Question # 1

To find longest wavelength radiation in Ballmer series, the value of n used is:

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2

3

4

∞

The minimum energy required to remove an electron is called:

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Stopping potential

Work function

Kinetic energy

None of these

The hydrogen atoms are excited to the stationary state designated by the principal quantum number n=4, the number of maximum spectral lines are observe:

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2

3

4

6

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

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 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

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

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

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

The shortest wavelength of X-rays emitted from an X-rays tube depends on the:

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Current in the tube

Voltage applied to the tube

Nature of gas in the tube

Nature of material of tube

A proton and an 𝑎 − 𝒑𝒂𝒓𝒕𝒊𝒄𝒍𝒆 are accelerated through same voltage, the ratio of their de- Broglie wavelength will be:

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1:2

√2: 1

2√2: 1

2:1

Light of frequency 1.5 times the threshold frequency is incident on a photo sensitive material. If the frequency is halved and intensity is doubled the photo electric current becomes

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Four times

Half

Double

Zero

As the intensity of incident light increases:

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Photoelectric current increases

Photoelectric current decreases

Kinetic energy of emitted photoelectrons increases

Kinetic energy of emitted photoelectrons decreases

Figure represents a graph of kinetic energy (K) of the photoelectrons (in eV) and frequency (v) for a metal used as cathode in photoelectric experiment. The work function of metal is:

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1 eV

2 eV

1.5 eV

3 eV

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

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

The maximum energy of the electrons released in a photo cell is independent of:

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Frequency of incident light

Intensity of incident light

Nature of cathode rays

None of these

The threshold frequency depends on the nature on:

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Natural frequency

Photosensitive anode

Photosensitive cathode

Photon

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

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

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

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