1. The ? of a wave depends only on the medium in which it is travelling.

a. Frequencyb. Periodc. Speedd. Wavelength

2. When a wave passes from one medium to another, the ? must stay the same.

a. Amplitudeb. Frequencyc. Speedd. Wavelength

3. A wave in which the medium moves parallel to the medium is called a ? wave.

a. Electromagneticb. Longitudinalc. Mechanicald. Transverse

4. The vertical distance from the top of a crest to the bottom of a trough is 34.0 cm. The amplitude of this wave is

a. 8.5 cmb. 17.0 cmc. 34.0 cmd. 68.0 cm

1. The ? of a wave depends only on the medium in which it is travelling.

a. Frequencyb. Periodc. Speedd. Wavelength

(c) speed

2. When a wave passes from one medium to another, the ? must stay the same.

a. Amplitudeb. Frequencyc. Speedd. Wavelength

(b) frequency

3. A wave in which the medium moves parallel to the medium is called a ? wave.

a. Electromagneticb. Longitudinalc. Mechanicald. Transverse

(b) longitudinal

4. The vertical distance from the top of a crest to the bottom of a trough is 34.0 cm. The amplitude of this wave is

a. 8.5 cmb. 17.0 cmc. 34.0 cmd. 68.0 cm

(b) 17.0 cm

3. A wave in which the medium moves parallel to the medium is called a ? wave.

a. Electromagneticb. Longitudinalc. Mechanicald. Transverse

(b) longitudinal4. The vertical distance from the top of a crest to the

bottom of a trough is 34.0 cm. The amplitude of this wave is

a. 8.5 cmb. 17.0 cmc. 34.0 cmd. 68.0 cm

(b) 17.0 cm

5. A pulse goes into a medium that is less dense. The reflected pulse is

a. Fasterb. Invertedc. Largerd. Upright

(d) upright

6. Resonance occurs when one object causes a second object to vibrate. The second object must have the same natural

a. Amplitudeb. Frequencyc. Speedd. Wavelength

7. A wave source has a period of 0.20 s. What is the frequency?

a. 0.20 Hzb. 1.0 Hzc. 5.0 Hzd. 20. Hz

(c) 5.0 Hz

(b) frequency

3. A wave in which the medium moves parallel to the medium is called a ? wave.

a. Electromagneticb. Longitudinalc. Mechanicald. Transverse

(b) longitudinal4. The vertical distance from the top of a crest to the

bottom of a trough is 34.0 cm. The amplitude of this wave is

a. 8.5 cmb. 17.0 cmc. 34.0 cmd. 68.0 cm

(b) 17.0 cm

5. A pulse goes into a medium that is less dense. The reflected pulse is

a. Fasterb. Invertedc. Largerd. Upright

(d) upright

6. Resonance occurs when one object causes a second object to vibrate. The second object must have the same natural

a. Amplitudeb. Frequencyc. Speedd. Wavelength

(b) frequency7. A wave source has a period of 0.20 s. What is the

frequency?a. 0.20 Hzb. 1.0 Hzc. 5.0 Hzd. 20. Hz

(c) 5.0 Hz

1. The direction a wave moves isa. Parallel to the wavefronts.b. Perpendicular to the wavefronts.c. In the direction of increasing density.d. In the direction of increasing wavelength.

(b) Perpendicular to the wavefronts.

2. The process by which a wave bounces off an obstacle in its path is calleda. Diffractionb. Reflectionc. Refractiond. Superposition

(b) Reflection

Check Your Learning

1. The direction a wave moves isa. Parallel to the wavefronts.b. Perpendicular to the wavefronts.c. In the direction of increasing density.d. In the direction of increasing wavelength.

(b) Perpendicular to the wavefronts.

2. The process by which a wave bounces off an obstacle in its path is calleda. Diffractionb. Reflectionc. Refractiond. Superposition

(b) Reflection

3. The bending of waves as they go through a small opening is calleda. Diffractionb. Reflectionc. Refractiond. Superposition(a) Diffraction

4. The bending of waves as they go from one medium to a new medium is calleda. Diffractionb. Reflectionc. Refractiond. Superposition

(c) Refraction

Check Your Learning

3. The bending of waves as they go through a small opening is calleda. Diffractionb. Reflectionc. Refractiond. Superposition(a) Diffraction

4. The bending of waves as they go from one medium to a new medium is calleda. Diffractionb. Reflectionc. Refractiond. Superposition

(c) Refraction

Check Your Learning

5. When two waves interfere with one another, the word interfere meansa. One wave prevents the other wave from finishing its cycle.b. One wave stops moving while the other passes.c. The motion we observe is the sum of the motions of the two individual waves.d. The wave with the larger amplitude grows and the wave with the smaller amplitude shrinks.

(c) The motion we observe is the sum of the motions of the two individual waves.

Check Your Learning

5. When two waves interfere with one another, the word interfere meansa. One wave prevents the other wave from finishing its cycle.b. One wave stops moving while the other passes.c. The motion we observe is the sum of the motions of the two individual waves.d. The wave with the larger amplitude grows and the wave with the smaller amplitude shrinks.

(c) The motion we observe is the sum of the motions of the two individual waves.

Check Your Learning

1. Which of the following is NOT a property of sound?a. Amplitudeb. Frequencyc. Massd. Wavelength

(c) Mass

2. The average human ear cannot hear frequencies abovea. 20 Hzb. 2000 Hzc. 20000 Hzd. 200000Hz

(c) 20000 Hz

Check Your Learning

1. Which of the following is NOT a property of sound?a. Amplitudeb. Frequencyc. Massd. Wavelength

(c) Mass

2. The average human ear cannot hear frequencies abovea. 20 Hzb. 2000 Hzc. 20000 Hzd. 200000Hz

(c) 20000 Hz

Check Your Learning

3. When we describe something as supersonic we mean it isa. Faster than the speed of soundb. Higher in frequency than 20000 Hzc. Lower in frequency than 20 Hzd. Slower than the speed of sound

(a) Faster than the speed of sound

4. When the amplitude of a sound wave increases,a. The wavelength of the sound decreasesb. The sound gets louderc. The pitch increasesd. The speed of sound increases

(b) The sound gets louder

Check Your Learning

3. When we describe something as supersonic we mean it isa. Faster than the speed of soundb. Higher in frequency than 20000 Hzc. Lower in frequency than 20 Hzd. Slower than the speed of sound

(a) Faster than the speed of sound

4. When the amplitude of a sound wave increases,a. The wavelength of the sound decreasesb. The sound gets louderc. The pitch increasesd. The speed of sound increases

(b) The sound gets louder

Check Your Learning5. Sound is a longitudinal wave because

a. The oscillations in pressure are in the same direction as the wave moves.b. The oscillations in pressure are perpendicular to the direction that the wave

moves.c. The wavelength is long compared to light waves.d. The wavelength is always longer than the amplitude.

(a) The oscillations in pressure are in the same direction as the wave moves.6. The wavelength of a sound wave can be calculated by

a. Multiplying the amplitude by the frequencyb. Dividing the amplitude by the frequencyc. Multiplying the speed by the frequencyd. Dividing the speed by the frequency

(d) Dividing the speed by the frequency (the wave equation)

Check Your Learning5. Sound is a longitudinal wave because

a. The oscillations in pressure are in the same direction as the wave moves.b. The oscillations in pressure are perpendicular to the direction that the wave

moves.c. The wavelength is long compared to light waves.d. The wavelength is always longer than the amplitude.

(a) The oscillations in pressure are in the same direction as the wave moves.6. The wavelength of a sound wave can be calculated by

a. Multiplying the amplitude by the frequencyb. Dividing the amplitude by the frequencyc. Multiplying the speed by the frequencyd. Dividing the speed by the frequency

(d) Dividing the speed by the frequency (the wave equation)

Check Your Learning

8. A person is behind an ambulance as it moves away from her. The pitch of the sound that she hears isa. Lower than if the ambulance was stationary.b. The same as if the ambulance was stationary.c. Higher than if the ambulance was stationary.

(a) Lower than if the ambulance was stationary, since the wavelength will be larger behind the ambulance.

Check Your Learning

8. A person is behind an ambulance as it moves away from her. The pitch of the sound that she hears isa. Lower than if the ambulance was stationary.b. The same as if the ambulance was stationary.c. Higher than if the ambulance was stationary.

(a) Lower than if the ambulance was stationary, since the wavelength will be larger behind the ambulance.

ExampleA 512.0 Hz tuning fork is sounded at the same time as a key on a piano. You count 23 beats over 8.0 s. What are the possible frequencies of the piano key?

ExampleA 512.0 Hz tuning fork is sounded at the same time as a key on a piano. You count 23 beats over 8.0 s. What are the possible frequencies of the piano key?

1 512.023

8.0beats

f HzNt s

==

=238.02.9

beatsNft

Hz

=

=

=

2 1

2

| |2.9 512.0beatf f f

f= -

± = -

2

2

2.9 512.0

514.9

f

f Hz

= -

=2

2

2.9 512.0

509.1

f

f Hz

- = -

=

Solution

A guitar string produces a beat frequency of 4 Hz when sounded with a 350 Hz tuning fork and a beat frequency of 9 Hz when sounded with a 355 Hz tuning fork. What is the frequency of the string?

A guitar string produces a beat frequency of 4 Hz when sounded with a 350 Hz tuning fork and a beat frequency of 9 Hz when sounded with a 355 Hz tuning fork. What is the frequency of the string?

Using the first beat frequency, the possible frequencies of the string are 346 Hz or 354 Hz. Using the second beat frequency, the possible frequencies of the string are 346 Hz or 364 Hz.Since the only frequency in common is 346 Hz, this must be the frequency of the string.

346f Hz=

Solution

A hiker shouts toward a vertical cliff 685 m away. The echo is heard 4.00 s later. The wavelength of the sound is 0.750 m.

a. What is the speed of sound in air?b. What is the frequency?c. What is the period of the wave?

Solutiona. 685

2.000.750?

d mt s

mvl

D ====

6852.00343 /

dvt

m s

D=

=

=

b.

343 (0.750)

457

v ff

f Hz

l==

=

c.

3

1

14572.19 10

Tf

s-

=

=

= ´

A 120-cm guitar string is under a tension of 400N. The mass of the string is 0.480 grams.

Calculate (a) the mass per unit length of the string and (b) the speed of waves in it.

(c) In a diagram show the number of (1/2)λ's that appear in this string if it is oscillating at a frequency of 2083Hz.

The speed of waves in a stretched string depends on the tension F in the string as well as the mass per unit length µ of the string.The more a string is stretched, the faster waves travel in it.

A 120-cm guitar string is under a tension of 400N. The mass of the string is 0.480 grams.

Calculate (a) the mass per unit length of the string and (b) the speed of waves in it. (c) In a diagram show the number of (1/2)λ's that appear in this string if it is oscillating at a frequency of 2083Hz.

Solution:(a) µ = M/L ; µ = 0.480x10-3kg/1.20m = 4.00x10-4 kg/m.

(b) v = (F/µ)1/2 ; v = [400N/4.00x10-4kg/m]1/2 = 1000 m/s.

(c) v = f λ ; λ = v/f ; λ = (1000m/s)/(2083/s) = 0.480m.(1/2)λ = 0.480m/2 = 0.240m.The number of (λ/2)'s that fit in this string length of 120cm is1.20m/0.240m = 5.00, as shown

The speed of waves in a stretched string depends on the tension F in the string as well as the mass per unit length µ of the string.The more a string is stretched, the faster waves travel in it.

Water waves have a wavelength of 3.2 m and a frequency of 0.78 Hz.

a. At what rate does a stationary boat bob up and down?

b. If the boat starts moving into the waves (in the opposite direction to) at a

speed of 5.0 m/s, at what rate will the boat bob up and down now?

Solution

a. Since the boat is not moving, it will bob up and down at the same frequency as the waves.

0.78f Hz=

b. 3.20.785.0 /?

w

w

b

b

mf Hzv m sf

l ===

=

(3.2)(0.78)2.5 /

w w wv f

m s

l===

5.0 2.57.5 /

rel b wv v v

m s

= += +=

7.5 (3.2)

2.3

rel b

b

b

v ff

f Hz

l==

=

Water waves have a wavelength of 3.2 m and a frequency of 0.78 Hz.

a. At what rate does a stationary boat bob up and down?b. If the boat starts moving into the waves (in the opposite direction to) at a speed of 5.0 m/s, at what rate

will the boat bob up and down now?

Water waves in a lake travel 4.4 m in 1.8 s. The period of oscillation is 1.2 s. What is the speed and wavelength of the water waves?

Water waves in a lake travel 4.4 m in 1.8 s. The period of oscillation is 1.2 s. What is the speed and wavelength of the water waves?

4.41.81.2??

d mt sT svl

D =====

4.41.82.4 /

dvt

m s

D=

=

=

1

11.20.83

fT

Hz

=

=

=

2.4 (0.83)

2.9

v f

m

ll

l

==

=

Solution