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The work functions of sodium and copper are 2.3 eV and 4.5 eV, respectively. The ratio of the corresponding threshold wavelengths is closest to

1. 1: 2
2. 4: 1
3. 2: 1
4. 1: 4

Correct answer: 2: 1

Solution

The threshold wavelength is inversely proportional to the work function, meaning that a lower work function corresponds to a longer wavelength. Since sodium has a work function of 2.3 eV and copper has 4.5 eV, the ratio of their threshold wavelengths is approximately 2:1, indicating that sodium's wavelength is twice that of copper's.

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