Question:
Assertion (A) : Electron emission from surface of zinc occurs when yellow light is incident on it.
Reason (R) : Energy of a photon of yellow light is more than the work function of zinc.
Assertion (A) : Electron emission from surface of zinc occurs when yellow light is incident on it.
Reason (R) : Energy of a photon of yellow light is more than the work function of zinc.
Show Hint
Zinc has a work function of about 4.3 eV. A yellow photon has only about 2.1 eV, so no emission occurs.
Updated On: Oct 21, 2026
- Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of the Assertion (A).
- Both Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation of the Assertion (A).
- Assertion (A) is true, but Reason (R) is false.
- Both Assertion (A) and Reason (R) are false.
Show Solution
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The Correct Option is D
Solution and Explanation
Step 1: Understanding the Concept:
In the photoelectric effect, electrons are emitted only if the photon energy \(h\nu\) is at least the work function \(\phi_0\) of the metal.
Step 2: Get the values:
The work function of zinc is about 4.3 eV. Its threshold wavelength is about 290 nm, which is in the ultraviolet region.
Yellow light has a wavelength of about 580 nm. Its photon energy is:
\[ E = \frac{1240 \text{ eV nm}}{580 \text{ nm}} \approx 2.1 \text{ eV} \]
Step 3: Check the Assertion:
Since \(2.1\) eV is less than \(4.3\) eV, yellow light cannot free electrons from zinc. No emission occurs. The Assertion is FALSE.
Step 4: Check the Reason:
The energy of a yellow photon (2.1 eV) is less than the work function of zinc (4.3 eV). The Reason says the opposite, so it is FALSE.
Step 5: Eliminate options:
(A) and (B) need both statements true. (C) needs A true. None of these fits.
Final Answer:
Both A and R are false. This is option (D). \[ \boxed{\text{Option (D)}} \]
In the photoelectric effect, electrons are emitted only if the photon energy \(h\nu\) is at least the work function \(\phi_0\) of the metal.
Step 2: Get the values:
The work function of zinc is about 4.3 eV. Its threshold wavelength is about 290 nm, which is in the ultraviolet region.
Yellow light has a wavelength of about 580 nm. Its photon energy is:
\[ E = \frac{1240 \text{ eV nm}}{580 \text{ nm}} \approx 2.1 \text{ eV} \]
Step 3: Check the Assertion:
Since \(2.1\) eV is less than \(4.3\) eV, yellow light cannot free electrons from zinc. No emission occurs. The Assertion is FALSE.
Step 4: Check the Reason:
The energy of a yellow photon (2.1 eV) is less than the work function of zinc (4.3 eV). The Reason says the opposite, so it is FALSE.
Step 5: Eliminate options:
(A) and (B) need both statements true. (C) needs A true. None of these fits.
Final Answer:
Both A and R are false. This is option (D). \[ \boxed{\text{Option (D)}} \]
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