Question

Consider the following statements about photoelectric effect:
(i) There is time lag between the striking of light beam and the ejection of electrons from the metal surface.
(ii) The number of electrons ejected is directly proportional to the intensity or brightness of light.
(iii) For each metal, there is a characteristic minimum frequency, known as threshold frequency (\(\nu_0\)) below which photoelectric effect is not observed.
(iv) At a frequency greater than \(\nu_0\), the ejected electrons come out with certain kinetic energy. The kinetic energies of these electrons increase with the increase of the wavelength of the light used.
Which of the above statements are true?

• A. (i), (ii) and (iii)
• B. (i) and (iv)
• C. (ii) and (iii)
• D. (i) and (iii)

Hint:

Remember: Intensity affects the number of electrons (current), while frequency affects the energy of the individual electrons. These two variables are independent in the photoelectric effect.

Answer 1

The Correct Option is C

Step 1: Understanding the Concept:
The photoelectric effect is the emission of electrons from a metal surface when light of a specific frequency strikes it. It follows Einstein's photoelectric equation: \(h\nu = h\nu_0 + K.E._{max}\).

Step 2: Detailed Explanation:
1. Statement (i): Incorrect. There is no time lag; it is an instantaneous process.
2. Statement (ii): True. The photocurrent (number of electrons) depends on the intensity of light, provided the frequency is above the threshold.
3. Statement (iii): True. \(\nu_0\) is the minimum frequency required to overcome the work function of the metal.
4. Statement (iv): Incorrect. Kinetic energy \(K.E. = h\nu - h\nu_0\). Since \(\nu = c/\lambda\), as wavelength (\(\lambda\)) increases, frequency (\(\nu\)) decreases, and consequently, kinetic energy decreases.

Step 3: Final Answer:
Statements (ii) and (iii) are the only true statements.