AP Physics Physics: Waves & Optics 2 — Questions and Answers
Question 1: A wave on a string has a frequency of 4 Hz and a wavelength of 0.5 m. What is the wave speed?
- 0.125 m/s
- 4.5 m/s
- 2 m/s (Correct answer)
- 8 m/s
Correct answer: 2 m/s
Wave speed v = fλ = 4 Hz × 0.5 m = 2 m/s.
Question 2: Which phenomenon explains why a straw appears bent when placed in a glass of water?
- Diffraction
- Reflection
- Refraction (Correct answer)
- Dispersion
Correct answer: Refraction
Refraction occurs when light changes speed at the water-air interface, bending the apparent position of the straw.
Question 3: Two identical waves traveling in opposite directions on a string create a standing wave. The distance between two adjacent nodes is 0.3 m. What is the wavelength of the original traveling waves?
- 0.15 m
- 0.3 m
- 0.6 m (Correct answer)
- 1.2 m
Correct answer: 0.6 m
Adjacent nodes are separated by λ/2, so λ = 2 × 0.3 m = 0.6 m.
Question 4: A sound source emitting 500 Hz moves toward a stationary observer at 34 m/s. If the speed of sound is 340 m/s, what frequency does the observer hear?
- 450 Hz
- 500 Hz
- 550 Hz (Correct answer)
- 560 Hz
Correct answer: 550 Hz
Using the Doppler formula f' = f(v/(v−vs)) = 500(340/306) ≈ 556 Hz, closest to 550 Hz.
Question 5: In a double-slit experiment, the slit separation is doubled while keeping all other variables constant. What happens to the fringe spacing?
- It doubles
- It stays the same
- It is halved (Correct answer)
- It quadruples
Correct answer: It is halved
Fringe spacing Δy = λL/d; doubling d halves the fringe spacing.
Question 6: A light ray travels from glass (n = 1.5) into air (n = 1.0). What is the critical angle for total internal reflection?
- 19.5°
- 33.6°
- 41.8° (Correct answer)
- 48.2°
Correct answer: 41.8°
sin θc = n2/n1 = 1.0/1.5 = 0.667, so θc = arcsin(0.667) ≈ 41.8°.
Question 7: Which type of wave requires a material medium to propagate?
- X-rays
- Radio waves
- Mechanical waves (Correct answer)
- Gamma rays
Correct answer: Mechanical waves
Mechanical waves (e.g., sound, water waves) require a medium, unlike electromagnetic waves.
AP Physics Physics: Waves & Optics 2
A wave on a string has a frequency of 4 Hz and a wavelength of 0.5 m.
What is the wave speed?