Question

Photoelectric effect:a) In the wave picture of light, what determines the following properties?

i. Color of the light

ii. Brightness/intensity of the light

iii. Energy of the light

b) In the photon picture of light, what determines the following properties?

i. Color of the light

ii. Brightness/intensity of the light

iii. Energy of the light

Answer 1

Photoelectric is the phenomena in which if we shine a beam of light on a metal surface, electrons are emitted from the surface.the light has to exceed a certain energu un order to eject electrons. below that, no electrons will be emitted.

1) the color of the light determines the wavelength of the light used and hence the energy. If the energy of the incident light is less than the work function, no electrons will be ejected. photons of shorter wavelength ( blue color) have more energy and will eject more electrons from the metal surface than the longer wavelength (red color) . these shorter wavelengths will give a capacitor a greater charge than longer wavelenghts.

2) we have for photoelectric effect, E= h(v -v₀), we see that the energy here is independent of the intensity if the light.when the intensity is increased, the energy does not increase, only the number of photons increase and hence the photocurrent increases.

3) the energy as mentioned above is given by the relation E= h(v -v₀). For the light to eject electrons from the metal surface, the energy of the incident photons must be greater than the work function (h v ₀). if the energy is les thn work function, no electrons will be ejected, if energy is same as work function, elestorns will be emitted, but with no energy. if the energy is greter than work function, the electrons emitted will have some kinetic enerrgy as well. Visible light is copmosed of photons with energy 2-3 eV.

B)

1) the color of the light in the photon picture represents the energy/wavelength of the light. different colors define different photon energies.

2) Intensity is a measure of the energy flux over an area. it measures how much energy travels through a certain region during a certain period. In the photon picture of light, the intensity is understood as the number of photons travelling through a given region in certain oeriod of time, multiplied by the energy of each photon. The energy of each photon depends on it color.

3) we know that energy of a photon is

v = frequency, c = speed of light, h = plancks constant, = wavelength

the energy of photon id the energy difference between two energy levels when an atom form excited state makes a transition to a lower state emitting a photon

or when an atom absorbs a photon of particluar energy to move to excited state.