An experimental apparatus consists of a potassium cathode inside an evacuated photoemissive cell. When illuminated with high-intensity yellow light, no electrical current is registered in the circuit. However, when the cathode is illuminated with very low-intensity blue light, a current is detected instantly.
Explain these observations in terms of the photon model of light.
The maximum wavelength of electromagnetic radiation incident on the surface of a metal plate that causes electrons to be emitted (the threshold wavelength) is 4.8×10−7 m4.8 \times 10^{-7}\text{ m}4.8×10−7 m.
Calculate the maximum kinetic energy, in joules, of the electrons emitted from the surface of this metal plate when each incident photon has an energy of 3.5 eV3.5\text{ eV}3.5 eV.
