JEE Main · 2021 · 25 Feb 2021 · Shift 1 · Wave Optics

Two coherent light sources having intensity in the ratio

2 x

produce an interference pattern. The ratio

\frac{I _{max} - I _{min}}{I _{max} + I _{min}}

will be :

(A) $\frac{2 x}{x + 1}$
(B) $\frac{2 x}{2 x + 1}$
(C) $\frac{2 2 x}{2 x + 1}$ ✓ Correct
(D) $\frac{2 2 x}{x + 1}$

Answer: (C)

Solution

Two coherent beams give

I_{m a x} = (I_{1} + I_{2})^{2}, I_{m i n} = (I_{1} - I_{2})^{2}

so that

\frac{I _{m a x} - I _{m i n}}{I _{m a x} + I _{m i n}} = \frac{4 I _{1} I _{2}}{2 ( I _{1} + I _{2} )} = \frac{2 I _{1} I _{2}}{I _{1} + I _{2}}

Dividing the numerator and the denominator by

I_{2}

and putting

\frac{I _{1}}{I _{2}} = 2 x

gives

\frac{2 2 x}{2 x + 1}

JEE Main · 2021 · 25 Feb 2021 · Shift 1 · Single correct option

Practise more: all JEE Main PYQs on Wave Optics →

More JEE Main questions on Wave Optics

Given below are two statements:
Statement I: In a Young's double slit experiment, the angular separation of fringes will increase as the screen is moved away from the plane of the slits
Statement II : In a Young's double slit experiment, the angular separation of fringes will inc …
JEE Main 2026View solution →
In a Young's double slit experiment set up, the two slits are kept 0.4 mm apart and screen is placed at 1 m from slits. If a thin transparent sheet of thickness $20 μ m$ is introduced in front of one of the slits then centre bring fringe shifts by 20 mm on the screen …
JEE Main 2026View solution →
In two separate Young's double-slit experimental set-ups, two monochromatic light sources of different wavelengths are used to get fringes of equal width. The ratios of the slit separations and that of the wavelengths of light used are $2 : 1$ and $1 : 2$ respectively. The correspo …
JEE Main 2026View solution →
When an unpolarized light falls at a particular angle on a glass plate (placed in air), it is observed that the reflected beam is linearly polarized. The angle of refracted beam with respect to the normal is $____$ .
( $tan^{- 1} (1.52) = 57. 7^{\circ}$ , refractive indices of air a …
JEE Main 2026View solution →
Given below are two statements:

Statement-I: A plane wave after passing through prism remains as plane wave but passing through small pin hole may become spherical wave.
Statement-II: The curvature of a spherical wave emerging from a slit will increase for increasing slit width. …
JEE Main 2026View solution →
In the Young's double slit experiment the intensity produced by each one of the individual slits is $I_{0}$ . The distance between two slits is 2 mm. The distance of screen from slits is 10 m. The wavelength of light is $6000 \overset{˚}{A}$ . The intensity of light on the screen in front of …
JEE Main 2026View solution →