Tag: physics

Quizzes (598) Questions (13441)

Questions Related to physics

Multiple choice introduction to induction electromagnetic induction electromagnetic induction and alternating currents physics

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.

  1. L=8.90 H

  2. L=6.75 H

  3. L=7.25 H

  4. L=6.5 H
Reveal answer Fill a bubble to check yourself
B Correct answer
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 $L$=$\dfrac{R}{2 \pi f}$=$\dfrac{2122.22}{2 \pi 50}$=$6.75H$

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

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

  1. 0.02 W

  2. 400 W
  3. $5\times 10^{-10}W$

  4. 0.2 W
Reveal answer Fill a bubble to check yourself
A Correct answer
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.

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

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 $m/s^{2}$

  1. 3.92 watts

  2. 39.2 watts

  3. 392 watts

  4. 3920 watts
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Work = mgh = 9000 kg * 9.8 m/s^2 * 120 m = 10,584,000 J. Power = Work / time = 10,584,000 J / 3600 s = 2940 W. Given 75% efficiency, the required power input is 2940 / 0.75 = 3920 W.

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

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? 

  1. Zero

  2. Positive

  3. Negative

  4. Nothing can be said
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

If we consider work done against gravity, walking from one point to the antipodal point involves moving away from Earth's center then descending back down. The net work against gravity is zero (positive climbing cancels negative descending). However, the question is poorly specified as the person does positive muscular work throughout.

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

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 

  1. 100 litre

  2. 1000 litre

  3. 1200 litre

  4. 2000 litre
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Power = 4000 W. Time = 60 s. Work = Power * time = 240,000 J. Work = mgh -> 240,000 = m * 10 * 20 -> 240,000 = 200m -> m = 1200 kg. Since 1 kg of water = 1 liter, the volume is 1200 liters.

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

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

  1. amplitude

  2. frequency

  3. wavelength

  4. Intensity

  5. speed
Reveal answer Fill a bubble to check yourself
E Correct answer
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.

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

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.

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

Statement 1 is true because the ionosphere reflects radio waves, enabling long-distance communication. Statement 2 is also true because the refractive index of plasma depends on the electron density and the frequency of the wave, but the statement as written is a common physics textbook fact that the refractive index varies with frequency, making the statement 'independent' false. However, given the options, the question implies both are true but unrelated.