Electricity & Magnetism

Prof. Jennifer M. Blain Christen

BioElectric Systems and Technology

Electricity and Magnetism

Electricity to Your Home

Power Plant Transformer Transformer Homes Schools Stores

Transmission LinesDistribution Lines

What is Electricity?

Conversion of energy from other sources.

Name 5 sources of energy.

Which sources are renewable?

Where does electrical power come from?

Movement of electrons or charge

All atoms have electrons. Electrons move around the nucleus.

Some atoms like to share their electrons, some atoms don’t like to share.

Charge had units of coulombs.

What is exactly is electricity?

Electricity: Static & CurrentStatic electricity has to do with the

separation of charge.

Static electricity is the build up of charges on an object. The charges build up because they are separated by an insulator.

Insulators “resist” the flow of electrons.

Insulators & Conductors

Insulators resist the flow of electrons into and through them.

Conductors allow electrons to flow into and through them easily.

Electrons

How does the structure of an atom affect which materials are insulators and conductors?

What is exactly is electricity?

Periodic Table

Which elements do we use to make wires?

Experiment: Insulators and Conductors

Choose 5 object that you have.

This could be a pen, necklace, book, paper, etc.

Use your multimeter to check if each item is an insulator or a conductor.

Record your results for the homework.

Electrical Current

Definition: the rate of charge past a given point

The more electrons that move through a wire in a given time, the larger the current.

Current is measured in amperes or amps.

Current can only exist in a complete circuit

A complete circuit includes– Source of electrons, power supply– Something to use the electrons (one or many)– Path for the electrons

This is called a closed circuit.

If the path is broken or incomplete, it is called an open circuit.

AC/DC

I don’t mean the band!

AC/DC

AC – Alternating CurrentThis is what is generated by power plants.

The direction of the current alternates.

DC – Direct CurrentThis is what you get from a battery.

The direction of the current is the same.

SAFETY NOTICE: If you want to do experiments with electricity at home, always use a battery. This is not because they are DC supplies, but because they will limit the power.

Voltage is a potential difference.

It is measured in volts.

We can think of it like the height of a hill; only the relative difference matters.

Current flows from higher voltage to lower voltage.

Power

The amount of electrical energy used in a given time.

We measure power in Watts.

We can calculate power by multiplying current and voltage.

1 watt = 1 amp x 1 volt

Let’s review units

Coulombs, C, are units of charge.

Amps, A, are the rate of charge past a given point, so amps are coulombs per second.

Watts, W, are energy used per time or Joules per second. Watts are also Amps x Volts.

Volts, V, are a measure of potential difference. Volts are usually measure with respect to ground. Volts are watts divided by amps.

About that light bulb…

Thomas Edison…

is famous for it.

Joseph Swan… had the first patent on it, in England.

Lewis Latimer… made the first one that worked for more than a few seconds!

Electromagnetics

In the early 1831 Michael Faraday put a magnet in a coil of wire and measured the current.

Let’s try it!

Is the current we observe AC or DC?

Generators

Power plants use the same principle to generate the power that we use everyday.

They generate an AC current that changes direction 120 times per second or 60 complete cycles per second. We call this 60 Hertz.

Generator

We are going to make generators today.

You will work in groups and follow the instructions given in the handout.

I have also included the parts list, so you can make one at home with your parents or siblings.