1

(ii) 1/R = 1/2 + 1/5 + 1/10 1 1

= 8 / 10 W 1 1

R = 10 / 8 = 1.25 W 1 1

(b) Current larger in (ii) 1 1

current inversely proportional to resistance 1 1

smaller resistance means larger current 1 1

TOTAL / 8

QUESTIONSHEET 8

(a) = 4W 1 1

= 2 1

Total resistance = 2 + 4 = 6W 1 1 1

(b) I = V / R 1 1

= 12 / 6 1 1

= 2 A 1 1

= 7 1 1

I = 12 / 7 or 1.7 A 1 1

(d) R = 3 + 6 = 9 W 1 1

I = V / R = 12 / 9 1 1

= 1.33 A 1 1

TOTAL / 11

QUESTIONSHEET 9

(a) C 1 1

(b) (i) a complete path 1 1

for electricity to flow 1 1

when connected to a voltage supply 1 1

(ii) A & D (both) 1 1

No electricity flows in the last circuit, because the cells are the opposite way round from each other,

so they cancel out.

TOTAL / 5

QUESTIONSHEET 10

(a) switch shown in either of the positions indicated 1

(b) Parallel 1 1

= 0.5 A 1 1

(d) 12 V 1 1

TOTAL / 5

QUESTIONSHEET 11

(a) Resistance in circuit alters current 1 1

ammeter resistance must be low so it doesn’t affect

current flow 1 1

(b) (i) In parallel across component 1 1

(ii) voltmeter must have high resistance 1 1

little current flows through voltmeter 1 1

most current flows through component 1 1

For two parallel resistors, 1/R = 1/R₁ + 1/R₂. So if one resistor (the voltmeter) R₂ has a high resistance, 1/R₂ is very small and the total resistance is almost the same as without the voltmeter.

TOTAL / 6

QUESTIONSHEET 12

Text Box: pd/v

(a)

axes labelled + units 1 1

correct plotting 2 2

smooth curve drawn 1 1

(b) (i) no 1 1

(ii) the graph is not a straight line 1 1

or V / A ¹ R 1 1

(iii) filament lamp 1 1

TOTAL / 8

QUESTIONSHEET 13

(a) Voltage is proportional to current 1

for a metal conductor at constant temperature 1

(b)

circuit symbols correct 1

ammeter in series 1

voltmeter in parallel 1

variable resistor in series 1

TOTAL / 6

QUESTIONSHEET 14

(a) A = metal wire 1 1

B = diode 1 1

C = lamp filament 1 1

(b) A 1 1

An ohmic conductor obeys Ohm’s law, so a graph of I against V must be a straight line through the origin.

The gradient of graph C decreases so the resistance must be increasing.

TOTAL / 5

QUESTIONSHEET 15

(a) (i)

MACHINE

two switches 1 1

in series 1 1

with machine 1 1

(ii) each switch must be able to turn off machine 1 1

(b) switches not in series 1 1

each must be able to switch light on or off 1 1

needs two parallel parts of circuit 1 1

TOTAL / 7

QUESTIONSHEET 16

(a) Set up Ohm’s law circuit 1 1

Test component

measure pd across wire and current through it 1

measure length of wire 1 1

change length of wire and repeat experiment 1 1 1

(b) (i)

Length (cm)

Resistance (W)

(ii) as length increases 1

resistance increases

directly proportional 1

(iii) as length varies, resistance varies 1 1

current varies 1 1

and light dims or brightens 1 1

The first two or three marks of this question could be obtained by drawing a labelled diagram.

TOTAL / 12

QUESTIONSHEET 17

(a) A = battery 1 1

B = lamp/light bulb 1 1

C = switch 1 1

D = variable resistor 1 1

(b) varies current in a circuit / acts as dimmer switch 1

You must be able to recognise circuit components. Look at the syllabus or ask your teacher which ones you must know. Note that a battery is made up of two or more cells joined in series

TOTAL / 5

QUESTIONSHEET 18

(a) (i) 1.5 V 1 1

(ii) 0 V 1 1

(iii) 3.0 V 1 1

(iv) 1.5 V 1 1

(v) 1.5 V 1 1

(b) car bulb needs 12 v 1 1

TOTAL / 7

QUESTIONSHEET 19

(a) silver too expensive 1 1

(b) copper is too heavy 1 1

(d) water will conduct electricity 1 1

would get shock with wet hands 1 1

TOTAL / 7

QUESTIONSHEET 20

(a) One connected after another in line 2 1

(b) 240 / 20 1 1

= 12 V 1 1

higher voltage would cause it to blow 1 1

(d) (i) fuse would blow repeatedly 1 1

(ii) fault would not blow fuse 1 1

could be dangerous to operator 1 1

TOTAL / 9