(a) describe briefly three experimentally observed features in the phenomenon of photoelectric effect.
(b) Discuss briefly how wave theory of light cannot explain these features.
OR
(a) Write the important properties of photons which are used to establish Eintein's photoelectric equation .
(b) Use this equation to explain the concept of (i) threshould frequency and (ii) stopping potential .3.

Explanation

### Step-by-Step Solution

#### Part (a): Three Experimentally Observed Features of the Photoelectric Effect

1. **Definition of Photoelectric Effect**:
The photoelectric effect is defined as the phenomenon where electrons are ejected from a metal surface when light of suitable frequency falls on it.

2. **Feature 1: Threshold Frequency**:
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