Brainscape's Knowledge GenomeTM

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


See full index

⭐️raj vigya > earth's magnetism and electro magnetism > Flashcards

earth's magnetism and electro magnetism Flashcards

1
Q

what is the effect which causes earth’s magnetism called

A

dynamo effect

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

why do we believe that on a magnet, some other magnetic force is definitely acting?

A

because when a magnet is freely suspended, it always assume a north-south position

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

how are the geographic and magnetic poles aligned to each other

A

geo north pole is magnetic south pole and vice versa

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

how are the the lines of force of the earth’s magnetic field

A

equidistant and parallel to each other and directed towards north

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

how much is the horizontal component of earth’s magnetic field

A

it varies from place to place but its average value is 0.4 gauss or 0.4x10^-4 tesla

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

what is the law of force between pole of magnets

A

the force between two poles of a magnet is directly proportional to the multiple of the strengths of the two poles and inversely proportional to the square of the distance between the two poles

i.e F∝m1m2/r^2

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

define electromagnetism

A

it is a process where a magnetic field is created by introducing the current in the conductor

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

when does a conductor generates magnetic field lines

A

when it is electrically charged

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

what is an electromagnet

A

it is a solenoid coil with a metallic core like soft iron in which magnetism is generated due to electric current

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

what kind of current is in an electromagnet or solenoid

A

magnetic current

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

what is a solenoid

A

if the insulated wire is wrapped around a cylindrical hollow tube, it is called solenoid. the cylindrical tube is called its core.

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

in which devices is solenoid used

A

eg dynamo, transformer, electric bell, telephone, generator motor etc also in lifting heavy objects

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

3 factors on which the intensity of the magnetic field produced by an electromagnet depends upon?

A

1 number of turns in the solenoid coil
2 nature of core material
3 magnitude of current

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

how does increase or decrease in number of turns in a solenoid coil affects magnetic field

A

as the number of turns increase, the intensity of magnetic field also increases
aka
directly proportionate

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

how does nature of core material in an electromagnet affects its magnetic field

A

core like a soft iron increases the intensity of the magnetic field

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

how would increasing the current in an electromagnet affects its magnetic field

A

greater the magnitude of current, more intense the field

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

in which case magnetic flux is maximum

A

when all the magnetic lines are perpendicular to the surface

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

minimum magnetic flux scenario magnetic lines direction?

A

parallel

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

flux formula when magnetic lines are on an angle from surface

A

BAcostheta

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

what is magnetic flux

A

the total number of magnetic lines passing perpendicular to a surface in a magnetic field is called the magnetic flux of that surface

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

SI unit of magnetic flux?

A

weber

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

flux formula?

A

theta=B.A

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

who discovered electromagnetic induction and when

A

faraday in 1831

24
Q

what did faraday discover in 1831

A

that when the number of magnetic lines of force passing through a circuit or a closed coil changes, and electromotive force is produced in the coil, as a result current flows in the coil

25
Q

on what the current in electromagnetic induction is dependent on

A

the change in electromagnetic field lines
as long as the electromagnetic field lines continue changing, the current continues flowing

26
Q

what are the electromotive force produced in the coil and the produced current called in electromagnetic induction

A

induced electromotive force and induced current

27
Q

3 ways in which the magnetic flux passing through a coil can be changed

A

1 moving magnet with respect to the coil
2 rotating the coil in magnetic field
3 changing value of current flowing in the coil

28
Q

where would the galvanometer deflect when a magnet is kept stationary near the coil

A

no deflection meaning no electric current

29
Q

if the movement of magnet is faster now, would the current be less of more?

A

more
faster the movement, more the current

30
Q

how does the number of turns in coil affect the strength of the induced electromotive force?

A

as turns increase, the induced electromotive force increase

31
Q

what are the two laws of faraday MAINS

A

1 the current keeps flowing as long as the number of magnetic lines keep changing
2 amount of induced electromotive force produced in a closed coil is directly proportional to change in magnetic flux

32
Q

what did lenz add to discoveries of faraday

A

direction. according to him, the induced current or emf in a coil is produced in such a direction that it can oppose the cause which produced itself.

33
Q

if we move the north pole of the magnet near the coil, according to lenz law, how would the coil react?

A

induced current in the coil would flow in such a direction that the coil in front of the magnet acts as the north pole

34
Q

lenz law explain with diagram

A
35
Q

what is the process of self induction

A

the phenomenon of electromagnetic induction in which the change in current flowing in a coil produces an induced current in the same coil itself is called self induction

36
Q

number of turns are N and current I is flowing. the magnetic flux is theta. how they relate?

A
37
Q

unit of self inductance?

A

henry

38
Q

what is mutual inductance?

A

two coils close to each other and pass electric current in one of them through a battery or change the amount of current flowing or stop the current in it, the emf is generated due to electromagnetic induction in the other coil called mutual induction

39
Q

unit of mutual induction

A

same as self induction i.e. henry

formula is also same
the coefficient changes to M i.e. the coefficient of mututal inductance

40
Q

what are eddy currents

A

induced current caused by the induced emf caused by the change in value of magnetic flux of a coil which is formed in closed loops which represents whirl pods or eddies and are called eddy currents

41
Q

who discovered eddy currents and when

A

Leon Foucalt in 1851

42
Q

the value of eddy currents depends on which property of the conductor

A

resistance

43
Q

what is the relation between eddy currents and resistance of the conductor

A

if resistance is high, eddy currents become weak, if resistance is less, eddy currents become stronger
thus: inverse relation

44
Q

MAINS list disadvantages of eddy currents

A

in a dynamo or an electric motor if they are made of soft iron, eddy currents are generated in them and the electric energy is lost in form of thermal energy aka less electrical efficiency due to eddy currents

45
Q

MAINS how is the eddy current forming in dynamo or electrical motor resulting in lack of efficiency solved

A

instead of making the core of these instruments only from soft iron, it is made by joining thin plates of soft iron which increases resistance of the core, thus decreases eddy currents

46
Q

MAINS what are the applications of eddy currents

A

1 electromagnetic damping
2 induction motor
3 speedometer
4 energy meter
5 electric break

47
Q

what is an electric break

A

usually used in trains. a strong magnetic field is applied to the drum attached to the wheels which causes generation of eddy currents in the drum opposing the motion of the drum thus stopping the wheels along with the drum

48
Q

what is magneto motive force of MMF
compare it to electrical energy

A

the work done to bring a unit magnetic pole from one point to another in magnetic circuit is equal to the magneto motive force (MMF) between two points
just like in electricity the work done in moving a unit charge from one point to another is equal to the potential difference between two points

49
Q

what is the source of establishing the magnetic flux in a magnetic circuit

A

MMF

50
Q

how is the MMF calculated in a magnetic circuit

A

MMF is equals to the product of number of turns and current

MMF=NI

51
Q

what is the unit of MMF

A

ampere-turn

52
Q

what is reluctance

A

just like the resistance in an electric circuit, the reluctance in a magnetic circuit is property of a magnetic medium which opposes the establishment of magnetic flux.

53
Q

formula for magnetic reluctance

A

magnetic reluctance (s) = MMF/magnetic flux

54
Q

what is permeance

A

the inverse of reluctance like conductivity in an electric circuit
permeance=1/reluctance

55
Q

what is the unit of permeance

A

henry or weber/ampere-turn

56
Q

MAINS draw a comparison between a magnetic circuit and electric circuit

A

bullet points M and C

1M- MMF causes magnetic flux C- EMF causes flow of current
2 M- flux=MMF/reluctance C- current=emf/resistance
3 unit of MMF= ampere turn C- unit of emf= volt
4. M permeance=1/S C conductance (G)=1/R
5 M reluctance C resistance
6 M magnetic permeability on a constant temp depends on the total magnetic flux C- conductivity of the circuit does not depend on the intensity of the current
7. M some magnetic materials possess some amount of magnetic field even after removal of MMF C- value of current in an electric circuit becomes zero if EMF is completely removed

⭐️raj vigya (23 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions