6.3.1 Magnetic Fields

What causes magnetic fields

Permanent Magnets
Moving Charges- Electric current

Where do magnetic field lines go from

North to South AND they NEVER OVERLAP

What does the arrow represent

Direction at which a free north pole would move

Equally spaced Parallel lines indicate what?

Uniform field

What is the rule for attraction/repulsion

Opposite Attract!

Can one pole exist alone?

No. Either two poles or no poles. Magnetic poles always exist in pairs; a single pole cannot be isolated.

Natural magnetic Elements are

Iron Cobalt and Nickel

What are two methods of showing the magnetic field around a bar magnet

1- Using iron filings
2- Using small compasses

How can iron filings be used to show magnetic field around a bar magnet

1- Place the magnet
2- Place a piece of paper on top of the magnet
3- Sprinkle iron filings on the paper and gently tap it. The filings will align along the magnetic field lines, visually representing the field.

What is a disadvantage of using iron filings

They do not represent the direction of the magnetic field lines

How can we identify magnetic field using compasses

1- Place the compass around a bar magnet
2- Draw a dot at which the North pole of the compass points
3- Continue by placing the compass at the same point
4- Draw an arrow where the North pole pointed

How does the magnetic field strength vary around the bar magnet

It decreases further from the pole. The spacing between the field lines increases, showing a weaker field strength

Is copper magnetic

NO!

Why does a needle on a compass deflect near a current carrying wire

Electrons move producing a change in the electric field which generates a magnetic field that interacts with the needle causing it to deflect . This can be explained by the right hand rule

How to represent current/ magnetic field going into and out of the page

How to represent the magnetic field pattern around a coil of wire attached to a battery

What is a solenoid

a current-carrying coil of wire

Why does the strength of the magnetic field around a current-carrying wire increase when the wire is made into a solenoid

Magnetic field adds up because they point in the same direction making a stronger magnetic field.
So,
Field line concentration increases and the field superpose

How does the strength of the magnetic field vary around the solenoid? Inside and Outside

Inside:

-The field is uniform(represented by equidistance field lines)

-Strong: the magnetic field created by each turn is concentrated and aligned in the same direction
Outside:
- Non-uniform
- Weak: It gets weaker further from the solenoid

What Fleming’s Left-Hand Rule

thuMb- Motion
First finger- Field

seCond finger- Current

What is magnetic flux density

the amount of magnetic flux passing through a unit area that is perpendicular to the direction of the magnetic field.
it is a vector quantity

How to calculate the force on a current-carrying conductor

F=BILsin(theta)

F- force (N)

B-magnetic flux density (Tesla-T)

I-current (A)
L- length of wire ( m)

What happens when a wire cuts a magnetic field at 90 degrees

The force is at its maximum. Sin(90)=1

What happens to the magnitude of the magnetic field when the wire is not perpendicular to the field

When the wire is rotated, component of current perpendicular to the field decreases so magnetic force decreases

How to determine the uniform magnetic flux density between the poles of a magnet using a current carrying wire and digital balance

• Place the magnet on a digital balance

• Place inflexible wire between the magnets

• Calibrate the balance and zero it before turning on the current

• Close the switch to allow current to flow

• The wire will be pushed by the magnet according to Fleming’s Left Hand Rule

• The wire exerts an equal and opposite force on the magnets ( Newton’s 3rd law)

• This will show a reading on the balance

What happens to the reading if the wire is at an angle

• The component of current perpendicular to the magnetic field decreases

• Magnetic force decreases

• The reading on the balance decreases