Chapter 7 :

Electricity and Magnetism

Section 2 : Electric Current

Connecting Concepts

• We studied:

1) Exothermic Reactions

2) Energy transformations

3) Electric Charges

Energy Transformation and Batteries

• Inside the battery, a series of exothermic

chemical reactions take place.

• Chemical Energy is transformed into

Electrical Energy

• The connection between the - and +

terminals of batteries triggers the chemical

reactions and the electrons will flow from the

– terminal to the + terminal.

• The flow of e- is called Electric Current

What is an electric current?

• It is a continuous movement.

Electric current is the flow of electric charges

( electrons).

Electrons will move along a wire, or a battery

Electric Current can be measured

• Electric Current is measured in a SI unit called Ampere. (A)

• Ampere is the amount of charges that flow in and out of the wire in one second.

• In one second, about six billion charges flow into and out of the wire

Electric Current can be measured

• An ammeter is an instrument used to measure the flow of an electric current

Electric Circuit

• When you watch TV, you need the TV to keep functioning continually so you can watch an entire show.

• You need electrons flowing non stop generating enough electricity to power the TV.

You need Electric Circuits!

• Electric Circuits are a closed path in which electric charges can flow without interruption.

***Why are circuits important?

• Electrical Circuits provide means of

transferring electrical energy from

sources such as batteries or other

generators, to devices that will transform

these energy into light ( light bulb,

television), heat ( electric heater),

sound ( radio or television).

From Electric Fields.

All charged objects have an electric field that surrounds.

*A force must be exerted on electric charges to make them flow.

Where is this force coming from?

In a battery: The (-) and (+) terminals of the battery produce an electric field.

The electric field exerts force on the electrons.

This force causes the electrons to have electrical energy and flow.

Electrons flow from the negative to the positive terminal of the battery.

EX of an Electric Circuit :

You need: a battery, a bulb and a switch to make electrons flow.

For the electrons to flow, the switch needs to be closed.

• When you

turn on a light

by flipping a

switch, you

are closing

the circuit.

• The electric

current will

flow and the

light will turn

on.

Simple, Series and Parallel Circuits

• Electric Circuits are a closed path in which electric charges can flow without interruption.

• There are three types of circuit:

Simple, Series and Parallel Circuits

• 1)In a simple circuit, there is only one light bulb and only one closed path for the current to flow.

• 2)In a series circuit, there are more than one light bulb that are connected so there is only one closed path for the current to follow.

• If any part of this path is broken, current will no longer flow in the circuit.

Simple Circuit only one lamp – one path

Series Circuitmore than one bulb – one path

3)Parallel Circuits

• In a parallel circuit, devices are connected so there is more than one closed path for current to follow.

• If the current flow is broken in one path, current will continue to flow in the other paths.

• That is what happens when you have only one light on in your house..

• Classroom lights are another example – we can have only one on and the other off.

Parallel Circuit

Drawing of a circuit x Circuit Diagram

Electric Resistance

• + and – charges are constantly colliding inside the wire.

• this cause electrons to change direction, creating resistance to the flow..

Electric Resistance

• The measure of how difficult it is for electrons to flow in an object is called the electric resistance of the object.

• The unit for electric resistance is the ohm, symbolized by Ω ( omega – Greek letter)

In what type of material there will be less resistance?

Insulators or Conductors?

**Why are resistors important?

**Resistors: fight current flow by using up

some of the energy in the flow.

So a resistor is used to lower and to control

the flow of electrons.

EX: If you have a 12 volt battery and a 9 volt

lamp, the lamp will 'blow' pretty quickly.

A resistor will drop the 3 extra volts.

If you have a flow of charges too high for your

circuit, you can lower it by adding a resistor.

Voltage

• **Voltage measures the amount of energy that will be carried by the electrical charges in a circuit.

• The higher the voltage, the higher will be the electric energy that will flow.

• Ampere is the amount of charges that flow in and out of the wire in one second.

• The voltage between two points in a circuit can be measured with a voltmeter.

• The SI unit for Voltage is the volt (V)