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Shane Macguire Grade: upto college level
`        The work function of a photoelectric material is 4.0 eV. (a) What is the threshold wavelength? (b) Find the wavelength of light for which the stopping potential is 2.5 V.`
3 years ago

## Answers : (1)

Jitender Pal
365 Points
```										Sol. ∅ = 4 eV = 4 * 1.6 *10^-19 J
a) Threshold wavelength = λ
∅ = hcλ
⇒ λ = hC/∅ = 6.63 * 10^-34 *3 * 10^8/4 * 1.6 *10^-19 = 6.63 * 3/6.4 * 10^-27/10^-9 = 3.1 * 10^7 m = 310 nm.
b) Stopping potential is 2.5 V
E = ∅ + eV
⇒ hcλ = 4 * 1.6 * 10^-19 + 1.6 * 10^-19 * 2.5
⇒ λ = 6.63 *10^-34 *3 * 10^8/λ * 1.6 * 10^-19 = 4 + 2.5
⇒ 6.63 * 3 * 10^-26/1.6 * 10^-19 * 2.5 = 1.9125 * 10^-7 = 190 nm.

```
3 years ago
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