Current Electricity

Current Electricity

• Current Electricity is due to a charged electrical particle called an Electron.

• Two or more charges that are alike repel each other.

• Two or more charges that are opposite attract each other.

Properties of Charged Particles

Current

•The charge pump creates the FLOW of charged particles.

•This is called a CURRENT.

•Current is symbolized by the letter I.•It is measured in amperes, A.

•LIKE HEAT….

•When the ends of an electric conductor are at different electric potentials, charge flows from one end to the other.

•This means there is a potential difference, or voltage.

• The amount of work needed to move charges a certain distance is known as Voltage or Potential Difference.

Voltage• A measure of the energy

available to move electrons• The electrical potential

difference between two points • Voltage is measured like

potential energy• Voltage drops as it gets used

Voltage Sources

• Dry Cells-Batteries

• Wet Cells

• Generators

Electric Current• Direct Current Flows in 1 Direction Only• DC is produced when stored electrical

energy is tapped• Batteries and Solar Cells have this

electrical potential• Alternating Current changes direction

periodically• AC is produced by a generator

Power•A charge moving in a circuit expends energy.

•This might result in heating the circuit, or turning a motor.

•The rate at which electrical energy is converted to another form, such as mechanical, heat or light, is called Electric Power.

•Electric Power=Current x Voltage

=ampere x voltwatt = watt

P = I x V

•Example 2-A 6 volt battery delivers 0.5 A of current to an electric motor connected across its terminals. What is the power of the motor?

•What energy does the motor use in 5 minutes?

Resistance• Resistance: Measure of how

easily current flows through a circuit

-- higher resistance: harder for charge to go through

-- Low Resistance: easier for charge to go through

• Resistance increases current goes down

• Resistance decreases current goes up

• Resistance is measure in Ohm’s

• Two types of resistors--Fixed: always has the same value--Variable: value changes

Ohm’s Law• OHM’S LAW• Discovered in the 18th century• Ratio between potential difference

and the current flowing through the wire

• Law states: “the current that flows through a given wire varies directly with the applied voltage”

• Formula: I=V/R or V=IR

Ohm’s Law-Current Flow

• Symbol for ohm is (see board); 1 ohm is the resistance which permits a current of 1 A to flow between a voltage of 1

• To obtain a higher voltage, higher charge is needed; higher voltage=electric field to be more intense=more electrons to move

Effects of Various Electric Current on the Body

Current in Amps Effect

0.001 Can be felt

0.005 Painful

0.010 Muscle Spasms

0.015 Loss of Muscle Control

0.070 Fatal if longer than1 sec

Series Circuit• Current can ONLY travel in 1

path

Series Circuit-math• Formula to find “total resistance”

RT = R1 + R2 + etc

To find the current flow: use Ohm’s Law

The sum of the voltage is equal to the voltage of the entire circuit put together

Series Circuit• Series Circuit- break in the circuit, stops

the current• Resistors connected in “series”, the

current travels through EACH resistor exactly the same way

• Current encounters resistance by each resistor; opposed by the sum of the resistors; total resistance is the sum

Parallel Circuit• Current can follow many paths

Parallel Circuit• Placing resistors in parallel

always decreases the total resistance of the circuit!

• Total resistance decreases because each new resistor has a “different” path for the electrons to flow

Parallel Circuit-Math• Formula to find total resistance for a

parallel circuit:

1/RT = 1/R1 + 1/R2 + 1/R3 + etc

Total current is the “sum” of the currents in the separate branches

Voltage is equal to the voltage of the generator