In an experiment on the photo-electric effect Singly ionized helium is excited electronically to different energy levels. The light emitted by ionised helium is incident on photo-electric plate in a photocell. When helium is excited to fourth energy level, then the observed stopping potential of the photocell is found to be five times the stopping potential measured when the photoelectrons are produced by using light emitted by hydrogen atom, excited to the third energy level. Determine the work function of the material of the photo-electric plate.

Explanation

To solve the problem, we will follow these steps:

### Step 1: Understand the Problem
We have two cases: one where singly ionized helium is excited to the fourth energy level and another where hydrogen is excited to the third energy level. The stopping potential for helium is five times that of hydrogen.

### Step 2: Define Variables
Let:
- \( V_1 \) = Stopping potential for helium
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