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.
Important Questions from Miscellaneous
- An electromagnetic wave with its magnetic field $B = 0.3\cos(ky-10^8t)i$ tesla is propagating in a non-magnetic dielectric medium of refractive index 2. The wavelength of the wave is
For a given system of resistors having resistances R, 2R, R$_0$ and 2R (shown in the figure), what will be the value of resistance of the resistor R$_0$, when there is NO current in the galvanometer G?
- A cyclotron has an oscillator frequency of $12\times10^6$ Hz and 'Dee' radius of 21 inches. The value of magnetic induction (field) needed to accelerate a deuteron (mass = $3.34 \times 10^{-27}$ kg and charge = $1.6\times10^{-19}$ C) is
- Why do we prefer to have a liquid and not a gas to be used as the fluid in a hydraulic machine?
- A threshold frequency for photoelectric emission in copper is $1.1\times10^{15}$ Hz. When the light of frequency $1.2\times10^{15}$ Hz is directed on the copper surface, the maximum energy of emitted particles would be (Planck's constant is $6.62\times10^{-34}$ J-s and the charge on the electron is $1.6\times10^{-19}$ C)
