Electricity

Energy

Is the ability to do work Comes in 2 main types (but many

forms)• Potential energy is stored energy like

gravity, chemical, nuclear and electrical

• Kinetic energy is the energy of moving objects like light, sound and mechanical

Energy can be converted from

one form to another

Electrical Energy

A battery holds Electrical Potential Energy (Potential, because it is stored energy)

Voltage is a measure of the difference in electrical energy between 2 places in a circuit

A 12 volt battery has 12 volts of potential energy difference between the positive terminal and the negative terminal

A voltmeter measure the “potential difference” between 2 points in a circuit

each volt equals 1 joule of energy per charge

Voltage (symbol V) units are the volt (V)

Electric Current

is the measure of how many charges are passing a point in a circuit every second

Symbol is I Unit is the Amp (A) Is measured using an ammeter

Resistance

Is a measure of how hard it is for charges to pass through an object

Higher resistance means more energy is needed to pass through

Resistance, voltage and current are all related• If the voltage is kept the same, but the resistance is

increased, the current decreases

Resistance (R) is measured in ohms (symbol Ω)

Name Voltage Current Resistance

Symbol V I R

Unit (Symbol)

Volts (V) Amps (A) Ohms (Ω)

Assignment

Pg 275 reading check 1,2,3,4,5,6,9 Pg 279 Checking Concepts 1,2,3,5,6 Pg 279 Understanding Key Ideas 1,2

Ohm’s Law

“the current through an object is equal to the voltage across the object divided by the resistance”

I = V/R If V =6 V and R = 2 Ω then

The current (I) = 6/2 = 3 Amps

Ohms Law

Use the triangle to help solve ohms law problems

V= I x R I = V /R R = V/I

V

I R

Ohms Law Problems

1. A 1.5 volt battery is connected to a light bulb and produces 0.5 amps of current. What is the RESISTANCE of the bulb

V = 1.5 V, I = 0.5 A R = V/I = 1.5/0.5 = 3.0 ohms (Ω)

2. A different battery is put in the circuit above and the current changes to 1.5A. What is the voltage of the new battery?

I=1.5 A, R = 3.0 ΩV = I x R = 1.5 x 3.0 = 4.5 V

Now you try a couple:

1. A 6 Volt battery creates a current of 0.6 amps when connected to a motor. What is the resistance of the motor?

2. A 4.5 Volt IPod has a resistance of 900 ohms. What is the current when the ipod is turned on?

V = 6.0 V, I = 0.6 A

R = V/I, R = 6.0/0.6 = 10 Ω

V = 4.5 V, R = 900 Ω

I = V/R = 4.5/900 = 0.005 A (5 mA)

Ohms Law Problems

Handout Text book “Practice Problems” page 293

and page 294 Pg 301 #1-5, 8-10,12,13

Circuit types

Series circuits• Have one pathway for electricity to flow

• Current decreases as more loads (resistors) are added (if voltage is kept the same)

Parallel circuits• Have more than one path for electricity to flow

• Current increases as more loads are added

Series Circuit

Parallel Circuit

Circuit Analysis

The voltage drop over each load sums to the voltage across the battery

The current through each path sums to the current supplied by the battery

In a series circuit, the voltage drop across each device can differ, but the current through each device is the same

In a parallel circuit, the voltage drop across each device is the same, but the current through each device can differ.

A Parallel Circuit

Still needed:

Static Electricity Insulators and conductors Total resistance in a series circuit How the current and voltage change as

more loads are added to• A series circuit

• A parallel circuit