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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.

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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.


These charges create electrical fields


Charles Coulomb realized electrical force can be calculated.


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!


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.

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.


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.

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

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!!


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