Question

# How many photons of a radiation of wavelength $$\lambda=5\times 10^{-7}$$ m must fall per second on a blackened plate in order to produce a force of $$6.62\times 10^{-5}N$$?

A
3×1019
B
5×1022
C
2×1022
D
1.67×1018

Solution

## The correct option is B $$5\times 10^{22}$$Momentum of photon is given by,$$p=\dfrac{h}{\lambda}$$Momentum of n photons, $$=n\dfrac{h}{\lambda}$$Force is the change in momentum. Since, the plate is blackened, all the photons are being absorbed. Thus, change in momentum and hence the force is given by$$F=\dfrac{dp}{dt}=n\dfrac{h}{\lambda}$$$$n=F\dfrac{\lambda}{h}=\dfrac{6.62\times{10}^{-5}\times 5\times {10}^{-7}}{6.62\times{10}^{-34}}=5\times{10}^{22}$$PhysicsNCERTStandard XII

Suggest Corrections

0

Similar questions
View More

Same exercise questions
View More

People also searched for
View More