ELECTRICITY NOTES

ELECTRICITY

• ELECTRICITY: form of energy that occurs when electrons move from place to place

• Electricity can form whenever (e-) electrons are gained or lost

• All substances are made up of ATOMS which contain electrically charged particles called PROTONS and ELECTRONS

• PROTONS have a positive (+) charge

• ELECTRONS have a negative (-) charge

• How can neutral substances become electrically charged?– When a neutral object slides past

another object and picks up extra e-

– An object with more protons has a + charge

– An object with more electrons has a - charge

STATIC ELECTRICITY

• STATIC ELECTRICITY is a buildup of electrons on an object

• CONDUCTORS: allow electrons to pass through easily– Examples: METALS, WATER

• INSULATORS: do NOT allow electrons to pass through easily– Examples: NONMETALS

When 2 objects are rubbed together they become CHARGED

Objects with like charges REPEL

Objects with opposite charges ATTRACT

INDUCTION

• INDUCTION occurs when a neutral object becomes charged by holding a charged object close to it (NOT touching)

How is Earth’s Surface Charged by Induction?

An ELECTROSCOPE is a devise that detects electric charge. A metal knob is connected to 2 metal leaves. When a charged object touches the knob, the leaves SEPARATE

GROUNDING

• GROUNDING: touching a charged object to the ground to remove extra charges

Moving charges produce CURRENT ELECTRICITY which flows along a path called a CIRCUIT.

Current that only flows in one direction is called DIRECT CURRENT (battery powered).

Current that reverse its direction constantly is called ALTERNATING CURRENT (AC) (power company)

ELECTRIC CURRENT(I)

• THE FLOW OF e- (how many are flowing through each second)

• Units: AMPERES (A)1 AMPERE = 6.25 X1018 e- EACH

SECOND

ELECTRIC CELL

• An ELECTRIC CELL is a devise that converts chemical energy into electrical energy. 2 or more electric cells combined make up a BATTERY.

• An electric cell contains two different substances called ELECTRODES. The electrodes are places in a conducting mixture called an ELECTROLYTE. Chemical reactions take place between the ELECTRODES and the ELECTROLYTE.

• Wet Cell: a battery with a liquid electrolyte…acid (car battery)

• Dry Cell: battery whose electrolyte is a paste instead of a liquid (AA, C, D batteries, etc)

• Anode: - end of battery where e- leave the battery

• Cathode: + end of battery where e- return to the battery

• VOLTAGE (V) also called POTENTIAL DIFFERENCE. It is the difference between one end of the power source and the other end.– Units: VOLTS (V)

RESISTANCE (R)

• RESISTANCE is the opposition to electron flow. Conductors have LOW resistance. Insulators have HIGH resistance.– Units: Ohms Ω

• Resistance depends on TEMPERATURE, DIAMETER, LENGTH, METVAL vs. NONMETAL

Ohms Law

V = IR

voltage = current x resistance

The filament in a light bulb uses a current of 0.5 A when the voltage is 120V. What is its resistance?

Circuits

• A path for electrons to travel through is called an ELECTRIC CIRCUIT

• If an electron can flow in a complete path, the circuit is A CLOSED CIRCUIT

• If a connection is broken along the circuit, it becomes AN OPEN CIRCUIT

• Switch: A DEVICE THAT CAN OPEN A CIRCUIT

Simple Circuits

• Made up of 1. power source (battery, generator)2. conductor (wire)3. load (bulb, resistor, motor)

SAFETY DEVICES on CIRCUITS that PREVENT

FIRES1. CIRCUIT BREAKER: switch that

opens when current is too high2. FUSES: a switch that melts

when current is to high

TYPES OF CIRCUITS

• A SERIES CIRCUIT only has 1 path for electrons

• A PARALLEL CIRCUIT has more than one path for electrons.

Short Circuits

• Short Circuit: when uninsulated wires touch and the e- take a shorter path; can overheat and cause a fire

Electric Power

The amount of electrical energy used each second is called ELECTRIC POWER , RATE AT WHICH ENERGY IS CONVERTED

Units : Watts (w) or Kilowatts (kW)

Formula: P = VIPower = Volts x Current

How much electrical power is used by a TV that uses a current of 0.5A when connected to a voltage of 120V?

Electrical Energy Power

E = Ptenergy = power x time

A hairdryer with a power rating of 1500W is used for 120 seconds. How much electrical energy does it use?

Kilowatt-hour

• The unit for energy used by the power company