Question

hello, im kind of new to double slit diffration stuff. please help! thank you!

3. Laser light of wavelength 2 is incident on a mask containing two very narrow slits. A screen is placed beyond the mask. The photograph shows the pattem of bright spots (shown in white) and dark spots (shown in black) that appears near the center of the screen. Point D in the center is the brightest. (a) If the wavelength of the light is decreased, would the location of the bright spot labeled A move in toward the center, move out away from the center, or stay at the same location? Explain. (b) Return to the original pattem created by laser light of wavelength A. If the distance between the slits increased, would the location of the bright spot labeled A move in toward the center, move out arway from the center, or stay at the same location? Explain. (e) Return to the original patten created by laser light of wavelength 2 and the original distance between the slits. If one of the slits is covered, will the dark spot between A and B become brighter, become darker, or remain the same? Explain. 4. A bicycle wheel is mounted on a fixed, frictionless axle, with a light string wound around its rim. The wheel has moment of inertia I, mass m, and radius r. The wheel is rotating counterelockwise with angular speed o when at time t 0 someone starts pulling the string with a force of magnitude F. Assume that the string does not slip on the wheel. Suppose that after a certain time, the string has been pulled through a distance L What is the final rotational speed ansl of the wheel? Express your answer in terms of some or all of the given quantities.

Answer 1

Angle between OA and OD, where O is center of slits, is equal to 3$\lambda / d$. 3 in 3$\lambda / d$ is because point A is third bright spot point starting from central bright spot  D. $\lambda$ is wavelength of light and d is distance between slits.

a) If wavelength decrease, angle between OA and OD decrease. There is no change in position of central bright spot. So A moves towards center.

b) Again angle decrease with increase in distance between slits, so A moves towards center.

c) Alternate Bright and dark spots are due to interference between light from two slits. As one slit is covered, only diffraction of light is observed from single slit. Light intensity continuously decrease from central bright spot D. Hence dark spot between A and B becomes brighter.