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

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 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?

A closed–open tube of length L resonates at f1 (fundamental). Which harmonic series is produced?

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

In air at 20 °C the speed of sound is approximately 343 m/s. What is the wavelength of a 1.5 kHz (= 1500 Hz) tone in air at this temperature?

A tube closed at one end has its first resonance (fundamental) at 170 Hz. If the speed of sound is 340 m/s, what is the length of the tube? (For closed–open tube fundamental ? = 4L.)

A student measures phase difference between two coherent sources and finds 180° (p radians). What kind of interference will occur at a point equidistant from the sources?

What equation links wave speed v, frequency f and wavelength ? for sound?

A moving-coil microphone diagram shows a coil attached to a diaphragm inside a magnetic field. What electrical quantity is produced directly when the diaphragm vibrates?

An ultrasound pulse (1 MHz) is emitted into tissue where speed is 1540 m/s. What is the pulse wavelength in tissue?

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?