PHYS 242
EXAM #5
Name:
1. Light from a monochromatic source shines through a double slit onto a screen 5.00 m away. The slits are 0.180 mm apart. The dark bands on the screen are measured to be 1.70 cm apart. What is the wavelength of the incident light? Hint: d sinθ = mλ (where d is the slit separation, θ is the angle of the dark band, m = 0, ±1, ±2, …) for destructive interference; and for small θ, tanθ ≈ θ = y_m / L. First get expression for y_m for m = 0 and m = 1.
A) 457 nm
B) 306 nm
C) 392 nm
D) 612 nm
E) 784 nm
2. In a double-slit experiment, the slit separation is 2.0 mm, and two wavelengths, 750 nm and 900 nm, illuminate the slits simultaneously. A screen is placed 2.0 m from the slits. At what distance from the central maximum on the screen will a bright fringe from one pattern first coincide with a bright fringe from the other? Hint: d sinθ = mλ (m = 0, ±1, ±2, …) for constructive interference. For small θ, use the approximation sinθ ≈ θ in radians. Hence, y_m = mλL/d for the first wavelength, and it is y_n = nλL/d for the second wavelength.
A) 1.5 mm
B) 3.0 mm
C) 4.5 mm
D) 6.0 mm
E) 9.0 mm
3. Light from a 600 nm source goes through two slits 0.080 mm apart. What is the angular separation of the two first-order maxima occurring on a screen 2.0 m from the slits? Hint: d sinθ = mλ (m = 0, ±1, ±2, …) for constructive interference. Use the small angle approximation, noting that θ is in radians, which you can then convert into degrees.
A) 0.15°
B) 0.86°
C) 0.015°
D) 0.0075°
E) 1.75°