Light of wavelength 6000Å is incident on a thin glass plate of refractive index 1.5 such that angle of refraction into the plate is `60^(@)`. Calculate the smallest thickness of plate which will make it appear dark by reflection.

Explanation

To solve the problem, we need to calculate the smallest thickness of a thin glass plate that will make it appear dark by reflection when light of wavelength 6000 Å (angstroms) is incident on it at an angle of refraction of 60°.

### Step-by-Step Solution:

1. **Convert Wavelength to Meters**:
The given wavelength of light is 6000 Å. We need to convert this into meters.
\[
\lambda = 6000 \, \text{Å} = 6000 \times 10^{-10} \, \text{m} = 6 \times 10^{-7} \, \text{m}
...