Question

Light of which of the following colours will have the maximum energy in a photon associated with it?

Options

• Red light

• Yellow light

• Green light

• Blue light

Answer 1

Blue light

Explanation:

The energy of a photon is given by Planck’s equation:

E = hv

= `(h c)/lambda`

Where:

h = Planck’s constant

 ν = frequency

λ = wavelength

Thus, a higher frequency gives higher energy, and a shorter wavelength gives higher energy.

In the visible spectrum, red colour gives the longest wavelength and the lowest frequency. The yellow colour gives a shorter wavelength and higher frequency than the red colour. Green colour gives a shorter wavelength and higher frequency than yellow colour. Blue colour gives a shorter wavelength and higher frequency than green colour.

Since energy is inversely proportional to wavelength:

E ∝ `1/lambda`

The colour with the shortest wavelength has the maximum photon energy. Blue light has the highest frequency and hence maximum photon energy.