Waves, Light and Sound Review
General Wave Characteristics
1. What is a wave? What does it do?
A wave is a disturbance that transfers energy from one location to another. Mechanical waves (like
sound) need a medium to pass through. Electromagnetic waves (like light) can travel in a vacuum.
2. Distinguish between transverse and longitudinal waves. Draw a picture of each and label key
components. Give examples of each.
Transverse waves, like light, oscillate perpendicular to the axis of the wave.
crest
trough
Longitudinal waves, like sound, oscillate parallel to the axis of the wave.
3. Differentiate between period and frequency of a wave.
Period is the time for one complete wave cycle, measured in seconds. Frequency is the number of
waves per second, measured in Hertz, or 1/sec.
1
𝑓=
𝑇
4. How do you calculate the velocity of a wave? What are the accepted values for the velocity of light and
sound?
Velocity = distance/time. In waves, the distance of interest is the wavelength () and the time of
interest is the period (T) so..
v = T or v = f
vlight = 3x108 m/s
vsound = 343 m/s
5. If the velocity of a wave stays the same, what is the relationship between frequency and wavelength?
They have an inverse relationship. As the frequency increases, the wavelength decreases.
6. What is interference? Describe the difference between constructive and destructive interference.
Wave interference is the phenomenon that occurs when two waves meet while traveling along the
same medium. The interference of waves causes the medium to take on a shape that represents the
combination of the two individual waves.
Constructive interference occurs when the pulses meet on the same side of the medium, they add
together to create a larger pulse.
Destructive interference occurs when the pulses meet on opposite sides of the medium, ideally they
cancel each other out and create a flat spot.
7. What is a standing wave?
A standing wave occurs when the wave patterns interfere with each other in such a way that it looks
like the wave is no longer traveling down the medium, but oscillating in a fixed location
Light
1. Visible light is a part of the electromagnetic spectrum, what are some other examples of
electromagnetic waves?
Radio, Microwaves, Infrared, Visible light, Ultraviolet, X-rays, Gamma Rays (see the back of this review
for the EM spectrum details!)
2. What is the law of reflection? What is the difference between diffuse and regular reflection?
Law of Reflection states that when light bounces off a surface its angle of reflection is equal to its angle
of incidence.
Regular reflection (Specular reflection) occurs when the surface is smooth and allows all the light to
reflect in the same direction. Diffuse reflection occurs on a rough surface and the light disperses.
3. What is refraction? Give an example of when this phenomenon happens.
Refraction is the bending of light rays as they pass through different mediums. Light travels fastest in a
vacuum and slows down with denser materials.
For example when light passes through a prisms, it bends, each color bending a little more or less
based on its wavelength. Shorter wavelengths bend more than longer wavelengths creating the
rainbow spectrum.
4. Using the law of refraction, calculate 2 (the angle the light travels in a piece of glass, nglass = 1.5) if it
comes in from the air (nair = 1) at an angle 1 = 30 degrees. (n1sin1= n2sin2)
n1sin1= n2sin2
(1)sin(30) = (1.5)sin
0.5 = 1.5 sin
sin = 0.33333
 degrees
5. What is the difference between a concave and a convex mirror? How are they used in real life?
Concave mirrors bend inwards and creates an image that is inverted and smaller when you are outside
of the focal point. When you come inside the focal point the image becomes upright and magnified.
These mirrors are used for magnification mirrors in things like microscopes and telescopes.
Convex mirrors bend outward and create images that are smaller and upright. They are used for a wide
range of view, like rearview mirrors for cars.
6. What is the difference between a converging (double convex) and diverging (double concave) lens?
7. How does a prism form a rainbow?
See question 3 on refraction.
Sound
1. What is the average range of sound that humans can hear? What do we call the sound above and
below this range?
The human ear can hear a range of frequency from 20 Hz to 20,000 Hz. Anything below 20 Hz is called
infrasonic, and anything about 20,000 Hz is called ultrasonic.
2. How do we measure/describe the loudness of a sound?
The intensity of a sound wave describes the amount of energy that the wave transports it is equivalent
to the power/area and measured in watts/meter2. This inverse square relationship shows that the
intensity varies inversely with the square of the distance from the source. So if you are twice as far
away from the source the sound is quartered (decreased by a factor of 4).
The decibel scale is logarithmic scale based on the power of 10, which compares sound intensity to the
threshold of human hearing.
3. How is pitch related to frequency of a sound?
They are directly related. Higher frequency = higher pitch.
4. What is resonance and how does this relate to an object’s natural frequency?
All objects have a natural frequency, or the frequency that they vibrate at when tapped or dropped. If
you can match this frequency with another source, the amplification is increased in the vibration of the
object, causing resonance.
5. Describe the Doppler Effect? What are some common applications?
Doppler effect occurs when you have a moving source of waves. The waves in front of the source get
compressed and have shorter wavelengths and therefore higher frequencies. The waves behind the
source are stretched out and have longer wavelengths and lower frequencies. In sound this changes
the pitch that you hear as something is moving either toward or away from you. In astronomy, this
changes the color of light that you see based on the changing wavelength.