Ultraviolet light of wavelength 280 nm is used in an experiment on photoelectric effect with lithium `( varphi = 2.5 eV)` cathode. Find (a) the maximum kinetic energy of the photoelectrons and (b) the stopping potential.

Explanation

To solve the problem, we will follow these steps:

### Given Data:
- Wavelength of light, \( \lambda = 280 \, \text{nm} = 280 \times 10^{-9} \, \text{m} \)
- Work function of lithium, \( \varphi = 2.5 \, \text{eV} \)

### Step 1: Calculate the frequency of the light
Using the relation between speed of light, frequency, and wavelength:
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