Unit 4 (lesson 12-13) Flashcards
1
Q
electrostatistics
A
the study of electric charges at rest
2
Q
what do electrical forces come from?
A
arise from particles in atoms.
3
Q
atoms
A
- every atom has a positively charged nucleus surrounded by negatively charged electrons
- all electrons are identical; each has the same mass and same quantity of negative charge as every other electron
- nucleus is composed of protons and neutrons
- atoms have as many electrons as proton, so a neutral atom has zero net charge
4
Q
fundamental rule at the base of all electrical phenomena is that
A
like charges repel and opposite charges attract
5
Q
ion
A
a charged atom
6
Q
an object that has unequal numbers of electrons and protons is
A
electrically charged
7
Q
conservation of charge
A
principle that electrons are neither created nor destroyed
8
Q
Coulomb’s Law
A
states that for charged particles or objects that are small compared with the distance between them, the force between the charges varies directly as the product of the charges and inversely as the square of the distance between them
9
Q
Coulomb’s law equation
A
F = k((q(1)q(2)/d^2)
10
Q
coulomb
A
SI unit of charge, abbreviated C
11
Q
charge of 1 C
A
6.24 * 10^18 electrons
12
Q
electrical proportionality constant k
A
9,000,000,000N*m^2/C^2
13
Q
conductors
A
materials through which electric charge can flow
- electrons are “loose”
- electrons move easily
14
Q
insulators
A
materials that are poor conductors of electricity
-electrons move poorly
15
Q
semiconductors
A
materials that can be made to behave sometimes as insulators and sometimes as conductors
16
Q
two ways electric charge can be transferred without touching
A
by friction and by contact
17
Q
if a charged object is brought near a conducting surface, even without physical contact, electrons will….
A
move in the conducting surface
18
Q
induced
A
electric charge that has been redistributed on an object because of the presence of a charged object nearby.
19
Q
induction
A
charging of an object without direct contact
20
Q
charge polarization can occur in…
A
insulators that are near a charged object
21
Q
electrically polarized
A
when one side of the atom or molecule is induced to be slightly more positive (or negative) than the opposite side
22
Q
three ways objects are electrically charged
A
- when electrons are transferred by friction from one object to another
- when electrons are transferred from one object to another by direct contact without rubbing.
- when electrons are caused to gather and disperse by the presence of nearby charge. (induction)
23
Q
Gravitational Force
A
- Attraction between two masses
- Increases as masses increases
- Decreases as distance increases following inverse square law
- Includes a constant (G)
24
Q
Electric Force
A
- Attraction or repulsion between two charges
- Increases as charges increase
- Decreases as distance increases following inverse square law
- Includes a constant (k)
25
proton
Positive
Large
Nucleus
26
neutron
Neutral
Large
Nucleus
27
electron
Negative
Small (almost nothing)
Electron cloud
28
how does an atom become charged?
by gaining or losing electrons
29
how does an object become charged
by gaining or losing electrons or by having the electrons take on an unbalanced arrangement.
30
How can a charged comb attract an uncharged piece of paper?
The charges on the comb induce a charge on the paper and attract the close end of the paper more strongly than they repel the far end of the paper.
31
What is happening when you rub a balloon on your hair and stick it to the wall?
The balloon picks up electrons from your hair, becoming negatively charged. Then it induces a charge in the neutral wall.
32
Can you charge an insulator?
Insulators can become "charge polarized" when they are near a charged object. The electrons do not leave their nuclei, but they do "move over" so that the charge is not evenly distributed.
33
If electrical forces are so large compared to gravitational forces, why don't we feel the effects of electrical forces every day?
1. you are essentially neutral
| 2. electric forces can cancel while masses cannot.
34
There are approximately 5 thousand billion, billion electrons in a penny and they are all repelling each other. Why don't they fly out of the penny?
The electrons are attracted to the same number of protons in the penny.
35
what is the function of a lightning rod?
prevent a lightning discharge from occuring
36
what is lightning?
an electrical discharge between oppositely charged parts of clouds
37
Because charges exert forces on other charges, we can...
store energy and do work.
38
electric field
a force field that surrounds an electric charge or a group of charges
39
an electric field has both...
maginitude and direction
40
how can the magnitude (strength) of an electric field be measured?
by its effect on charges located in the field
41
the direction of an electric field at any point, by convention, is the...
direction of the electrical force on a small positive test charge placed at that point
42
how represent electric fields
electric field lines (lines of force). where lines are farther apart, the field is weaker.
43
if a charge on a conductor is not moving, the electric field inside the conductor is...
exactly zero
44
the electrical potential energy of a charged particle is increased when...
work is done to push it against the electric field of something else that is charged
45
electrical potential energy
the energy a charge has due to its location in an electric field
46
electric potential is...
electrical potential energy per charge
47
volt
- SI unit of measurement for electric potential
| - 1 volt = 1 joule/coulomb
48
capacitor
electrical devices that store large amounts of energy slowly and then release the energy rapidly.
49
the energy stored in a capacitor comes from...
the work done to charge it
50
the voltage of a Van de Graaff generator can be increased by...
increasing the radius of the sphere or by placing the entire system in a container filled with high-pressure gas
51
electric field lines
vectors drawn to show the direction and size of an electric field.
52
How does the direction of an electric field line compare with the direction of force that would act on an electron in that field?
Because the field lines are drawn to show the direction of force on a POSITIVE test charge, they are in the opposite direction to the force that would be experienced by an electron.
53
Why can an object be shielded from an electric field but not from a gravitational field?
Masses cannot cancel each other out while electric charges can.
54
What will happen to the electrical potential energy of a charge particle in an electric field when the particle is released and free to move?
The electrical potential energy is converted to kinetic energy as the particle moves.
55
Where does the energy stored in a capacitor come from?
It comes from the work done to charge the capacitor.
56
How is a capacitor different from a battery?
A battery converts chemical energy to electric energy and acts like a "pump," while a capacitor simply stores electric energy and acts like a pressure release valve.
57
How does the amount of charge on the inside surface of a Van de Graaf generator compare with the charges on the outside of the sphere?
There are no charges on the inside of the sphere as all charges repel each other toward the outside.
58
electric dipole
a separation of positive and negative charges
59
how can objects be completely shielded from electric fields
- place a charged object inside a hollow conductor, it will not be attracted to the hollow conductor because the net electric field inside it is zero.
- bring a new charged object near this system, the charges on the hollow conductor will rearrange themselves so that the net electric field inside the hollow conductor is still zero, so that the test charge will not be affected by the electric field of the new charge.
60
what is the relationship between the amount of work you do on an object and its potential energy
Work equals the change in potential energy
61
If you do more work to move more charge a certain distance against an electric field, and increase the electrical potential energy as a result, why do you not also increase the electric potential?
because if you increase both the electric potential energy and the charge, then the increase in each cancels out resulting in the same electric potential.
62
why is an electric field considered a vector quantity?
since it has both magnitude and direction
63
why are occupants safe inside a car struck by lightning
electrons that shower down upon the car are mutually repelled and spread over the outer metal surface, finally discharging when additional sparks jump from car's body to the ground
64
can electric fields be shielded
yes. need to surround self with conducting surface
65
electric current only exists
when charges are flowing.
66
batteries and generators supply
the voltage needed to create a flow of charge.
67
electric resistance
the friction that is generated when charges move.
| -measure in Ohms
68
Ohm's law
- Volts (V) = Current (I) x Resistance (R).
- states that the current in a circuit is directly proportional to the voltage impressed across the circuit and is inversely proportional to the resistance of the circuit.
- 1 ampere = 1 volt/1 ohm
- current = voltage / resistance
69
when the ends of an electric conductor are at different electric potentials, charge flows...
from one end to the other
70
potential difference
difference in potential (voltage) between the ends of a conductor
71
charge flows when there is...
a potential difference between the ends of a conductor
72
what must be done to attain a sustained flow of charge in a conductor?
some arrangement must be provided to keep one end at a higher potential than the other.
-flow of charge will continue until both ends reach a common potential.
73
electric current
the flow of electric charge
74
conduction electrons
electrons that carry the charge through the circuit because they are free to move throughout the atomic network
75
a current-carrying wire has a net electric charge of...
zero
76
voltage source
something that provides a potential difference
77
voltage sources supply energy that
allows charges to move steadily.
| -batteries and generators
78
charges flow through a circuit because of an...
applied voltage across the circuit.
79
what does the the resistance of a wire depend on?
- conductivity of the material used in the wire
- the thickness, diameter, and length of the wire
- temperature
80
superconductivity
the resistance of some materials becomes zero at very low temperatures
81
what are the damaging effects of electric shock the result of?
current passing through the body
82
what may electric current be?
direct current or alternating current
83
direct current.
DC. refers to a flow of charge that always flows in one direction.
84
alternating current
AC. electric current that repeatedly reverses direction.
85
with an AC-DC converter, one can operate a battery-run device on...
AC instead of batteries.
86
diode
a tiny electronic device that acts as a one-way valve to allow electron flow in only one direction
87
how are conduction electrons accelerated?
by the field
88
in a current-carrying wire, collisions interrupt the motion of electrons so that...
their actual drift speed, or net speed through the wire due to the field, is extremely low
89
the source of electrons in a circuit is the
conducting circuit material itself
90
electric power
the rate at which electrical energy is converted into another form such as mechanical energy, heat, or light
91
electric power is...
equal to the product of current and voltage
| electric current = voltage * current
92
power in watts equation
1 watt = (1 ampere) * (1 volt)
93
how AC is converted to DC
transformer lowers the voltage => the converter uses a diode to allow electrons to flow in only 1 direction
