What is the energy of a phonton of light having a wavelength of 4.5 x10-7 meters

We can use 2 equations to solve this.

First one, C = fλ

Where C is speed of light (3 x 10⁸ m s⁻¹), f is the frequency (Hz) and λ is the wavelength of the wave (m).

Second one, E = hf

Where E is the energy (J), f is the frequency (Hz) and h is the planck's constant (6.626 * 10⁻³⁴ J s).

From first equation,

C = f λ

f = C/λ

= 3 x 10⁸ m s⁻¹ / 4.5 x 10⁻⁷ m

From second equation,

E = hf

= 6.626 * 10⁻³⁴ J s x (3 x 10⁸ m s⁻¹ / 4.5 x 10⁻⁷ m)

= 4.417 x 10⁻¹⁹ J

Hence, the energy of the photon is 4.417 x 10⁻¹⁹ J.