Light and sound: Practice Questions

A sound wave is produced by a vibrating guitar string. Which property of the sound wave determines the pitch of the sound heard?

An optical fibre consists of a central core surrounded by cladding. For total internal reflection to occur continuously along the core-cladding boundary, what condition must be met regarding the refractive indices and the angle of incidence?

In a physics experiment, a student measures the speed of sound by standing \(165\text{ m}\) from a large vertical wall and clapping two wooden blocks together. The student adjust the timing of the claps so that each clap coincides exactly with the echo of the previous clap. If the student makes 20 claps in 20 seconds, what is the calculated speed of sound in air?

An oscilloscope is used to study the sound produced by a tuning fork. The screen displays a wave with a total of 4 complete cycles across a horizontal distance of 8 divisions. If the time-base setting of the oscilloscope is \(0.5\text{ ms/div}\), determine the frequency of the sound wave.

The critical angle for a specific type of transparent plastic is known to be \(42^\circ\). Determine the refractive index of this plastic. Give your answer to 2 decimal places.

A sound wave travels through air with a time period of \( 0.00004\text{ s} \).
Calculate the frequency of this wave and explain whether it can be heard by a person with a normal hearing range of \( 20\text{ Hz} \) to \( 20,000\text{ Hz} \).

An equilateral glass prism is surrounded by air. A ray of monochromatic light strikes one face of the prism at an angle of incidence of \(42.0^\circ\). The refractive index of the glass is \(1.50\).

(a) Calculate the angle of refraction inside the prism at the first boundary. Give your answer to 1 decimal place.

(b) Determine the angle of incidence at the second face of the prism, calculate the critical angle for the glass-air boundary, and explain whether the ray emerges into the air or undergoes total internal reflection.

A student investigates the behavior of light using a triangular glass prism of refractive index \(1.50\).

(a) A ray of monochromatic light is incident on the first face of the prism at an angle of \(42.0^\circ\). Calculate the angle of refraction inside the glass prism. Give your answer to 1 decimal place. (2 points)

(b) Determine the critical angle \(c\) for the glass-air boundary. Give your answer to 1 decimal place. (1 point)

(c) After passing through the prism, the internal ray strikes another internal face at an angle of incidence of \(45.0^\circ\). State and explain whether the ray will refract out into the air or undergo total internal reflection at this face. (2 points)

(d) Explain one practical advantage of using total internal reflection in optical instruments, such as right-angled prisms in binoculars, over standard plane mirrors. (2 points)

A student conducts an experiment to investigate the behavior of light and sound waves. In the first part of the experiment, a ray of monochromatic light is directed from air into a semi-circular glass block.

(a) The ray enters the flat face of the glass block at an angle of incidence of \( 40.0^\circ \) and is refracted at an angle of \( 25.0^\circ \). Calculate the refractive index, \( n \), of the glass block. Give your answer to 3 significant figures. (2 points)

(b) Using the refractive index calculated in part (a), determine the critical angle, \( c \), for the boundary between the glass and air. (2 points)

(c) The student then directs the light ray from inside the glass block towards the flat boundary at an angle of incidence of \( 55.0^\circ \). Describe the subsequent path of the light ray and explain why this specific phenomenon occurs. (2 points)

(d) Sound waves are also known to refract when moving between different media. Explain how the behavior of sound waves differs from light waves when transitioning from air into a solid medium, such as glass, in terms of change in speed and the direction of refraction. (2 points)