Answers to Physics 112 Exam Theory Review Sheet
Wave Characteristics
1. A wave is seen as the sequential displacements of a medium's particles
as energy passes through it.
2. transverse and longitudinal.
3. see notes.
4. transverse: particle vibration direction is normal to energy motion.
longitudinal: " " " " parallel " " "
5. oval, rising to a crest and falling to the trough.
6. Mechanical waves, e.g., sound, needs a medium through which to pass
while electromagnetic
waves, e.g., light, radio, TV, heat, need no medium,
although they can do so.
7. concentric circles spreading out from their disturbance center.
8. inversely related.
9. Pulse = a single crest; ripple = a small waveform; wavetrain = a
series of waves.
10. As a bundle of energy moves out through a medium, it is continuously
diminished as it displaces each
particle it encounters; waves further
from the source are therefore smaller.
11. to easily show wave direction.
12. Rays are normal to wave fronts.
13. See diagram.
14. Constructive and destructive interference.
15. See diagram.
16. Constructive interference causes a surprisingly loud volume of
sound, destructive the opposite.
17. Theatre design, anything to do with the quality of sound in an
enclosed space.
18. Constructive interference causes a sudden springing up, destructive
the opposite.
19. Light behaves like particles and waves.
20. Light shining through a narrow aperture onto a screen creates a
pattern that is evidence of its wave
nature while just widening the aperture
results in a pattern that is evidence of particle behavior.
Wave Behavior
1. See diagrams.
2. A car travels in a straight line on a highway (material "A"), heading
gradually over to the gravel shoulder
(material "B"). When it runs onto the dirt shoulder
(the boundary between the two materials), the change
in friction between the gravel and the tires causes
the car to change direction, more into the gravel. Once
all wheels are in the gravel, it once again travels
in a straight path. Similarly, when a light ray crosses the
boundary between water and air, the change in properties
of the transmitting materials causes its path to
change.
3. A smooth surface creates regular reflection while a rough surface
creates diffuse reflection.
4. Foggy weather shows the path of headlights.
5. Diamond faces are cut to maximize the chance of trapping light due
to the critical angle.
Light and Color
1. 80%
2. The lens and retina show much evolutionary change.
3. See notes.
4. Undistorted; blurry; no image.
5. ROYGBIV; electrons falling to lower orbitals release light.
6. An absorption spectrum lacks exactly the colors its matching bright
line spectrum contains.
7. No; too far away in the spectrum.
8. Yes; neighbouring colors in the spectrum.
9. See notes; the center is white, the sum of light.
10. They are the "opposite" because primaries are called secondaries
and visa versa.
11. See notes; the black center shows the sum of mixing pigments.
12. The true intensity (luminous intensity) becomes lessened to a perceived
intensity (illumination).
13. Light passing through a polarizing filter or reflecting from a
smooth surface, e.g., water, the road.
14. They block the ribbons of polarized light vibrating parallel to
the reflecting surface.
15. Turn the lenses normal to each other and no light passes through.
16. S M E = solar eclipse; S E M = lunar eclipse.
17. Umbra is a small central jet black shadow surrounded by the larger
penumbra which grades from full
light (outer edge) to dark grey (boundary
with umbra).
18. Total and partial eclipses.
Mirrors and Lenses
1. Fill in the following comprehensive chart.
| Optical device |
outline |
shape name |
behaviour name |
# of cases |
f |
si |
so |
image type |
| curved mirror |
|
concave |
|
6 |
+ |
+ |
+ |
real |
|
|
|
|
case 6 |
- |
- |
|
virtual |
|
|
convex |
|
1 |
- |
- |
+ |
virtual |
| lens |
|
|
converging |
6 |
+ |
+ |
+ |
real |
|
|
|
|
case 6 |
- |
- |
|
virtual |
|
|
|
diverging |
1 |
- |
- |
+ |
virtual |
Sound
1. See text.
2. Pinna (outer ear) - gather sound. Ear canal - direct it to
tympanum (ear drum). Tympanum - transmit
vibrations to middle ear. Middle ear bones
- transmit sound to cochlea. Cochlea - transmit vibrations to
cochlear fluid. Cochlear fluid - transmit
vibration to nerve hair cells. Nerve hair cells - respond to
vibrations and create nerve impulses that are interpreted
by the brain as sound.
3. Infrasonic - sounds below 20 Hz (a frequency value.)
Ultrasonic - sounds above 20 000 Hz (a frequency value.)
Pain level - 120 dB (an intensity value.)
4. The passage of sound energy through a material causes longitudinal
waves to form.
5. Wave height (the sum of the two amplitudes) corresponds to loudness.
6. The singer sings a pure note. The sound energy is felt by all the
strings but causes only the appropriate
one(s) to resonate (vibrate in response to the absorbed
sound energy.)
7. Beats occur when at least two sounds of different frequencies are
sounded together. They are the result
of con- and destructive interference which occurs
as the sounds from the two sources mix..
8. Beats are heard a series of quivering sounds.
9. A fundamental tone is the lowest pitch that can be made by a vibrating
string. The string would be
vibrating as a single unit.
10. See diagrams.
11. A violin is a closed tube because it has one opening.
12. Whenever there is relative motion between a sound source and a
listener, the Doppler Effect causes
the characteristic rising and falling
of pitch. (The necessary increase and decrease of loudness is not part
of the Doppler effect.)
13. An echo is the reflection of an energy pulse from a barrier.
Electrostatics
14. Two types of charging are contact and induction charging.
15. Induction charging occurs when a charged object approaches and
oppositely charges another object but
without directly contact it.
16. A lightning rod works if it prevents a lightning strike.
It does so by bleeding off + charges into the air
before they build up to the point
of attracting down electrons from over head storm clouds. It is a
misunderstanding that they are to intended
carry a strike to the ground instead of through a building.
This is a beneficial but secondary purpose.
If the strike occurs, the lightning rod has failed in its primary
purpose.
17. Whenever a large + charge builds up in the ground under a storm
cloud, a lightning discharge may
occur.
About Magnetism and Magnetic Induction
1. Electrons orbiting the nucleus (like the earth around the sun) creates
diamagnetism. Permanent
magnetism is due to the combination of electrons'
orbiting and spinning (around their own axes)
motions. Note: do not confuse duration of
magnetic properties, e.g., permanent magnetism, with strength
of magnetic interaction, e.g., ferromagnetism.
2. Ferromagnetic materials, e.g., iron, steel (it contains iron),
nickel (most modern nickel coins do not
contain nickel), cobalt, show a strong attraction
to magnets. Paramagnetic materials show a weak
attraction. Diamagnetic materials show a
weak repulsion. Note: ferro and para are both attractions; para-
and dia- are both weak in strength.
3. See your notes or the text book.
4. Transformers are commonly used to change AC voltage. As a consequence,
the AC current will be
changed, but in the inverse fashion. For example,
if the secondary voltage is increased, the secondary
current will decrease.
5. Transformers used to be a safety measure when most electrical devices
had metal cases. If the line cord
were frayed and current leaked onto the metal case,
a shock hazard existed because the user, not the line
cord, could provide a route for the return current
to the earth. If a device had a transformer and the
secondary wires frayed, there was no danger because
the secondary current has no impulse to return to
the ground -- it was created within the transformer
and so stayed within the device or on its metal case.
Today, the plastic cases of electrical devices are
intended to protect the user from shock.