1 A monochromatic lamp emits a 700 W beam of light which has

1.
A monochromatic lamp emits a 70.0 W beam of light which has a wavelength of 460 nm.
(a) How many photons does the lamp emit each minute?

(b) Would this number be bigger, smaller, or the same if the lamp had the same power but emitted light with wavelength 630.2 nm instead?
biggersmaller     the samemore information is needed
2.

When an ultraviolet photon is absorbed by a molecule, the photon\'s energy can be converted into vibrational energy of the molecular bonds. Excessive vibration damages the molecule by causing the bonds to break. Suppose ultraviolet light of wavelength less than 294 nm causes significant damage to a molecule; ultraviolet light of longer wavelength causes minimal damage. What is the threshold photon energy, in eV, for molecular damage?

3.

In the photoelectric effect, electrons are never emitted from a metal if the frequency of the incoming light is below a certain threshold value. This is because
The electric field of low-frequency light does not vibrate the electrons rapidly enough to eject them.The number of photons in low-frequency light is too small to eject electrons.     Low-frequency light does not penetrate far enough into the metal to eject electrons.Photons of lower-frequency light don\'t have enough energy to eject an electron.
4.

A light sensor is based on a photodiode that requires a minimum photon energy of 1.15 eV to create mobile electrons. What is the longest wavelength of electromagnetic radiation that the sensor can detect?
1240 nm

940 nm     

1080 nm

1430 nm
5.

What is the wavelength of a photon whose energy is twice that of a photon with a 574 nm wavelength?

Solution

1. energy of single of photon of light

Energy of single photon = h c / lambda = (6.626 x 10^-34 x 3 x 10^8 ) / (460 x 10^-9)

= 4.321 x 10^-19 J

Energy by lamp each minute = Power x time

= 70 x (60 sec) = 4200 J

no of photons = (4200) / (4.321 x 10^-19) = 9.72 x 10^21 photons

b) wavelength is increased hence energy of each photon will decrease.

so number of photons will increase.