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A convex lens of focal length $40 cm$ forms an image of an extended source of light on a photoelectric cell. A current $I$ is produced. The lens is replaced by another convex lens having the same diameter but focal length $20 cm$ . The photoelectric current now is

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Important Questions on Dual Nature of Matter and Radiation

MEDIUM

Physics>Modern Physics>Dual Nature of Matter and Radiation>Photoelectric Effect

Light of wavelength

500 nm

is incident on a metal with work function

2.28 eV

. The de Broglie wavelength of the emitted electron is:

HARD

Physics>Modern Physics>Dual Nature of Matter and Radiation>Photoelectric Effect

In a historical experiment to determine Planck's constant, a metal surface was irradiated with light of different wavelengths. The emitted photoelectron energies were measured by applying a stopping potential. The relevant data for the wavelength

(λ)

of incident light and the corresponding stopping potential

(V_{0})

are given below:

$λ (μ m)$	$V_{0} (v o l t)$
0.3	2.0
0.4	1.0
0.5	0.4

Given that

c = 3 \times 10^{8} m s^{- 1} and e = 1.6 \times 10^{- 19} C,

Planck's constant (in units of

J s

) found from such an experiment is :

MEDIUM

Physics>Modern Physics>Dual Nature of Matter and Radiation>Photoelectric Effect

Photons with energy of

5 eV

are incident on a cathode,

C

in a photoelectric cell. The maximum energy of emitted photoelectrons is

2 eV.

When photons of energy

6 eV

are incident on

C

, no photoelectrons will reach the anode,

A

, if, the stopping potential of

A

relative to

C

HARD

Physics>Modern Physics>Dual Nature of Matter and Radiation>Photoelectric Effect

In a photoelectric experiment, a parallel beam of monochromatic light with the power of

200 W

is incident on a perfectly absorbing cathode of work function

6.25 eV

. The frequency of light is just above the threshold frequency so that the photoelectrons are emitted with negligible kinetic energy. Assume that the photoelectron emission efficiency is 100%. A potential difference of

500 V

is applied between the cathode and the anode. All the emitted electrons are incident normally on the anode and are absorbed. The anode experiences a force

F = n \times 10^{- 4} N

due to the impact of the electrons. The value of

n

is __________. Mass of the electron

m_{e} = 9 \times 10^{- 31} kg a n d 1.0 eV = 1.6 \times 10^{- 19} J

MEDIUM

Physics>Modern Physics>Dual Nature of Matter and Radiation>Photoelectric Effect

The anode voltage of a photocell is kept fixed. The wavelength

λ

of the light falling on the cathode is gradually changed. The plate current

I

of the photocell varies as follows :

MEDIUM

Physics>Modern Physics>Dual Nature of Matter and Radiation>Photoelectric Effect

The continuous part of

X

-ray spectrum is a result of the

MEDIUM

Physics>Modern Physics>Dual Nature of Matter and Radiation>Photoelectric Effect

When a certain metallic surface is illuminated with monochromatic light of wavelength

λ,

the stopping potential for photoelectric current is

3 V_{0}

and when the same surface is illuminated with light of wavelength

2 λ,

the stopping potential is

V_{0} .

The threshold wavelength of this surface for photoelectric effect is

MEDIUM

Physics>Modern Physics>Dual Nature of Matter and Radiation>Photoelectric Effect

A laser light of wavelength

660 nm

is used to weld Retina detachment. If a laser pulse of width

60 ms

and power

0.5 kW

is used, the approximate number of photons in the pulse are (Take Planck's Constant,

h = 6.62 \times 10^{- 34} J s)

HARD

Physics>Modern Physics>Dual Nature of Matter and Radiation>Photoelectric Effect

A metal plate of area

1 \times 10^{- 4} m^{2}

is illuminated by a radiation of intensity

16 mW m^{- 2}

. The work function of the metal is

5 eV .

The energy of the incident photons is

10 eV

and only

10 %

of it produces photo electrons. The number of emitted photo electron per second and their maximum energy, respectively, will be:

[1 eV = 1.6 \times 10^{- 19} J]

HARD

Physics>Modern Physics>Dual Nature of Matter and Radiation>Photoelectric Effect

The radiation corresponding to

3 \to 2

transition of hydrogen atom falls on a metal surface to produce photoelectrons. These electrons are made to enter a magnetic field of

3 \times 1 0^{- 4} T

. If the radius of the largest circular path followed by these electrons is 10.0 mm, the work function of the metal is close to :

MEDIUM

Physics>Modern Physics>Dual Nature of Matter and Radiation>Photoelectric Effect

Photons of wavelength

λ

are incident on a metal. The most energetic electrons ejected from the metal are bent into a circular are of radius R by a perpendicular magnetic field having a magnitude B. The work function of the metal is (Where symbols have their usual meanings).

EASY

Physics>Modern Physics>Dual Nature of Matter and Radiation>Photoelectric Effect

When a certain photosensitive surface is illuminated with a monochromatic light of frequency

ν,

the stopping potential of the photo current is

- \frac{V_{0}}{2} .

When the surface is illuminated by monochromatic light of frequency

\frac{ν}{2},

the stopping potential is

- V_{0} .

The threshold frequency for photoelectric emission is

MEDIUM

Physics>Modern Physics>Dual Nature of Matter and Radiation>Photoelectric Effect

On a photosensitive material, when the frequency of incident radiation is increased by

30 %

, the kinetic energy of emitted photoelectrons increases from

0.4 eV

0.9 eV

. The work function of the surface is

MEDIUM

Physics>Modern Physics>Dual Nature of Matter and Radiation>Photoelectric Effect

When a metallic surface is illuminated with radiation of wavelength

λ

, the stopping potential is

V

. If the same surface is illuminated with radiation of wavelength

2 λ

, the stopping potential is

\frac{V}{4}

. The threshold wavelength for the metallic surface is:

MEDIUM

Physics>Modern Physics>Dual Nature of Matter and Radiation>Photoelectric Effect

The maximum velocity of the photoelectrons emitted from the surface is

v

when light of frequency

n

falls on a metal surface. If the incident frequency is increased to

3 n

, the maximum velocity of the ejected photoelectrons will be:

MEDIUM

Physics>Modern Physics>Dual Nature of Matter and Radiation>Photoelectric Effect

Photons of energy

7 eV

are incident on two metals

A

and

B

with work functions

6 eV

and

3 eV

, respectively. The minimum de-Broglie wavelengths of the emitted photoelectrons with maximum energies are

λ_{A}

and

λ_{B}

, respectively, where

\frac{λ_{A}}{λ_{B}}

is nearly,

MEDIUM

Physics>Modern Physics>Dual Nature of Matter and Radiation>Photoelectric Effect

In a photocell circuit, the stopping potential, $V_{0}$ is a measure of the maximum kinetic energy of the photoelectrons. The following graph shows experimentally measured values of stopping potential versus frequency, $(ν)$ of incident light.

Question Image

The values of Planck's constant and the work function as determined from the graph are (taking the magnitude of electronic charge to be, $e = 1.6 \times 10^{- 19} C$ ),

EASY

Physics>Modern Physics>Dual Nature of Matter and Radiation>Photoelectric Effect

Maximum kinetic energy of a photoelectric varies with the frequency

(f)

of the incident radiation as

EASY

Physics>Modern Physics>Dual Nature of Matter and Radiation>Photoelectric Effect

A photoelectric surface is illuminated successively by monochromatic light of wavelength

λ

and

\frac{λ}{2}

. If the maximum kinetic energy of the emitted photoelectrons in the second case is 3 times that in the first case, the work function of the surface of the material is:
(

h

= Planck's constant,

c

= speed of light)

HARD

Physics>Modern Physics>Dual Nature of Matter and Radiation>Photoelectric Effect

The magnetic field associated with a light wave is given, at the origin, by

B = B_{0} [\sin (3.14 \times 10^{7}) c t + \sin (6.28 \times 10^{7}) c t] .

If this light falls on a silver plate having a work function of

4 .7 eV,

what will be the maximum kinetic energy of the photoelectrons?

(c = 3 \times 10^{8} m s^{- 1}, h = 6 .6 \times 10^{- 34} J s)

A convex lens of focal length 40 cm forms an image of an extended source of light on a photoelectric cell. A current I is produced. The lens is replaced by another convex lens having the same diameter but focal length 20 cm. The photoelectric current now is

Important Questions on Dual Nature of Matter and Radiation

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A convex lens of focal length $40 cm$ forms an image of an extended source of light on a photoelectric cell. A current $I$ is produced. The lens is replaced by another convex lens having the same diameter but focal length $20 cm$ . The photoelectric current now is