week 2: magnetism

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Introduction to Magnetism

SCIENCES 9

Transformers

Oersted's Experiment

Magnetic Fields

Magnets

Outline

What is

Magnetism

MAGNETISM

-Magnetism is the properties and interactions of magnets - The earliest magnets were found naturally in the mineral magnetite which is abundant the rock-type lodestone. These magnets were used by the ancient peoples as compasses to guide sailing vessels. Magnets produce magnetic forces and have magnetic field lines

Electricity and Magnetism – how are they related?

What is

MAgnet

MAGNETS

A. Magnets have two poles (ends) 1. North pole 2. South pole A magnet will attempt to line itself up with the magnetic field of the Earth

Wand Magnet

Disc Magnet

Ring Magnet

Rod Magnet

Horseshoe Magnet

Types of Magnets

Bar Magnet

1. Unmagnetized iron can be magnetized by placing it near a strong permanent magnet or stroking it with a magnet 2. Process is reversible with heat or hammering

Permanent magnets

Magnetic material properties

Diamagnetic

A groups of objects that can't be attracted by a magnet Ex: silver, gold, copper, bismuth

Paramagnetic

A group of objects that are weakly attracted by a magnet Ex: magnesium, molybdenum, and lithium

Ferromagnetic

A group of objects that can be strongly attracted by a magnet. Ex: iron, steel, nickel, and cobalt

MAGNETS

Magnetic material is classified by how it retains its magnetism a. Soft – easy magnetized, but easily lose the magnetism b. Hard – not easily magnetized, but once magnetized retain magnetism

• 1. Like poles repel (south-south, or north-north)
• 2. Opposite poles attract (south-north)

Magnetic forces

Magnetic poles always occur in pairs 1. Magnetic poles can never be isolated 2. If you break a magnet, each piece will have a north and a south pole

Magnet Force VS Electric Force

ELECTRIC FORCE

the interaction between electric charges

Magnetic Force

the interaction between magnetic poles

THE EXPERIMENTAL JAPANESE MAGLEV TRAIN USES MAGNETIC FORCES FOR BOTH SUPPORT AND PROPULSION.

JAPANESE MAGLEV TRAIN

- A region in which a magnetic force can be detected - Direction of a magnetic field is the direction in which the north pole of a compass needle points at that location - Magnitude of the field is higher closer to the pole

MAGNETIC FIELDS

Earth’s field is like a bar magnet buried in the Earth - Convection current in Earth’s liquid iron outer core are the source of the field - Related to planet rotation.

Magnetic declination – difference between compass pointing at magnetic north and true / geographic north

True North vs. Magnetic North

Earth's magnetic field serves to protect Earth's inhabitants from cosmic radiation that can endanger health

Earth's magnetic field

Magnetotactic bacteria

Whale

Spiny Lobster Migration

Turtle Migration

Salmon Migration

The Application of the earth's magnetic field for animal migration

Bird Migration

Technological applications of magnetism

1. Large electromagnets used to pick up heavy loads 2. Magnets used in meters, motors, loudspeakers 3. Magnetic tapes used in audio and video recording, and computer disks 4. Regulation of controlled nuclear fusion research 5. Maglev trains

Hans Christian Oersted (1777-1851)

Hans Christian Oersted discovered in 1820 that an electric current near a compass causes the compass needle to be deflected. Oersted's experiment showed that every electric current has a magnetic field surrounding it.

Oersted’s Experiment

• According to the right-hand rule, the electron current in a wire and the magnetic field it generates are perpendicular to each other

Oersted’s Experiment

An electromagnet can be used to move large quantities of metal. When the current is on the magnet will pick up the metal. When you want to drop it you turn off the power and the electromagnet is disabled and the metal drops.

ELECTROMAGNETS

ELECTROMAGNETS

An electromagnet consists of an iron core placed inside a wire coil. The magnetic field strength of a wire coil carrying an electric current increases in direct proportion to the number of turns of the coil.

Do YOU KNOW THIS?

Magneto

Transformers

A transformer is a device composed of two unconnected coils, usually wrapped around a soft iron core, that can increase or decrease the voltage of ac current.

TRANFORMERS

A moving coil activated by voice vibrations is used as a microphone. The coil induces a current in the magnet that can be amplified or recorded.

A transformer is used to step the voltage down and the current up (P=IV) so that we can use it. Low power is desired for the transport of electricity long distances to avoid loss of energy to heat loss. Transformers must use AC current.

TRANSFORMERS

Answer:

Example 1

A voltage transformer has 1500 turns of wire on its primary coil and 500 turns of wire for its secondary coil. What will be the turns ratio (TR) of the transformer.

Answer:

Example 2

If 240 volts rms is applied to the primary winding of the same transformer above, what will be the resulting secondary no load voltage

Answer:

Example 3

If 240 volts rms is applied to the primary winding of the same transformer above, what will be the resulting secondary no load voltage

TRANSFORMER EFFICIENCY

LET'S PRACTICE

TRANSFORMER CALCULATION

THANKS!