A light source hits the surface of platinum metal and no electrons are emitted. What change should be made to the light source to eject electrons?

12A

Question

A light source hits the surface of platinum metal and no electrons are emitted. What change should be made to the light source to eject electrons?

12A

BlackTom AI · Accepted Answer

In the photoelectric effect, electrons are ejected only if the energy of incoming photons is at least equal to the work function of the material. Platinum has a work function that requires photons with energy above a certain threshold; otherwise no electrons are emitted.
Option 1: 'Increase the wavelength of the light source.' Increasing wavelength decreases the energy per photon (since photon energy is E = hc/λ). If the current photons do not have enough energy to overcome the work function, making the wavelength longer will not help and will make emission even less likely.
Option 2: 'Increase the intensity of the light source.' Raising intensity increases the number of photons hitting the surface, provided the photon energy already exceeds the threshold. If the photons are below the threshold energy, simply increasing intensity cannot overcome the energy deficit per photon; no electrons will be emitted because each photon still lacks sufficient energy.
Option 3: 'Decrease the intensity of the light source.' Decreasing intensity reduces the photon flux, which would decrease the number of emitted electrons even if emission were possible. This would not enable emission to occur when it wasn’t happening before.
Option 4: 'Decrease the wavelength of the light source.' Shortening the wavelength increases the energy per photon. If the current photons are not energetic enough to overcome the work function, moving to a shorter wavelength raises photon energy and can reach or exceed the threshold, enabling electron emission.

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A light source hits the surface of platinum metal and no electrons are emitted. What change should be made to the light source to eject electrons? 12A

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