CIRCUITSObjectives:3.11 Analyze the distribution of current in various combinations of circuit elements3.12 Explain the distribution of electric potential in various combinations of circuit elements3.13 Explain the concept of electric potential difference in circuits using an analogical model3.14 to 3.18 Activities

Circuits:

A circuit is made up of a power supply, connecting wires & various elements that allow current to leave a power source, travel through the elements & return back to the power source.

Common Electric Symbols

Battery/Power Source

Bulb

Common symbols (cont’d)

Switch

Push-button Switch

Resistor

Voltmeter

Ammeter

V

A

Circuits

Power Supply

Resistor

A

Ammeter

v

Voltmeter

Types of Circuits:

There are 2 types of circuits: 1. Series Circuit 2. Parallel Circuit

SERIES

Trick to help identify type of circuit:

Series: Pen follows wire

Parallel: Pen can go in more than one direction

PARALLEL

Series or Parallel?

AA

SERIES

SERIES

PARALLEL

PARALLEL1.

4.3.

2.

Resistance, current intensity & potential difference are all related.

Formula:

Important Formula to Solve Circuits!!!

I

V

1

R

Resistance

Current Intensity

Potential Difference

VERY IMPORTANT!!!

Math – Cross Multiplication

Ex. 10 = x 1 2

x = 20

Always multiply the two numbers that are diagonal from each other together.

Then divide by the “left-out” number

“Friend by friend divided by foe”

10 x 2 ÷ 1 = 20

Diagonal to each other

“Friend times friend”

“Left-out”

“Divided by Foe”

4

8

6x

x

10

2

5

3

6

x

8

710

x

1.

2.

3.

4.

6 x 8 ÷ 4 = 12

10 x 2 ÷ 5 = 4

8 x 3 ÷ 6 = 4

10 x 7 ÷ 1 = 12

Sneaky one….anything by itself is considered to be over 1

71

10 x

REMEMBERFriend x Friend ÷ Foe

A circuit has a resistance of 10Ω & a current intensity of 5A. What is the potential difference?

R = 10 Ω

V = ? V

I = 5 A

10 = ? 1 5 V = 50V

R = V

1 I

A circuit has a resistance of 20Ω & a potential difference of 100V. What is the current intensity?

R = 20 Ω

V = 100 V

I = ? A

20 = 1001 ?

I= 5 A

R = V

1 I

A circuit has a potential difference of 16V & a current intensity of 2A. What is the resistance?

R = ? Ω

V = 16 V

I = 2 A

? = 16 1 2

R= 8 Ω

R = V

1 I

KEY POINTS

Cross multiplication (friend x friend ÷ foe)

Formula

Helpful Summary Chart

R V=

1 I

SERIES PARALLEL

Current (I) SAME DIFFERENT

Potential Difference (V)

DIFFERENT SAME

Resistance (R) Req = R1 + R2 + R3 + …

1 2 3

1 1 1 1= + +

Req R R R

Electricity and Flowing Water

How and why electricity does what it does can be explained by using a river as a comparison.

•The water goes downstream because there is a difference in altitude. This is the same as potential difference where a difference in charge exists between two points in a circuit.

•The quantity of water in a river can be compared to the current. Lots of water, large current. Little water, small current.

•Rocks and boulders found in the stream slow the flow of water. Resistors along the circuit tend to slow the movement of electrons.

Activities

Worksheet #11 -13

References

Science Quest Student Study Guide http://www.qesnrecit.qc.ca/mst/phs_

sci_4.php#practice Animation Factory Google Images

Alternative Educational Experiences through e-Learning