Revision Summative 1

A transformer has a turns ratio of 1/4. If the electrical energy is converted to heat in the windings and the core at the rate of 4 W, what is the current in the secondary

• 0.1 A

• 0.4 A

• 0.5A

• 0.8 A

Calculate the peak value of an iron box that uses a 220 V ac source?

• 310 V

• 110 V

• 156 V

• 440 V

The number of turns on the transformers is as shown in the figure below.

What is the output voltage of the transformers, if the input voltage of the transformers is 5 V?

• 10 V

• 20 V

• 30 V

• 40 V

Why do we transfer electricity over long distances as a.c. current? Because…

• transformers are used to reduce power loss due to heating effect power loss

• a.c. generates are used

• power lines are over head or underground

• high voltages are normally used

A power station generates electrical power at a rate of 10 MW. This power is to be transmitted along cables whose total resistance is 10 Ω. Calculate the power loses in the cable if the voltage is transmitted at 50 kV.

• 300 kW

• 500 kW

• 400 kW

• 200kW

Which of the following graphs best represents the variation with time t of the current I through the segment AB in the circuit below?

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A sinusoidal current of peak value I₀ dissipates power in a resistor at a mean rate P. What are the values for the mean current in the resistor and the maximum instantaneous power dissipated? (Mean current, Mean Power)

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The circuit below shows a connection of four ideal rectifiers with a sinusoidal alternating voltage applied to it. The terminals P and Q are joined by a load resistor.

Which of the following traces would be seen on a cathode-ray-oscilloscope (CRO) connected across PQ?

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The ratio of turns of the primary coil to the secondary coil is 10/1. The primary voltage and current are 20 V and 3 A respectively. The efficiency of the transformer is 0.9. Which statement is wrong

• The secondary voltage is 2 V.

• The output power is 60 W.

• The secondary current is 27 A

• Energy lost is 6 W.

A coil which has an inductance of 0.4 H and a resistance of 5 Ω is in series with a resistor whose resistance is 25 Ω. The pair are connected across a 200 V RMS supply alternating at 50 /π Hz. Calculate the RMS current.

• 3.0 A

• 4.0 A

• 5.0 A

• 6.0 A