Current, potential difference and resistanceEdexcel International A Level Physics: Subtopic test

1. 1
   A student connects a small electric motor to a 6.0 V battery of negligible internal resistance. The motor draws a steady current of 0.50 A for 3.0 minutes, and the whole 6.0 V is across the motor.

   (a)

   Calculate the charge that flows through the motor in this time.

   [1 mark]

   • A0.0028 C
   • B1.5 C
   • C90 C
   • D360 C

   (b)

   Calculate the energy transferred to the motor in this time.

   [1 mark]

   • A3.0 J
   • B540 J
   • C15 J
   • D0.067 J

   (c)

   Calculate the number of electrons that pass through the motor in this time. (Elementary charge e = 1.60 × 10⁻¹⁹ C.)

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A student investigates a length of nichrome wire kept at a constant temperature in a water bath. She measures the current for different potential differences across the wire and records: 0.10 A at 0.50 V, 0.20 A at 1.00 V, 0.30 A at 1.50 V and 0.40 A at 2.00 V.

   (a)

   Assuming the wire continues to obey Ohm's law, what current would flow at 3.0 V?

   [1 mark]

   • A0.60 A
   • B0.50 A
   • C1.7 A
   • D15 A

   (b)

   Which statement is Ohm's law?

   [1 mark]

   • AThe resistance of any component is V/I, so every component obeys Ohm's law.
   • BThe current in a conductor is inversely proportional to the potential difference across it.
   • CThe power dissipated in a conductor is proportional to the current through it.
   • DThe current through a metallic conductor is directly proportional to the potential difference across it, provided the temperature is constant.

   (c)

   Use the student's data to decide whether the wire obeys Ohm's law. Justify your answer.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   During a thunderstorm a lightning flash lasts 2.0 ms. A total charge of 24 C is transferred between the cloud and the ground through a potential difference of 1.5 × 10⁸ V. A metal lightning conductor on a nearby building carries the discharge and has a resistance of 0.015 Ω.

   (a)

   Calculate the mean current during the flash and the energy transferred.

   [3 marks]

   (b)

   Assume the lightning conductor carries the mean current from part (a) for the whole 2.0 ms. Calculate the potential difference across the conductor and the energy transferred in it.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A teacher gives students a length of constantan wire and a small filament lamp and asks them to find out which of the two obeys Ohm's law. They have a variable d.c. power supply, an ammeter, a voltmeter and connecting leads. For the lamp they record: 0.50 A at 2.0 V, 0.80 A at 4.0 V and 1.00 A at 6.0 V.

   (a)

   Describe how the students could obtain results with the constantan wire and use them to decide whether it obeys Ohm's law.

   [6 marks]

   (b)

   Calculate the resistance of the lamp at each p.d. and explain, with reference to what happens inside the filament, why the lamp does not obey Ohm's law.

   [6 marks]

   Total for question 4: 12 marks

End of questions