Electromagnetism

A study of the relationship between magnets & electricity.

Electricity

• Electricity is the movement of electrons.

• Electricity can be one of 2 types.

– 1) Static

– 2)Current

Static Electricity• - If you rub your feet on carpet and touch a

doorknob, it will shock you. This is called static electricity. (an accumulation of electrical charges made by gaining or losing electrons).

• Static electricity was discovered and tested by Thales, a Greek who lived in 600 BC. He observed and noted what happened when amber was rubbed with wool.

• In 1570 English scientist William Gilbert named it electricity after the Greek word for amber elektron

• Electrical Charge -- a concentration of electricity. This is caused by having either a concentration of protons (+) or electrons (-).

• Unlike Charges -- Charges which are different -- one (+) and one (-)

– Unlike charges attract.• Like Charges -- Charges which are the

same -- Either both (+) or both (-) Like charges repel.

• **REMEMBER from our study on atoms that objects want to be neutral.

Thales (left) & William Gilbert (right)

Current Electricity• Lightning produces light. • Is light from a light bulb produced the

same way? No!! • Lightning is caused by negative (-)

charges in clouds that are attracted to positive (+) on the ground or in other clouds (static).

• A light bulb needs a continuous flow of electricity.

• It takes energy to separate the charges. You can provide electrical energy by rubbing some materials together. However, electrical energy can be better generated and stored for later use with a battery or other item.

• Current – how much electrical charge flows past a point in a given time is acurrent. (– Current is measured in Amperes (A)

also known as amps)– Current = Charge(Q) divided by

time(t) or Q/t

Circuits• Circuit -- A complete and closed path

through which a charge can flow • 2 types of circuits

– 1) Series circuit (any break causes electricity to stop flowing/ Christmas tree lights)

– 2) Parallel circuit (a break only causes part of circuit not to work/ most houses are parallel)

• Circuit Requirements– a source of potential difference

( something to separate charges/a battery or generator)

– a conducting path (wire)– resistance (something

to slow charges down or convert electricity to another energy form/ a light bulb heating unit or motor).

Ohm’s Law

*I is the current, measured in amperes

*V is the potential difference measured in volts

• *R is the resistance measured in ohms

Formula for Ohm’s Law

Magnetism• Magnetism is a force.• One end of a magnet points

North & the other points South. These 2 ends of a magnet are called magnetic poles. (North magnetic pole or South magnetic pole.)

• Similar to electrical charges, magnetic poles of 2 magnets can have like poles & unlike poles.– *Like poles (2 North poles or

2 South poles) repel.– **Unlike poles (1 North & 1

South) attract.***If you break a magnet into

smaller pieces, all the pieces are a complete magnet each with their own North & South poles.

Unlike poles -attract

Like poles- repel

What causes magnetism?• Every atom has a tiny

magnetic field around it caused by the spinning of electrons

• . Metallic atoms have stronger magnetic fields because most of their electrons spin the same way.

• You can align the magnetic fields of several atoms and create a domain.

• *****If an object has all of its domains in line & working together it has induced magnetism & is now a magnet.

Domains of an unmagnetized object

Domains of a magnetized object

How do you make a magnet?

• Ways to align domains or ways to induce magnetism– 1.Introduce object to an

existing magnetic field. (Rub it on a magnet).

– 2.Run an electrical current through it.

– 3. Heat it. (Rare)– 4. Strike it so as to align

domains. (Very rare)

Magnetism History• Lodestone = Magnetite

– a naturally found magnetic rock named after Magnesia a region of Europe (Greece) the rock was found in.

• Magnets were originally associated with sorcery.

• Many still believe in their healing ability.

Magnetic Fields

• A magnetic field is a region around a magnet in which a magnetic force acts.

• The Earth has a magnetic field around it called the magnetosphere with layers that keep out radiation called the Van Allen radiation belts. The magnetosphere is caused by the Earth’s core being made of iron & nickel.

Above: A magnetic field shown with iron filings around a bar magnetBelow: the magnetosphere

Electromagnetism

• Electromagnet- a magnet produced by passing a current through a coil of wire wrapped around a metal core.

• Electromagnets can be turned on & off, but are usually stronger than permanent magnets.Current (I) through a wire produces a

magnetic field (B). The field is oriented according to the right-hand rule.

Effects of Magnets on Electricity

• A magnetic field has no effect on a static charge, but it does exert a force on the wire that carries a current. The force is at a right angle (900) to the direction of the current flow.

• ******The right hand rule lets you see the relationship between the current flow and the magnetic force.

Effects of Magnets on Electricity (cont.)

• Electric motors – uses electromagnets to spin a material that changes electrical energy to mechanical energy (kinetic energy of moving machine parts.)– A commutator is a magnetic

device that reverses the flow of electricit9y in a motor causing the motor to spin.

• Induced current- an electrical current produced by using a magnet. (Don’t confuse this with induced magnetism).

• Electrical generator – a device that changes kinetic mechanical energy to electricity. It uses magnets to rotate a coil in a magnetic field. (the opposite of a motor)

Faraday's Magnet Induced Current

Just for Fun• Thor (Electricity)

Versus Magneto (Magnetism)