*Electric Current and Circuits

5.5.14

*Electricity

Electricity refers to the presence of electric current in wires, motors, light bulbs, and other devices.

Electricity carries power. Power (P) is defined as a rate of change in work or energy over a period of time. Its unit is Joules/second or Watt.

*Current is a flow of charge

*These batteries have a voltage of 1.5 volts. (a difference of 1.5 volts of energy between the + and - ends) *If you connect batteries positive-to-negative, each battery adds 1.5 volts to the total.*Three batteries make 4.5 volts. *Each unit of current coming out of the positive end of the three-battery stack has 4.5 joules of energy.

* A battery uses chemical energy to move electrons. It is a voltage source.

*A fully charged battery adds energy proportional to its voltage.

*The resistance of electrical devices

*The resistance of electrical devices ranges from very small (0.001 Ω) to very large (10×106 Ω).

*Each device is designed with a resistance that allows the right amount of current to flow when connected to the voltage the device was designed for.

*Changing resistance*The resistance of many materials, including those in light bulbs, increases as temperature increases. *A graph of current versus voltage for a light bulb shows a curve. *A device with constant resistance would show a straight line on this graph.

*Electrical ConductivityElectrical conductivity describes a material’s ability to pass electric current.

Yes, my children, copy this table

There are two types of electrical circuits through which current can flow.

In series circuits, current can only take one path. The amount of current is the same at all points in a series circuit.

In parallel circuits the current can take more than one path. Because there are multiple branches, the current is not the same at all points in a parallel circuit.

Calculate: How much current flows in a circuit with a 1.5-volt battery and three 1 ohm resistances (bulbs) in series?

R

VI

321 RRRRtotal

1

V5.1

R

V

3totalR

3

V5.1I

A5.0I?I

What you know:

This is a series circuit.

Calculate: Two bulbs with different resistances are connected in parallel to batteries with a total voltage of 3 volts. Calculate the total current supplied by the battery.

R

VI

A13

V31

I

A65.0

V32

I

7A6AA1 totalIYou must add

up the currents in

each branch.

Calculate: A circuit contains a 2 ohm resistor and a 4 ohm resistor in parallel. Calculate the total resistance of the circuit.

21

111

RRRtotal

4

1

2

11

totalR

4

31

totalR

3

4totalR

You must finish the problem giving the

inverse of your additions.

4

1

4

21

totalR

You must find common

denominator in order to add….