Question # 1

The frequency and work function of an incident photon are n and𝝋𝟎. If f0 is the threshold frequency, then necessary condition for the emission of photo electron is:

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< 𝑓0

𝑓 ≥ 𝑓0

f = 𝑓0/2

None of these

Intensity of light from a point source at the edge of unit sphere will be:

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𝑃

P(4π)

4𝜋

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 proton, accelerated through a p.d V has a certain de Broglie wavelength. In order to have the same de Broglie wavelength, an 𝑎 −particles must be accelerated through a potential difference:

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4V

8V

V/4

V/8

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

What is the momentum of a photon of light of wavelength 500 nm in kgm/s:

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1.32 × 10−21

1.32 × 10−23

1.32 × 10−25

1.32 × 10−27

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

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Infrared

Visible

Ultraviolet

X-rays

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

Which one is the correct express of de-Broglie equation for the length of atoms of mass m at temp? T(k=Boltzmann’s constant):

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An electron in the n=1 orbit hydrogen atom is bound by 13.6 eV. If a hydrogen atom is in the n=3 state, how much energy is required to ionize it:

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13.6 eV

4.53 eV

3.4 eV

1.51eV

For X-rays which of the following is not correct:

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Cause of ionization in air when they pass through it

Can be deflected by electric and magnetic fields

Can be used to detect flaws in metal casting

Travel with the speed of light

Monochromatic light of wavelength 300 nm is incident normally on a surface of area 4 cm2.

If the intensity of light is 150 mW/m2; the rate at which photon strike the surface:

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2.53 × 1019

7.5 × 1019

9.1 × 1013

2.53 × 1013

Light of frequency 4f0 is incident on the metal of the threshold frequency f0. The maximum kinetic energy of the emitted photoelectrons is

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3h f0

3/2h f0

2h f0

1/2h f0

Choose incorrect about properties of photon

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Rest mass of photon is zero

A photon is never at rest

Photon is not deflected by electric field not by magnetic field

The velocity of photon is different in different media

electrons from the surface of a metal when:

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It is heated to a high temperature

Radiation of suitable wavelength falls on it

Electrons of suitable velocity strike it

It is placed in a strong electric field

The threshold frequency depends on the nature on:

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Natural frequency

Photosensitive anode

Photosensitive cathode

Photon

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

A photo cell receives light from a source at 50 cm away and produces 40mAcurrent inthe circuit. When the same source at is at distance 1 m from photo cell,current in the circuit will be

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20 mA

80mA

60 mA

10 mA

Which of the following statement is true about soft X-rays?

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They have large wavelength

They have high energy

They have low energy

Both A and C

When ultraviolet rays are incident in metal plate, then photoelectric effect does not occur. It occurs by the incidence of:

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x-rays

Infrared rays

Radio wave

Greenhouse effect

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