Tag: electric power

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

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

  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.
Reveal answer Fill a bubble to check yourself
C Correct answer
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 .

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

Which of the following can be true?

  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.
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

In an AC circuit, the instantaneous power p = v*i can be negative if the voltage and current have opposite signs, which occurs when the phase difference is between 90 and 270 degrees.

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

The wire having a green plastic covering is a:

  1. Live wire

  2. Neutral wire

  3. Earth wire

  4. None of these
Reveal answer Fill a bubble to check yourself
C Correct answer
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

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

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

  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.
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

A power rating of 60 W at 220 V means that when the bulb is operated across a 220 V supply, it consumes electrical energy at the rate of 60 joules per second.

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

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 _____ .

  1. $220 W$
  2. $440 W$
  3. $660 W$
  4. $880 W$
Reveal answer Fill a bubble to check yourself
B Correct answer
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)

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

The electrical appliances in a house are connected in :

  1. series

  2. parallel

  3. either in series or parallel

  4. both in series and parallel
Reveal answer Fill a bubble to check yourself
B Correct answer
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.