Tag: electric power

Questions Related to electric power

Alternating current can not be measured by $D.C$. ammeter because 

physics electrical circuits domestic electric circuits and safety precautions domestic and commercial circuit electric power

  1. $A.C$. cannot pass through $D.C$.

  2. $A.C$. changes direction

  3. average value of current for complete cycle is zero

  4. $D.C$. ammeter will get damaged.

Show answer
Correct Option: C
Explanation:

While for half-circle, the value of current is different at different points and for complete cycle its average value is zero.

So, we can't measure current by $D.C$ ammeter .

The frequency of ac mains in India is:

physics electrical circuits domestic electric circuits and safety precautions domestic and commercial circuit electric power

  1. $30$ Hz

  2. $50$ Hz

  3. $60$ Hz

  4. $120$ Hz

Show answer
Correct Option: B
Explanation:

Frequency of AC mains in India is 50 Hz,similar to most European countries. Whereas USA uses 60 Hz

Various distribution circuits are connected in

physics electrical circuits domestic electric circuits and safety precautions domestic and commercial circuit electric power

  1. series

  2. parallel

  3. series or parallel

  4. nothing can be decided

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Correct Option: B
Explanation:

Parallel circuit configuration limits the amount of power in each circuit and if one circuit breaker goes out, power remains on in the rest of the home.

Which of the following can be true?

physics electrical circuits domestic electric circuits and safety precautions domestic and commercial circuit electric power

  1. The instantaneous power output of an ac source can be negative.

  2. The average power output of an ac source can be negative.

  3. The instantaneous power output of an ac source can NOT be negative.

  4. The average power output of an ac source can NOT be negative.

Show answer
Correct Option: A

The wire having a green plastic covering is a:

physics electrical circuits domestic electric circuits and safety precautions domestic and commercial circuit electric power

  1. Live wire

  2. Neutral wire

  3. Earth wire

  4. None of these

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Correct Option: C
Explanation:

During wiring in our houses , we use the traditional concept of using red colour wire as live , black as neutral and green for earth.
These colour codes are used to distinguish between live , earth and neutral

Marking on a bulb is 60 W, 220 V. What does it signify ?

physics electrical circuits domestic electric circuits and safety precautions domestic and commercial circuit electric power

  1. The bulb is connected across 220 volts, 60 joules of energy is released in every second.

  2. The bulb is connected across 220 volts, 60 joules of energy is released in every minute.

  3. 60 A of current will flow in the bulb.

  4. 220 A of current will flow in the bulb.

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Correct Option: B

Which one of the following is the best material for making connecting wires?

physics electrical circuits domestic electric circuits and safety precautions domestic and commercial circuit electric power

  1. Nichrome

  2. Tungsten

  3. Copper

  4. Manganese

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Correct Option: C

The current through a lamp decreases by $1 \%$ The percentage change power of the lamp is

physics electrical circuits domestic electric circuits and safety precautions domestic and commercial circuit electric power

  1. 0.5%

  2. 1%

  3. 1.5%

  4. 2%

Show answer
Correct Option: D
Explanation:

The current through a lamp decreases by $1\%$ then percentange change power of the lamp is $2\%$.

Hence, option $D$ is the correct answer.

An electric iron uses a power of $1320 W$ when set to higher temperature. If set to lower temperature one third of higher temperature current is used. If iron is connected to a potential of $220 V$, then power used to lower temperature is _____ .

physics electrical circuits domestic electric circuits and safety precautions domestic and commercial circuit electric power

  1. $220 W$

  2. $440 W$

  3. $660 W$

  4. $880 W$

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Correct Option: B
Explanation:

Power, $P = VI$ (power at high temperature) 


$1320 = 220 I$ (current at high temperature)

Current at high temperature, $I _t = 6A $

$I _{LT} = \dfrac{6}{3} = 2A$ (current at low temperature) 

$P _{LT} = 220 \times2 \ W$

$ = 440 \ W$ (power at low temperature)

The electrical appliances in a house are connected in :

physics electrical circuits domestic electric circuits and safety precautions domestic and commercial circuit electric power

  1. series

  2. parallel

  3. either in series or parallel

  4. both in series and parallel

Show answer
Correct Option: B
Explanation:

A parallel connection is preferred in a household circuit.
The main advantages of the parallel system are that the supply can be tapped at any convenient point in the house; moreover each appliance is operated by a separate fuse. If the fuse blows off, only that appliance is to be checked. This system involves less wiring and is cheaper to set up.