Dispersion Phenomenon Explained

When white light, which is a combination of different colours, passes through a glass prism, it splits into its constituent colours. This splitting of white light into its component colours upon passing through a medium like a prism is known as the dispersion of light. Each colour has a different wavelength.

Understanding Angle of Deviation

The angle of deviation ($\delta$) is the angle formed between the direction of the incident ray and the direction of the emergent ray after the light has passed through the prism. This angle depends on the prism's material and the wavelength of the light passing through it.

Refractive Index and Wavelength Relation

The key reason for dispersion is that the refractive index ($n$) of the prism material (glass) varies for different wavelengths (colours) of light. Typically:

• Light with shorter wavelengths (like violet and blue) experiences a higher refractive index.
• Light with longer wavelengths (like red and orange) experiences a lower refractive index.

The angle of deviation is directly related to the refractive index. A higher refractive index leads to a greater angle of deviation.

Colour Deviation Order in Prism

The order of colours in the visible spectrum based on their wavelengths, from longest to shortest, is:

Red > Orange > Yellow > Green > Blue > Indigo > Violet

Consequently, the angle of deviation generally follows the reverse order, from smallest to largest:

Red < Orange < Yellow < Green < Blue < Indigo < Violet

Identifying Highest Deviation Colour

Among the colours provided in the options (yellow, green, orange, red):

• Red has the longest wavelength and thus the lowest refractive index, resulting in the smallest angle of deviation.
• Orange has a shorter wavelength than red, leading to a slightly higher refractive index and angle of deviation.
• Yellow has a shorter wavelength than orange, resulting in a higher refractive index and angle of deviation compared to orange.
• Green has a shorter wavelength than yellow, orange, and red. This means it has the highest refractive index among these four colours, causing it to bend the most and thus have the highest angle of deviation.

Therefore, the angle of deviation will be the highest in green light among the given choices when passing through a glass prism.