Question # 1

Light elements do not emit X-rays because

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Electrons in it have high binding energy

These materials are non- material

There is a small difference in their energy shells

Electrons in it require very large energy to remove from these materials

The nature of thermal radiation is smaller to:

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Ultraviolet rays

Light rays

Both of them

None of these

Two point charges +2 coulombs and +6 coulombs repel each other with a force of 12 N if a charge -4 coulomb is given to each of these charges the force will be:

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4N repulsive

8N repulsive

4N attractive

8N attractive

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

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

There are two electric bulbs of 40 W and 100 W. They are first connected in series and then in parallel across a source:

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40W bulb will be brighter in series and 100W in parallel

100W bulb will be brighter in series and 40W in parallel

40W bulb will be brighter in both the cares

100W bulb will be brighter in both the cares

When resistances are connected in Parallel, the effective resistance will be

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Product of the reciprocals of the individual resistances

Product of the individual resistances

Sum of the reciprocals of the individual resistances

Sum of the individual resistances

Potassium cathode in photocell emits electrons for a light:

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Visible

Infrared

Ultraviolet

X-rays

Of electron of 50 keV strike a heavy target. Then radiation emitted by target will be

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Visible light

Radio waves

Ultraviolet

None of these

While dealing with the processes i thermodynamics, the working substances is usually:

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Oxygen gas

Hydrogen gas

Ideal gas

None of these

Only those processes are probable to take place for which entropy os the system:

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Increases

Remains constant

Both A and B are correct

None of above

When heat is added to the system, the entropy change is:

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Positive

Negative

Zero

None of these

The ratio of the longest and shortest wavelength of the Lyman series is approximately:

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4/3

9/4

9/5

16/7

A pulsating DC can be converted into constant voltage by using

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Filter

Full wave rectifier

Half wave rectifie

Bridge rectifier

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

If P is the pressure and V is the volume, Then PV will represent:

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Power

Work

Force

None of these

What will be the number of photons emitted per second by 25 W source of monochromatic light of wavelength 600 nm:

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7.5 × 1017

7.5 × 1019

5.5 × 1019

5.5 × 1017

A certain engine coverts 20% of available heat energy into work. Then its efficiency will be:

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20%

80%

50%

None of these

In a full wave rectifier:

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DC current is twice that of half wave rectifier

DC pulses are twice per cycle that of half wave rectifier

DC voltage is twice that of half wave rectifier

All are correct

If source and observer are moving towards each other with same speed and aftercrossing they are receding each other then frequency observed by observer:

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Decreases

Remains constant

Increases

First Increases then decreases

Electromagnetic waves emitted by hot bodies are called:

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Photoelectrons

Alpha rats

Thermal radiation

None of these

A sonar depth finder in a boat uses sound signals to determine the depth of water. Fourseconds after the sound leaves the boat it returns to the boat because of reflection fromthe bottom. Assume the speed of sound in water is 1,460 meters per second. The depth of the water is, in meters, :

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2,200

4,800

4,400

2,920

Joule-second is the unit of:

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Energy

Heat

Planck’s constant

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

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

Avogadro number is known as number of molecules in:

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One kg of a substance

Unit volume of a substance

One mole of a substance

None of these

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

If a transverse wave has a speed of 10 m/ sec and frequency of 10 cycle/ sec itswavelength is:

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1 m

10^-2 cm

10 m

10 cm

With the propagation of longitudinal waves through a material medium, the quantitiestransferred in the direction of propagation are:

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Energy, momentum and mass

Energy and momentum

Energy and mass

Energy

Which combination of 7 identical resistors of 3-ohm will give 12/13 ohm:

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3 series, 4 parallel

5 series, 2 parallel

2 series, 5 parallel

4 series, 3 parallel

In which region of the electromagnetic spectrum does the Lyman series of hydrogen atom lie?

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Infrared

Visible

Ultraviolet

X-rays

The fundamental frequency in a stretched string is 10 Hz. To double the frequency, the tension in it must be changed to:

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T₂ = 2T₁

T₂ = 4T₁

T₂ = T₁

none of these

A charge is 90C passes through a wire in 1 hour and 15 minutes. Wat is the current in the wire?

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10mA

20mA

15mA

25mA

In photoelectric effect, if we increase the frequency of the incident light then of the electrons increased

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Number

K.E

P.E

Frequency

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)

A circuit that converts Pulsating DC into smooth DC contain :

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Filter

Capacitor

Inductor

LC circuit

Capacitance of a capacitor does not depend upon

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Separation between plates

Thickness of the plates

Area of the plates

Medium between the plates

When two semiconductors of p- and n-type are brought into contact, they from a p-n junction which act like a:

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Conductor

Amplifier

Oscillator

Rectifier

The power needed to lift amass of 5000g to height of 1min 2 second is

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2.45 watt

24.5 watt

245 watt

2.45 k watt

Threshold wavelength for metal having work function 𝝋 is 𝝀. What is the threshold wavelength for metal having work function 2 𝒊𝒔:

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/𝟐

2

4

𝝀/𝟒

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