Electricity

The flow of charges

AtomsMade up of:

Nucleus: Protons and neutrons

Electrons: negative charge orbit nucleus

CurrentFlow of electrons

Measured in Amperes (Amps)Electrons passing per second

Circuit Must have complete, unbroken

path for current to flow 3 Parts:

1. Load: device run by electricity2. Wires: path for electron flow3. Source: moves the electrons

through the wire Battery, generator, wall socket (power

plant)

A break in the circuit stops electricity from flowing

Conductors Materials allowing electrons to flow

Examples: metals: electrons loosely held, move easily

Copper is one of the best

Insulators Do not allow electricity to flow

Examples: rubber, plastic Electrons held tightly, will not move easily

Voltage Measures the force “pushing”

electrons Volt (v) as unit

Higher voltage is higher potential to push electrons through circuit

Water dam

Lower Potential energy =Low voltage

Higher Potential energy=high voltage

Resistance Force working against (“resisting”) the

flow of electrons Measured in Ohms (Ω) All parts of circuit “slows the flow”

Ohm’s Law Tells how current, voltage, resistance

are relatedCurrent = voltage

resistance

I = VR

Practice Ohm’s Law

A 9 volt battery is used to light 3 bulbs with a resistance of 0.5 Ω each. Wires and a switch add another 3 ohms of resistance. How much current (amps) is flowing through the circuit? Plan

What information is given? 9 volts, 3 bulbs x 0.5 ohms = 1.5 ohms plus 3 ohms for

total of 4.5 ohms. What formula do I use?

I = v / r I = 9 v / 4.5 Ω

Solve I = 2 amps

Check:Does it make sense? The current is less than the voltage because the

resistance is reducing the flow

Circuits and Current Direction

Series Circuit Only one path for

electricity to flow What happens if

one bulb goes out? Will the bulbs be

dimmer or brighter than a parallel?

Load (bulb)

Switch

Parallel circuit More than one path

for electricity to flow Each load on

separate circuit What happens if

one bulb goes out? Compare

series/parallel to water supply

Current Direction Current always flows in one direction:From negative to positive

AC vs. DC

Direct CurrentDC

Charges always flow in same direction, from negative terminal to positive terminal Battery (cells)

Cells and Batteries Convert chemical

energy to electrical energy Potato clock

Electron acceptor

Electron donor

anode collector

plastic sealanode

plastic sleeve

steel jacket

Case sleeve

Cell straps

Negative terminal

Positive terminalelectrolyte

cathode collector

cathode

9 Volt Battery

Other sources of DC Thermocouple: convert heat to

electricity Solar cells: convert solar energy to

electricity

Alternating CurrentAC

Charges flow from negative to positive but switch directions back and forth (alternate) House current

Producing AC current Induction: Coil of wire and magnet produce

electricity It’s electro-magnetism!

Generator: converts mechanical energy to electrical energy

Motor: converts electrical energy to mechanical energy

Electromagnetism Magnetism and Electricity are closely

related Electric current causes magnetic

fields Cell phones, television, light

Magnets can cause an electric current to flow Generators

Power Measures how fast energy is

transferred from one form to another Measured in Watts

Power = voltage x current P= V I A 100 watt light bulb changes or uses

electrical energy to light energy twice as fast as a 50 watt bulb

Brainpop on current