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 = fλ
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.

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