Alternating Current

What is alternating current?

• The current changes direction periodically

• The current changes randomly

• The current remains constant

Root mean square of ac current is the

• average current

• instantaneous value of current

• value of dc that dissipates same power as ac through a resistor

• value of dc that dissipates same heat as ac through a resistor

The graph shows the instantaneous power dissipated by heating a coil. If the resistance of the coil is 100 Ohm, what is the rms current?

• 3.16 A

• 4.47 A

• 20.0 A

• 28.3 A

Which of the following graphs shows the variation of current across the inductor?

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Which phasor diagram shows the correct phase difference between current and voltage for pure capacitor in ac circuit?

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What is the reactance for inductor?

• wL

• wC

• 1/wL

• 1/wC

Which of the following is true about capacitors in ac circuit?

• Voltage across capacitor leads current

• The current decreases when frequency decreases

• Instantaneous power is zero

• Mean power is zero

Which of the following is the correct phasor diagram?

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A bulb of resistance 10 Ohm and a capacitor of capacitance 800 uF are connected in series to a source of alternating voltage V = 200 sin 300t. Calculate the impedance of the circuit

• 4.17 Ohm

• 10.8 Ohm

• 18.5 Ohm

• 10.0 Ohm

If the potential difference across the resistor is 10 V, what is the potential difference across the capacitor?

• 10.0 V

• 15.0 V

• 19.0 V

• 23.0 V