Question

If a photon is reflected from the mirror, then the change in momentum of photon is
a)zero
b)2h/lemda
c)h/lemda
d)F

Solve

Answer 1

$\huge\mathfrak\pink{\underline{\underline{AnSwer}}}$

your answer is option (b) 2h/lembda

as we know,

P = h/lembda

and momentum is a vector quantity. ..so, we must use sign (+,-) to indicate direction.


now, let initial momentum be P1

P1 = h/lembda

and after reflection momentum = P2

P2 = - h/lembda (h and wavelength will nt change as they are constant)

[negative sign due to opposite direction]

so,《 p1 = p2》=P

now,

change in momentum = final -initial

momentum = -P2 - P1

=> -2P

=> | -2P| = 2P

and 2P = 2h/lembda


happy to help!

:)