Question

Photon of which light has maximum energy

A. Red

B. Blue

C. Violet

D. Green

Answer 1

Hint: The amount of energy is directly proportional to the photon's electromagnetic frequency and this equivalently is inversely proportional to the wavelength. The higher the photon's frequency, the higher is the energy of the respective coloured light.

Complete Solution :

We know that, from Planck’s energy formula, the energy-frequency relation of a photon is given by:

E = hv

Where h = Planck’s constant, and v = frequency of light.

Therefore, we can say,  $ E\propto v $ 

So, for a light having high frequency, its energy will also be high.

- Now, let us know the frequency of the various coloured light:

Frequency of Red light  $ =4\times {{10}^{14}}Hz $ 

Frequency of Blue light  $ =6.5\times {{10}^{14}}Hz $ 

Frequency of Violet light  $ =7.5\times {{10}^{14}}Hz $ 

Frequency of Green light  $ =5.4\times {{10}^{14}}Hz $ 

On the basis of frequency, let us arrange the coloured light in increasing order of their frequency:

Violet > blue > green > red

As the frequency of violet light is highest, therefore, we can conclude, violet light has the maximum energy.

So, the correct answer is “Option C”.

Note: We can also determine which light has maximum energy on the basis of its wavelength.

From Planck’s relation,  $ E=\dfrac{hc}{\lambda } $ , we can conclude,  $ E\propto \dfrac{1}{\lambda } $ , that is, energy of a photon is inversely proportional to the light’s wavelength.

- Hence, the light having the lowest wavelength will have maximum energy.

- On the basis of wavelength, red has the maximum wavelength, then green, then comes blue and lastly violet. Therefore, violet has the maximum energy.