Magnetic Fields

It is a Field ForceAP 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.

These charges create electrical fields

Charles Coulomb realized electrical force can be

calculated.

Electrical ForceF = q

AqBr2K What does this

equation look like?Gravitational Force!!

Electrical ForceF = q

AqBr2K Charge (q) is measured in coulombs!The charge on one electron is -1.60× 10-19 coulombs. This is the elementary charge!

Electrical ForceF = q

AqBr2K

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!

The Earth’s magnetic field protects us from cosmic radiation from the Sun!

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!

Where is the Earth’s Magnetic North Pole?

Electrical Flow and Magnetic Fields

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.

Solenoids

The strength of the magnetic field inside a solenoid.

𝐵=𝜇0𝑁 𝐼ℓis 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.

The Right Hand Rule

The Right Hand Rule

Magnetic Force• Electromagnets exert a magnetic force . The

direction of the force is dependent on the direction of the current.

Relating it to an Electrical Current

Force on a current carrying wire in a magnetic field.

I is the electrical current measured in amperes(A).ℓ is the length of the wire measured in meters(m).B is the magnetic field strength measured in teslas(T).T = 1N/A∙mForce is still in Newtons (N).

𝐹𝐵=𝐵 𝐼 ℓ sin𝜃

Force on a current carrying wire in a magnetic field.

Angle θ is the angle between the current and the magnetic field.𝐹𝐵=𝐵 𝐼 ℓ sin𝜃

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

q is the charge on the particle in coulombs(C).v is the velocity of the particle measured in meters per second(m/s).B is 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.

𝐹𝐵=|𝑞|𝑣 𝐵sin 𝜃

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!!

𝐹𝐵=|𝑞|𝑣 𝐵sin 𝜃

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

from the wire.

𝐵=𝜇0

2𝜋𝐼𝑟is called the magnetic permeability of a vacuum.

This was discovered by H.C. Ørsted and is often referred to as Ørsted’s Equation.𝜇0=4 π ×10−7T ·𝑚/ 𝐴

Electromagnetic Induction

Faraday’s brilliant insight!!

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.

Using a strong magnet or

solenoid we should be able

to generate electrical current.

The End!!