Interference and Young's double-slit experiment
- If the monochromatic source in Young's double slit experiment is replaced by white light, then Answer: 4. there will be a central bright white fringe surrounded by a few coloured fringes. Key idea: Each colour makes its own fringe patt... 1
- For Young's double slit experiment, two statements are given below:Statement I : If screen is moved away from the plane of slits, angular separation of the fringes remains constant.Statement II : If the monochromatic source is replaced by another mon… Answer: 4. Statement I is true but Statement II is false. Fringe width β=λ D/d , so angular separation θ=β/D=λ/d . Statement I: θ does not d... 1
- In a Young's double slit experiment, a student observes 8 fringes in a certain segment of screen when a monochromatic light of 600 nm wavelength is used. If the wavelength of light is changed to 400 nm, then the number of fringes he would observe in… Answer: 1. 12 Fringe width is β=λ D/d . For a fixed region of the screen, the number of fringes is N∝ 1/β∝ 1/λ . N₂=N₁λ₁/λ₂=8×600/400=12 Opt... 1
- In Young's double slit experiment, if the separation between coherent sources is halved and the distance of the screen from the coherent sources is doubled, then the fringe width becomes : Answer: 3. four times Fringe width β=λ D/d . With d→ d/2 and D→2D : β'=λ(2D)/d/2=4β The fringe width becomes four times. Answer: option 3. 1
- In a double slit experiment, when light of wavelength 400 nm was used, the angular width of the first minima formed on a screen placed 1 m away, was found to be 0.2^°. What will be the angular width of the first minima, if the entire experimental app… Answer: 2. 0.15^° For the first minimum, sinθ=λ/d . The angle is small, so θ∝λ . In water, λ'=λ/μ=3/4λ . θ'=3/4×0.2^°=0.15^° . 1
- In Young's double slit experiment the separation d between the slits is 2 mm, the wavelength λ of the light used is 5896 Å and distance D between the screen and slits is 100 cm. It is found that the angular width of the fringes is 0.20^°. To increase… Answer: 3. 1.9 mm Angular fringe width is θ=λ/d , so θ∝1/d for fixed λ . d₂/d₁=θ₁/θ₂⇒ d₂=2×0.20/0.21≈1.9\ mm The slit separation must be dec... 1
- Young's double slit experiment is first performed in air and then in a medium other than air. It is found that 8^th bright fringe in the medium lies where 5^th dark fringe lies in air. The refractive index of the medium is nearly : Answer: 3. 1.78 Key idea: compare fringe positions using bright fringe y_n=nλ D/d and dark fringe y_n=(2n-1)λ D/2d . In air, 5th dark fringe... 1
- The interference pattern is obtained with two coherent light sources of intensity ratio n. In the interference pattern, the ratio I_max-I_minI_max+I_min will be Answer: 1. 2sqrt n/n+1 With intensities I₁:I₂=n (take I₁=nI₂ ), I_max=(√(I₁)+√(I₂))² and I_min=(√(I₁)-√(I₂))² . fracI_max-I_minI_max+I_min=4... 1
- The intensity at the maximum in a Young's double slit experiment is I_0. Distance between two slits is d = 5λ, where λ is the wavelength of light used in the experiment. What will be the intensity in front of one of the slits on the screen placed at… Answer: 4. I₀/2 Key idea: find the phase difference at the point in front of one slit, then use I=I₀cos²(φ/2) . The point is d/2 from the ce... 1