Electrical power and I-V characteristicsEdexcel A-Level Physics: Subtopic test

1. 1
   An electric kettle is rated 2.3 kW when connected to the 230 V mains supply. Its heating element is a single piece of resistance wire.

   (a)

   Calculate the current in the heating element when the kettle operates at its rated power.

   [1 mark]

   • A0.10 A
   • B10 A
   • C100 A
   • D5.3 × 10⁵ A

   (b)

   What is the resistance of the heating element at its operating temperature?

   [1 mark]

   • A0.10 Ω
   • B10 Ω
   • C2.3 Ω
   • D23 Ω

   (c)

   The kettle is switched on for 3.0 minutes at its rated power. Calculate the energy transferred by the element. Give your answer in joules.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A student investigates a filament lamp using a variable power supply. At a p.d. of 2.0 V the current in the lamp is 0.50 A, and at a p.d. of 12 V the current is 1.5 A.

   (a)

   What is the resistance of the lamp at a p.d. of 12 V?

   [1 mark]

   • A8.0 Ω
   • B18 Ω
   • C0.13 Ω
   • D10.5 Ω

   (b)

   What is the power dissipated in the lamp at a p.d. of 12 V?

   [1 mark]

   • A8.0 W
   • B13.5 W
   • C18 W
   • D144 W

   (c)

   Explain why the resistance of the lamp at 12 V is greater than its resistance at 2.0 V.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A silicon diode is connected in series with a 220 Ω resistor and a 6.0 V battery of negligible internal resistance. When the diode is forward-biased the p.d. across it is 0.70 V.

   (a)

   Calculate the current in the circuit.

   [3 marks]

   (b)

   The battery is now reversed so the diode is reverse-biased. Describe and explain the current in the circuit, and state the approximate p.d. across the diode.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A technician investigates three components in turn, each connected to a variable d.c. supply: a fixed resistor kept at constant temperature, a filament lamp and a negative temperature coefficient (NTC) thermistor. The p.d. across each is increased from 0 to 10 V and the current recorded.

   (a)

   Describe and explain the shape of the I–V characteristic for each of the three components.

   [6 marks]

   (b)

   The thermistor has a resistance of 500 Ω at 25 °C and 40 Ω at 80 °C, and its maximum safe power is 0.50 W. Evaluate whether the technician can safely connect it directly across a constant 10 V supply with no other component in the circuit.

   [6 marks]

   Total for question 4: 12 marks

End of questions