Circuits

Chapter 23

Circuit Elements and Design Circuit Diagram – a logical picture

of what is connected to what in a circuit

Replace pictures of the circuit elements with symbols

Basic Symbols Used for Electric Circuit Drawings

Circuit Diagrams

The longer line at one end of the battery symbol represents the positive terminal

The emf is shown beside the battery Capacitance and resistance are shown beside

the symbols Wires are shown as straight line connections

between circuit elements Higher potentials are put toward the top of the

diagram

Reading Quiz 2. Which terminal of the battery has a higher potential?

A. the top terminalB. the bottom terminal

Slide 23-4

2. Which terminal of the battery has a higher potential?A. the top terminal

Slide 23-5

Answer

Checking Understanding

The following circuit has a battery, two capacitors and a resistor.

Which of the following circuit diagrams is the best representation of the above circuit?

Slide 23-9

The following circuit has a battery, two capacitors and a resistor.

Which of the following circuit diagrams is the best representation of the above circuit?

Slide 23-10

Answer

Kirchhoff’s Laws

Analyzing a circuit Find:

The potential difference across each circuit component

The current through each circuit component

Kirchhoff’s Junction Law

Kichhoff’s Loop Law

To apply the loop we must identify which potential differences are negative and which are positive.

Kirchhoff’s Loop law can only be true if at least one of the potential differences ΔVi is negative

Kichhoff’s Loop Law The net change in the electric potential

around any loop or closed path must be zero

If we add all the potential differences around the loop formed by the circuit, the sum of these potential difference must be zero.

Kirchhoff’s Laws

Slide 23-11

ΔVbat can be – or +

ΔVR is always – because potential across a resistor always decreases along the direction of the current

Voltage “drop” across the resistor Ohm’s law only considered magnitude of

current

ΣVi = 0 = ΔVbat + ΔVR ΔVbat = +ε

ΔVR = -IR ε – IR = 0 I = ε/R

The diagram below shows a segment of a circuit. What is the current in the 200 resistor?A. 0.5 AB. 1.0 AC. 1.5 AD. 2.0 AE. There is not enough information to decide.

Slide 23-13

Clicker Question

The diagram below shows a segment of a circuit. What is the current in the 200 resistor?

B. 1.0 A

Slide 23-14

Answer

The diagram below shows a circuit with two batteries and three resistors. What is the potential difference across the 200 resistor?

A. 2.0 VB. 3.0 VC. 4.5 VD. 7.5 VE. There is not enough information to decide.

Slide 23-15

Clicker Question

The diagram below shows a circuit with two batteries and three resistors. What is the potential difference across the 200 resistor?

A. 2.0 V

Slide 23-16

Answer

Series and Parallel Resistors

Two bulbs are connected in series if they are connected directly to each other with no junctions in between.

If two bulbs are connected at both ends in a circuit they are in parallel

We use equivalent resistance (the resistance of a single resistor which would replace more than one series or parallel resistors in a circuit) to solve circuit problems

Series Resistors

Slide 23-17

021 vvvi

i

2121 IRIRvv

21 RRReq

21 RRRI

eq

Parallel Resistors

Slide 23-18

21 IIIbat

21212

2

1

1 11

RRRRR

V

R

VIbat

1

21

11

RRII

VR

bateq

There is a current of 1.0 A in the circuit below. What is the resistance of the unknown circuit element?

What is the current out of the battery?

Slide 23-19

515

1

15

1

15

11

eqR

Av

Ibat 15

5

91

9

A

v

I

vR

bateq

5.35.2393R