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Physics > Magnetism | 9 > Flashcards

Magnetism | 9 Flashcards

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1
Q

Properties of Magnets

A

2 ends of the magnet are called 2 poles

They are North pole (North seeking pole)
And South pole (South seeking pole)

Like poles repel (N-N repel, S-S repel)
Unlike poles attract (N-S attract)

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2
Q

How to identify Magnet sides

A

A freely suspended magnet (magnet tied
to a string) will have one end pointing in
Northern direction. This is called the
north pole (N)

See how it behaves next to a labeled magnet

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3
Q

Magnet Material

A

Material can get attracted to a magnet
Material can be made into a magnet

Examples: Iron, Cobalt, Nickel, alloys
like Steel, Alnico etc.

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4
Q

Hard Magnets

A

Can be made into a magnet
(magnetized)
Retains its magnetism permanently
Used for making permanent magnets
Example – Steel

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5
Q

Soft Magnets

A

Can be made into a magnet
(magnetized)
Retains its magnetism only for a short
time.
Used for making temporary magnets

Example – Iron

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6
Q

Where does magnetism come from

A

Electrons in an atom carry negative
charge, and also orbit the positve nucleus.

This gives the atom a tiny magnetic
property.

So, every atom behaves like a tiny
magnet, called DOMAIN.

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7
Q

How to Magnetize magnets

A

Attaching the material to a magnet

Stroking the material in the same
direction on a magnet

By passing current through a wire
(electromagnets) – we will learn this later.

All of this unifies the directions of the domain in the magnet , making it magnetic

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8
Q

De - magnetizing magnets

A

Hitting / hammering the magnet repeatedly

Dropping the magnet from a height

Heating it to a high temperature

All the above actions disturb the domain
arrangement, causing the magnet to lose its
property.

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9
Q

Earth’s magnetic field

A

The earth behaves likes a huge, but weak bar magnet.

Studies show that it is because of the iron core and movement of charges in it.

The magnetic south pole in the compass gets attracted to the geographic north pole

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10
Q

Magnetic Field

A

The region around a magnet till which it’s force of attraction or repulsion can be felt.

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11
Q

Magnetic field lines of force

A

We know that any force can be represented as a line with an arrow.
Likewise, magnetic force can also be represented using arrows.

Are semi-circular (roughly) in shape

Always point from N pole to S pole

Never intersect (criss cross)

Crowded near poles, spaced out at the middle

Strong magnets – more lines of force, weak
magnets – less lines of force.

Strong magnets – large field, weak magnets - small field.

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12
Q

Magnetic effect of electric current

A

When current flows through a wire, it creates a magnetic field around it.

Concentric circles

Closer near the wire and spaced out as we move far away

Right hand grip rule

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13
Q

Factors affecting magnetic field

A

Current / Voltage

Length / Area of wire

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14
Q

Solenoid

A

coil of wire , has magnetic field around it

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15
Q

How to find north and south pole of a solenoid

A

Imagine that you hold the coil with your right hand.

Your fingers should point in the direction of
current in the side of the coil you face.

The position of thumb gives the N-pole, the other end is the S-pole.

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16
Q

Making a electromagnet

A

By placing a nail (called the core) inside the
solenoid, the nail can become a magnet.

This is called an Electromagnet.

It can be stronger by:

Increasing current / voltage

Increasing number of turns in solenoid

(eg. Dump yard crane , miniature circuit breaker , MRI scan)

17
Q

Advantages of electromagnet

A

Magnetism can be turned on / off ( put magnet in a.c solenoid and it’s magnetism will get shuffled)

We can decide the strength of the magnet.

Cheaper

18
Q

Magnetic relay

A

A relay is a switch in a low power circuit that
is used to turn on a high power circuit.

Used to ensure safety for operators.

19
Q

Thrust

A

Thrust on the wire in between magnetic field - causing wire to move

20
Q

How do you find out the direction of the thrust

A

Using Fleming’s left hand rule.

Place three fingers (Thumb, forefinger, and second finger) of your left hand mutually perpendicular to each other

Forefinger – should point in Field direction
second finger – should point in the direction of Current (in this case towards you / out of paper)

Then…
Thumb – points out the thrust (movement)
direction on the wire.

21
Q

Thrust factors

A

Can be increased by

Increasing strength of magnetic field

Increasing current

Increasing area of wire

(no thrust if wire is along the magnetic field)

22
Q

What causes thrust

A

The wire carrying current has a circular
magnetic field around it.

This magnetic field interferes with the
magnetic field from pole pieces.

This interference causes the lines of force to
realign, thereby pushing the wire.

23
Q

Rotational effect on a coil

A

When a coil is left on a magnetic force field , it flips over , turning Electrical energy to kinectic enery

Similar to a motor

this is not useful as it does not give us a uniform turning motion

24
Q

How to make motor power by electricity

A

the battery rotates with the coil.
This causes the current direction to flip in the left and right arms, causing the motor rotation to flip.
If we can isolate the battery from the coil, this problem can be solved.
To do that, we introduce 2 components – split ring commutators, and carbon brushes

25
Q

In the motor which parts move and which parts dont

A

parts move
Coil and split ring commutator

parts do not move
Magnet pole pieces, carbon brushes, battery

26
Q

Split ring commutator

A

Looks like a ring split into 2 parts.

Rotates along with the coil

Isolates the battery from the rest of the circuit.

Ensures that left side of the coil and right side of the coil always carry current in the same direction

Ensures uniform direction of rotation in motor.

27
Q

Carbon brushes

A

Establishes contact between the coil and the
commutator.

28
Q

Electromagnetic induction

A

When a wire is moved inside a magnetic field, the wire cuts the magnetic field lines.

This causes a voltage (called induced emf) to be produced.

If this wire is part of a complete circuit, the
induced emf will cause a current to flow.

This is called induced current.

The whole phenomenon is called Electromagnetic induction.

29
Q

How do we find the direction and magnitude of the induced current?

A

Fleming’s right hand rule

Forefinger – Field
Thumb – Thrust
second finger – induced Current

The value and direction of induced current is measured using a Galvanometer (Centre-zero ammeter + can measure current both sides).

30
Q

What can increase the induced emf and current?

A

Stronger magnetic field

Faster movement of wire

More area / length of wire / windings (coil)

31
Q

Lenz law

A

The induced current always opposes the
movement of the coil

32
Q
A

Physics (9 decks)

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