Question

The energy of light of wavelength 45 nm is
a) 6.67 × 10¹⁵J
b) 6.67 × 10¹¹J
c) 4.42 × 10⁻¹⁸J
d) 4.42 × 10⁻¹⁵J

Answer 1

Answer ⇒ Option (b). 4.42 × 10⁻¹⁸ J.


Given conditions ⇒

Wavelength of the light = 45 nm.
 = 45 × 10⁻⁹ m.

Velocity of the light = 3 × 10⁸ m/s.
Plank's constant = 6.62 × 10⁻³⁴ J-s. 

Using the Formula, 

 λ = hc/E
45 × 10⁻⁹ = (6.62 × 10⁻³⁴ × 3 × 10⁸)/E
∴ E = (19.86 × 10⁻²⁶)/(45 × 10⁻⁹)
    =  0.442 × 10⁻¹⁷
    = 4.42 × 10⁻¹⁸ J.


Hence, Option (c). is correct.


Hope it helps.