Tag: physics

Questions Related to physics

Which of following circuit element stores energy in electromagnetic field?

introduction to induction electromagnetic induction electromagnetic induction and alternating currents physics

  1. inductor

  2. condenser

  3. variable resistor

  4. capacitor

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Correct Option: A
Explanation:

Inductor stores energy in the electromagnetic field.
Capacitor and condenser stores energy in the electrostatic field and resistance doesn't store energy in any field.

Find the necessary inductance. if 110 V, 10 W rating bulb is to be used with 220 V A.C source having frequency 50 Hz.

introduction to induction electromagnetic induction electromagnetic induction and alternating currents physics

  1. L=8.90 H

  2. L=6.75 H

  3. L=7.25 H

  4. L=6.5 H

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Correct Option: B
Explanation:

Given, $V=110v$ ,$P=10W$ ,$V _0=220 w$ ,$f=50Hz$

Current through series inductor,
Current through bulb=$\dfrac{P}{V}=\dfrac{10W}{110V}=0.09A$
Voltage across inductor,$V _{ind}=\sqrt{V _0^{2} -V^{2}}$=$\sqrt{220^{2}-110^2}=191V$
Reactance of inductor,$R=\dfrac{V _{ind}}{I}=\dfrac{191}{0.09}=2122.22$
Also,$R=2 \pi fL$ or $L$=$\dfrac{R}{2 \pi f}$=$\dfrac{2122.22}{2 \pi 50}$=$6.75H$

If the heart pushes 1 cc of blood in one second under pressure of 20000$Nm^{-2}$, the power of heart is

power work and power energy and its forms work, energy and power physics

  1. 0.02 W

  2. 400 W

  3. $5\times 10^{-10}W$

  4. 0.2 W

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Correct Option: A
Explanation:

Given,

$P=20000Nm^{-2}$
$\dfrac{dV}{dt}=1cc/s$
Power, $P=\dfrac{W}{t}=F.v=PA\dfrac{dx}{dt}$   (as, $F=PA$)
$P=P.\dfrac{dV}{dt}$
$P=20\times 10^3\times \dfrac{1}{(10^2)^3}$
$P=\dfrac{2}{100}=0.02W$
The correct option is A.

A pump can hoist 9000 kg of coal per hour from a mine of 120 m deep. calculate the power of the pump, in watts, assuming its efficiency is 75%, g=9.8 $m/s^{2}$

power work and power energy and its forms work, energy and power physics

  1. 3.92 watts

  2. 39.2 watts

  3. 392 watts

  4. 3920 watts

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Correct Option: D

A man starts walking from a point on the surface of earth (assumed smooth) and reaches diagonally opposite point. What is the work done by him? 

power work and power energy and its forms work, energy and power physics

  1. Zero

  2. Positive

  3. Negative

  4. Nothing can be said

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Correct Option: A

The power of water pump is 4 kW. If g = 10 $ms^{-2}$, the amount of water it can raise in 1 minute to a height of 20 m is 

power work and power energy and its forms work, energy and power physics

  1. 100 litre

  2. 1000 litre

  3. 1200 litre

  4. 2000 litre

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Correct Option: C

Fill the blank space with the best suitable option. All electromagnetic waves have the same _________ while travelling in a vacuum.

physics electromagnetic waves and communication system maxwell's equations the nature of light introduction to electromagnetic waves

  1. amplitude

  2. frequency

  3. wavelength

  4. Intensity

  5. speed

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Correct Option: E
Explanation:

All electromagnetic waves (EM waves) travel with the speed of light in vacuum but these have different frequency, amplitude, wavelength and intensity.

Thus option E is correct.

This question has statement-1 and statement-2. Of the four choices given after the Statements, choose the one that best describes the two statements.
Statement 1: Short wave transmission is achieved due to the total internal reflection of the e-m wave from an appropriate height in the ionosphere.
Statement 2: Refractive index of a plasma is independent of the frequency of e-m waves.

physics electromagnetic waves and communication system maxwell's equations the nature of light introduction to electromagnetic waves

  1. Statement 1 is true, Statement 2 false.

  2. Statement 1 is false, Statement 2 is true

  3. Statement 1 is true, Statement 2 is true but statement 2 is not the correct of statement 1.

  4. Statement 1 is true, statement 2 is true and statement 2 is the correct explanation of statement 1.

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Correct Option: C

The waves which can not travel in vacuum are :

physics observing space: telescopes maxwell's equations the nature of light introduction to electromagnetic waves

  1. X-rays

  2. radio-waves

  3. infrasonic waves

  4. ultra-viloet rays

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Correct Option: C

Light can pass through

physics observing space: telescopes maxwell's equations the nature of light introduction to electromagnetic waves

  1. Vacuum

  2. Glass

  3. Air

  4. All of the above

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Correct Option: D
Explanation:

Light can pass through vacuum,glass and air.