Question # 1

How many photons per second does a one-watt bulb emit if its efficiency is 10% and the wavelength of light is 500 nm:

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2.53 × 1017

2.53 × 1019

7.5 × 1019

7.5 × 1017

First law of thermodynamics is merely a statement of law of conversation of:

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Energy

Angular momentum

Change

Linear momentum

The efficiency of full wave rectifier is:

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25.6%

81.2%

81.6%

71.2%

The frequency of an open pipe is f. if one end is closed then its fundamental frequencywill be:

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f/2

3f/4

f

2f

An electric motor exerts a force of 40 N on a cable and pulls it by a distance of 30 m in one minute. The power supplied by the motor in watts is

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20

200

2

10

In an explosion a body breaks up into two pieces of unequal masses. In this:

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Both parts will have numerically equal momentum

Lighter part will have more momentum

Heavier part will have more momentum

Both parts will have equal kinetic energy

A.H Compton studied the scattering of X-rays by loosely bound electrons from a graph target in:

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1905

1911

19251

1923

Interference and diffraction of light confirms its:

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Particle nature

Dual nature

Wave nature

Electromagnetic nature

The wavelength of light observed on the earth, form a moving star is found todecrease by 0.05%. Relative to the earth the star is

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moving away with a velocity of 1.5 x 10⁵m/s

moving away with a velocity of 1.5 x 10⁴m/s

coming closer with a velocity of 1.5 x 10⁵m/s

coming closer with a velocity of 1.5 x 10⁴m/s

In order to increase the K.E of ejected photo electrons, there should be an increase in:

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Intensity of radiation

NoneI

Frequency of radiation

Both (b) & (c)

Car X is traveling at half the speed of car Y. Car X has twice mass of car Y.

Which statement is correct?

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Car X has half the kinetic energy of car Y

Car X has one quarter of the kinetic energy of car Y

Car X has twice the kinetic energy of car Y

The tow cars have the same kinetic energy

Maximum speed of electrons in X-rays tube which is producing X-rays photons of frequency f is

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If a body changes its momentum from 100 N s to 200 N s in 10 s then the unbalanceexternal force responsible to change the momentum is

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5 N

2.5 N

2n

10n

Two bodies moving towards each other collide and move away in opposite directions. There is some rise in temperature of bodies because a part of the kinetic energy is converted into

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heat energy

electrical energy

nuclear energy

mechanical energy

The specific resistance of a wire varies with its:

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Length

Cross-section

Mass

Material

A ball is thrown vertically upwards. Neglecting air resistance, which statement is correct?

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The kinetic energy of the ball is greatest at the greatest height attained

The potential energy of the ball increase uniformly with time during the ascent

By the principle of conservation of momentum. The momentum of the ball is constant throughout its motion

By the principle of conservation of energy, the total energy of the ball is constant throughout its motion

Inverting amplifier circuits have

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A very high input impendance

A very low input impendance

A low output impendance

Both A and C

The maximum kinetic energy of emitted photoelectrons depends upon:

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The intensity of incident light

Frequency of the incident light

Temperature of the surface

All of above

The mud flies off the tyre of a fast moving car in the direction

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parallel to the moving tyre

anti parallel to the moving tyre

tangent to the moving tyre

none of these

The temperature scale approved in SI units is:

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Calslus scale

Kelvin scale

Fehrenhelt scale

None of these

A rigid uniform bar of length 2.4 m is pivoted horizontally at its mid-point, weights are hung from two points of the bar as shown in diagram. To maintain horizontal equilibrium, a couple is applied to the bar: What is the torque and the direction of couple?

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40 N m clockwise

40 N m anti-clockwise

80 N m clockwise

80 N m anti-clockwise

The relative permittivity of air is

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1

3.7

7.8

1.0006

Interference and diffraction confirm:

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Particle nature

Wave nature

Dual nature

None of these

A man pushes a wall and fails to displace it. He does:

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Negative work

Positive but not maximum work

No work at all

Maximum work

If velocity time graph is a straight line parallel to time axis then body is

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Moving with zero acceleration

Moving with constant velocity

Covering equal displacement in equal intervals of time

All of these

A satellite moving round the earth constitute

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An inertial frame of reference

Non inertial frame

Neither inertial nor non inertial

Both inertial and non-inertial

When an electron in an atom goes from a lower to higher its:

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K.E. increases, P.E. decreases

K.E. increases

P.E increases

K.E. decrease, P.E. increases

A body moving in a circular path with a constant speed has a

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Constant velocity

Constant kinetic energy

Constant acceleration

Constant displacement

Truth of kinetic energy theory is confirmed by:

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Diffusion of gases

Brownian motion

Both A and B

None of these

If the range of a projectile is R, the potential energy will be maximum after the projectile has covered (from start) distance equal to:

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R/2

R/4

R

R/9

Because of large mass when 𝑎 −paricle enters the atom or molecule it:

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Moves in zigzag path

Moves along straight line

Moves along circular path

None of these

A body revolved around the sun 27 times faster then the earth what is the ratioof their radii

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1/27

1/4

1/9

1/3

The potential difference applied to an X-rays tube is increased. As a result, in the emitted radiation

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The intensity increases

The minimum wavelength decrease

The intensity remains unchanged

Both B & C

For a body moving with constant speed in a horizontal circle, which of the following remains constant?

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Velocity

Centripetal force

Acceleration

Kinetic energy

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