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

1. 1
   A phone charger delivers a constant current of 2.0 A at a potential difference of 5.0 V. A phone is charged for 45 minutes.

   (a)

   Calculate the charge that flows through the phone during charging.

   [1 mark]

   • A5.4 × 10³ C
   • B90 C
   • C0.044 C
   • D2.7 × 10³ C

   (b)

   Calculate the energy transferred to the phone during charging.

   [1 mark]

   • A1.1 × 10³ J
   • B5.4 × 10³ J
   • C1.35 × 10⁴ J
   • D2.7 × 10⁴ J

   (c)

   Calculate the number of electrons that pass through the charger cable each second. The charge of an electron is 1.60 × 10⁻¹⁹ C.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A student investigates a filament lamp. When the potential difference across the lamp is 6.0 V the current is 1.5 A, and when it is 12 V the current is 2.0 A.

   (a)

   Which statement is Ohm's law?

   [1 mark]

   • AThe resistance of any conductor is always constant
   • BThe current in a conductor is directly proportional to the potential difference across it, provided the temperature is constant
   • CThe current in a conductor is inversely proportional to the potential difference across it, provided the temperature is constant
   • DThe resistance of a conductor is directly proportional to the current in it

   (b)

   What is the resistance of the lamp when the p.d. across it is 12 V?

   [1 mark]

   • A0.17 Ω
   • B4.0 Ω
   • C6.0 Ω
   • D24 Ω

   (c)

   Use the data to explain why the filament lamp does not obey Ohm's law.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   The heating element of an electric kettle is connected to a 230 V supply. When the water is boiling the element carries a steady current of 8.7 A for 3.0 minutes.

   (a)

   Calculate the charge that passes through the element and the energy it transfers in this time.

   [3 marks]

   (b)

   When the kettle is first switched on with the element cold, the initial current is 10.5 A at the same 230 V. Calculate the resistance of the element when it is cold and when the water is boiling. Explain the difference and deduce whether the element obeys Ohm's law.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A student has a component inside a sealed box with two terminals. She connects it into a circuit with a variable power supply, an ammeter and a voltmeter, to find out whether the component obeys Ohm's law.

   (a)

   Describe how the student should use the apparatus to find out whether the component obeys Ohm's law, and how she should interpret her results.

   [6 marks]

   (b)

   The student records the following pairs of readings of p.d. and current: 1.0 V and 0.10 A; 2.0 V and 0.20 A; 3.0 V and 0.30 A; 4.0 V and 0.38 A; 5.0 V and 0.44 A; 6.0 V and 0.48 A. Calculate the resistance at 2.0 V and at 6.0 V, deduce whether the component obeys Ohm's law over the whole range, and suggest an explanation for the results.

   [6 marks]

   Total for question 4: 12 marks

End of questions