NAME: ____________________________________________DATE: _______________________ BLOCK: 1 | 2 | 3 | 4
UNIT IV: WAVES – Test 5 Study Guide
QUESTIONS:
1.
2.
What causes waves (in general)? What do waves transfer?
 Waves are caused by vibrations

Pulse = single vibration / Oscillation – repeating vibration

ENERGY
What does the period of a pendulum depend upon?
 The period (T) of a simple pendulum depends on (1) the length of the pendulum, & (2) acceleration due to gravity.

3.
It is NOT affected by the mass of the plumb bob.
Label the parts of the waves below:
TRANSVERSE
TYPE OF WAVE: ________________________
CREST
WAVELENGTH (λ)
LONGITUDINAL
TYPE OF WAVE: ________________________
COMPRESSION
RAREFRACTION
WAVELENGTH (λ)
AMPLITUDE
TROUGH
SOUND
EXAMPLE: ________________
LIGHT
EXAMPLE: ____________
4.
Do longitudinal waves require a medium through which to travel? Do transverse waves?
 Longitudinal waves DO require a medium

Transverse waves DO NOT require a medium
5.
What is the unit of measure of a wavelength?
 METERS (m)
6.
If the amplitude of a wave is 5 m, how much is the top-to-bottom disturbance?
 10 m
7.
As waves dissipate, what happens to the wave’s amplitude?
 Amplitude decreases as the wave’s energy dissipates (turns into) to heat.
8.
What does frequency tell you? What is the unit of frequency?
 The number of waves that pass a given point in a period of time (usually 1 second). The unit is the Hertz (Hz).
9.
What is interference? What type of interference occurs when waves are in phase? Out of phase?
 Interference is occurrence of multiple waves in the same place at the same time.

Waves in phase exhibit constructive interference / waves out of phase exhibit destructive interference.
10. What causes the Doppler effect and when does it occur?
 The Doppler effect is the observed shift in frequency caused by motion – either the source or the observer.

It occurs when objects move at a rate less than the speed of sound.
11. What is the equation for wave speed? What are the units for wave speed?
 𝒗= 𝝀∙𝒇

Units are meters/second (m/s)
12. If a wave has a wavelength of 20 meters and a frequency of 0.5 Hz, what is its speed?
G
U
E
S
S
λ = 20 m
f = 0.5 Hz
𝒗=?
𝒗= 𝝀∙𝒇
𝒗 = (20 m)(0.5 Hz)
𝒗 = 10 m/s
13. Does the speed of light change in a vacuum? What is the speed of light in a vacuum?
 NO

The speed of light (c) = 3.00x108 m/s
14. Light travels fastest through which phase of matter? Why is this?
 Air, because the molecules in the air are the most spread out, therefore slowing light down less.
15. How does the speed of light change when going from a gas to a liquid to a solid?
 Light slows down when going from gas to liquid, and from liquid to solid (and vice versa).
16. If a beam of light leaves water and moves into air, how is the beam bent?
 As light speeds up when entering the air, the angle is bent away from the normal.

When moving from air into water (the reverse), the angle is bent toward the normal.
17. What is reflection?
 When a wave bounces off a material & goes in a new direction.
18. What is refraction?
 When a wave passes through a material & bends.
19. What is diffraction?
 When a wave bends around or passes through an opening in a material.

When plane waves go through an opening, they become circular waves
20. What is an echo and what property of waves is responsible for it (reflection, refraction, diffraction)?
 An echo occurs when a sound wave reflects off a distant surface / the observer hears the sound wave returning.
21. What causes a rainbow?
 Refraction of visible (white) light through a prism (in nature, rain droplets in the air)
22. List all components of the electromagnetic spectrum from lowest frequency to highest?
23. If a light ray strikes a flat mirror at a given angle, at what angle will the reflected ray be?
 An equal angle on the opposite side of the normal.

If the angle of incidence (𝜽𝒊 ) is 39°, the angle of reflection (𝜽𝒓 ) is _________.
pg. 2 of 4
24. What is a virtual image and how does it differ from a real image?
 A virtual image is seen in the mirror (behind the mirror) – light rays DO NOT actually come together.

A real image is seen reflected back out of the mirror.
25. Which type(s) of mirror(s) form a real image? Which form a virtual image?
 REAL – Concave mirror (when object is behind the focal point)

VIRTUAL – Plane mirrors, Convex mirrors, & Concave mirrors (when object is in front of the focal point).
26. When you look at a flat mirror, how do you see your image? (use the terms virtual, real, upright, or inverted), (2 terms apply)
 VIRTUAL & UPRIGHT
27. When looking at a flat mirror from a distance X m, your reflected image appears to be how far away from the mirror? How far is
it from you?
 Reflected image is X m away from the mirror.

The distance from you is 2X m.
28. Why are ray diagrams used?
 Ray diagrams are used to find out where an image will be located.
29. What is the difference between red and blue light?
 frequency (wavelength)
RAY DIAGRAMS: Complete the following
30. Plane Mirror
__________________________________________________
31. Concave Mirror – Behind Focal Point
___________c________f________..__________________
32. Concave Mirror – In Front of Focal Point
___________c________f________..__________________
33. Convex Mirror
___________..________f________c__________________
pg. 3 of 4
34. Converging Lens
_________________f_____.._____f_________________
35. Diverging Lens
_________________f_____..._____f_________________
PROBLEMS: Answer the following questions regarding wave speed, wavelength, frequency & period:
36. The lowest pitch that the average human can hear has a frequency of 20.0 Hz. If sound with this frequency travels through air
with a speed of 331 m/s, what is its wavelength?
G
U
𝒇 = 20.0 Hz
𝒗 = 331 m/s
𝝀=?
𝒗
𝝀=𝒇
E
𝟑𝟑𝟏 𝒎/𝒔
𝟐𝟎.𝟎 𝑯𝒛
S
𝝀=
S
𝝀 = 16.6 m
37. Cicadas produce a buzzing sound that has a wavelength in air of 2.69 m. If the speed of sound in air is 346 m/s, what is the
frequency of the sound produced by a cicada? What is its period?
G
U
𝝀 = 2.69 m
𝒗 = 346 m/s
𝒇=?
𝒗
𝒇=𝝀
E
G
U
E
𝟑𝟒𝟔 𝒎/𝒔
𝟐.𝟔𝟗 𝒎
S
𝒇=
S
𝒇 = 129 Hz
S
S
𝒇 = 129 Hz
𝑻=?
𝟏
𝒇
𝟏
𝟏𝟐𝟗 𝑯𝒛
𝑻=
𝑻=
T = 7.75 x 10-3 s or 0.00775 s
38. A dolphin can typically hear sounds with frequencies up to 150 kHz. What is the speed of sound in water if a wave with this
frequency has a wavelength of 1.0 cm?
G
𝒇 = 150 kHz
= 150,000 Hz
𝝀 = 1.0 cm
= 0.010 m
U
𝒗=?
E
𝒗= 𝝀·𝒇
S
𝒗 = (𝟎. 𝟎𝟏𝟎𝒎)(𝟏𝟓𝟎, 𝟎𝟎𝟎 𝑯𝒛)
S
𝒗 = 1500 m/s
pg. 4 of 4