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When ultraviolet radiation is incident on a surface, no photoelectrons are emitted. If a second beam causes photoelectrons to be ejected, it may consist of:

1. infra-red waves
2. X-rays
3. visible light rays
4. radio waves

Correct answer: X-rays

Solution

For photoelectrons to be emitted, the incident radiation must have energy greater than the material's work function. X-rays have higher energy than ultraviolet radiation, so they can eject photoelectrons when ultraviolet cannot.

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