Bellwork

Draw a circuit diagram that has one battery and two light bulbs.

Bellwork

1) If I remove a light bulb from the below circuit, then what happens to the other light bulbs?

2) If I remove a light bulb from the below circuit, then what happens to the other light bulbs?

Two Types of Electric Circuits

• Series

• Parallel

Series Circuits

•Provide a single path through the circuit

If one bulb is removed all light bulbs turn off

Parallel CircuitsEach device connects to the voltage source

If one bulb is removed others will remain on

Noticing the difference

• Series or parallel?

SeriesParallel

Series or Parallel?• Ask yourself: Does the circuit provide more

than one path for the current?

Yes = Parallel

NO = Series

Series or Parallel?

Parallel

Series

Once More!

Series Parallel

BellworkLabel the circuit diagrams below as either parallel or series.

Current and Potential Difference across Series Circuits

IT = I1 = I2 = I3 = ….

VT = V1 + V2 + V3 + ….

IT

VT

I2

V2

I3 V3

I1 V1

Current and potential difference across Parallel Circuits

IT = I1 + I2

VT = V1 = V2

IT

VT

I2

V2

I1

V1

1st - Interpret correctly

V

A

V

A

V

V

V

A

Typical Problem

• If each Volt meter measures a potential difference of 10 V what is the potential difference at the battery?

V2

V1

V3

In this series circuit, if ammeter 1 shows a current of 1.0 amperes, what

will be the reading of ammeter 2?

A2A1 I2I1

In this circuit, if voltmeters 1 and 2 both show measurements of 1.5

volts, what will be the reading of the voltmeter VT?

V2V1

VT

In this parallel circuit, if ammeters 1 and 2 both show measurements of 0.5 amperes, what will be the current IT measured by ammeter

AT?

A1

AT

A2

I2

I1

IT

Series Circuit

Req = R1 + R2 + R3 + ….

R1

R2

R3

Req

Equivalent Resistance

The total amount of resistance of a complete circuit

Example

• What is the equivalent resistance of this circuit?

R1 = 15 ohm

R2 = 10 ohm

R3 = 5 ohm

Req = ?

Example

• Find the resistance in R2?

R1 = 20 ohm

R2 = ? ohm

R3 = 5 ohm

Req = 45 ohm

Example:

• A student needs a 10 ohm resistor to complete a circuit, but only 2 ohm resistors are available. Which of the following should be done to complete the circuit?

a. Connect five 2 ohm resistors in parallel

b. Connect five 2 ohm resistors in series

c. Connect three 2 ohm resistors in series and two 2 ohm resistors in parallel

d. Connect two 2 ohm resistors in series and three 2 ohm resistors in parallel

Example

• A student needs a 20 ohm resistor to complete a circuit, but only 2 ohm resistors are available. What should be done to complete the circuit?

Parallel Circuit

R1Req R3R2

...1111

321 RRRReq

• Find the equivalent resistance

R1 = 20ΩReqR3 = 20 ΩR2 = 20 Ω

• Find the equivalent resistance

R1 = 20ΩReqR3 = 5 ΩR2 = 10 Ω

• Find the equivalent resistance

R1 = 30 ΩReqR3 = 10 ΩR2 = 15 Ω

Law of Conservation of current

• At any junction in a circuit the sum of the currents entering the circuit must equal the sum of the currents leaving the circuit

P

7A

3A

4A

Toward point P

Away from point P

Typical Question

• The diagram below represents currents in branches of a circuit. What should be the reading in ammeter A?

P6A

5A

A

Example 2

• The diagram below represents currents in branches of a circuit. What should be the reading in ammeter A?

P 2A

6A

A

5A

Example 3• Which diagram represents the correct current

direction in a segment of an electric circuit

4 A

2 A

2 A

a) 4 A

2 A

2 A

b)

4 A

2 A

2 A

c) 4 A

2 A

2 A

d)

One More!

• What is the reading in ammeter A

A

4 A 3 A

5 A