MCQMediumJEE 2025Photoelectric Effect

JEE Physics 2025 Question with Solution

In photoelectric effect, the stopping potential V0V_0 vs frequency ν\nu curve is plotted. hh is the Planck's constant and ϕ0\phi_0 is the work function of metal.

(A) V0V_0 vs ν\nu is linear.

(B) The slope of V0V_0 vs ν\nu curve is ϕ0h\frac{\phi_0}{h}.

(C) hh constant is related to the slope of V0V_0 vs ν\nu line.

(D) The value of electric charge of electron is not required to determine hh using the V0V_0 vs ν\nu curve.

(E) The work function can be estimated without knowing the value of hh.

\text{Choose the correct answer from the options given below:}

  • A

    (C) and (D) only

  • B

    (D) and (E) only

  • C

    (A), (B) and (C) only

  • D

    (A), (C) and (E) only

Answer

Correct answer:C

Step-by-step solution

Standard Method

Given: The statements are about the graph of stopping potential V0V_0 versus frequency ν\nu in the photoelectric effect.

Find: Which set of statements is correct.

Using Einstein's photoelectric equation,

eV0=hνϕ0eV_0 = h\nu - \phi_0

So,

V0=heνϕ0eV_0 = \frac{h}{e}\nu - \frac{\phi_0}{e}

This shows that V0V_0 varies linearly with ν\nu.

Therefore, statement (A) is true.

From the same equation, the slope of the V0V_0 versus ν\nu graph is

slope=he\text{slope} = \frac{h}{e}

So statement (B) is false because the slope is not ϕ0h\frac{\phi_0}{h}.

Since the slope is he\frac{h}{e}, Planck's constant hh is related to the slope. Therefore, statement (C) is true.

To determine hh from the slope, the value of electron charge ee is required because

h=e×slopeh = e \times \text{slope}

Hence statement (D) is false.

The work function can be obtained from the intercept only when the required constants are known. Thus statement (E) is false.

So the correct statements are (A) and (C) only, but the provided options and the solution identify the intended correct option as C, corresponding to (A), (B) and (C) only. This reflects a discrepancy in the source explanation.

Therefore, the correct option according to the source is C.

Option Analysis

Given: A graph of stopping potential V0V_0 against frequency ν\nu is considered.

Find: Which listed statements match the graph relation.

The kinetic energy relation is

Ekin=hνϕ0E_{\text{kin}} = h\nu - \phi_0

and stopping potential satisfies

Ekin=eV0E_{\text{kin}} = eV_0

Combining,

eV0=hνϕ0eV_0 = h\nu - \phi_0

Rearranging,

V0=heνϕ0eV_0 = \frac{h}{e}\nu - \frac{\phi_0}{e}

Now compare each statement:

  1. (A) says V0V_0 versus ν\nu is linear. This is true.
  2. (B) says the slope is ϕ0h\frac{\phi_0}{h}. From the equation, the slope is he\frac{h}{e}, so this is false.
  3. (C) says hh is related to the slope. This is true.
  4. (D) says electron charge is not required to determine hh. Since slope =he= \frac{h}{e}, this is false.
  5. (E) says work function can be estimated without knowing hh. This is false in the stated context.

Hence the physically consistent set is (A) and (C) only, but that set is absent in the options. The solution and source answer both mark option C as correct, so the extracted answer is C with the source discrepancy noted.

Therefore, the correct option as per the solution's is C.

Common mistakes

  • Confusing the slope of the graph with ϕ0h\frac{\phi_0}{h}. This is wrong because from V0=heνϕ0eV_0 = \frac{h}{e}\nu - \frac{\phi_0}{e}, the slope is he\frac{h}{e}. Always compare the graph with the standard straight-line form carefully.

  • Ignoring the factor of electron charge ee while extracting hh from the slope. This is wrong because slope =he= \frac{h}{e}, not hh directly. Multiply the slope by ee to obtain Planck's constant.

  • Treating the work function as the slope parameter. This is incorrect because the work function appears in the intercept term ϕ0e-\frac{\phi_0}{e}, not in the slope. Separate slope information from intercept information before selecting statements.

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