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# Magnetic Fields PowerPoint PPT Presentation

Magnetic Fields. It is a Field Force AP Physics. Electricity and Magnetism. For many years it was believed electricity and magnetism were separate and unrelated. . Ions of + and - charge. In chemistry you learned protons and electrons have charges equal in magnitude but opposite in charge.

Magnetic Fields

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## Magnetic Fields

It is a Field Force

AP Physics

### Electricity and Magnetism

• For many years it was believed electricity and magnetism were separate and unrelated.

### Ions of + and - charge

• In chemistry you learned protons and electrons have charges equal in magnitude but opposite in charge.

• Therefore atoms and molecules can have charge and areas of partial charge (δ).

• These electrical charges can attract (if opposite) or repel (if the same) one another.

### Electrical Force

qA

qB

What does this equation look like?

F

=

K

r2

Gravitational Force!!

### Electrical Force

qA

qB

Charge (q) is measured in coulombs!

F

=

K

r2

The charge on one electron is -1.60× 10-19 coulombs. This is the elementary charge!

### Electrical Force

qA

qB

F

=

K

r2

qA and qB is the charges on the objects, measured in coulombs(C).

r is the distance between the objects in meters(m).

K is the constant in 9.0 × 109 N∙m2/C2.

F is force in Newtons (N)

### Magnetic Fields

• Some objects are magnetized, have North and South polar ends.

• Using iron filings, this is the magnetic field of a simple polarized piece of metal.

• Metals such as Aluminum, Nickel, Cobalt, and Neodymium readily create magnetic fields.

### The Magnetic Poles

• The poles are at opposite ends of a magnet.

• Opposite poles attract one another, like poles repel one another.

• The upper picture shows the repulsion of two like poles.

• The Earth itself also has a magnetic field, which is why compasses work!

### What Causes Magnets?

• Magnetic fields are caused by d-orbital electrons spinning in the same direction.

• The more the fields of the atoms are aligned, the stronger the magnet.

• Magnetic Fields travel from the North to South pole!

### Putting Electricity and Magnetism Together

In 1820 it was first observed that electrical current flowing through a wire caused a magnet to turn at right angles to the current.

### Electromagnetism

• Faraday concluded that as current (I) flowed through a metal it created a magnetic field around it.

• A compass always pointed at right angles to the electrical flow because it was in the magnetic field.

### Solenoids

• A coil of wire with electrical current running through it is called a solenoid.

• The magnetic field of each loop adds to the magnetic field of other loops.

• The South Pole is where current flows in.

• The North Pole is where the current flows out.

### Solenoids

• Grip a solenoid by the right hand with fingers curling in the same direction of the current.

• This way the thumb points to the north pole of the magnetic field.

### The strength of the magnetic field inside a solenoid.

is called the magnetic permeability of a vacuum.

N is the number of turns in the coil.

ℓ is the length of the solenoid.

I is the current.

### Magnetic Force

• Electromagnets exert a magnetic force . The direction of the force is dependent on the direction of the current.

### Force on a current carrying wire in a magnetic field.

Iis the electrical current measured in amperes(A).

ℓis the length of the wire measured in meters(m).

Bis the magnetic field strength measured in teslas(T).

T= 1N/A∙m

Force is still in Newtons (N).

### Force on a current carrying wire in a magnetic field.

Angle θ is the angle between the current and the magnetic field.

### Force of a magnetic field on a charged, moving particle.

qis the charge on the particle in coulombs(C).

vis the velocity of the particle measured in meters per second(m/s).

Bis the magnetic field strength measured in teslas(T).

Force is still in Newtons (N).

Angle θ is the angle between the direction of the velocity and the magnetic field.

### Force of a magnetic field on a charged, moving particle.

Why does the particle have to be charged??

Neutral particles, such as neutrons, are not deflected by magnetic fields!!

### The strength of the magnetic field around a wire with current decreases the further away from the wire.

is called the magnetic permeability of a vacuum.

This was discovered by H.C. Ørsted and is often referred to as Ørsted’s Equation.

## Electromagnetic Induction

### Electromagnetic Induction

• Oersted was the first to observe that an electric current through a wire creates an effect on a compass.

• Faraday, in order to prove a magnetic field was created by electrical current, decided to see if the reverse was true.

• Faraday was able to get a magnetic field to create an electrical current, proving electricity and magnetism were a unified force.

### Electromagnetic Induction

Moving a magnet through an electrical coil causes an electrical current to be induced!

### What was the impact??

• Electrical motors and electrical generators which power our modern world.

• Even modern electrical generators powered by nuclear or hydroelectric stations use magnets to generate electrical current.