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: Understanding the Concept:
The photoelectric effect is the emission of electrons when light shines on a material. This question tests the key experimental observations and their explanations based on the quantum (photon) model of light.
Step 2: Detailed Explanation:
Let's evaluate each statement:

(A) There is no time interval... This is a correct and crucial observation. The emission is practically instantaneous, which contradicts the classical wave theory of light that predicted a significant time lag for energy to accumulate.

(B) Higher the frequency of light, more is the kinetic energy... This is correct. Einstein's photoelectric equation is \( KE_{max} = hf - \phi \), where \(f\) is the frequency. This shows a linear relationship between the maximum kinetic energy of photoelectrons and the frequency of the incident light (above the threshold frequency).

(C) A bright light yields more photo-electrons... This is correct. The brightness (intensity) of light is proportional to the number of photons incident per unit time. A higher intensity means more photons are available to interact with electrons, leading to the emission of more photoelectrons (a higher photocurrent).

(D) Blue light emits slower electrons than red light. This is incorrect. Blue light has a higher frequency than red light. According to Einstein's equation, the higher frequency of blue light will result in photoelectrons with *higher* maximum kinetic energy (and thus higher speeds) compared to those emitted by red light (assuming both frequencies are above the threshold).
Step 3: Final Answer:
Statements (A), (B), and (C) are correct descriptions of the photoelectric effect. Statement (D) is incorrect. Thus, the correct option is (A).