Question # 1

The efficiency of full wave rectifier is:

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25.6%

81.2%

81.6%

71.2%

The energy of photon of wavelength 620 nm is:

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0.5 eV

1.0 eV

1.5 eV

2.0 eV

The reverse process of photo-electric effect is called:

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Pair production

Compton effect

Annihilation of matter

X-rays

A body is in translational equilibrium if

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P = 0

L = 0

F = 0

 = 0

During a negative β-decay

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An atomic electron is ejected

A neutron in the nucleus decays emitting an electron

An electron which already present within the nucleus is ejected

A part of binding energy of nuclei is converted into electron

A longitudinal sinusoidal wave has wavelength of 1cm and a period of 2sec. Its wavevelocity is:

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50 cm/ sec

0.5 cm/ sec

5 m/ s

0.005 m/ sec

The uranium Nucleus 𝟐𝟑𝟖 𝑼 undergoes successive decays, emitting respectively 𝑎 − 𝒓𝒂𝒚,𝖰 − 𝒓𝒂𝒚 𝒂𝒏𝒅 − 𝒓𝒂𝒚𝒔. What is the atomic number and atomic mass of the resulting nucleus:

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90, 238

91, 234

92, 236

92, 238

The maximum wavelength of a transverse wave that can be set up in a string of length Lis

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L

2L

V

4L

A piece of Aluminium (Al) and a piece of Germanium (Ge) are cooled T1 K to T2 K. The resistance of:

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Each of them increases

Each of them decreases

Al increases and Ge decreases

Al decreases and that of Ge increases

The rate of decay radioactive substance:

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Is constant

Decrease exponentially with time

Varies inversely with time

Decrease linearly with time

Which statement about geostationary orbit is false?

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A geostationary orbit must be directly above the equator

All satellite in a geostationary orbit must have the same masses

The period of geostationary orbit must be 24 hours

There is only one possible radius for a geostationary

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

The ratio of output work per cycle to input energy per cycle is called:

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Entropy

Internal energy

Efficiency

None of these

Pressure may be defined as_____per second per unit area:

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Change in force

Change in momentum

Change in energy

Work done

Real gases strictly obey gas laws at:

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High pressures and low temperatures

Low pressures and high temperatures

High pressures and & temperatures

None of these

An elevator's motor produces 3000 W power. The speed With Which it can lift a 1000 kg load is:

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30.6ms^-1

0.306ms^-1

3.06ms^-1

300.3ms^-1

When a person lifts a body from ground work done by lifting force is?

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Positive

Negative

Zero

Half of positive maximum

A stationary wave is established in a string which vibrates in four segments at afrequency of 120 Hz. Its fundamental frequency is:

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15Hz

60Hz

30Hz

430Hz

Thermal radiations are a type of:

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Mechanical waves

Electromagnetic waves

Alpha rays

Electrons

The force which can do no work on the body on which it acts:

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Frictional force

Elastic force

Gravitational force

Centripetal force

A parallel plate air capacitor is charged and then isolated. When a dielectric material is inserted between the plates of the capacitor , then which of the following does not change:

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Electric field between the plates

Charge on the plates

Potential difference across the plate

Energy stored in the capacitor

The momentum of a particle is numerically equal to its K.E. What is the velocity of a particle?

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9 ms^-1

3 ms^-1

2 ms-1

1 ms^-1

Photo cells is a device which convert light into:

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Wave nature

Particle nature

Particle wave nature

Dual nature

An electron and a proton are accelerated through the same potential. If their masses are me and mp respectively, then the ratio of their de-Broglie wavelength is:

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1

mp/me

me/mp

. A force "F1" acts on a body through distance "S1" in the direction of motion and does work "W1". Similarly another force "F2" act on same body through distance "S2" but in opposite to the direction of motion and does work "W2". Now if F1 = F2 and S1 = S2 then which statement is correct.

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W1 = W2

W2< W2

W1 > W2

W1 = W2= 0

The emf of a cell of negligible internal resistance is 2V. It is connected to the series combination of 𝟐𝛀, 𝟑𝛀 𝐚𝐧𝐝 𝟓𝛀 resistance. The potential difference across 𝟑𝛀 resistance will be in volt:

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0.6

2/3

3

6

In photoelectric effect, electrons are emitted:

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Slowly

Intermittently

Both (a) & (b)

Instantly

The potential difference between head and tail of an "electric eel" can be upto.

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6V

60V

6000V

600V

A charge of 2C experiences a force 2000N in a uniform electric field. In this fieldthe potential difference between two points separated by a distance 1cm is

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2V

10V

5V

20V

In full wave rectification, the output DC voltage across the load is obtained for.

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The positive half cycle of input AC only

The negative half cycle of input AC

The completes cycle of input AC only

All of the above

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

Diesel engine coverts ____________ of available heat energy into work.

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20% to 25%

25% to 30%

30% to 35%

35% to 40%

Ultraviolet radiation of 6.2 eV falls on an aluminium surface having work function ∅ = 𝟒. 𝟐 𝒆𝑽.

The kinetic energy of the fastest electron emitted is:

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4 eV

2 eV

2.2 eV

1.2 eV

If temperature of the sink is decreased, efficiency of a carnot engine.

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Remains constant

Decreases

Increases

None of these

The radius of orbit of a geostationary satellite depends upon:

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Mass of satellite and its time period

Mass of satellite and mass of earth

Mass of earth, mass of satellite and time period of satellite

Mass of earth and time period of earth

The efficiency of half wave rectifier is:

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25.6%

1.2%

40.6%

66.6%

The most penetrating radiations out of the following is that of

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𝛾-rays

β-rays

α-particles

X-rays

The stopping potential for a certain metal is 10 volt, the max. Energy of emitted electron is:

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10 J

100 J

1.6 × 10-18 J

1.6 × 10-19 J

The maximum kinetic energy of emitted photoelectrons depends upon:

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The intensity of incident light

Frequency of incident light

Metal surface

Both frequency of incident light and metal surface

Photo cells are used for :

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Security and counting system

Automatic door system

Automatic street lighting

All of these

A listener observes the frequency “f” of stationary source. If it move toward with 3 times of velocity of sound. Then the apparent frequency of the sound will be

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f

3f

f/2

4f