Alternating current and voltaage


1. A sine wave has a periodic time of 0.25 ms. Which one of the following gives the frequency of the sine wave?




2. A sine wave has an r.m.s. value of 200V. Which one of the following gives the approximate peak-peak value of the voltage?




3. The reactance of a capacitor is 100 ohm at 50 Hz. What will the reactance be at 400 Hz?




4. The reactance of an inductor is 600 ohm at 2 kHz. What will the reactance be at 500 Hz?




5. The current flowing in a capacitor:




6. A circuit consists of a resistance of 300 ohm connected in series with a reactance of 400 ohm. Which of the following gives the impedance of the circuit?




7. At resonance, the impedance of a series L-C-R tuned circuit will be:




8. A typical application for the component shown below is:






9. A suitable material for use as the core of a power transformer is:




10. A transformer has a turns ratio of 20:1. If the primary is fed from a 240V AC supply and a load of 30 ohms is connected to the secondary, which one of the following gives the primary current?




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