Additional - Topic 2.2 - Electricity

Question 1

The power of the kettle when it is heating water is 1.8 kW.
The mains voltage is 230 V.
(i) Calculate the current in the kettle.
(3)

Answer 1

Substitution (1)
1800 = 230 x I
Transformation (1)
I = 1800 / 230
Evaluation (1)
7.8 (A)
substitution and transposition
can be in either order

Question 2

The heating element of the kettle contains a resistor made from a long length
of wire. Explain why an electric current in a resistor makes the resistor heat up.

Answer 2

An explanation linking two from
Energy is transferred (1)
(as a result of) collisions of
electrons (1)
with ions/atoms / lattice (1)

Question 3

The normal operating potential difference (voltage) and current of the filament
lamp is 6 V, 0.4 A.
Calculate the energy supplied to the lamp under these conditions in 20 s.
(2)

Answer 3

substitution
0.4 x 6 x 20
(1)
evaluation
48 (J)
(1)
Ignore any unit given by the
candidate

Question 4

The current in a wire is 3.7 A.
Calculate the charge that flows into the wire in 13 s.
(2)

Answer 4

substitution (1)
3.7 x 13
evaluation (1)
48 (C)

Question 5

A resistor is a circuit component.
Two other circuit components are a light dependent resistor (LDR) and a
thermistor.
Explain how LDRs and thermistors can be used to control the current in a circuit.
(6)

Answer 5

A explanation including some of the following points
Light dependent resistors (LDR)
• Resistance changes with light intensity
• Bright light , low resistance
• No light (dark), high resistance
• Low resistance gives high current.(RA)
Thermistor
• Resistance changes with temperature
• Negative temperature coefficient
• High temperature, low resistance
• Low temperature, high resistance
• Low resistance gives high current (RA)

Question 6

Calculate the resistance of the lamp when the current is 0.44 A and the potential
difference is 10.0 V.

Answer 6

substitution (1)
10/0.44 or 250/11
evaluation (1)
23 (ohms)

Question 7

The supply voltage is 12 V.
At 20 °C the current is 0.047 A.
Calculate the resistance of the thermistor at this temperature.
(3)

Answer 7

Substitution: (1)
12 = 0.047 x R
Transposition: (1)
R = 12/0.047
Evaluation: (1)
R = 260

Question 8

explain the relationship
between resistance and temperature for a thermistor.
(2)

Answer 8

An explanation linking
• current increases with
temperature (1)
with
• (so) resistance
decreases(1)
or
• the voltage is constant (1)
with
• (so) resistance decreases
(with temperature
increase)(1)

Question 9

When there is an electric current in a resistor, the resistor gets hot.
Explain why the resistor gets hot.
(2)

Answer 9

An explanation linking
• {electrons / negative
charges} (1)
• collide with
{ions/lattice/electrons} (1)

Question 10

Suggest why the thermistor in a temperature gauge might indicate a
temperature slightly higher than the actual temperature of its surroundings.

Answer 10

A suggestion including
energy transfer in {the
thermistor/ any component part
of the electrical circuit} causes a
rise in temperature of thermistor
(above surroundings)(1)

Question 11

The current is 0.26 A and the potential difference (voltage) across the lamp is
6.0 V.
Calculate the resistance of the lamp.
(2)

Answer 11

Substitution
R = 6.0 / 0.26 (1)
Evaluation
= 23 (1)

Question 12

Some electrical energy is transferred to light energy in the lamp.
Explain why only some of the electrical energy is transferred to light energy in the
lamp.
(2)

Answer 12

An explanation linking the
following points
Heat/thermal energy is produced
(1)
In the lamp/bulb / variable
resistor / connecting wires
(1)

Question 13

The students use a different lamp in the circuit.
The current in this lamp is 0.4 A.
The potential difference (voltage) across the lamp is 5 V.
Calculate the power being supplied to the lamp.

Answer 13

substitution (1)
0.4 x 5
evaluation (1)
2 (W)