JEE Main 2021 · PhysicsMultiple choiceSingle correctMediumCalculation

JEE Main 25 February 2021, Shift 1, Physics Q13

Question 13 of 90 in this shift, Physics question 13 of 30, Section A.

Two coherent light sources having intensity in the ratio

2x

produce an interference pattern. The ratio

\frac{I_{max}-I_{min}}{I_{max}+I_{min}}

will be :

(1) $\frac{\sqrt{2x}}{2x+1}$
(2) $\frac{2\sqrt{2x}}{2x+1}$ Official answer
(3) $\frac{\sqrt{2x}}{x+1}$
(4) $\frac{2\sqrt{2x}}{x+1}$

Official answer

Option 2

NTA final key.

Chapter: Wave Optics
Topic: Young's Double Slit
Idea tested: Fringe Visibility and Contrast

Same topic in other shifts

All Young's Double Slit questions

2 Apr 2026, Shift 2 · Q46In a Young's double slit experiment, the intensity at some point on the screen is found to be $\frac{3}{4}$ times of the maximum of the…MediumNumerical value
4 Apr 2026, Shift 2 · Q50In a double slit experiment, when one of the slits is covered by a transparent mica sheet of refractive index 1.56, the central fringe…MediumNumerical value
5 Apr 2026, Shift 1 · Q39In Young's double slit experiment, the fringe width of the interference pattern produced on the screen is $2.4\ \mu$ m. If the experiment…EasySingle correct
5 Apr 2026, Shift 2 · Q42The maximum intensity in a Young's double slit experiment is $I_0$ . Distance between the slits ( $d$ ) is $5\lambda$ , where $\lambda$ is the…MediumSingle correct
6 Apr 2026, Shift 1 · Q36In interference experiment the path difference between two interfering waves at a point $A$ on the screen is $\lambda/3$ , where $\lambda$ …EasySingle correct
6 Apr 2026, Shift 2 · Q45In a Young double slit experiment, the wavelength of incident light is 6000 Å, the separation between slits $S_1$ and $S_2$ is 5 cm and…MediumDiagram basedHas a figure

Question text from the official JEE Main paper published by NTA; answer from the final answer key. Chapter, topic and idea tags, difficulty and skill are Lumi’s. Lumi analyses 108 of the 174 JEE Main shifts held from 2017 to 2026.