# Alternating Current - Online Test

Q1. Domestic power supply in India is
Explaination / Solution:

The standard voltage and frequency of alternating current supply in India is set to 220 V and 50Hz respectively by the government of India because when power has to be transmitted from a power plant, the biggest challenge is to cut the transmission losses. For this purpose, the current value should be small and potential difference(Voltage) should be more. Also losses are minimal at 50 Hz/60 Hz frequency.

Q2. The main reason for preferring usage of AC voltage over DC voltage
Explaination / Solution:

By using the phenomenon of mutual induction, transformers allow us to easily change voltage of AC. This is necessary to cut down poer losses while supplying electricity to our homes

Q3. Alternating current is so called because
Explaination / Solution:

Alternating Current is the current in which the polarity of source continuously changes on a fixed frequency. So the positive and the negative terminals ‘alternate’

Q4. In a circuit containing Resistance only, voltage and current are
Explaination / Solution:

The electrical current that flows through an AC resistance varies sinusoidally with time and is represented by the expression, I(t) = I sin(ωt + θ) Now by ohm's law, V= IR So, for the AC circuit, V= IR sin(ωt + θ) Clearly both V and I have zero phase difference and hen are in phase

Q5. If  is the maximum current, then the average value of power dissipated in a resistance R over a cycle is
Explaination / Solution:

As in the case with DC power, the instantaneous electric power in an AC circuit is given by P = VI, but these quantities are continuously varying. So the average power is given by

Pavg = VI cosφ

where φ is the phase angle between the current and the voltage and where V and I are understood to be the effective or rms values of the voltage and current.

Now RMS value of I is =

So, RMS value of V=

Therefore, Power will be

P=           (because cosφ= 1 for circuit containing resistance only)

Q6. Phasor diagrams show
Explaination / Solution:

By convention phasor diagrams are made to show the rotation of phasor in counterclockwise direction with constant speed

Q7. Average power supplied to an inductor over one complete cycle
Explaination / Solution:

In the first half of the cycle, power is supplied to the inductive circuit. In the next half the inductor dissipates the energy supplied by circuit. Thus overall no power is supplied to the circuit

Q8. Average power supplied to a capacitor over one complete cycle
Explaination / Solution:

We know that in capacitor Current leads Voltage by 90degree. Over one complete cycle, in first quarter cycle Capacitor charges and next quarter cycle it's discharge. This will continue in next negative half cycle. So the NET POWER ABSORB IS ZERO.

Q9. In a series LCR circuit supplied with AC
Explaination / Solution:

In series circuits, the current always remains same while potential is different across different circuit components

Q10. If  , , and V represent the voltage across the inductor, resistor, capacitor and the source, respectively, on the phasor diagram
Explaination / Solution:

In Series LCR Circuit, current is same across all elements. Since for a resistor both current and voltage are in same phase, Vis along the same direction as current in the phasor diagram.

In capacitor voltage lags current by 900 so it is at right angle with VR and in an inductor voltage leads current by 900 so it is at right angle with VR and directly opposite to Vc