Electrostatics Flashcards
1
Q
What is electricity
A
name give to a wide range of electrical phenomena
- phenomena associated with the presence and flow of electric charges
2
Q
give 3 examples of electrical phenomena
A
- lightning
- static electricity
- electrical currents
3
Q
Define electrical force
A
positive and negative particles are pulled together by the enormous attraction of the electrical force
4
Q
Define electrostatics
A
branch of physics that deals with phenomena and properties of stationary electric charges
5
Q
Symbol of electric charge
A
Q
6
Q
Units of electric charge
A
C; coulombs
7
Q
Define electric charge
A
Physical property of matter that causes it to experience a force when near other electric charges
8
Q
What are the two types of electric charge
A
positive
negative
9
Q
true or false; what the charge is called is the result of a choice made by Benjamin Franklin. Could have been the other way around as well
A
true
10
Q
true or false; mass is always positive
A
true
11
Q
define elementary charge
A
the smallest possible unit or charge
12
Q
symbol of elementary charge
A
e
13
Q
amount of e?
A
1.602 * 10^-19 C
14
Q
What is the charge of an electron
A
-e
15
Q
what is the charge of a proton
A
+e
16
Q
true or false; matter is composed of atoms
A
true
17
Q
true or false; positively charged nucleus surrounded by negatively charged electrons
A
true
18
Q
Define the CHARGE of an object
A
the sum of all the elementary charges contained in the object
19
Q
What is the expression of charge
A
Q= ne - mp = e(n-m)
20
Q
What does n stand for?
A
number of protons
21
Q
what does m stand for?
A
number of electrons
22
Q
Describe a negative charge
A
more electrons than protons
Qn
23
Q
Describe a positive charge
A
more protons than electrons
Q>0
n>m
24
Q
true or false; the charge of an electron is equal in magnitude but opposite in sign tot eh charge of a proton
A
true
25
true or false; like charges repel
true
26
true of false; opposite charges repel
false; they attract
27
What are charged atoms called?
ions
28
What does an object experience when it is charged?
it experiences a force around it
29
true or false; an electrically charged object has an excess or deficiency of some number or electrons
true
30
true or false; a charge must be a whole number multiple of elementary charges
true
31
When is an electron considered not charged/ neutral
when equal amounts of protons and electrons are present
32
what are electrons and protons made of/
quarks
33
State the conservation of charge
Net electric charge can neither be created or destroyed
| - electric charge in the universe is conserved
34
true or false; electrons can flow from one object to another but no new electrons are created and no electrons are destroyed
true
35
what does charging mean
a process of moving electrons; transferring electrons from one place to another
36
What does it mean by electric force
force experienced by an ELECTRIC CHARGE when near other electric charges
37
true or false; electric force is some 10^36 times stronger than gravity
true
38
true or false; protons don't move due to their massiveness because they are tightly bound to the nucleus
true
39
What are the 3 types of charging
1. ) charging by friction
2. charging by contact
3. ) charging by induction
40
What does charging by friction mean?
electrons are transferred by friction when one material rubs against another
41
Define electron affinity
eagerness of a material to take electrons
42
true or false; gravity (mass) is always attractive
true
43
How come when you walk on a wool rug then touch a door knob you feel a mild of electric shock?
this is because the excess electrons you have gathered desperately wants to move from you to the doorknob;
the shock you feel is a result of millions of electrons flowing away from your hand
44
What does charging by contact mean?
electrons are transferred when a charged object touches a neutral object
45
Which of the charges below are possible for an object?
a. ) +2e
b. ) -2e
c. ) +5368 e
d. ) -5.368 e
All of them except d, because charges are quantized
46
What does charging by induction mean?
electrons can be moved even without physical contact
47
Give an example of charging by induction
- two neutral objects touching each other
- negative charge brought close to one object
- electrons repelled and wants to get as far away as possible
- now separate the objects, one will be positive and the other one negative
- remove the original charged object, left with two charged objects
48
give an example of charging by friction
rubber is more electrons affinite than animal fur and hence rubbing a balloon on a cat or human hair results in electrons transferring form the cat to the balloon, The balloon becomes negatively charged while the cat becomes positively charged
49
Give an examples of charging by contact
Positive charge attracts electrons from the neutral object; both are positive afterwards (vice versa if negative; both negative afterwards)
50
During a thunderstorm clouds can become charged as pictured below. How will this influence the charge on earth?
this will induce a positive charge onto the Earth due to the negatively charged underside of the cloud
51
What are the 2 forces that govern everything in your life?
electric force
| gravitational force
52
true or false; almost all the forces we experience in fay to day life are because of the EM force
true
53
true or false; atoms are 99.99% empty space
true
54
true or false; when we touch a table; the electrons in our hands get closer and closer the electrons of the table and start to repel
true
- nothing ever touches anything (due to repulsion of electric force)
- but the table still feels solid
55
Why don't electrons collapse into the nucleus of an atom?
Electrons are waves rather than particles. In particular, electron waves solve the Schrodigner equation and the solutions tell what is the probability that the electron is some distance from the core. this probability turns out to be zero at the core
56
What does the Schrodinger equation solve?
the probability that the electron is some distance from the core
57
Why don't protons fly out of the nucleus? Shouldn't they repel each other?
strong interactions: short range force that glues protons and neutrons together. Aprrox. 100 times stronger than the electromagnetic force; but only short range
58
What is Coulombs law?
electric force depends on the charges and their separation
59
What is the expression of Coulomb's law?
F = k q1*q2/ d^2
d: separation
q1: charge 1
q2: charge 2
k: constant 9*10^9 Nm^2/C^2
60
what does k stand for in Coulombs law?
9*10^9 Nm^2/C^2
61
What does F stand for in Coulombs law?
electric force
62
how to calculate gravitational force using Coulombs law
```
F = G m1*m2/d^2
d: separation (m)
m1: mass of object 1
m2: mass of object 2
G: constant 6.7 * 10^-11 m^3/ (kg*s^2)
```
63
What is the Van de Graaf generator
a device that can store a large static charge
64
why does when touching a Van de Graaf generator ones hair stand up?
charge accumulated on the generator migrates into the person. This makes individual hair strands charged. Because the sign of the charge they posses is identical, they repel each other; they want to get as far away from each other as possible, and to do so they stand up
65
What is an electric field?
property that describes the space surrounding charged particles
- aura surrounding charges particles
66
How can particle 1 push particle 2 since they do not touch?
P1: sets up an electric field
P2: "knows" about particle 1 because it is affected by the electric field set up by particle 1
P1 pushes P2, not by touching ti, but by means of the electric field produced by P1
67
true or false; electric field has a magnitude and a direction
true
68
What does magnitude mean?
force per unit charge.
69
expression of electric field magnitude
E= F/q
70
What are the units of electric field magnitude
N/C = v/m
71
What indicates the direction of magnetic field
arrows (+) ---> (-)
72
What are electric field lines
- a pictorial description of an electric field
| - field lines NEVER cross
73
true or false; positive charge moves along the line
true
74
true or false; negative charge moves against the line
true
75
true or false; electric fields can be shielded (blocked) by certain materials whilst gravity cannot
true
76
What shields an electric field?
by a material where electrons are free to move (conductor)
| - always so in metals
77
true or false; in electrostatics, the electric field inside a metal object is always zero
true
78
true or false; the electric field inside a conductor is not zero ONLY IF AN ELECTRIC CURRENT FLOWS INSIDE THE OBJECTS
true
79
why does electric shielding occur
the internal electric field exactly cancels the external electric field; test charge would not move anywhere E=0
80
What happens when internal electric field does not equal zero
the free moving electrons would pack to one edge which would raise the internal electric field; continues until the internal electric field exactly cancels the external field; equilibrium
81
What is a faraday cage?
hollow enclosure formed by conducting material or a mesh of such material
- electric shielding possible surrounding an object with conducting material
