Dual Nature Of Radiation And Matter | Physics JEE previous year questions with Solutions

Q 1 :
Given below are two statements: one is labelled as Assertion (A) and the other is labelled as Reason (R).

Assertion (A): Number of photons increases with increase in frequency of light.

Reason (R): Maximum kinetic energy of emitted electrons increases with the frequency of incident radiation.

In the light of the above statements, choose the most appropriate answer from the options given below: [2024]

Both A and R are correct and R is not the correct explanation of A.
Both A and R are correct and R is the correct explanation of A.
A is correct, but R is not correct.
A is not correct, but R is correct.

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(D) Intensity of light $I = \frac{n h ν}{A}$ , Here $v$ is no. of photons per unit time.

$n = \frac{I A}{h ν}$ , so on increasing frequency $v,$ $n$ decreases taking intensity constant. Number of photons remains unchanged with increase in frequency.

$k_{\max} = h ν - ϕ$

So on increasing $v$ , kinetic energy increases.

Q 2 :
Which of the following statement is not true about stopping potential $(V_{0})$ ? [2024]

It depends upon frequency of the incident light.
It increases with increase in intensity of the incident light.
It is 1/e times the maximum kinetic energy of electrons emitted.
It depends on the nature of emitter material.

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(B) $K E_{m a x} = h ν - ϕ_{0} = e V$

Q 3 :
In photoelectric experiment energy of 2.48 eV irradiates a photo sensitive material. The stopping potential was measured to be 0.5 V. Work function of the photo sensitive material is : [2024]

2.48 eV
0.5 eV
1.98 eV
1.68 eV

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(C) $e V_{s} = h ν - ϕ$

$0.5 e V = 2.48 e V - ϕ$

Work function, $ϕ = (2.48 - 0.5) e V = 1.98 e V$

Q 4 :
When UV light of wavelength 300 nm is incident on the metal surface having work function 2.13 eV, electron emission takes place. The stopping potential is [2024]

4.1 V
2 V
4 V
1.5 V

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(B) Energy incident on the metal surface,

$E = \frac{h c}{λ} = \frac{1240}{300} e V \Rightarrow E = 4.13 e V$

Work function, $ϕ = 2.13 e V$

$E = ϕ + e V_{s} = 4.13 e V - 2.13 e V = 2 e V_{s} \Rightarrow V_{s} = 2 V$

Q 5 :
UV light of 4.13 eV is incident on a photosensitive metal surface having work function 3.13 eV. The maximum kinetic energy of ejected photoelectrons will be [2024]

4.13 eV
1 eV
3.13 eV
7.26 eV

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(B) As we know that

${(K . E .)}_{m a x} = E_{p h o t o n} -$ work function $= h ν - ϕ$

${(K . E .)}_{m a x} = 4.13 e V - 3.13 e V$

Max $K . E . = 1 e V$

Q 6 :
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 [2024]

$\frac{I}{2}$
$4 I$
$2 I$
$I$

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(D) As amount of energy incident on cell is same so current will remain same.

Q 7 :
The threshold frequency of a metal with work function 6.63eV is [2024]

$16 \times 10^{15} H z$
$16 \times 10^{12} H z$
$1.6 \times 10^{12} H z$
$1.6 \times 10^{15} H z$

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(D) $ϕ_{0} = h ν_{0}$

$6.63 \times 1.6 \times 10^{- 19} = 6.63 \times 10^{- 34} ν_{0}$

$ν_{0} = \frac{1.6 \times 10^{- 19}}{10^{- 34}}$

$ν_{0} = 1.6 \times 10^{15} Hz$

Q 8 :
The work function of a substance is 3.0 eV. The longest wavelength of light that can cause the emission of photoelectrons from this substance is approximately [2024]

215 nm
414 nm
400 nm
200 nm

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(B) For photoelectric effect: $λ \leq \frac{h c}{W_{e}}$

$λ \leq \frac{1240 nm - eV}{3 eV}$

$λ \leq 413.33 nm$

$λ_{\max} \approx 414 nm$

Q 9 :
When a metal surface is illuminated by light of wavelength $λ$ , the stopping potential is 8V. When the same surface is illuminated by light of wavelength $3 λ$ , stopping potential is 2V. The threshold wavelength for this surface is [2024]

$9 λ$
$3 λ$
$4.5 λ$
$5 λ$

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(A) $E = ϕ + K_{\max}$

$ϕ = \frac{h c}{λ_{0}}$

$K_{\max} = e V_{0}$

$8 e = \frac{h c}{λ} - \frac{h c}{λ_{0}}$ ...(i)

$2 e = \frac{h c}{3 λ} - \frac{h c}{λ_{0}}$ ...(ii)

On solving (i) and (ii) $λ_{0} = 9 λ$

Q 10 :
In a photoelectric effect experiment a light of frequency 1.5 times the threshold frequency is made to fall on the surface of photosensitive material. Now if the frequency is halved and intensity is doubled, the number of photo electrons emitted will be [2024]

Doubled
Quadrupled
Zero
Halved

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(C) Since $\frac{f}{2} < f_{0}$

i.e. the incident frequency is less than threshold frequency. Hence there will be no emission of photoelectrons.

$\Rightarrow$ current = 0

Topic Question Set

Q 2 :
Which of the following statement is not true about stopping potential $(V_{0})$ ? [2024]

Q 3 :
In photoelectric experiment energy of 2.48 eV irradiates a photo sensitive material. The stopping potential was measured to be 0.5 V. Work function of the photo sensitive material is : [2024]

Q 4 :
When UV light of wavelength 300 nm is incident on the metal surface having work function 2.13 eV, electron emission takes place. The stopping potential is [2024]

Q 5 :
UV light of 4.13 eV is incident on a photosensitive metal surface having work function 3.13 eV. The maximum kinetic energy of ejected photoelectrons will be [2024]

Q 6 :
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 [2024]

Q 7 :
The threshold frequency of a metal with work function 6.63eV is [2024]

Q 8 :
The work function of a substance is 3.0 eV. The longest wavelength of light that can cause the emission of photoelectrons from this substance is approximately [2024]

Q 9 :
When a metal surface is illuminated by light of wavelength $λ$ , the stopping potential is 8V. When the same surface is illuminated by light of wavelength $3 λ$ , stopping potential is 2V. The threshold wavelength for this surface is [2024]

Q 10 :
In a photoelectric effect experiment a light of frequency 1.5 times the threshold frequency is made to fall on the surface of photosensitive material. Now if the frequency is halved and intensity is doubled, the number of photo electrons emitted will be [2024]

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Topic Question Set

Q 2 : Which of the following statement is not true about stopping potential (V0) ? [2024]

Q 3 : In photoelectric experiment energy of 2.48 eV irradiates a photo sensitive material. The stopping potential was measured to be 0.5 V. Work function of the photo sensitive material is : [2024]

Q 4 : When UV light of wavelength 300 nm is incident on the metal surface having work function 2.13 eV, electron emission takes place. The stopping potential is [2024]

Q 5 : UV light of 4.13 eV is incident on a photosensitive metal surface having work function 3.13 eV. The maximum kinetic energy of ejected photoelectrons will be [2024]

Q 6 : 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 [2024]

Q 7 : The threshold frequency of a metal with work function 6.63eV is [2024]

Q 8 : The work function of a substance is 3.0 eV. The longest wavelength of light that can cause the emission of photoelectrons from this substance is approximately [2024]

Q 9 : When a metal surface is illuminated by light of wavelength λ, the stopping potential is 8V. When the same surface is illuminated by light of wavelength 3λ, stopping potential is 2V. The threshold wavelength for this surface is [2024]

Q 10 : In a photoelectric effect experiment a light of frequency 1.5 times the threshold frequency is made to fall on the surface of photosensitive material. Now if the frequency is halved and intensity is doubled, the number of photo electrons emitted will be [2024]

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Q 2 :
Which of the following statement is not true about stopping potential $(V_{0})$ ? [2024]

Q 3 :
In photoelectric experiment energy of 2.48 eV irradiates a photo sensitive material. The stopping potential was measured to be 0.5 V. Work function of the photo sensitive material is : [2024]

Q 4 :
When UV light of wavelength 300 nm is incident on the metal surface having work function 2.13 eV, electron emission takes place. The stopping potential is [2024]

Q 5 :
UV light of 4.13 eV is incident on a photosensitive metal surface having work function 3.13 eV. The maximum kinetic energy of ejected photoelectrons will be [2024]

Q 6 :
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 [2024]

Q 7 :
The threshold frequency of a metal with work function 6.63eV is [2024]

Q 8 :
The work function of a substance is 3.0 eV. The longest wavelength of light that can cause the emission of photoelectrons from this substance is approximately [2024]

Q 9 :
When a metal surface is illuminated by light of wavelength $λ$ , the stopping potential is 8V. When the same surface is illuminated by light of wavelength $3 λ$ , stopping potential is 2V. The threshold wavelength for this surface is [2024]

Q 10 :
In a photoelectric effect experiment a light of frequency 1.5 times the threshold frequency is made to fall on the surface of photosensitive material. Now if the frequency is halved and intensity is doubled, the number of photo electrons emitted will be [2024]