Question

Q) the wavelength of light beam a is twice the wavelength of light beam

b. the energy of a photon in beam a is ?

Answer 1

We have the relation E = hc / λ
Thus, energy of the photon is inversely proportional to wavelength of the light beam.

Let the wavelength of light beam 'a' be λ1 and that of 'b' be λ2.
It is given in the data that λ1 = 2 λ2

From the relation between E and λ mentioned above, we can say that

$\frac{E1}{E2}$  = λ2 / λ1 

$\frac{E1}{E2}$ = λ2 / 2 λ2 (as  λ1 = 2 λ2)

$\frac{E1}{E2} = \frac{1}{2}$

E2 = 2 E1

E1 = E2 / 2

Thus, energy of a photon in beam 'a' is half that of a photon in beam 'b'.