Electricity and Electric Circuits

Chapter 20 -23

I. Electricity – the flow of electric current (electrons)

A. Two types of electricity:– Static Electricity– Current Electricity

Static electricity

B. Facts about electric current:

1. flow of electrons

2. flows through metals

3. Flows through liquids that have free electrons.

4. carries ENERGY.

5. powerful and dangerous.

C. Materials associated with electricity:

1. Conductors- a substance that allows heat and electricity to flow through.

– Ex: gold, copper

List of conductors from best to worst:

Conductors: silver

copper gold

aluminum iron steel brass

bronze mercury graphite

dirty water concrete

2. Insulators– a substance that does not allow heat and electricity to flow through.

Ex: glass, wood,

plastic

List of insulators

Insulators: glass

rubber oil

asphalt fiberglass porcelain ceramic quartz

(dry) cotton (dry) paper (dry) wood

plastic air

diamond pure water

II. Circuit - a pathway for electricity to travel through.

A. Parts of a circuit:

1. a battery (or energy source)

2. a resistor – anything that uses electricity (bulb)

3. a wire – creates the pathway

4. a switch – to turn on and off

B. Electric symbols:

• Wire-

• Battery-

• Resistor-

• Bulb-

• Switch-

C. Batteries -A battery produces an electrical current

from chemical Energy

Chemical reactions occurring in the battery produces free electron-’s to create an electric current

There are 2 types of batteries:

1. dry cell – A, AA, C, D batteries (1.5V)

2. wet cell – car batteries

D. Examples of complete circuits:

1. a blender plugged into the wall and

turned on

2. lightning – (clouds, ground and

lightning)

3. nerves in your body (are transmitting

an electrical message)

E. Types of circuits

1. Open circuit – a circuit when the switch is open and current doesn’t flow; device is OFF.

2. Closed circuit – switch is closed allowing current to flow; device is ON.

3. Series circuit – a circuit in which the electricity can take only one path.

• ex: Christmas tree lights: when one goes off, they all go off.

• ***The total current gets divided among all resistors.***

4. Parallel circuit - a circuit in which the electricity can take more than one pathway.

ex: most household circuits (when one is off, the others stay on)

**All resistors receive the full amount of current.

Identify this circuit

Identify this circuit

Identify this circuit

IV. History of Electricity

A. Michael Faraday – discovered the principle of the electric motor in 1820.

B. Thomas Edison – invented the electric light bulb in 1879

C. Benjamin Franklin – studied electricity

Thomas Edison

Michael Faraday

Benjamin Franklin

V. Charge – (electric charge)the source of shock and sparks; fundamental property of matter

A. Types of charges:1. Negative charges- comes from electrons

2. Positive charges – comes from protons

3. Neutral charges – comes from the neutrons; when the number of protons = the number of electrons

Build up of charges

B. Laws of attraction:

1. opposites ATTRACT (+ -)

2. likes REPEL (+ +), (- -)

C. Static electricity- a build up of positive and negative charges.

ex. Noticeable in winter when humidity is low…like when you are wearing slippers and you touch a doorknob…you get shocked

- getting laundry out of the dryer

- Lightning is static electricity

D. COULOMB – (C) unit of electric charge

named in honor of Charles- Augustin

de Coulomb, a french physicist

An attractive force – the attractive force between one proton and one electron is 9,000,000,000 N that are one meter apart. (2,000,000,000 lbs.)

VI. An Electroscope – a device used to detect

charged objects.

An electroscope has 2 light leaves that hang down.

The leaves attract or repel each other depending on the nearby charge.

By watching the leaves you can tell what kind of charges are near and roughly how strong they are.

The more complex the electroscope, the more exact you can measure the charge.

VII. Voltage – potential difference;the amount of potential energythat unit of electricity has.

A. Voltage drops when energy is used

B. Battery is a device that uses chemical energy to move charges.

C. Moving charges = electricity

D. Every point in a circuit connected to the same wire is at the same voltage.

E. Volt- unit of voltage

F. Joules – unit of work and energy

G. A, AA, AAA, C, D battery ALL have 1.5 volts

H. Square batt with plugs at top = 9V

I. Car battery – 12V battery = each charge that flows carries 12 joules of energy.

J. Rechargeable batt – cell phone, cordless phone (nickel-cadmium)

VIII. Current- the flow of electric charges

A. Amperes- unit of current (amps); one amp is the flow of one coulomb per second.

B. Resistance- the property of a substance that determines how much current will flow. Resistance is equal to voltage divided by current

C. Resistance – (unit = Ohms) 1. Low resistance is necessary for TV’s,

radios, VCR, etc. You do not want to lose energy in the form of heat.

2. Losing energy in the form of heat can be a hazardous situation. A fire could start.

3. High resistance is necessary for devices that are intended to get hot: toaster, iron, oven, stove, curling iron, hairdryer, hot water heater, space heater, light bulb.

D.Ohm’s Law

• I – current (amps)

• V- voltage (volts)

• R – resistance (Ohms)

• Current = voltage

resistance

I = V

R

E. Types of current:

1. AC current – alternating current; the direction of the current changes back and forth 60 times every second.

*Your house has AC current

*Your house has a ground wire b/c current can flow in or out of the wire. The ground wire prevents the current from going through you by sending the current to the ground.

• 2. DC current – direct current; the current does not change direction. Any current from a battery is direct current.