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2 marksAlternating Currents

CAPE Physics Unit 2 · 2002 · Paper 2 · Question 6(c)(iii)

Electric power of 8000 kW is transmitted via transformers S and T and transmission cables at 300 kV r.m.s., generated and consumed at 10 kV r.m.s. (Figure 9).

Calculate the current in the transmission supply cable.

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Other parts of this question

  1. 6(a)(i)State THREE ideal properties of operational amplifiers (Op-Amps).[3 marks]
  2. 6(a)(ii)For the Op-Amp circuit shown in Figure 8, show that the output voltage is given by Vo = - (Rf / R1) V1 - (Rf / R2) V2.[3 marks]
  3. 6(a)(iii)Suggest a practical use for this summing amplifier circuit.[1 mark]
  4. 6(b)(i)Write an equation relating the r.m.s. value and the peak value of an alternating current.[1 mark]
  5. 6(b)(ii)A car battery-charger operates from a 120 V r.m.s. a.c. line and supplies 10 A d.c. at 14 V. If it is 80% efficient, calculate the current drawn from the a.c.…[3 marks]
  6. 6(b)(iii)If electricity costs 16 cents/kWh, calculate the cost of operating the charger for 10 hours.[3 marks]
  7. 6(c)(i)Calculate the r.m.s. current supplied to the consumer.[2 marks]
  8. 6(c)(ii)Determine the turns ratio Ns / Np for EACH transformer, S and T.[2 marks]

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