AP Physics Physics: Waves & Optics 5

Question 1

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)

Accepted Answer

100 Hz

Answer

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

Question 2

A virtual image is formed by which of the following?

Accepted Answer

A plane mirror

Answer

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

Question 3

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?

Accepted Answer

30°

Answer

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

Question 4

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?

Accepted Answer

9

Answer

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

Question 5

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

Accepted Answer

Decreasing the slit separation

Answer

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

AP Practice Test

AP Practice Test

AP Physics Physics: Waves & Optics 5