Sound Waves (physics Only) (ht Only) (GCSE Physics)

Two pure tones of frequencies 400 Hz and 406 Hz are played together. What is the beat frequency (the frequency of amplitude modulation heard)?

A sound wave in air has frequency 500 Hz and intensity I0. If the amplitude of pressure oscillation is doubled, what is the new intensity in terms of I0? (Intensity ? amplitude^2.)

Two speakers separated by 0.5 m emit the same pure tone coherently. At a point far away along the perpendicular bisector the path-length difference is zero. If the frequency is increased so the wavelength becomes 0.25 m, what will be the interference at that distant point?

A whistle on an ambulance emits frequency f0 = 700 Hz. A stationary observer hears 700 Hz. If the ambulance approaches the observer at 30 m/s and c = 343 m/s, what approximate frequency does the observer hear? f` = f0 (c/(c - v_source)) for moving source; choose correct approx.

A moving listener hears frequency f` from a stationary source frequency f due to the Doppler effect. If the listener moves toward the source at speed v_l (<< speed of sound c), which approximate relation applies?

A student measures a sound level of 60 dB and another of 90 dB. How many times larger is the intensity (power per unit area) of the 90 dB sound compared with the 60 dB sound? (Use 10 log10 rule.)

A moving-coil loudspeaker uses alternating current in a coil placed in a permanent magnetic field. Which property of the output sound is changed by increasing the amplitude of the alternating current (keeping frequency constant)?

A moving-coil microphone (like the one in the exam diagrams) converts sound pressure variations into an electrical signal by moving a coil in a magnetic field. Which physical law describes the force on the coil that causes it to move?

A room has a single-frequency standing sound wave set up. If two adjacent nodes are 0.25 m apart, what is the wavelength of the standing wave? (Node–node distance = ?/2)

A tube open at both ends supports a standing sound wave whose fundamental frequency is 256 Hz. If the speed of sound is 340 m/s, what is the length of the tube? (For an open–open tube the fundamental has ? = 2L.)

A student measures the minimum audible level at a frequency and finds 20 arbitrary units for a young person and 60 units for an older person. Which physical effect could explain the older person’s raised threshold at high frequencies?