1. 1
   A technician connects an ammeter in series with a mobile phone charging cable to measure the current flowing into the phone's battery while it charges.

   (a)

   What quantity does the ammeter reading actually represent?

   [1 mark]

   • AThe total energy transferred to the phone
   • BThe rate of flow of charge through the cable
   • CThe total charge stored in the phone's battery
   • DThe voltage across the charging cable

   (b)

   The technician needs to select an ammeter to measure this small charging current accurately. Which type of ammeter range would be most suitable?

   [1 mark]

   • AAn ammeter with a low current range, giving finer readings for small currents
   • BAn ammeter with the largest possible range, regardless of the current size
   • CA voltmeter connected in series instead
   • DAny ammeter, since range does not affect the accuracy of small readings

   (c)

   The ammeter shows a steady reading while the phone charges. Define electric current and state the equation linking current, charge and time, including the unit of each quantity.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A factory production line is powered partly by the mains alternating current supply and partly by a large battery bank used as backup power for a conveyor motor, and engineers must understand the difference between the two supplies.

   (a)

   A factory production line is powered partly by the mains supply and partly by a large battery bank used as backup power for a conveyor motor. Which of these correctly describes direct current (d.c.), as supplied by the battery bank?

   [1 mark]

   • ACurrent that continuously reverses direction
   • BCurrent that only flows through insulators
   • CCurrent that flows in one direction only
   • DCurrent that has no measurable value

   (b)

   The mains supply to the factory is alternating current (a.c.). How does this differ from the direct current (d.c.) from the battery bank?

   [1 mark]

   • Aa.c. cannot be measured with an ammeter
   • Ba.c. flows in one direction only, while d.c. periodically reverses
   • CThere is no difference between a.c. and d.c.
   • Da.c. periodically reverses direction, while d.c. flows in one direction only

   (c)

   Explain, in terms of the movement of free electrons, how the conveyor motor's copper wiring is able to conduct current from the battery bank.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A simple torch circuit contains a cell, a switch and a lamp connected by copper wires, and a student investigates the current flowing when the switch is closed.

   (a)

   When the switch is closed, a steady current of 0.30 A flows for 4 minutes before the switch is opened again. Calculate the total charge that has passed through the lamp during this time.

   [3 marks]

   (b)

   Explain the direction in which conventional current is said to flow in the torch circuit when the switch is closed, and explain how this direction compares with the actual direction of movement of the free electrons in the copper wire.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   In the early years of electrical power distribution, engineers debated whether homes and factories should be supplied with direct current (d.c.) from batteries and dynamos, or alternating current (a.c.) from generators driven by steam or water power.

   (a)

   Explain what is meant by direct current and alternating current, how each is produced or supplied, and how the flow of charge differs between the two, using ideas about conventional current and the movement of free electrons in a conductor.

   [6 marks]

   (b)

   A historian researching this early debate finds that some engineers argued a.c. supplies were more dangerous because the current direction is constantly changing, while others argued d.c. supplies could be equally hazardous. Using ideas about current as a flow of charge, and the effect of current passing through a person's body, explain why either type of electric current, a.c. or d.c., can be dangerous, and why simply knowing the direction of current flow does not, by itself, make a supply safe or unsafe.

   [6 marks]

   Total for question 4: 12 marks

End of questions