1. 1
   A hobbyist testing components for an electronics kit connects a voltmeter across a resistor and an ammeter in series with it, in order to determine the resistor's resistance.

   (a)

   The voltmeter reads 6.0 V and the ammeter reads 2.0 A. Which equation should the hobbyist use to find the resistance?

   [1 mark]

   • A$R = \frac{V}{I}$
   • B$R = VI$
   • C$R = \frac{I}{V}$
   • D$R = V + I$

   (b)

   Using the readings of 6.0 V and 2.0 A, what is the resistance of the component?

   [1 mark]

   • A12 ohms
   • B8.0 ohms
   • C3.0 ohms
   • D0.33 ohms

   (c)

   Describe how the hobbyist should connect the voltmeter and the ammeter in the circuit to correctly measure the resistance of the component.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A cable manufacturer tests samples of copper wire of different lengths and different cross-sectional areas to decide which cable is suitable for a new industrial wiring order.

   (a)

   A cable manufacturer tests two copper wires of the same cross-sectional area but different lengths, keeping the temperature constant. Compared to a short sample, how does the resistance of a much longer sample of the same wire compare?

   [1 mark]

   • AThe longer wire has zero resistance
   • BThe longer wire has a smaller resistance
   • CLength has no effect on resistance
   • DThe longer wire has a greater resistance

   (b)

   The manufacturer then compares two wires of the same length and material but different cross-sectional areas. Compared to a thin wire, how does the resistance of a much thicker wire (larger cross-sectional area) compare?

   [1 mark]

   • AThe thicker wire has a greater resistance
   • BThe thicker wire has a smaller resistance
   • CCross-sectional area has no effect on resistance
   • DThe thicker wire conducts no current at all

   (c)

   State, qualitatively, how the resistance of a metallic wire depends on its length and on its cross-sectional area.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A student investigates the current–potential difference behaviour of a filament lamp and, separately, a diode, using a variable power supply, an ammeter and a voltmeter.

   (a)

   A student investigates a filament lamp by recording the current through it for a range of increasing potential differences, then sketches a current–potential difference graph. Describe the shape of the current–potential difference graph obtained for a filament lamp, and explain this shape in terms of the resistance of the filament as the current increases.

   [3 marks]

   (b)

   The student then repeats the investigation using a diode in place of the filament lamp, reversing the connections to test both directions. Describe the current–potential difference graph obtained for the diode, contrasting its behaviour in the two directions, and compare this overall behaviour with that of a resistor of constant resistance.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   An electricity supply company must choose the length and thickness (cross-sectional area) of copper cable used to connect a substation to a small housing estate several kilometres away, while also fitting rectifying diodes at a local workshop for a separate small d.c. project.

   (a)

   Explain, using the ideas that resistance is directly proportional to length and inversely proportional to cross-sectional area, the trade-offs the company faces in choosing a long cable route with a large cross-sectional area versus a shorter route with a smaller cross-sectional area, and why simply using extremely thick cable everywhere is not a realistic solution.

   [6 marks]

   (b)

   At a small workshop nearby, an engineer builds a simple circuit that uses a diode to convert an alternating current supply into a current that flows in one direction only, ready to charge a battery. Explain, using the current–potential difference behaviour of a diode, how connecting a diode in series with the a.c. supply and the battery achieves this, and explain what would happen differently if a resistor of constant resistance were used in place of the diode.

   [6 marks]

   Total for question 4: 12 marks

End of questions