Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

Physics 1 > Electricity & Magnetism 2 > Flashcards

Electricity & Magnetism 2 Flashcards

1
Q

Current

A

Rate of change of charge

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

Electric circuit

A

Charges follow conductive path that forms a closed loop
Electric potential energy transferred from a source to a device in which that energy is stored or converted

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

Electrons do not escape from metal as

A

They are attracted to its positive ions

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

With steady electric field E in the conductor, electric force F=qE imposes

A

A small drift in the direction of the force

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

Microscopic view of Ohm’s law

A

Electrons speed up nd colllide with stationary ions which vibrate around equilibrium position
Much electrical energy wasted as heat instead of moving electrons
Each collision randomly changes direction of motion
Net effect: in addition to radndom motion, there is a very slow net motion, drift velocity CONSTANT

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

Drift velocity

A

F=ma and F=qe gives a=qe/m
V=u+at but with mean free time

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

Drift velocity for E=0

A

Typical electron has V0 at random direction so average velocity over many electrons is zero

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

Drift velocity for E not =0

A

Electric field causes acceleration a=qE/m of every electron

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

Why is switching on a light almost instantaneous

A

Electric field in metal travels close to c so electrons everywhere start moving with drift velocity

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

Electron concentration

A

Conductor with n atoms per unit volume
n=Nap/A

=avogadro. Density/ atomic mass

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

Direction of drift

A

Constant velocity in direction opposite to E

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

Total charge through cross section A of conductor in time dt

A

dQ=nqAvddt

no= free charge per volume
Avddt= volume

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

Current is

A

I=dQ/dt=nqAvd =JA where J is current density

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

Current density

A

J=I/A

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

Conductivity (sigma)

A

Scalar depending on conductor material

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

Resistivity

A

1/conductivity ( unit ohm m)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

Ohm’s law

A

J=signage=E/p

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

Does J change

A

Vector
Can vary around a circuit as A changes

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

Conductivity and thermal conductivity

A

Good electrical conductors are also good thermal conductors

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q

Perfect conductor

A

Zero resistivity

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
21
Q

Perfect insulator

A

Infinite resistivity

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
22
Q

Greater resistivity,

A

Greater field needed to cause given current density

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
23
Q

Non ohmic materials

A

Resistance has non linear response

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
24
Q

Resistivity

A

Material property that is temperature dependent , increases with T for metal conductors

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
25
Q

For a conductor to have steady state current

A

Must be part of path that forms a closed loop/complete circuit

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
26
Q

Four components of electric circuit

A

Source of electrical power
Conductors (wire with low R)
A load
A means of control (etc)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
27
Q

In an electric circuit, charge moves

A

From higher to lower electric potential (similar to water in fountain due to gravity)
Source of emf causes charges to move against electrostatic force

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
28
Q

Ideal source of emf

A

Maintains constant potential difference between conductors

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
29
Q

Real sources of emf

A

Have different potential difference than E
Ring due to charge moving through material of the emf source

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
30
Q

Voltaic cell

A

Voltage generated by connecting different metals in circuit due to different electronegativities

Daniel cell uses copper and zinc electrodes in electrolytes

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
31
Q

Idealised voltmeter

A

Infinite,y large resistance so no current flow

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
32
Q

Idealised ammeter

A

Zero resistance so no voltage drop associated with it

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
33
Q

Closed circuit condition

A

R —>0
I—> E/Rint

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
34
Q

Short circuit condition

A

R=0
Vab =0
I —> infinity for small Rint

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
35
Q

Open circuit condition

A

Vab=E
I—>0

36
Q

Power

A

dUdt

37
Q

What does E.I represent

A

It is rate of work done by forces in source

Represents rate of conservation of non electrical energy to electrical energy within the source

38
Q

I^2.Rint

A

Rate of dissipation of energy

39
Q

Junction

A

Point where three or more conductors meet

40
Q

Loop

A

Any closed conducting path

41
Q

Junction rule

A

Algebraic sun of currents into any junction is zero

In +, out -

42
Q

Loop rule

A

Algebraic sum of potential differences in any loop must equal zero

43
Q

Sign conventions for junction rule

A

In +
Out -

44
Q

Loop rule - sign conventions for emfs

A

+E travel direction from - to +
-E travel direction from + to -

45
Q

Loop rule - sign conventions for resistors

A

+IR travel opposite to current direction
-IR travel in current direction

46
Q

Easier way to set up junction rule

A

Flows in = flows out

47
Q

Where to start when using Kirchoff’s rules

A

Highest potential in the loop

48
Q

Thevenin’s theorem

A

Any combination of batteries and resistors with two terminals can be replaced by a single voltage source e and a single series resistor r

49
Q

Thenevin voltage e

A

The open circuit voltage between terminals A and B

50
Q

Thenevin resistance r

A

resistance seen between terminals A and B when voltage sources are replaced with short circuits

take load out and calculate Vab

51
Q

Thenevin steps

A

Short all voltage sources
Find the equivalent resistance

52
Q

Charge conservation

A

In junction rule

53
Q

Energy conservation

A

In loop rule

54
Q

Open loop systems

A

No way of checking if results have been achieved
Eg central heating without a thermostat

55
Q

Closed loop systems

A

A KE to correct themselves in order to meet target results

56
Q

Feedback

A

Sensor used to look at the output and adjust the process accordingly

57
Q

Op amp main purpose

A

To amplify signals

58
Q

How we treat op amp

A

Like a black box
Analysing only it’s external behaviour

59
Q

Three fundamental properties of op amps

A
  1. Gain A (multiplier between differential input and output represented by diamond shape)
  2. Input impedance (Rin) resistance at the input of the circuit, very high
    Output impedance (Rout) resistance seen from output of the circuit, very low
60
Q

Closed loop system response

A

Distinguish between negative and positive feedback depending on the phase relationship

61
Q

Negative feedback

A

Portion of the output is combined out of phase with the input

Promotes stability and setting to equilibrium

62
Q

How does negative feedback loop reduce perturbations

A

Fluctuation in input cause flux. in out which fed back to in compensating original fluc so minimising out fluc

63
Q

Examples of negative feedback loop

A

Thermo regulation (sweating)predator and prey population (more mice = more food for cats, more cats = more mice eaten, less mice = less cats

64
Q

Closed loop positive feedback

A

Portion of output is combined in phase with the input

Minus sign in equation

65
Q

What does positive feedback promote

A

Instability and chaos through exponential growth

66
Q

Example of positive feedback

A

Panic buying toilet roll

Motivation and success

67
Q

Condition A0B=1 results in

A

Gain becoming infinite

68
Q

Non inverting op amp

A

Produces bigger version of original graph

69
Q

Inverting op amp

A

Bigger and flipped version of original

70
Q

Graph of Vin against Vout

A

Horizontal- saturation region
Slope = gain A0 through linear region
Horizontal + saturation region

71
Q

Ideal op amp

A

Slope is infinite (vertical line) A0= infinity
Linear region only occurs at Vin=0 (virtual short circuit)

72
Q

2 golden rules for circuit analysis with op amps

A
  1. Both input terminals are at the same voltage
  2. No current flows in or out of either input
73
Q

Transfer function

A

Independent of gain A
Non inverting

74
Q

Non inverting op amp

A

Vout/Vin=R2+R1/R1

75
Q

Inverting op amp

A

Vout/Vin = =Rf/Rin

76
Q

Summing op amp

A

If Rf=R1=R2 then Vout=-[v1+v2]

77
Q

Subtracting op amp

A

Vout=-[V1-V2]

78
Q

Rules for adding binary numbers

A

As expected except 1+1=0 carry 1

79
Q

Logic gate

A

Idealised or physical device implementing a Boolean function

Made of transistors or diodes acting as electronic switches

80
Q

AND gate

A

Read as A,B,AandB

0,0,0
0,1,0
1,0,0
1,1,1

A AND B need to be 1 for A and B to be 1

81
Q

OR gate

A

If A or B is high then output high

82
Q

XOR gate

A

Same as or except if both inputs are 1, output 0

83
Q

NAND gate

A

0,0,1
0,1,1
1,0,1
1,1,0

84
Q

NOR gate

A

Inverse
So
0,0,1
0,1,0
1,0,0
1,1,0

85
Q

Half adder

A

Performs binary addition on two input numbers

86
Q

Flip flop

A

Basic data storage

Stores a single bit of data

87
Q

SR latch

A

Made from two cross coupled NAND gates

Physics 1 (10 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2025 Bold Learning Solutions. Terms and Conditions