Electricity

Ch. 11

Electric Charge

• All matter is made of atoms• Atoms contain 2 charged particles

—what are they?

• These charges produce attractive and repulsive forces

Electrical Force

• This is the force between 2 charged objects

• Size of the force is determined be two things:• Size of the charges involved• How close the charges are to one

another

Electric field

• This is where the charges interact with one another

• An active area where protons are constantly being pulled together or pushed apart

How can neutral atoms be charged?

• Atoms start with an equal number of protons and electrons

• It must gain or lose electrons to become charged

• There are three ways to accomplish this:•Friction, Conduction, and

Induction

Charge by Friction

• Rub a balloon on your head:•What happens?

•Why?

Charge by Conduction

• Touch a plastic ruler to a metal rod:•What happens?

•Why?

Charge by Induction

• You rub a balloon against your head and then stick it on a wall• What happens?

• Why?

What Produces Electrical Current?

• Electrical current is produced by electrical pressure

• Electrons push against one another from one side

• This causes a repulsive force• This pressure is referred to as

voltage

Voltage Equation

•Potential EnergyCharge

The stronger the battery, the greater the potential energy

This equals more voltage

Controlling Electric current

• Different electrical sources need different amounts of current

• This is controlled with resistors• These control the amount of

current that is passed from a power source to the energy source (light, appliance, etc.)

Ohm’s Law

• States the relationship between current, voltage, and resistance

• Current = VoltageResistance

*Current is proportional to voltage*And is inversely related to resistance

What does this mean?

1. The higher the voltage, the larger the current and vice versa

2. The greater the resistance the smaller the current

Sample Problem

• How much current flows through a lamp with a resistance of 60 ohms when the voltage across the lamp is 12 Volts?

Algebra Anyone?

• What is the resistance of an electric frying pan that draws a current of 12 amps when connected to a 120 volt circuit?

• (HINT: Use the same equation, but solve for a different variable. You must get resistance by itself.)