Chapter 11.3

Electric Current

www.retailcanada.com/ upload/1220_A006N.jpg

D4

Explain the relationship among voltage, current and resistance in a simple series circuit.

Remember:

Stationary electrons =

Moving electrons =

Remember:

Stationary electrons = static electricity

Moving electrons = electrical current

www.fotosearch.com/ comp/ART/ART158/TOT007.jpg

commiechink.com/. ../static.gif

Circuit –

This is where electrons are moving in a closed and continuous pathway.

There are 3 components to a circuit:

1.Source of electrons

2.Pathway through which to travel

3.Source of energy “push” or “pressure” to move electrons

A

V

Battery

Wire

SwitchResistor(this can be something that uses electricity)

Parts of a circuit

Voltmeter

Ammeter

Bulb

Types of Circuits

Resistors in circuits can be connected in 2 ways

Series Parallel

V3

V1

V2

R3

R1

R2

I

I

I3I2I1

Series Circuit

Series Circuits

• The electricity in this type of circuit only has ONE PATH to follow.

• If the circuit is interrupted, the flow of electricity will STOP.

Types of Circuits

Series – resistors lie along a single pathway in the circuit. Amount of current is the same anywhere in the circuit. (same amount of current to do work; work done at the resistors) Resistance is additive. All resistors are affected.

V3

V1

V2

R3

R1

R2

I

Req = R1 + R2 + R3 etc….. Req – resistance equivalent

If resistors are added, all lights would get dimmer.

If resistors were taken away all lights would get brighter.

What would happen if 1 light burnt out? Hint: Each resistor acts like a switch

Parallel Circuit

Parallel Circuits

• The flow of electricity has MORE THAN ONE path to follow.

• If the flow of electricity is disrupted, the electricity may be able to find another pathway

Types of Circuits

Parallel- current flows through many pathways & resistors lie on different pathways. Each pathway only draws the current it needs, the current is split, but the voltage is the same through out.

I

I3I2I1

Sources of energy for electrical current

•Electrochemical Cells – aka “Batteries”

Chemical reactions can be transformed into electrical energy

Chemical Energy Electrical Energy

Wet Cells e.g. car battery

Electrodes – plates made out of: lead (Negative electrode) and

lead oxide (Positive electrode)

Liquid Conductor (Electrolyte Solution) Electrodes are immersed in electrolyte Sulfuric Acid.

www.tiscali.co.uk/.../ images/c00011.jpg

Chemical reaction between lead, lead oxide, and sulfuric acid

release e-s

www.tiscali.co.uk/.../ images/c00011.jpg

Electrons move from negative lead electrode to positive lead oxide electrode

through the sulfuric acid electrolyte

Dry Cells - similar to wet cells, but electrolyte is “Dry” (not water)

e.g. Zinc electrode

Carbon electrode

Ammonium chloride electrolyte

Wires are connected to electrodes to conduct electrons “from” and “back to”

the battery.

www.discovery.panasonic.co.jp/.../ a05_img01.gif

Types of Current

DC – Direct Current, electrons flow in one direction

AC – Alternating Current, electrons flow in one direction first, then in the opposite direction

American homes use AC electricity that changes directions

120 times per second

Current – rate at which electric charge flows through the wire.

Measured by counting the number of electrons passing by a specific point in the circuit in one second.

Current Symbol - Measured in amperes (amps) Amperes Symbol - A

Voltage – amount of electric energy available by potential difference to move electrons.

More Voltage = More Work

Remember (w = f d)

Voltage Symbol - V

Measured in volts - V

Resistance – force opposing the flow of electrons in the current

Good conductors = low resistance

Poor conductors = high resistance

Resistance

Long wires > Short wires

Thin wires > Thick wires

Hot wires > Cool wires

> Means greater

than

Resistance symbol – R

Measured in ohms

Ohms Symbol - (Greek letter omega)

home.att.net/ ~basicelectronics/ohmchart.gif

Born: 16 March 1789 in Erlangen, Bavaria (now Germany)Died: 6 July 1854 in Munich, Bavaria, Germany

http://www-groups.dcs.st-and.ac.uk/~history/Mathematicians/Ohm.html

Power Equation

• P = I × V

• Power (watts) = current (A) x voltage (V)

• Watts is the information that you typically associate with a light bulb

Ohm’s Law

I = V/R

V = R

R = V /

I = current

V= voltage

R= resistance

Remember Ohm’s Law V = IR

For a series circuit, since the current is the same throughout the circuit,

then:

V = V1 + V2 + V3 + etc….

V = IR1 + IR2 + IR3 + etc..

V = IReq

Req = R1 + R2 + R3 + etc…

(Req = Resistance equivalent)

I

V

R

V1

V2

V3

R1

R2

R3

- +

V = 12vI

R1

R2

R3

Type of circuit ___________

Req =

I =

R1 = 50

R2 = 100

R3 = 40

- +

V = 12vI

R1

R2

R3

Type of circuit = Series

Req = R1 + R2 + R3

= 50 + 100 + 40

= 190

I = V / Req

= 12v / 190

= 0.063 A R1 = 50

R2 = 100

R3 = 40

Homework

• Read text pp.593-607

• Complete SR pg. 607 #1-4, and 6