Week 6 and above until thermo Flashcards
1
Q
charge carriers in metals
A
electrons
2
Q
drift speed
A
net motion on a field of electrons where they flow in one direction
3
Q
electron current
A
The number of electrons passing through cross section of wire per second
4
Q
electron current depends on
A
electron’s drift speed
5
Q
Ne formula for number of electron that pass through the cross section during the time interval t
not the ne one
A
:)
6
Q
ie vs Ne
A
ie is the amount of electron that pass through per second. Ne is amount per time interval
7
Q
the electrons travel a distance of:
*in a wire segment
| formula
A
;
8
Q
Volume of the cylinder of charge
formula
A
A is cross section area
9
Q
total number of electron in cyclinder
A
number of electron per cubic meter times volume
10
Q
number of electron per cubic meter is
A
ne
11
Q
Formula for electron current in wire
hind start with Ne formula
A
12
Q
electron current
A
number of electron per second moving through the wire
13
Q
You can increase electron current by (3)
A
making them move faster, having more of them per cubic meter and increasing size of pipe they are moving through.
14
Q
Why is discharging a capacitor so fast?
+how much does the electron actually move?
A
Because the wires used are already full of e-. The electrons dont need to move the full length of the wire. The e- in wire will just be pushed out as the electron in capacitor enter wire. SO if you have a capacitor plate on neg side thats -16nC that is approximately 10^11 electrions. So 10^11 electrons (excess) would leave capacitor and enter wire and in the wire 10^11 electrons occupy xmeters in the wire so the excess electrons push 10^11 electrons which moves xmeters on the end of the wire.
15
Q
what would eventually happen to the sea of electron current in a conductor and why?
A
collisions between electrons and atoms of the metal transform the electron’s kinectic energy into thermal energy and the sea of electrons will quickly slow down and stop
16
Q
conductors with electrons moving within it are not
A
at electrostatic equilibrium
17
Q
establishing E field in wire
A
caused by nonuniform distribution of surface charges
18
Q
Surface charge density in the wire at +/- and midpoint of wire
A
+ at positive plate
- at negative plate
0 at the midpoint
19
Q
E field of a ring
A
where Z is the ring distance to the center point between the 2 ring
20
Q
Why do electrons move in a through a wire as a current?
A
Bc E field inside the wire created by nonuniform surface charge pushes them
21
Q
temp of wire is raised bc of
A
collision between electron and positive non-moving ions transefer KE into thermal energy
22
Q
each collision of electron with the ion…..its velocity
A
resets
23
Q
repeadtedly process of electron colliding and speeding up results …. thus the magnitude of the electrons average velocity is
A
a non zero average velocity
its drift speed
24
Q
Drift speed formula
A
where v0=0
25
electron current and electric field strength relationship
They are porportional
| stronger E field causes stronger current
26
collision rate formula
where t= mean time betwen the collisions
27
current formula with Q
Current is the rate at which charge crosses a point on a circuit. A high current is the result of several coulombs of charge crossing over a cross section of a wire on a circuit.
28
ie and I diff
ie is amount of electrion per seconf
I is amount of charge per sec
29
direction of current in metal is
opposite the direction of motionof the electrons as current is the direction in which positive charges seem to move
30
I ie and E which is in which direction in wire?
ie is opposite of E and I which r same direction
31
Current formula without resistor
| Hint think about relationshio with ie
32
Current density (J)
I/A
33
the rate of electron entering bulb is
the same as it leaves
current doesnt change
34
Kirchoff's Junction law
sum of current in a junction equals
sum of current leaving junction
35
Conductivity formula
36
Conductivity and current density (J) relationship
37
Diff conducting metals have diff conductivity bc
they have diff electron density and mean time between electron collisions
38
resistivity+ what does it tell?
| +formula
inverse of conductivity,
tell us how relunctant electrons are willing to move
39
relationship between current and potential difference at ends of the conductor
directly porprotional
40
Resistance is a specific property of the conductor because...
depends on the length, diamater as well as resistvity of the material
41
DIff between resistivity and resitance
42
Ohm's Law
43
Magnitude of the current is determined by
the battery (V) and the resistance of wire
44
Kirchoff's junction law vs loop law diff
Junction law says that total current going in equal comming out
Loop states the total change in potential energy for charges in a loop is 0.
45
For ideal battery neg to positive direction change in Vbat is
46
For ideal battery positive to neg direction change in Vbat is
47
For a resistor change in voltage is
48
load
resistor
49
loop equaltion with E
50
The current the battery delivers depends on (2)
emf of battery (V) and the resistance load
51
The same brightness bc the current us the same in series circuit
52
Tell me the energy flow in the circuit to light a bulb
battery transfer chemical energy in battery to potential on the charges this then turns into thermal energy on the bulb filaments that make it glow
53
power delivered by battery or rate power is transfered to the moving charges formula:
54
what is Pbat?
Energy transfered per second from battery's store of chemicals to moving charges that make up the current
55
Thermal energy
| formula
56
power transfered from current to resistor
remember P=IE (three looking thingy) so the "E" in here the the voltage diff in the resistor
56
power transfered from current to resistor
remember P=IE (three looking thingy) so the "E" in here the the voltage diff in the resistor
57
The rate at which battery supply energy is ----- to the rate at which resistor dissipates energy
equal
58
power dissipated by resistor
59
The most power will be dissipated by the
largest resistor
60
equivalent resistor formula for series
61
Ammeter
measures the amount of current in a circuit
62
Current formula for a real battery
63
terminal voltage of a real battery
64
potential difference across terminal of the battery
65
short circuit current formula
66
Notation X for vectors
into page
67
notation . for vectors
out of page
68
orientation of the compass with RHR
point thumb to current icrection, curl hand, the direction of hand curl is the compass pointing direction of the north pole and direction of the magnectic field
69
magnectic field is weaker at
greater distance from the wire
70
Just a pic
71
What is this formula for and the variables mean?
Magnectic field intensity of a point charge
72
B is ---- to the circle drawn about the charg'es line of motion
tangent
73
B is ---- to the plane of r and v
perpendicular
74
B is ---- along the line of motion meaning....
Not perpendicular*
B is 0
meaning a charge has to be moving to generate magnectic field
75
If there are n moving point charges, the magnectic field formula is
VECTOR Sum of all the magnectic field of each point charge
76
RHR of negative charge
Use your left hand you dumbass and dont forget this.
77
magnectic field of a very short segment of current *not full long wire
78
magnectic field of infinite long striaght wire tell me generally how to find the formula
| +Formula :) + w3hat r represents
79
Magnectic field of a current loop (in formula)
+ how is this integrated?
+ What does the variables mean?
1. You take original current forumla for magnectic field . Change the r^2 to the z^2+R^2
2. For some reason you use Cos and find cos through the circule angle and sides
3. integrate only change in S
80
Magnetic field of current loop of N turns of wire at the center
| *derive this lucy...rememeber what happens to Z at the centre?
81
What happen to north pole and magnectic field emerging?
Repel, south pole attracts
MAGNECTIC FIELD EMERGE FROM NORTH POLE
82
WHats similiar between current look and magnet?
83
When Z is much bigger then loop diameter for a current loop
| What happens and how can we get this formula?
1. Make R=0
2. Multiply top and bottom by 2pi
84
distant field of magnectic loop depends on
current and area enclosed
85
magnectic dipole momemt
| Familiar to point charge dipole moment!!!!!!!!
86
On the axis of the magnectic dipole of current loop formula When its very far away*
| Similiar to E field of dipole on y axis!
87
Magnectic force is greatest at
90 degree between B and V
88
force on a negative charge in magnectic field is
| how to find
use ur left hand
89
Magnectic field and work relationship
| + why?
does no work
Because Work= F∙d and force is perpendicular to V in magnectic field so its not in the same plane as d and is always perpendicular and cos90=0
90
Megnectic force directionality
perpendicular to displacement which is in direction of velocity
91
kinectic energy after N turns in cyclotron
92
Hall effect steady voltage
93
Hall voltage (2)
V=IB/(tne)
94
Brightness of the bulb is determined by
Power
P = I^2R
95
How to caculate questions with internal resistance?
1. FInd current with total R (R+r) with internal resistance added on
2. Use current to find volt of stuff like bulbs but do not use internal resistance value after u used it to find current
96
Being grounded does not
affect the circuit's behaviour under normal conditions
97
In a grounded wire, the earth
is not part of a complete circuit so there is no current in this wire
98
Terminal volatge is the amount of...
terminal voltage represents the amount of electric potential energy (voltage) that is available to the circuit outside of (external to) the battery itself.
99
Magnectic materials are
attracted to both poles of a magnet
100
What do magnectic field lines tell us?
1. A tangent to a field line is in the direction of the magnectic field
2. The field lines are closer together where magnectic field strength is larger
101
The magnectic field exert forces on magnectic poles. The force on a north pole is.....the force on a south pole is.....
1. North pole is parallel to B
2. South pole is opposite of B
102
All charges create....but only moving charges create...
- electric fields
- magnectic fields
103
Is Magnetic field superposition?
Yes
103
Is Magnetic field superposition?
Yes
104
Brief me over finding the magnectic field of a string of current
Integration is summation!
We need to add up the magnectic field contributions of a vast number of current segments by letting the sum be an integral.
105
Electromagnet
a magnet created by a current in a coil of wire
106
In a loop, North pole is the side where the field...
emerge
107
uniform magnetic field is only generated in a
Solenoid
108
In a solenoid, with many loops along the same axis, the field in the centre is.... and roughly..... whereas the field outside the loop is...
1.within the centre is strong
2.and roughly parallel to the axis
3.very close to 0
109
The formula for magnectic field in a solenoid
| + hint: its the formula on formula sheet but it can further simplified
Where n=N/L
*Number of turns per unit length
110
magnetic force is always ----- to both the velocity and the magnetic field
perpendicular
111
magnectic force on particle moving parallel to field=
0
| aka what u will get on the final if u dont get ur ass tgt
112
2 scenarios where a charge will not have magnectic force:
1. a charge is at rest
2. charge is moving parallel or antiparallel to magnectic field
113
The force on a negative charge is
in the direction opposite of V X B
114
cyclotron motion
particle move perpendicular to magnetic field undergoes circular motion at constant speed
115
How is this formula derived?
Since force of cylotron is like the centripetal acceleration of circular motion.....
you equal that force in cyclotron through RHR to centripetal acceleration
116
As the E field in the cyclotron accelerates the proton across the gap it gains the kinectic energy:
eV
117
The ---- of the cyclotron orbit increases hence the proton follows a----- ----. But the ----- also increase so the ----- does not change
The **Radius** of the cyclotron orbit increases hence the proton follows a **Spiral path**. But the **Speed** also increase so the **Frequency** does not change
118
What does the E field and Magnectic field do in a cyclotron?
E field= provides the accelerating force for protons as they enter the gaps
Magnectic field provides the centripetal acceleration which stays constant as the Magnectic field doesnt change which is why the radius of cylotron gets bigger since the centripetal acceleration stays same but speed increase so its harder to turn.
119
Hall volatge what do you sub for? What do you start with?
| youtube version
You start with qvB=qE
Sub E as V/s
q cancels
isolate V thats your hall voltage
vBs=HV
Sub velocity as s/Time
Time= (I=Q/t)
120
You start with qvB=qE
Hall volatge what do you sub for? What do you start with?
| Textbook version
You start with qvB=qE
Sub E as V/s
q cancels
isolate V thats your hall voltage
vBs=HV
Velocity=. J=I/A. J=nevdA/A. Vd= I/Wtne
sub back into original formula
W cancels out
121
magnectic force on a current carrying wire is
| Not the formula
the net magnetic force on all the charge carrier in the wire
122
magnectic force on a current carrying wire is
| Formula+how do u find it? **One not on formula
So the basic QVBsintheta but sub V as x/t and make Q/t the current
Plus the formula should have sin theta
123
Tell me about parallel wires and attraction/repulsion
parallel wire carrying current in same direction attract eachother. Parallel wire carrying current in opposite direction repel eachother
124
What is direction of magnectic dipole?
The direction of μ⃗ is given by a curled-straight right-hand rule: Grasp the coil so that the fingers of your right hand curl around it in the direction of the current; your extended thumb then points in the direction of the dipole moment μ⃗.
125
2 ways to find cylotron motion:
1. K=2 N eV
2. K=1/2mv^2 sub V as qvb=mv^2/r
126
Faraday's law
There is a current in a coil of wire only if the magnectic field passing through is changing
127
motional emf
| +Formula
magnetic forces separate the charges and causes a potential diff between ends
*only present if conductor is moving through B fieild
*fromula derived by V=Es and E=vB
128
The induced current given by Ohms law is:
129
force needed to pull the induced current wire with constant speed
Use current version of force and sub in the current formula found by I=V/R=vlB/R
130
power provided to the current by pulling on the wire is
*rate of which energy is added due to pull
131
Magnetic flux
measures the amount of streamlines/field passing through the loop of area A if tilted
132
if flux is increasing, the induce current should make it
decrease
133
if flux is decreasing, induced current should make it
increase (additive to it)
134
the induced current stops as soon as
magnet stops moving
