Alternating currentsEdexcel A-Level Physics: Subtopic test

1. 1
   A sinusoidal alternating p.d. has a peak value of 12.0 V and a frequency of 50 Hz.

   (a)

   What is the root-mean-square (r.m.s.) value of this p.d.?

   [1 mark]

   • A8.5 V
   • B6.0 V
   • C17 V
   • D24 V

   (b)

   What is the period of the alternating p.d.?

   [1 mark]

   • A2.0 ms
   • B5.0 ms
   • C50 ms
   • D20 ms

   (c)

   Explain what is meant by the root-mean-square value of an alternating p.d., and why it is less than the peak value.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A heater of resistance 46 Ω is connected to the 230 V r.m.s. mains supply, which has a frequency of 50 Hz.

   (a)

   What is the peak p.d. of the mains supply?

   [1 mark]

   • A163 V
   • B325 V
   • C460 V
   • D650 V

   (b)

   What is the mean power dissipated in the heater?

   [1 mark]

   • A2300 W
   • B575 W
   • C1150 W
   • D5.0 W

   (c)

   Calculate the r.m.s. current in the heater and the peak current.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A student displays an alternating supply on an oscilloscope. The time-base is set to 5.0 ms per division and the Y-gain to 2.0 V per division. One complete cycle of the trace spans 4.0 horizontal divisions, and the trace reaches 3.0 divisions above and 3.0 divisions below the centre line.

   (a)

   Calculate the period and the frequency of the alternating supply.

   [3 marks]

   (b)

   Calculate the peak p.d. and the r.m.s. p.d. of the supply. The supply is then connected across a 15 Ω resistor. Calculate the mean power dissipated in the resistor.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A technician connects a filament lamp first to a 6.0 V d.c. supply and then to a 50 Hz alternating supply with a peak p.d. of 8.5 V. The resistance of the lamp when hot is 12 Ω. A student predicts that the lamp will be brighter on the alternating supply because 8.5 V is greater than 6.0 V.

   (a)

   Evaluate the student's prediction.

   [6 marks]

   (b)

   The lamp is left on the alternating supply for 2.0 minutes. Calculate the mean power and the peak power in the lamp, the energy transferred, and the number of complete cycles of the supply in that time.

   [6 marks]

   Total for question 4: 12 marks

End of questions