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CP PHYSICS
FINAL EXAM REVIEW – Spring 2012
ANSWERS
1.
How are positive ions formed? How are negative ions formed?
positive ions are formed by atoms losing electrons
negative ions are formed by atoms gaining electrons
2.
What is the fundamental rule regarding charge interactions?
Like charges repel and opposite charges attract.
3.
Can charges be created or destroyed?
No – They can only be transferred from one object to another or separated.
4.
How are conductors different from insulators?
Conductors have electrons that can move easily from one atom to the next, while
insulators hold their electrons tightly, so that they do not move.
5.
Explain how charges can be moved by:
a. conduction:
a neutral body is charged when touched by a charged object, it takes
the same charge as the charged object
6.
b. induction:
a neutral object becomes temporarily charged when a charged object
is brought near it, takes on the opposite charge
c. friction:
two neutral objects become charged when they are rubbed together
and electrons are transferred from one object to the other, results in
one object having a positive charge and the other object having a
negative charge so that they become attracted to each other
d. grounding:
a charged object’s excess charge moves from it through to the ground
when a pathway from it to the ground is provided
What happens to the electrical force experienced by two charged particles separated by some
distance if:
a. one of the charges doubles?
b. both charges double?
c. the distance is doubled?
d. the distance is tripled?
2F
4F
¼F
1/9 F
e. one of the charges doubles and the distance is doubled?
7.
Draw electric fields for the following:
a. weak positive charge
½F
b. strong negative charge
CP PHYSICS ,FINAL EXAM REVIEW – Spring 2012, page 2
7.
c. two positive charges
8.
Explain how each of the following factors affects resistance through a wire:
ANSWERS
d. a negative charge and a positive charge
a. conductivity:
greater conductivity = less resistance
b. thickness:
thicker the wire = less resistance
c. length:
longer the wire = more resistance
d. temperature:
colder the temperature = less resistance
9.
What are the relationships between current and voltage and current and resistance
according to Ohm’s Law?
current and voltage have a direct proportion – greater voltage = more current flow
current and resistance have an inverse proportion – more resistance = less current
10.
What relationship do current and resistance have?
current and resistance are inversely proportional
11.
If you increase the resistance, what happens to the current? If you decrease the resistance,
what happens to the current?
if the resistance increases, then the current will decrease
if the resistance decreases, then the current will increase
11.
Do you buy electrons from the power company?
NO, you buy energy from the power company. The electrons are in your devices
and they flow because of the energy received from the power company.
12.
What are two safety devices used in circuits? How do they work?
1) fuses – melt if current goes beyond a certain point, must be replaced
2) circuit breaker – breaker pops open if current exceeds a certain value, is reused
13.
What is the difference between direct current and alternating current?
direct current is current flow that moves only in one direction
alternating current is current flow that moves back and forth in two directions
14.
What is a source of direct current? of alternating current?
batteries provide direct current, while generators (like the power company) provide
alternating current
15.
How much current flows in a 175  resistor when a voltage of 5.0 V is across it?
R = 175 
V = IR
V = 5.0 V
5 = I(175)
I=?
I = 5/175
I = 0.29 A
CP PHYSICS ,FINAL EXAM REVIEW – Spring 2012, page 3
ANSWERS
16.
What is the resistance of a cold incandescent bulb filament if it draws a current of 0.43 A
when plugged into a 120 V circuit?
I = 0.43 A
V = IR
V = 120 V
120 = 0.43R
R=?
R = 120/0.43
R = 279.07 
17.
What is the resistance of an electric frying pan which draws 5.8 amps when connected to a
120 V circuit?
I = 5.8 A
V = IR
V = 120 V
120 = 5.8 R
R=?
R = 120/5.8
R = 20.69 Ω
18.
What is the power of the frying pan in #17?
I = 5.8 A
P = VI
V = 120 V
= (120)(5.8)
P=?
P = 696 W
19.
What current flows through a 100.0 W bulb connected to a 20.0 V electrical source?
P = 100.0 W
P = VI
V = 20.0 V
100 = 20I
I=?
I = 100/20
I=5A
20.
An electrical appliance uses 6.0 kWh in a month. If the power company chargesc$0.08/kWh,
what is the cost to use this electrical appliance?
E = 6.0 kWh
cost = E x rate
rate = $0.08/kWh
= (6)($0.08)
cost = ?
cost = $0.48
21.
What is a series circuit?
A circuit in which there is only one pathway for current to move.
22.
What is a parallel circuit?
A circuit in which there are two or more pathways for current to move.
23.
If one light goes out in a series circuit, do the remaining lights go out?
Yes, the circuit is essentially open, so no current flows.
24.
If one light goes out in a parallel circuit, do the remaining lights go out?
No, the remaining lights remain on because their branches make complete circuits.
25.
What happens to the equivalent (total) resistance in a series circuit when you add another
resistor to it?
the total resistance increases
26.
What happens to the equivalent resistance in a parallel circuit when you add another resistor
to it?
the total resistance decreases
27.
What does an ammeter measure? How is it connected into a circuit?
ammeters measure current, they are connected in series
28.
What does a voltmeter measure? How is it connected into a circuit?
voltmeters measure voltage (potential difference), they are connected in parallel
CP PHYSICS ,FINAL EXAM REVIEW – Spring 2012, page 4
ANSWERS
29.
If there are three lamps connected in series, how many paths can the current take?
One – series circuits have only one path for current flow.
30.
If there are three lamps connected in parallel, how many paths can the current take?
Three
31.
Determine the equivalent resistances for the following circuits:
Req = 15 Ω
32.
Req = 11 Ω
Calculate the values represented in the missing blanks for the following circuit diagrams.
Also, identify whether the circuit is a series or parallelcircuit.
Series
V1 = 40 V
R2 = 30 Ω
Parallel
V1 = 40 V
V2 = 40 V
RT = 10 Ω
IT = 2 A
I1 = 2 A
I2 = 2 A
R2 = 20 Ω
Series
RT = 110 Ω
V2 = 120 V
VT = 220 V
Parallel
RT = 15 Ω
V1 = 40 V
V3 = 60 V
VT = 60 V
CP PHYSICS ,FINAL EXAM REVIEW – Spring 2012, page 5
ANSWERS
33.
How is the magnetic field oriented around a magnet?
the magnetic field lines leave the north pole and enter the south pole
34.
Where is the magnetic field the strongest?
the field is strongest at the poles
35.
What is the smallest magnet?
36.
What happens to the magnetic field around a current-carrying wire if the current through it is
reversed?
it reverses direction also
37.
How does an electric motor work?
 a coil of wire is placed inside a magnet, when electricity goes through the wire it
becomes an electromagnet and interacts with the magnet’s magnetic field
 the wire then spins, every 180o the current reverses direction so that the wire keeps
spinning and spinning
 motors convert electrical energy into mechanical energy
38.
What are two ways to generate current in a wire?
1) move a wire in and out of a magnet
2) move a magnet in and out of a coil of wire
39.
How does an electric generator work?
 a coil of wire is located inside a magnet (just like a motor)
 when you turn the coil of wire, electricity is generated because the wire is moving
within a magnetic field
40.
What three factors does the strength of an electromagnet depend on?
1) the number of loops in the wire (more = stronger electromagnet)
2) the amount of current (more = stronger electromagnet)
3) presence/size of iron core (iron core = stronger electromagnet)
41.
What three factors does the voltage (and current) produced by a generator
depend on?
1) the number of loops in the wire (more loops = more voltage generated)
2) the strength of the magnetic field (stronger magnet = more voltage generated)
3) the speed of rotation of coil of wire (faster rotation = more voltage generated)
42.
Why is the kinetic molecular theory important to thermodynamics?
Kinetic molecular theory says that molecules have kinetic energy and are
constantly moving. The motion of molecules is related to the warmth they
provide—the faster they move, the more warmth associated with their motion.
43.
Describe the three ways that heat can be transferred:
an electron
a. conduction : transfer through direct contact, works best in solids
b. convection : transfer through the flow of fluids (gases and liquids)
c. radiation: transfer through empty space (EM spectrum)
44.
How is temperature related to kinetic energy? What are the three temperature scales?
It is the measure of the average kinetic energy of the molecules in the material.
Fahrenheit, Celsius (based on water), Kelvin (absolute scale, absolute zero)
CP PHYSICS ,FINAL EXAM REVIEW – Spring 2012, page 6
ANSWERS
45.
What is the difference between heat and internal energy?
Heat is the transfer of thermal energy due to a difference in temperature between
two materials, while internal energy is the total energy stored within a material.
46.
What is the first law of thermodynamics?
Thermal energy cannot be created or destroyed (restatement of law of cons. of
energy). Total internal energy equals the work done on the system and the heat
added. (Change in total internal energy equals the work done by the system and
the heat lost.)
47.
What is the second law of thermodynamics?
Thermal energy can only move from hot to cold. Entropy is always increasing.
48.
What is a heat engine?
Any engine that converts thermal energy into mechanical energy. (car engines)
49.
What is entropy?
The measure disorder in a system.
50.
Describe the three types of radioactive decay:
a. alpha: positive, Helium nucleus, stopped by paper
b. beta: negative, electron released when neutron decays, stopped by sheet of aluminum
c. gamma: massless energy, EM spectrum, stopped by several inches of lead
51.
What are isotopes? Are all isotopes radioactive – explain.
They are atoms of an element that have different numbers of neutrons. All
elements have isotopes, but they are not all radioactive. Only radioactive
isotopes undergo spontaneous decay.
52.
What is half-life? How is it calculated?
Half-life is the time that it takes for half of a radioactive sample to decay.
Calculated using: (1/2)n
n = number of half-lives
53.
What is fission? What is fusion?
Fission is the splitting of heavy nuclei to release energy.
Fusion is the fusing of light nuclei to produce heavier nuclei and releases energy.
54.
A sample of radon has a half-life of 15 hours. What fraction of the sample is left after 60
hours have passed?
n = 60/15 = 4
(1/2)4 = 1/16
55.
A radioactive polonium sample has a half-life of 103 years. How much of a 100 g sample
would remain after 412 years?
n = 412/103 = 4
100 x (1/2)4 = 6.25 g
56.
What happens to time, space, and mass when one is traveling close to the speed of light?
As one moves faster and faster and approaches the speed of light, time slows
down, mass increases, and lengths shrink.
57.
What effect does a large mass’ gravitational field have on rays of light?
They bend the light rays toward them.
CP PHYSICS ,FINAL EXAM REVIEW – Spring 2012, page 7
ANSWERS
58.
According to Einstein, how are mass and energy related to each other?
E = mc2 – It describes how matter can be converted into energy and vice versa.
59.
What does a wave do?
60.
Compare and contrast mechanical and electromagnetic waves. Give examples of each.
Mechanical waves require a medium. Water, seismic, sound
Electromagnetic waves do NOT require a medium and can travel through empty
space. Electromagnetic spectrum (radio, UV, visible light)
61.
Describe the motion of the medium in transverse and longitudinal waves. Give examples of
each.
Transverse: medium moves perpendicular to the direction of the wave front, water
and EM waves
Longitudinal: medium moves parallel to the direction of the wave front, sound
62.
What happens to the wavelength of a wave if the frequency increases? if it decreases?
wavelength decreases when frequency increases
wavelength increases when frequency decreases
63.
What determines the wave’s speed?
64.
Define the following:
transfers energy
the medium the wave travels through
a. reflection: the wave moves back into the same medium when striking a boundary
b. refraction: the wave bends as it moves into a new medium
c. diffraction: the wave bends and spreads out around a barrier
65.
What happens during constructive interference? during destructive interference?
Constructive: two wave crests meet and the wave becomes larger (in phase)
Destructive: a crest and a trough meet and the wave becomes smaller or becomes
none (out of phase)
66.
The speed of sound in air is 346 m/s. A sound wave has a frequency of 750.0 Hz. What is its
wavelength?
v = 346 m/s
v = λf
f = 750.0 Hz
346 = λ(750)
λ=?
750
750
λ = 0.46 m
67.
Waves of frequency 2.0 Hz are generated along a spring. The waves have a wavelength of
0.45 m. What is the speed of the waves along the spring?
f = 2.0 Hz
v = λf
λ = 0.45 m
v = (0.45)(20)
v=?
v = 9 m/s
68.
Identify the important characteristics of sound waves.
longitudinal wave, mechanical wave – must have a medium
sound waves created by the vibration of objects
travels faster through solids than gases
have wavelength, frequency, amplitude (related to energy of wave)
CP PHYSICS ,FINAL EXAM REVIEW – Spring 2012, page 8
ANSWERS
69.
What is Doppler shift?
The apparent change in frequency of a wave due to the motion of the source or
the receiver.
70.
What happens to the frequency of a sound if the source moves toward you? away from you?
as the source moves toward you the frequency increases
as the source moves away from you the frequency decreases
71.
What happens to the speed of sound as the temperature of the air increases?
it increases
72.
What frequencies make up the ranges for:
a. infrasonic sounds: less than 20 Hz
b. audible sounds:
20 – 20,000 Hz
c. ultrasonic sounds:
over 20,000 Hz
73.
How is pitch related to frequency?
pitch is how an individual interprets the frequency of a sound
if the sound has a higher frequency, then most people would say it has a higher pitch
and vice versa
74.
A person yells across a canyon and
340 m/s, how wide is the canyon?
t = 4.8 s
v = 340 m/s
d=?
75.
What is the wavelength of a sound
m/s?
f = 375 Hz
v = 530.0 m/s
λ=?
hears his echo 4.8 seconds later. If the speed of sound is
v
d
d
d
=
=
=
=
d/t  d = vt
(340)(4.8)
1632 m  2
816 m
wave that has a frequency of 375 Hz and a speed of 530.0
v = λf
530 = λ(375)
375
375
λ = 1.41 m
76.
List the seven types of electromagnetic radiation in order from the lowest energy to highest
energy. Which types has the longest wavelength? Which has the shortest frequency?
radio waves, microwaves, infrared, visible light, ultraviolet, x-rays, gamma
radio – longest wavelength
gamma – shortest frequency
77.
What velocity do all parts of the EM spectrum travel at?
all parts of the EM spectrum travel at the speed of light, c, 3 x 108 m/s
78.
What property of electromagnetic radiation determines its energy?
79.
What are the primary light colors? What are the primary pigment colors?
primary light: red, blue, green
primary pigment: cyan, yellow, magenta
80.
List the primary light colors and their complements.
two colors that produce white light when they are added together
red + cyan, green + magenta, blue + yellow
frequency
CP PHYSICS ,FINAL EXAM REVIEW – Spring 2012, page 9
81.
ANSWERS
A white light is shown on a combination of green and blue pigments. What color is seen?
R
G
B
G
B
Color seen is BLACK
82.
A white light is shown on a combination of yellow and red pigments. What color is seen?
R
G
B
Y
R
Color seen is RED
83.
List the seven colors of light from longest wavelength to shortest wavelength. Which
color of light has the highest frequency? lowest frequency? Which color of light has the
highest energy? lowest energy?
red, orange, yellow, green, blue, indigo, violet
violet = highest frequency, highest energy
red = lowest frequency, lowest energy
84.
What is the difference between regular reflection and diffuse reflection?
regular reflection: light rays reflected off smooth surface parallel to each other
diffuse reflection: light rays reflected off rough surface and are NOT parallel
85.
Describe the images formed by the following mirrors:
a. plane: virtual, upright, same size, left – right reversed, object dist = image dist
b. convex: only forms virtual, upright, reduced images (security mirrors)
c. concave: when object outside of F, forms real and inverted images (outside of C –
image is reduced, at C – same size, and between C and F – enlarged)
when object at F then image at infinity
when object between F and the mirror – virtual, upright, enlarged
86.
87.
Describe the images formed by following lenses:
a. concave:
only forms virtual, upright, reduced images
b. convex:
when object outside of 2F, forms real and inverted images (outside of 2F –
image is reduced, at 2F – same size, and between 2F and F – enlarged)
when object at F then image at infinity
when object between F and the lens – virtual, upright, enlarged
What is dispersion? Identify several everyday examples of dispersion.
the separation of light into its colors arranged according to their frequencies
examples: prisms, rainbows, diamonds
CP PHYSICS ,FINAL EXAM REVIEW – Spring 2012, page 10
ANSWERS
88.
What is nearsightedness and how is it corrected?
myopia, only see well close up, focal length too short, concave lenses
89.
What is farsightedness and how is it corrected?
hyperopia, see well far away, focal length too long, convex lenses
90.
What is the focal length of a mirror that has a radius of curvature of 25.0 cm?
12.5 cm
91.
What is the radius of curvature of a mirror that has a focal length of 25.0 cm?
50 cm
92.
A converging lens has a focal length of 15.0 cm. If an object is placed at 55.0 cm from the
lens, where will its image be located?
f = 15.0 cm
1/f = 1/do + 1/di  dido = fdi + fdo
do = 55.0 cm
55x = 15x + (15)(55)
di = x
55x = 15x + 825
-15x -15x
40x = 825
40
40
x = di = 20.6 cm
93.
If the object in #103 is 8.0 cm high, what is the size of its image?
ho = 8.0 cm
hi/ho = di/do
hi = x
x = 20.6
di = 20.6 cm
8
55
do = 55.0 cm
55x = 164.8
55
55
x = hi = 3.0 cm
94.
What image is formed for the following mirror?
Image: real, inverted, reduced
95.
What image is formed for the following ray diagram?
Image: real, inverted, same size (at 2F)