Question

Photoelectrons are emitted by making green light incident on a metallic surface. Which of the following lights can start photoelectric emission?

• A. Yellow
• B. Orange
• C. Blue
• D. Red

Answer 1

Answer: (C)

Blue

When green light is made incident on a metal, photoelectrons are emitted by it, this means frequency of green light is the threshold frequency. This is the minimum frequency due to which electron is able to knock out of the surface of metal.
The frequency of light is inversely proportional to the wavelength of light.
Since, the wavelengths of yellow, orange and red light are more than green light, their frequencies are lesser than green light hence, no photoelectrons will emitted when yellow or red light made incident on metal.
Since, the wavelength of blue light is less than green light, its frequency is greater than green light hence, photoelectrons will be emitted.

So, the answer is option (C).