A metal is illuminated by light above its threshold frequency. Which of the following properties of the light determines the number of electrons emitted by the metal?
color
frequency
intensity
speed
wavelength
The answer is intensity, which makes no sense to me! I thought modern physics said that only frequency determines the number of electrons emitted!
No, frequency determines if they will be emitted or not.
Think of it this way, every ‘‘unit’’ of light has energy proportional to its frequency and each electron needs a certain energy to leave the metal. So if this unit’s frequency rends its energy high enough to liberate the electron then it will. So if one unit liberates 1 electron then to liberate more electrons you need more units.
The intensity is concentration of light, it’s like the number of ‘‘units’’ per unit surface.
So the intensity is what says how many electrons will be liberated. If you have too many units however with insufficient energy then no electrons will be liberated.
Color is related with the wavelength that is related with the frequency, obeying the following equation c=wavelength*frequency, being c the speed of light in vacuum. The speed is the same for all electromagnetic radiation. The energy of a photon obeys the equation E=Planck constant*frequency, so as higher the frequency is the higher the energy is, and the energy after the threshold frequency only changes the kinetic ENERGY of the emitted electron, so what determines the number of electrons emitted is intensity of the light, if you consider the photon a particle, it’s like a collision of two bodies, the more bodies the higher quantity of electrons is emitted.