Waves：練習題

All electromagnetic waves in free space share which common characteristic?

A sound wave has a wavelength of \(0.85 \text{ m}\) and travels at a speed of \(340 \text{ m/s}\) in air. What is its frequency?

A point source of sound emits waves equally in all directions. At a distance \(d\) from the source, the amplitude of the oscillations is \(A\) and the intensity is \(I\).
If the power emitted by the source is increased by \(44\%\) and the distance from the source is increased to \(2d\), what is the new amplitude of the sound wave at this distance?

Which of the following describes a longitudinal wave?

A sound wave with a frequency of \(440 \text{ Hz}\) passes from air into a material where the speed of sound is \(1500 \text{ m s}^{-1}\). What is the wavelength of this sound wave inside the material?

Identify which physical property of a wave remains unchanged when it undergoes diffraction as it passes through a narrow gap.

A point source of light emits energy uniformly in all directions. At a distance of \( 4.0 \text{ m} \) from the source, the intensity of the light is \( I \). Calculate the intensity, in terms of \( I \), at a distance of \( 12.0 \text{ m} \) from the source, assuming no energy is absorbed by the medium.

The graph shows the variation with distance \( x \) of the displacement \( s \) of the particles in a longitudinal wave at a particular time. Identify the positions on the \( x \)-axis where the pressure of the medium is at a maximum and explain your reasoning in terms of the gradient of the graph.

(a) Define the wavelength of a progressive wave.

(b) State one difference between a transverse wave and a longitudinal wave in terms of the direction of oscillations and the direction of energy transfer.

(c) A radio wave travels through a vacuum at a speed of \(3.00 \times 10^8 \text{ m s}^{-1}\). The frequency of the wave is \(98.0 \text{ MHz}\). Calculate the wavelength of this radio wave.

A point source of sound emits energy equally in all directions. At a distance \( r = 2.5 \text{ m} \) from the source, the intensity of the sound is \( I \) and the amplitude of the oscillations is \( A \).
(a) The observer moves to a new distance of \( 7.5 \text{ m} \) from the source. Calculate the new intensity in terms of \( I \).
(b) Determine the new amplitude of the sound waves at this new distance in terms of \( A \).
(c) State the relationship between intensity and amplitude that you used in your calculation.