Light with an energy flux of 25 x 104 Wm-2 falls on a perfectly reflecting surface at normal incidence. If the surface area is 15cm2 the average force exerted on the surface is

(a)1.25x10-6N

(b)2.5x10-6N

(c)1.2x10-6N

(d)3.0x10-6N

Concept Questions :-

Particle nature of light
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When the energy of the incident radiation is increased by 20%, the kinetic energy of the photoelectrons emitted from a metal surface increased from 0.5 eV to 0.8 eV. The work function of the metal is:

1. 0.65eV

2. 1.0eV

3. 1.3eV

4. 1.5eV

Concept Questions :-

Einstein photo-electric equation
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If the kinetic energy of the particle is increased to 16 times its previous value, the percentage change in the de-Broglie wavelength of the particle is

1. 25

2. 75

3. 60

4. 50

Concept Questions :-

De-broglie wavelength
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For photoelectric emission from certain metal, the cut-off frequency is ν. If radiation of frequency 2ν impinges on the metal plate, the maximum possible velocity of the emitted electron will be (m is the electron mass)

1. hν/(2m) 

2. hν/(m) 

3. 2hν/(m) 

4. none of these

Concept Questions :-

Electron emission
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The wavelength λe of an electron and λp of a photon of same energy E related by:

(a)λpλe2

(b) λpλe 

(c) λpλe

(d)λp1λe

Concept Questions :-

De-broglie wavelength
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A 200W sodium street lamp emits yellow light of wavelength 0.6 μm. Assuming it to be 25% efficient in converting electrical energy to light, the number of photons of yellow light it emits per second is 

(a) 1.5×1020                                (b) 6×1018

(c) 62×1020                                 (d) 3×1019

Concept Questions :-

Electron emission
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An αparticle moves in a circular path of radius 0.83 cm in the presence of a magnetic field of 0.25 Wb/m2.The de-Broglie wavelength associated with the particle will be 

(a) 1 A0                                                   (b) 0.1 A0

(c) 10 A0                                                 (d) 0.01 A0

Concept Questions :-

De-broglie wavelength
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If the momentum of an electron is changed

by p, then the de-Broglie wavelength

associated with it changes by 0.5%. The 

initial momentum of the electron will be

 

(a) 200p

(b) 400p

(c) P200

(d) 100p

Concept Questions :-

De-broglie wavelength
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In the Davisson and Germer experiment, the

velocity of electrons emitted from the electron

gun can be increased by

(a) increasing the filament current

(b) decreasing the filament current

(c) decreasing the potential difference between

     the anode and filament

(d) increasing the potential difference  between

     the anode and filament

Concept Questions :-

Davisson and Germer experiment
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A radioactive nucleus of mass M emits a photon

of frequency ν and the nucleus recoils. The recoil

energy will be:

(a) h2ν2/2 Mc2

(b) zero

(C) hν

(d) Mc2-

Concept Questions :-

De-broglie wavelength
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Difficulty Level: