A small illuminated bulb is at the bottom of a tank, containing a liquid of refractive index `mu` upto a height H. Find the expression for the diameter of an opaque disc, floating symmetrically on the liquid surface in order to cut- off the light from the bulb.

Explanation

To find the expression for the diameter of an opaque disc floating symmetrically on the surface of a liquid in a tank containing a bulb at the bottom, we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Setup**:
- We have a small illuminated bulb at the bottom of a tank filled with a liquid of refractive index \( \mu \) up to a height \( H \).
- We need to find the diameter of an opaque disc that floats on the surface of the liquid and cuts off the light from the bulb.

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