Physics: Waves & Optics Flashcards

A pipe closed at one end and open at the other has a length of 0.85 m. What is its fundamental frequency? (speed of sound = 340 m/s)

Answer: 100 Hz

For a closed pipe, f = v/4L = 340/(4×0.85) = 100 Hz.

A virtual image is formed by which of the following?

Answer: A plane mirror

A plane mirror always produces a virtual, upright image located behind the mirror.

When light travels from air into a medium with index of refraction n = √2, and the angle of incidence is 45°, what is the angle of refraction?

Answer: 30°

Snell's law: sin 45° = √2 sin θr → sin θr = (√2/2)/√2 = 0.5, so θr = 30°.

The intensity of a sound wave decreases as 1/r² from a point source. If you move from 2 m to 6 m from the source, by what factor does the intensity decrease?

Answer: 9

I ∝ 1/r²; ratio = (6/2)² = 9, so intensity decreases by a factor of 9.

In Young's double-slit experiment, which change would produce brighter but fewer fringes per unit length on the screen?

Answer: Decreasing the slit separation

Decreasing slit separation increases fringe spacing (Δy = λL/d), producing wider, more spread-out fringes with no change in brightness per fringe.

Which term describes the superposition of two waves that results in a wave of reduced or zero amplitude?

Answer: Destructive interference

Destructive interference occurs when the crest of one wave aligns with the trough of another, reducing the resultant amplitude.

A photon of light has energy E = hf. If the frequency of the light is tripled, what happens to its wavelength?

Answer: It is reduced to one-third

Since λ = c/f, tripling f reduces λ to one-third (λ → λ/3).