Question

A photo-sensitive material would emit electrons if excited by photons beyond a threshold. To overcome the threshold, one would increase

• A. the voltage applied to the material
• B. the intensity of the light source
• C. the wavelength of light
• D. the frequency of light

Hint:

For the photoelectric effect, increasing the frequency of light provides more energy to emit electrons.

Answer 1

The Correct Option is D

Step 1: Understanding the photoelectric effect.
According to the photoelectric effect, electrons are ejected from a photo-sensitive material when it absorbs photons with energy greater than or equal to a certain threshold. The energy of a photon is given by \( E = h f \), where \( h \) is Planck's constant and \( f \) is the frequency of the light.
Step 2: Increasing the frequency.
To overcome the threshold and emit electrons, we need photons with energy greater than the threshold energy. Since energy is proportional to frequency, increasing the frequency will increase the photon energy and thus overcome the threshold.
Step 3: Conclusion.
Hence, the correct answer is option (4).

Final Answer: \[ \boxed{\text{(4) the frequency of light}} \]