CIRCUITS AND RESISTANCE

RECALL:

Current Potential Difference

DefinitionThe flow of electrons Causes electrons to

flow

Symbol I V

Units Amps (A) Volts (V)

Formula(if applicable)

I = Q t

V = E Q

How measured(if applicable) Ammeter Voltmeter

Circuits:

A circuit is made up of a power supply, connecting wires & various elements that allow electrons 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.

Symbol: RUnits: Ohms, Ω Resistance

Resistance is how difficult it is for current to flow

• A device with HIGH Resistance will have very little current passing through it

• A device with low resistance will have a large current passing through it

A resistor is used to slow current down

IF:R is High than I is lowR is Low than I is high

Equivalent Resistance - Req

Equivalent Resistance is the TOTAL resistance of a circuit Symbol: Req Units: Ohms = Ω

Formulae:

Series:

Req = R1 + R2 + R3 + …

Parallel:

...3

1

2

1

1

1

Re

1

RRRq

5

3 10

Type of circuit: Series

Formula: Req = R1 + R2 + R3

Req = 10 + 5 + 3

Req = 18

What is the equivalent resistance (Req) of the circuit below?

30

75

Type of circuit: Series

Formula: Req = R1 + R2

Req = 75 +30

Req = 105

What is the equivalent resistance (Req) of the circuit below?

Type of circuit: Parallel

Formula:

What is the equivalent resistance (Req) of the circuit below?

10 Ω

15 Ω

21

11

Re

1

RRq

1 ÷ 0.1666 = 6Ω

15

1

10

1

Re

1

q

0666.01.0Re

1

q

1666.0Re

1

q

6Req

Type of circuit: Parallel

Formula:

What is the equivalent resistance (Req) of the circuit below?

321

111

Re

1

RRRq

1 ÷ 0.3333 = 3Ω

15

1

5

1

15

1

Re

1

q

0666.02.00666.0Re

1

q

3333.0Re

1

q

3Req

15

5

15

KEY POINTS

321 R1

R1

R1

Req1

Symbols of circuit parts: Voltmeter, Ammeter, Power Supply, Resistor

Two types of circuits (series and parallel)

Formula for Req (equivalent resistance)

Series – Req = R1 + R2 + R3

Parallel -

RECALL:

Resistance Current Potential Difference

DefinitionSlows current

downThe flow of electrons

Causes electrons to flow

Symbol R I V

Units Ohms (Ω) Amps (A) Volts (V)

Formula(if applicable)

R = V I

I = Q t

V = E Q

How measured(if applicable) Calculated Ammeter Voltmeter