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⭐️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

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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

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3
Q

how are the geographic and magnetic poles aligned to each other

A

geo north pole is magnetic south pole and vice versa

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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

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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

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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

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7
Q

define electromagnetism

A

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

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8
Q

when does a conductor generates magnetic field lines

A

when it is electrically charged

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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

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10
Q

what kind of current is in an electromagnet or solenoid

A

magnetic current

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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.

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12
Q

in which devices is solenoid used

A

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

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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

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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

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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

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16
Q

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

A

greater the magnitude of current, more intense the field

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17
Q

in which case magnetic flux is maximum

A

when all the magnetic lines are perpendicular to the surface

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18
Q

minimum magnetic flux scenario magnetic lines direction?

A

parallel

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19
Q

flux formula when magnetic lines are on an angle from surface

A

BAcostheta

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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

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21
Q

SI unit of magnetic flux?

A

weber

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22
Q

flux formula?

A

theta=B.A

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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
on what the current in electromagnetic induction is dependent on
the change in electromagnetic field lines as long as the electromagnetic field lines continue changing, the current continues flowing
26
what are the electromotive force produced in the coil and the produced current called in electromagnetic induction
induced electromotive force and induced current
27
3 ways in which the magnetic flux passing through a coil can be changed
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
where would the galvanometer deflect when a magnet is kept stationary near the coil
no deflection meaning no electric current
29
if the movement of magnet is faster now, would the current be less of more?
more faster the movement, more the current
30
how does the number of turns in coil affect the strength of the induced electromotive force?
as turns increase, the induced electromotive force increase
31
what are the two laws of faraday MAINS
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
what did lenz add to discoveries of faraday
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
if we move the north pole of the magnet near the coil, according to lenz law, how would the coil react?
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
lenz law explain with diagram
35
what is the process of self induction
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
number of turns are N and current I is flowing. the magnetic flux is theta. how they relate?
37
unit of self inductance?
henry
38
what is mutual inductance?
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
unit of mutual induction
same as self induction i.e. henry formula is also same the coefficient changes to M i.e. the coefficient of mututal inductance
40
what are eddy currents
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
who discovered eddy currents and when
Leon Foucalt in 1851
42
the value of eddy currents depends on which property of the conductor
resistance
43
what is the relation between eddy currents and resistance of the conductor
if resistance is high, eddy currents become weak, if resistance is less, eddy currents become stronger thus: inverse relation
44
MAINS list disadvantages of eddy currents
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
MAINS how is the eddy current forming in dynamo or electrical motor resulting in lack of efficiency solved
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
MAINS what are the applications of eddy currents
1 electromagnetic damping 2 induction motor 3 speedometer 4 energy meter 5 electric break
47
what is an electric break
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
what is magneto motive force of MMF compare it to electrical energy
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
what is the source of establishing the magnetic flux in a magnetic circuit
MMF
50
how is the MMF calculated in a magnetic circuit
MMF is equals to the product of number of turns and current MMF=NI
51
what is the unit of MMF
ampere-turn
52
what is reluctance
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
formula for magnetic reluctance
magnetic reluctance (s) = MMF/magnetic flux
54
what is permeance
the inverse of reluctance like conductivity in an electric circuit permeance=1/reluctance
55
what is the unit of permeance
henry or weber/ampere-turn
56
MAINS draw a comparison between a magnetic circuit and electric circuit
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)

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