Q: A hospital uses ultrasound with a frequency of $$2.0 \times 10^6$\ \mathrm{Hz} to $$image internal organs. If the speed of sound in tissue is $$1.5 \times 10^3$\ \mathrm{m/s}$$, what is the wavelength of the ultrasound?

$$\lambda = 7.5 \times 10$$^{-4}$$\ \mathrm{m}$$

Question 1

Which of the following best describes the difference between constructive and destructive interference in sound waves?

Accepted Answer

Constructive interference occurs when two waves meet in phase, increasing amplitude, while destructive interference occurs when two waves meet out of phase, reducing amplitude.

Question 2

A sound wave travels through air at a speed of $$v = 343\ \mathrm{m/s}. If $$the frequency of the sound is $$f = 686\ \mathrm{Hz}$$, what is its wavelength?

Accepted Answer

$$\lambda = 0.5\ \mathrm{m}$$

Question 3

Which of the following statements about density is correct?

Accepted Answer

Density is defined as mass per unit volume, $$\rho = \dfrac{m}{V}.$$

Question 4

A hospital uses ultrasound with a frequency of $$2.0 	imes 10^6$\ \mathrm{Hz} to $$image internal organs. If the speed of sound in tissue is $$1.5 	imes 10^3$\ \mathrm{m/s}$$, what is the wavelength of the ultrasound?

Accepted Answer

$$\lambda = 7.5 	imes 10$$^{-4}$$\ \mathrm{m}$$

Question 5

Which of the following best explains why metals are good conductors of electricity?

Accepted Answer

Metals have free electrons that can move easily throughout the lattice.

Question 6

A pulse of light travels from air into water. Which of the following statements is true about its speed and wavelength?

Accepted Answer

The speed decreases and the wavelength decreases.

Question 7

Which of the following is the correct relationship between period $$T$$ and frequency $$f of a $$wave?

Accepted Answer

$$T = \dfrac{1}{f}$$

Question 8

A car horn emits a sound at $$500\ \mathrm{Hz}. If $$the car moves toward a stationary observer at $$30\ \mathrm{m/s} ($$speed of sound in air is $$340\ \mathrm{m/s}$$), what frequency does the observer hear? (Use the Doppler effect formula: $$f' = f \dfrac{v + v_o}{v - v_s}$$, where $$v_o = 0$$ and $$v_s is $$the speed of the source toward the observer.)

Accepted Answer

$$f' = 547\ \mathrm{Hz}$$

Question 9

Which of the following best describes the process of refraction?

Accepted Answer

The bending of a wave as it passes from one medium to another due to a change in speed.

Question 10

Which of the following is a correct statement about the atomic nucleus?

Accepted Answer

The nucleus contains protons and neutrons, but not electrons.

Question 11

A string fixed at both ends vibrates in its third harmonic. If the length of the string is $$L$$, what is the wavelength of the standing wave?

Accepted Answer

$$\lambda = \dfrac{2L}{3}$$

Question 12

Which of the following best describes the difference between atoms and molecules?

Accepted Answer

Atoms are single units of elements, while molecules are combinations of two or more atoms bonded together.

Question 13

A wave has a frequency of $$60\ \mathrm{Hz}$$ and a wavelength of $$2.5\ \mathrm{m}. $$What is the speed of the wave?

Accepted Answer

$$v = 150\ \mathrm{m/s}$$

Question 14

Which of the following is NOT a longitudinal wave?

Accepted Answer

Light wave

Question 15

Which of the following best explains why the pitch of a siren appears higher as an ambulance approaches you?

Accepted Answer

The sound waves are compressed, increasing their frequency due to the Doppler effect.

Question 16

Which of the following is the correct formula for the speed of a wave?

Accepted Answer

$$v = f \lambda$$

Question 17

A human can typically hear sounds in the range of $$20\ \mathrm{Hz} to$$ $$20,000\ \mathrm{Hz}. $$Which of the following frequencies is considered ultrasound?

Accepted Answer

$$40,000\ \mathrm{Hz}$$

Question 18

Which of the following best describes the relationship between amplitude and energy in a wave?

Accepted Answer

The energy of a wave is proportional to the square of its amplitude.

Question 19

Which of the following is a correct statement about the speed of sound in different media?

Accepted Answer

Sound travels faster in solids than in liquids or gases.

Question 20

A person shouts toward a cliff and hears an echo $$2.0\ \mathrm{s}$$ later. If the speed of sound in air is $$340\ \mathrm{m/s}$$, how far away is the cliff?

Accepted Answer

$$340\ \mathrm{m}$$

Exam 2 Study Guide: Chapters 11, 12, 19, 20 – Atomic Nature of Matter, Solids, Vibrations & Waves, Sound

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