Waves and Sound — High School Physics practice questions

A wave has a frequency of 200 Hz and a wavelength of 1.5 m. What is its speed?

1. 133 m/s
2. 0.0075 m/s
3. 300 m/s
4. 201.5 m/s

Answer: C — 300 m/s

C) Correct — v = fλ = 200 × 1.5. A) Divides f by λ. B) Divides λ by f. D) Adds.

A higher-pitched sound has a higher:

1. amplitude
2. wavelength
3. speed
4. frequency

Answer: D — frequency

D) Correct — Pitch is how we perceive frequency. A) Determines loudness. B) Higher pitch means shorter wavelength. C) Speed depends on the medium.

A wine glass shatters when a singer holds a note matching its natural frequency. This is:

1. the Doppler effect
2. refraction
3. resonance
4. destructive interference

Answer: C — resonance

C) Correct — Energy builds up at the natural frequency. A) Involves motion of a source. B) Is bending of waves. D) Would reduce the vibration.

Sound waves in air are:

1. transverse
2. electromagnetic
3. longitudinal
4. standing waves only

Answer: C — longitudinal

C) Correct — Air particles vibrate parallel to the wave's direction. A) Vibrations would be perpendicular, as in light. B) Sound needs a medium. D) Sound usually travels.

When two waves meet crest to crest, the result is:

1. destructive interference
2. constructive interference
3. refraction
4. the Doppler effect

Answer: B — constructive interference

B) Correct — The amplitudes add. A) Happens crest to trough. C) Is bending. D) Involves a moving source.

Astronauts can't hear each other directly in space because:

1. space is too cold
2. sound needs a medium to travel
3. sound travels too fast in space
4. their helmets reflect light

Answer: B — sound needs a medium to travel

B) Correct — Space is nearly a vacuum. A) Temperature isn't the reason. C) Sound doesn't travel there at all. D) Light is unrelated.

What is the wave equation relating speed, wavelength, and frequency?

v = fλ.

What is a wave?

A disturbance that transfers energy through space without a net transfer of matter.

WORKED EXAMPLE — Pendulum period (T = 2π√(L/g)): Find the period of a simple pendulum of length L = 1 m (g = 9.8 m/s²).

STEP 1 — Formula: T = 2π√(L/g). STEP 2 — Ratio: L/g = 1/9.8 ≈ 0.1020. STEP 3 — Square root: √0.1020 ≈ 0.3194 s. STEP 4 — Multiply by 2π ≈ 6.2832: T ≈ 6.2832 · 0.3194 ≈ 2.007 s. ANSWER: T ≈ 2.0 s. Key insight: period depends only on L and g — independent of mass and (for small angles) amplitude.

WORKED EXAMPLE — Wave equation (v = fλ): A guitar string vibrates at f = 440 Hz. The wave speed on the string is 264 m/s. Find the wavelength.

STEP 1 — Wave equation: v = fλ → λ = v/f. STEP 2 — Substitute: λ = 264 / 440. STEP 3 — Compute: λ = 0.6 m = 60 cm. ANSWER: λ = 0.6 m. Sanity check: typical guitar wavelengths are tens of cm — consistent.