Q: A laser pointer emits $$1.0\ \mathrm{mW} of $$power into a beam with a diameter of $$1.0\ \mathrm{mm}. $$What is the intensity $$I of $$the laser beam?

$$I = 1.3 \times 10^3$\ \mathrm{W/m^2$}$$

Q: A microwave oven emits waves with a wavelength of $$12\ \mathrm{cm}. $$What is the frequency of these microwaves? (Speed of light $$c = 3.00 \times 10^8$\ \mathrm{m/s})$$

$$2.5 \times 10^9$\ \mathrm{Hz}$$

Question 1

A sinusoidal wave is shown in the first image, traveling to the right with a speed of 200 m/s. What is the wavelength $$\lambda of $$the wave?

Accepted Answer

$$\lambda = 2.0\ \mathrm{m}$$

Question 2

Given the wave in the first image with a speed $$v = 200\ \mathrm{m/s}$$ and wavelength $$\lambda = 2.0\ \mathrm{m}$$, what is the frequency $$f of $$the wave?

Accepted Answer

$$f = 100\ \mathrm{Hz}$$

Question 3

Which of the following best describes the motion of particles in a transverse wave, as shown in the images?

Accepted Answer

Particles move perpendicular to the direction of wave propagation.

Question 4

A sound wave travels through air at $$v = 343\ \mathrm{m/s}. $$What is the wavelength of a 500 Hz sound wave?

Accepted Answer

$$\lambda = 0.69\ \mathrm{m}$$

Question 5

If the temperature of air increases, what happens to the wavelength of a sound wave of fixed frequency?

Accepted Answer

The wavelength increases.

Question 6

A physician uses ultrasound with a wavelength of $$0.50\ \mathrm{mm} in $$tissue where the speed of sound is $$1540\ \mathrm{m/s}. $$What frequency is required?

Accepted Answer

$$3.1\ \mathrm{MHz}$$

Question 7

Which of the following statements about electromagnetic waves is correct?

Accepted Answer

They travel at the same speed in a vacuum regardless of frequency.

Question 8

A laser pointer emits $$1.0\ \mathrm{mW} of $$power into a beam with a diameter of $$1.0\ \mathrm{mm}. $$What is the intensity $$I of $$the laser beam?

Accepted Answer

$$I = 1.3 	imes 10^3$\ \mathrm{W/m^2$}$$

Question 9

If the intensity of a sound increases by a factor of 100, by how many decibels does the sound intensity level increase?

Accepted Answer

$$20\ \mathrm{dB}$$

Question 10

A person shouts, emitting $$1.0\ \mathrm{W} of $$sound power. What is the sound intensity at a distance of $$1.0\ \mathrm{m}$$, assuming spherical spreading?

Accepted Answer

$$0.080\ \mathrm{W/m^2$}$$

Question 11

A police siren emits a frequency of $$550\ \mathrm{Hz} as it $$approaches and $$450\ \mathrm{Hz} as it $$recedes. If the speed of sound is $$343\ \mathrm{m/s}$$, what is the speed of the police car?

Accepted Answer

$$38.1\ \mathrm{m/s}$$

Question 12

Which of the following best describes a shock wave?

Accepted Answer

A wave produced when a source moves faster than the speed of sound, causing overlapping wave fronts.

Question 13

A moving observer approaches a stationary sound source. Which equation gives the observed frequency $$f'$$?

Accepted Answer

$$f' = f \left( \frac{v + v_o}{v} \right)$$

Question 14

Which of the following is true about the intensity of a spherical wave as distance from the source increases?

Accepted Answer

It decreases as $$1/r^2.$$

Question 15

A microwave oven emits waves with a wavelength of $$12\ \mathrm{cm}. $$What is the frequency of these microwaves? (Speed of light $$c = 3.00 	imes 10^8$\ \mathrm{m/s})$$

Accepted Answer

$$2.5 	imes 10^9$\ \mathrm{Hz}$$

Question 16

Which of the following best explains why bats use high-frequency sound for echolocation?

Accepted Answer

High-frequency sound has shorter wavelengths, allowing finer detail resolution.

Question 17

A wave on a string is described by $$y(x, t) = A \cos \left( 2\pi \left( \frac{x}{\lambda} - \frac{t}{T} \right) \right). $$What is the speed of the wave?

Accepted Answer

$$v = \lambda / T$$

Question 18

Which of the following is a correct statement about mechanical and electromagnetic waves?

Accepted Answer

Mechanical waves require a medium, but electromagnetic waves do not.

Traveling Waves, Sound, and the Doppler Effect: Physics with Calculus Study Notes

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