Optics Answers

Consider 575 nm wavelength yellow light falling on a diffraction grating having 1500 lines per centimeter.

Randomized Variables
λ = 575 nm


Find the angle (in degrees) for the third-order maximum for the yellow light.

When illuminated with monochromatic light, a double slit produces a pattern that is a combination of single-slit diffraction and double-slit interference. This can be easily seen if the separation between the slits and the size of slits are related by simple fractions.

Find the ratio of the width of each slit to the separation between the slits, if the first minimum of the single-slit pattern falls on bright fringe number 3 of the double-slit pattern. (This will greatly reduce the intensity of that maximum of the double-slit pattern.)

Suppose a 1.5 μm wide slit produces its first minimum for 410 nm violet light.

Randomized Variables
λv = 410 nm
λr = 730 nm
w = 1.5 μm


(a) Calculate the angle at which this occurs for violet light in degrees.
(b) Where is the first minimum (in degrees) for 730 nm red light?

A soap bubble is 125 nm thick and illuminated by white light incident perpendicular to its surface.

What is the longest wavelength in nm which is constructively reflected, assuming soap has the same index of refraction as water (n = 1.33)?

Anti-reflective coatings on lenses use thin-film interference to eliminate the reflection of a particular color. Suppose a glass lens (ng = 1.56) is covered with a thin film (nf = 1.39) to prevent green light (λ = 536 nm) from being reflected.

(a) Write an expression for the minimum thickness the film can have, t.
(b) Calculate the minimum thickness, t, in nanometers?

A laser beam is incident on two slits with separation d = 0.026 mm. A screen is placed L = 3.2 m from the slits. The wavelength of the laser light is λ = 4750 Å. θ1 and θ2 are the angles to the first and second bright fringes above the center of the screen.

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(a) Express sin(θ1) in terms of d and λ.
(b) Express sin(θ2) in terms of d and λ.
(c) Express the distance between the two bright fringes on the screen, y, in terms of θ1, θ2 and L.
(d) Solve for the numerical value of y in meters.

Two synchronized microwave sources, A and B, are emitting waves of wavelength 4.0 cm. Source A is located on the x-axis at x = 0, source B can be moved along the x-axis, and a microwave receiver is fixed on the x-axis at x = 84 cm. For each of the following positions of source B determine whether the waves from the sources will reach the receiver in phase (constructive interference), out of phase (destructive interference), or with a phase difference of π/2 rad.

(a) x = -8 cm.
(b) x = -6 cm.
(c) x = -5 cm.
(d) x = -4 cm.
(e) x = -3 cm.
(f) x = -2 cm.

Core refractive index -1.55
Cladding refractive index is 1.53wht is numerical aperture for optical fibre

A small convex mirror is placed 60 cm from the pole and on the axis of a large concave mirror of radius of curvature 200 cm.The position of the convex mirror is such that a real image of distant object is formed on the plane of a hole drilled through the concave mirror at its pole. Calculate ‘R’ of convex mirror and height of the real image if distant object forms 0.5 degree angle at the pole of the concave mirror.

A wave has frequency of 50 Hz and a wavelength of 2.3 m. What is the speed of the wave?