The Earth’s magnetic field is caused by movements in Earth’s outer core

The Earth’s magnetic field shield us from the stream of charged particles from the Sun called the solar wind

Magnetic north (actually the location of the south pole of the magnet) is in Hudson Bay some 1300 km from geographic north. It has moved about 700 km since 1904!!

Moving Charges Produce Magnetic Fields

Magnetic Materials

Magnetic Materials Ferromagnetic materials (ferrum – iron) have strong magnetic properties. Loadstone contains magnetite which contains iron.

Magnetite is an oxide of iron and has the composition Fe3O4.

Magnetizing Materials Magnetic Domains become aligned in External Magnetic Field.

B

Magnets • a magnet is electrically neutral • a magnet has two poles: north & south • like poles repel • unlike poles attract • No Magnetic Monopoles!

Smallest Magnet: Electron

Atomic Sources of Magnetic Fields

B: The Magnetic Field Magnetic Field Lines point from North (+) to South (-) The denser the field lines, the stronger the force.

Magnetic Compass

North seeking compass points to Earth’s Magnetic North which is really a South Pole. A compass’ arrow head is the north pole.

Use a compass to map out the field lines.

How does a compass work?

A compass is a small magnet.

Outside Field lines point from North to South.

A compass is a small magnet.

Inside the Magnet, the Field points from South to North.

Which way will the magnetic rotate? N N

S

S

External B Field

Like Poles repel, Unlike Poles Attract.

Which way will the magnetic rotate?

S

N

S

N

External B Field Magnets align themselves so that their internal field is aligned with the external B field.

Some typical B fields: surface of the Earth small bar magnet MRI magnet lab surface of neutron star

10-4 T 10-2 T 2-3 T 30 T 108 T

Currents Produce Magnetic Fields

Currents Produce Magnetic Fields

Electromagnets: Making Magnetic Fields with Electricity Multiple wraps of a wire is a solenoid. It produces a strong magnetic field inside the coil.

Magnetic Force A charged particle moving in an EXTERNAL magnetic field experiences a force that is perpendicular to both the velocity and field. Only the perpendicular components give rise to a force.

Electric & Magnetic Force The Electric Force acts parallel to the Electric Field. (Electric Field goes from + to -)

The Magnetic Force acts perpendicular to the Magnetic Field and the velocity. (Magnetic Field goes from N to S)

Cathode Ray Tube Electric Force makes the Electron gun. Magnetic Force directs the beam.

Cathode TV has 3 electron guns, one for each color RGB which scan 525 times in 1/30 of a second.

Magnetic Force: Centripetal Force The magnetic force is perpendicular to BOTH the velocity of the charged particle and the magnetic field, producing circular motion!

F F E

Magnetic Force The Mass Spectrometer The mass spectrometer is a very important instrument which can measure the masses and relative concentrations of atoms and molecules.

Question: Three particles with the same charge move through a constant Magnetic Field. Which particle has the greatest mass? Least mass?

1>3>2

Charged Particle in a Magnetic Field Magnetic Force: Centripetal Force

Earth’s Magnetic Field

Auroras

The colors are caused by energetic electrons colliding with oxygen and nitrogen molecules in the atmosphere. This excites the molecules, and when they decay from the excited states they emit the light that we see in the aurora.

Aurora surrounding the north geomagnetic pole as seen from space

Aurora as seen from space

Motors & Generators Inverse Effects! Motor Effect

Magnetic Force on Moving Charges in Loop: Motor Effect

Generator Effect

Magnetic Field Changing through Loop: Generator Effect

The Motor Effect An electric current in a magnetic field experiences a force that is perpendicular to both the direction of current and the direction of the field. If that current is bent into the shape of a loop, the magnetic force produces a torque that causes the loop to rotate. This is the basis of The Motor Effect.

The Motor Effect: Meters Galvanometer: measuring currents and voltage

Electromagnetic Induction A Changing Magnetic Flux Induces a Voltage & Current in a Coil

The greater the number of turns, the greater the voltage. The faster the CHANGE in flux the greater the voltage.

?Magnetic Flux? Flux: how much Magnetic Field flows through loop. B

Maximum Flux θ=0

Minimum Flux θ = 90

Maximum Flux θ = 180

Electromagnetic Induction The Generator Effect A magnet moving in a stationary coil induces a voltage and current.

You could also move the coil in a stationary magnet instead! This will also generate an ac current.This is the basis of an ac generator!

Electromagnetic Induction The Generator Effect A changing magnetic flux induces a voltage and an ac current. In the US the ac current has a frequency of 60 hertz.

Question: If the current is going on and off, why don’t we see the lights flicker?

Sources of Electrical Energy

One of these is not like the others? One of these things doesn’t belong! Which one and why? Solar doesn’t use a EM induction!!

Polluting Power Production: Coal, Nuclear, Oil or Gas It all comes down to making HOT WATER & STEAM to turn a turbine!

The Power Grid

Typical power plant can generate MegaWatts of Energy. US consumption of electricity is 90 Quadrillion BTUs/year. 1 quad = 1015 Btu = 2.931 x 1011 kW-hrs Hetch Hetchy: 2 billion kW-hrs per year Wind in CA: 4.5 million kW-hrs per year

Power Transmission: Transformers Step up Voltage & Step Down Current to reduce Power loss due to heat loss from resistance in the wires.

Transformers: Change the Voltage 9V Battery Recharger Step Down Decrease Voltage Increase Current

Step UP Increase Voltage Decrease Current

120V

15,000 V

Transformers: Auto Ignition Converting 12V to 40,000V

EM Inductance:Transformers The AC current is changing in Coil 1, producing a changing Magnetic Flux in Coil 2, which induces a voltage and current. Since Coil 2 has fewer wraps than Coil 1 it will have a smaller Voltage than Coil 1. Primary Voltage Secondary Voltage = Number of Primary Turns Number of Secondary Turns

EM Inductance:Transformers Primary Voltage Secondary Voltage = Number of Primary Turns Number of Secondary Turns If 100 V of dc are put across a 100-turn transformer primary, what will be the voltage output if the secondary has 200 turns? a) 200 V b) 100 V c) 50 V It has to be AC current to work so there is a changing magnetic flux through the coil!!! d) 0V If 100 V of ac are put across a 100-turn transformer primary, what will be the voltage output if the secondary has 200 turns? a) 200 V N2 200 V2 = xV1 = b) 100 V x100V = 200V N1 100 c) 50 V d) 0V

Motors & Generators Inverse Effects! Motor Effect

Magnetic Force on Moving Charges in Loop: Motor Effect

Generator Effect

Magnetic Field Changing through Loop: Generator Effect