Question

In Photo- electric effect
(A) There is no time interval (very small ~ 10⁻⁹s) between incidence of light and emissions of photo electrons.
(B) Higher the frequency of light, more is the kinetic energy of photo electrons emitted.
(C) A bright light yields more photo-electrons than dim light.
(D) Blue light emits slower electrons than red light.
Choose the correct answer from the options given below:

• A. (A), (B) and (C) only
• B. (A), (B) and (D) only
• C. (B), (C) and (D) only
• D. (A), (C) and (D) only

Hint:

To remember the photoelectric effect laws, think in terms of photons:
{Frequency (Energy of one photon):} Determines the kinetic energy of the ejected electron (\(KE = hf - \phi\)). Higher frequency \(\rightarrow\) higher KE.
{Intensity (Number of photons):} Determines the number of ejected electrons. Higher intensity \(\rightarrow\) more electrons (more current).

Answer 1

The Correct Option is A

Step 1: Concept Overview:
The photoelectric effect is the emission of electrons from a material when exposed to light. This question assesses understanding of key experimental observations and their explanations through the quantum (photon) model of light.

Step 2: Analysis of Statements:


(A) Instantaneous Emission: Correct. Electron emission occurs almost immediately upon light exposure. This observation contradicts classical wave theory, which predicted a delay for energy accumulation.

(B) Kinetic Energy vs. Frequency: Correct. Einstein's photoelectric equation, \( KE_{max} = hf - \phi \), demonstrates a linear relationship between the maximum kinetic energy of emitted electrons and the incident light's frequency, provided the frequency exceeds the threshold.

(C) Photoelectron Yield vs. Intensity: Correct. Light intensity, proportional to the number of incident photons per unit time, directly influences the number of photoelectrons emitted. Higher intensity means more photon-electron interactions, resulting in a greater photocurrent.

(D) Electron Speed and Light Color: Incorrect. Blue light has a higher frequency than red light. According to Einstein's equation, blue light will cause photoelectrons to be emitted with *higher* maximum kinetic energy (and thus higher speeds) than red light, assuming both frequencies are above the threshold.

Step 3: Conclusion:
Statements (A), (B), and (C) accurately describe the photoelectric effect. Statement (D) is inaccurate. Therefore, the correct option is (A).