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FAYETTEVILLE STATE UNIVERSITY
COLLEGE OF BASIC AND APPLIED SCIENCES
DEPARTMENT OF NATURAL SCIENCES
CSCI 110-04
FALL 2005
Nov. 10-05
Chapter 5 Waves
I) Basic concepts and Equations
1) Waves: are defined as periodic motions of the mater or energy (waves on water, electromagnetic waves), waves transport energy from one place to another.
2) Mechanical waves: this type of waves propagate through matter (water waves and sound waves)
3) Electromagnetic Waves: different from mechanical waves electromagnetic waves propagate in vacuum and matter (solar radiation, radio waves, microwaves). These waves are coupled electric and magnetic fields that propagate through space.
4) Wave Frequency: is defined as the number of crests that pass per second in a particular reference point.
c = λf
c speed of light in free space 3.00x108 m/s
λ wavelength m
f frequency Hz (Hertz)
5) Wave Length: defines the length between crest to crest or between through to through.
6) Amplitude: is the maximum displacement of a particle in a given medium where the wave propagates.
7) Period: defines the time required for a complete wave (a wavelength distance) to pass through a given point.
T =1/f
8) Doppler Effect: is a wave phenomenon, where the frequency of a wave changes with the relative motion of the source and the observer.
9) Resonance: occurs when an object (musical instrument) vibrate at one of its natural frequencies.
10) Reflection: is defined as the action of rebounding of a wave of particle when it hits a surface
11) Refraction: is defined as the change of direction caused by changes in speed of light in different mediums, where the waves propagate.
12) Index of Refraction of a Material: is defined as the ratio between the speed of light in free space and its speed in a given medium.
n = c/v
n refraction index for a particular material
v speed of light of a given material
h’ = h/n
h’ apparent depth in a liquid
13) Lens: a piece of transparent material of glass capable of producing an image by the effect of refraction of light.
14) Converging Lens: direct parallel rays of light to a single point (focal point) located at the focal length.
15) Diverging Lens: parallel rays of light are spread out in such a way that is seems that the come from a point behind the lens.
16) Real Image: image formed by rays of light that pass through the object.
17) Virtual Image: can only be seen by the eye, since light rays that give origin to it does not pass through the object.
18) White Light: It is made up of light many different frequencies each one characterized by one color. Due to the fact that the speed of light is slightly different for different frequencies, white light is dispersed into its separate colors when refracted in a glass prism o a water droplet.
Interference: is related to the interactions between waves, where waves can be added (constructive interference, larger amplitude) ore can be subtracted (destructive interference, small amplitude).
II) Multiple Choice Tests
Question 6.01 As a mechanical wave moves from one point in space to another, the elements of the medium
A) travel along with the wave.
B) don’t move.
C) move back and forth or up and down as the wave travels through.
Question 6.02 Two sound waves travel in air. The first wave has a higher frequency than the second. Which wave has a longer wavelength?
A) The first wave
B) The second wave
C) The two wavelengths are the same
Question 6.03 When a standing wave is produced in a string
A) each element of the string stops moving and a wave form is produced.
B) some elements of the string stop moving while others continue to move.
C) all elements of the string continue to move.
Question 6.04 About how far will sound travel in 1 second?
A) The length of a football field
B) The length of 3 football fields
C) The length of 10 football fields
D) The length of 100 football fields
Question 6.05 How much stronger is a 40 dB sound than a 20 dB sound?
A) Just as strong
B) Twice as strong
C) 10 times stronger
D) 100 times stronger
Question 6.06 Red light has a higher frequency than blue light. If your best friend runs toward you with a flashlight, what happens?
A) The light is noticeably bluer.
B) The light is noticeably redder.
C) The light is bluer, but the effect is too small to notice.
D) The light is redder, but the effect is too small to notice.
Question 6.07 While sound and light are both waves,
A) both need some kind of medium to travel through (e.g. sound can use air and light can use glass).
B) neither need a medium to travel through.
C) sound needs a medium but light doesn’t.
D) light needs a medium but sound doesn’t.
Question 6.08 Which kind of electromagnetic wave has a wavelength of 1 cm?
A) X rays
B) Visible light
C) Radio waves
D) Microwaves
Question 6.9 If white light is incident on a prism, which color travels the slowest?
A) Red
B) Yellow
C) Blue
D) All colors travel at the same speed
Question 6.10 If blue light falls on a red object, what color does the object appear to be?
A) Red
B) Blue
C) White
D) Black
Question 6.11 Why is the sky blue?
A) light from the sun is dispersed by water drops in the air and the blue light bends toward the surface of the earth
B) light from the sun is scattered off molecules and dust in the air and the blue side scatters better than the red side.
C) light from the sun is scattered off molecules and dust in the air and the red side scatters better than the blue side.
Question 6.12 When you look at the light produced by a rainbow
A) all the yellow light that you see has the same frequency.
B) some of the yellow light that you see can have different frequency.
C) you don’t actually “see” yellow light.
Question 6.13 Two houses sit about 10 m apart. Which kind of EM radiation most easily bends between the openings of the two houses?
A) X rays
B) Ultraviolet
C) Red light
D) Infrared
E) Radio waves
Question 6.14 The door to your classroom is open and is about 1 m wide. Suppose you hear a sound down the hallway outside the door. Even though sound and light are waves, you can hear what happens down the hallway but not see it because
A) sound and light both have wavelengths smaller than the width of the door.
B) sound and light both have wavelengths bigger than the width of the door.
C) sound has a wavelength smaller than the width of the door while the wavelength of the light is bigger.
D) sound has a wavelength bigger than the width of the door while the wavelength of the light is smaller.