Light of wavelength 750 nm appears red to the human eye. What is the energy of a photon of light of this wavelength? Answer in units of J.

2.65 × 10^-19 J

Explanation:

The energy of a photon of light of this wavelength can be calculated using;

E = hf

Where; E = Energy of photon (J)

h = Planck's constant (6.626 × 10^-34 Js)

f = frequency of photon

However, to get the frequency of the photon (f), we use:

f = c/λ

λ = wavelength = 750nm = 750 × 10^-9m

c = speed of light = 3 × 10^8m/s

f = frequency

f = 3 × 10^8/750 × 10^-9

f = 0.004 × 10^(8+9)

f = 0.004 × 10^17

f = 4 × 10^14 Hz

Since f = 4 × 10^14 Hz, h = 6.626 × 10^-34 Js

E = hf

E = 6.626 × 10^-34 × 4 × 10^14

E = 26.504 × 10^-20

E = 2.65 × 10^-19 J

the answer is d. 74.02