The work function of a photoelectric material is 4.0 e V. (a) What is the threshold wavelength? (b) find the wavelength of light for which the stopping potential is 2.5 V.

Explanation

To solve the problem step by step, we will break it down into two parts: (a) finding the threshold wavelength and (b) finding the wavelength of light for which the stopping potential is 2.5 V.

### Part (a): Finding the Threshold Wavelength

1. **Understanding the Work Function**: The work function (φ) is the minimum energy required to remove an electron from the surface of a material. It is given as 4.0 eV.

2. **Convert Work Function to Joules**:
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