Download presentation

Presentation is loading. Please wait.

Published byDeborah Campbell Modified over 5 years ago

2
Remember? An electron is moving downward with a velocity, v, in a magnetic field directed within the page, determine direction of force.

3
Moving conductor Conductors contain free electrons So when a conductor moves downward, electron will experience a magnetic force pulling them to the left. Lattice atoms on the right become positive… There is a potential difference now

4
Moving conductor E force produced wanting to push electrons to the right Forces are now balanced and electrons will stop moving What will happen if you connect a resistor to the metal conductor?

5
Moving conductor E force produced wanting to push electrons to the right Forces are now balanced and electrons will stop moving What will happen if you connect a resistor to the metal conductor? Current will flow from high to low potential ++++++ –––––– R R

6
Moving conductor What did we define emf previously as? Amount of chemical energy converted to electrical energy per unit charge ++++++ –––––– R R

7
Moving conductor What did we define emf previously as? Amount of chemical energy converted to electrical energy per unit charge We don’t have chemical energy here!!! Where does our energy come from here? ++++++ –––––– R R

8
Moving conductor Which direction were we pushing this conductor? Another force acting on conductor? ++++++ –––––– R R

9
Moving conductor Which direction were we pushing this conductor? Another force acting on conductor? Yes magnetic force… which direction is it acting? ++++++ –––––– R R

10
Moving conductor Which direction were we pushing this conductor? Another force acting on conductor? Yes magnetic force… which direction is it acting? – upward So when you’re pushing it downward, what energy is it gaining? ++++++ –––––– R R Force applied Magnetic force

11
Moving conductor Which direction were we pushing this conductor? Another force acting on conductor? Yes magnetic force… which direction is it acting? – upward So when you’re pushing it downward, what energy is it gaining? – EPE You are doing work If forces are equal, conductor is moving at constant v. ++++++ –––––– R R Force applied Magnetic force

12
Moving conductor EPE will be converted into heat Energy is conserved Now let’s define INDUCED EMF? Amount of mechanical energy converted into electrical energy per unit charge. ++++++ –––––– R R Force applied Magnetic force

13
Calculating induced EMF Maximum p.d. in conductor is when the magnetic force ON ELECTRON is equal to the electrical force – L

14
Calculating induced EMF Maximum p.d. in conductor is when the magnetic force ON ELECTRON is equal to the electrical force Electron will stop moving.. Therefore greatest p.d. Equate equations – L

15
Induced EMF equation **** The induced EMF will be the same as p.d. across conductor

16
Question If magnetic field not perpendicular to direction of motion… what will you do? v B

17
Question If magnetic field not perpendicular to direction of motion… what will you do? Take the B that is perpendicular to v

18
Flemings right hand rule FOR INDUCED CURRENT

19
QUESTION

21
THREE HAND RULES RIGHTLEFT

22
Faraday’s law What generated induced emf? What did it depend on?

23
Faraday’s law What generated induced emf? – moving conductor in a magnetic field What did it depend on? Faraday’s law: The induced emf is equal to the rate of change of flux

24
Flux VS flux density Let’s look at this analogy

25
Flux VS flux density How much grass do you have? Is it taking lots of area?

26
Flux VS flux density Pieces of grass is flux density (B) Area over which grass takes over is flux (Φ)

27
Flux VS flux density Flux unit: Tm 2, Wb

28
Flux VS flux density Normal to surface If area at angle from B Find component of B that will be perpendicular to area θ

29
Lenz’s law Moving conductor in magnetic field causes a force to oppose the direction of motion as seen earlier (if not true than energy will not be conserved) Lenz’s law is an extension to Faraday by stating that: the induced current will be in such a direction as to OPPOSE THE CHANGE IN FLUX that created the current.

30
Question

32
Determine direction of current

33
Question

37
Rail gun… how does it work? resistor

38
Question What will happen if you remove the magnetic field suddenly? resistor

39
Question BRING BACK THE FIIIEEEELLLDDD!!! LENZ’S LAW resistor

40
Question to get the field back, which direction should the induced current be? resistor

41
Question Current upward…. Force???? resistor

42
Question Current upward…. Force to the right… and off it goes….. resistor

43
Question

44
http://science.howstuffworks.com/rail-gun1.htm

45
Read Applications of EM induction on page 213

46
Alternating current (AC) What’s the difference between a motor and a generator?

47
Alternating current (AC) What’s the difference between a motor and a generator? Motor electrical to mechanical energy Generator mechanical to electrical

48
Alternating current (AC) What’s the direction of current induced here?

49
Alternating current (AC) What’s the flux going to be at angle 0?

50
Alternating current (AC) What’s the flux going to be at angle 0? Maximum since So how will the graph look like?

51
Alternating current (AC) Label the positions in graph

52
Alternating current Since we have many loops here we change the equation a bit and add “N” so that the total flux (called flux linkage): Can we substitute θ with something else?

53
Alternating current ..

54
Alternating current (AC) How will the emf graph with time look like? What’s the emf equation?

55
Alternating current (AC) How will the emf graph with time look like? What’s the emf equation? How can we get this value from the flux vs time graph?

56
Alternating current (AC) How will the emf graph with time look like? What’s the emf equation? How can we get this value from the flux vs time graph? ---- (negative the gradient)

57
Alternating current (AC)

58
So will the equation for emf have a sin or cos?

59
Alternating current (AC) So will the equation for emf have a sin or cos? Therefore at 90 degrees the emf in max and the flux is zero.

60
Alternating current (AC)

61
Emf and time Emf vs time graph… what will happen if you double the angular speed…

62
Emf and time Emf vs time graph… what will happen if you double the angular speed… Double emf and half the period

63
Current and time How can the current in the circuit be found?

64
Current and time How can the current in the circuit be found? ε 0 is equal to: Can you think from where this equation came from?

65
Graphs

66
Definitions AC: current delivered by rotating coil changing in direction and size over period of time DC: constant current delivered from battery

67
question

68
Answer

69
Power Equation(s)?

70
Power P=IV, let substitute… always positive

71
Power Average power is about 50W in example below… how about the average current and voltage from previous graphs?

72
Power Average power is about 50W in example below… how about the average current and voltage from previous graphs? ZERO???? How do we solve this?

73
RMS To solve this by calculating the root mean square (rms) Square voltage or current then divide by two then square root the answer

74
Question

76
Power loss Power transmitted through wire will be lost due to what factors?

77
Power loss Power transmitted through wire will be lost due to what factors? P= I 2 R [power loss to heating] To reduce heat loss we have to reduce I Reducing current, if DC was transmitted through power lines that feed homes, will have nothing left to run instruments.. AC, on the other hand, keeps on changing current and voltage…

78
Power loss P=IV So if we increased V then I will decrease since power supply in constant So if we increase voltage by 100V, then the current will be less ( I /100) So the power loss will be reduced by 100 2 (P= I 2 R) WOW very useful and can only happen in AC Ok… how can we do this? Transformers

79
Transformers NO! Not the movie :p

80
Transformer Current runs through primary.. What will it generate? iron

81
Transformer Current runs through primary.. What will it generate? iron

82
Transformer Current runs through primary.. What will it generate? A magnetic field will be generated in all iron (that’s why it has to be a magnetic metal) Now there is a magnetic field in in secondary coil.. What will happen? iron

83
Transformer Current runs through primary.. What will it generate? A magnetic field will be generated in all iron (that’s why it has to be a magnetic metal) Now there is a magnetic field in in secondary coil.. What will happen? NOTHING How can we make a current run through the secondary coil? iron

84
Transformer Current runs through primary.. What will it generate? A magnetic field will be generated in all iron (that’s why it has to be a magnetic metal) Now there is a magnetic field in in secondary coil.. What will happen? NOTHING How can we make a current run through the secondary coil? CHANGE THE FLUX – INDUCED EMF iron

85
Transformer CHANGE IN FLUX created a current Potential difference in primary coil is proportional to number of loops so iron

86
Transformer So lets look at the example above Number of loops in secondary is greater than primary So voltage in secondary will also be larger than primary So how about the current? iron

87
Transformer Look at above equation Since voltage is more than the current will be less (since the power is constant). So we just have MORE VOLTAGE (10/5 so double voltage) :D Step up transformer iron

88
Transformer Step up transformer to transport from plant to houses Step down transformer at home to devices iron

89
Transformer

90
Question

91
answer

93
Read For more information 218 and 219

Similar presentations

© 2021 SlidePlayer.com Inc.

All rights reserved.

To make this website work, we log user data and share it with processors. To use this website, you must agree to our Privacy Policy, including cookie policy.

Ads by Google