Chapter 2-3 Principles of Electric Circuits, Conventional Flow, 9 th ed., Floyd T. Elsarnagawy, mde207, 311 1

Chapter 2-3Chapter 2-3

Principles of Electric Circuits, Conventional Flow, 9th ed., Floyd

T. Elsarnagawy, mde207, 311

1




2

Electrical symbols




3

Basic circuit measurements




4

Meter symbols

Digital Bar graph Analog




5

Current measurement




6




7

Current measurement




8

Current measurement Ammeter connection (series)

+ -

!!Polarity a shown




9

Voltage measurement




10




11

Voltage measurementVoltmeter across the component (parallel)+ve to +ve-ve to -ve




12

Resistance measurement




13




14

Resistance measurement

Disconnect R then make the measurement




15

Safety note




16

Physical effects of electrical current




17

Ohm’s Law

V-I-RV-I-R


Principles of Electric Circuits, Conventional Flow, 9th ed.Floyd

T.Elsarnagawy, mde207, 311

18

Voltage is

Review of V, I, and R

the amount of energy per charge available tomove electrons from one point to another in a circuit.

Current is the rate of charge flow and is measured in amperes.

Resistance is the opposition to current and is measured in ohms.




19

The most important fundamental law in electronics is Ohm’s law, which relates voltage, current, and resistance.

Georg Simon Ohm (1787-1854) studied the relationship between voltage, current, and resistance and formulated the equation that bears his name. In terms of current, Ohm’s law states

VI

R

What is the current from a 12 V source if the resistance is 10 ? 1.2 A




20

Ohm’s law

If you need to solve for voltage, Ohm’s law is:

What is the voltage across a 680 resistor if the current is 26.5 mA? 18 V

V IR




21

Ohm’s law

If you need to solve for resistance, Ohm’s law is:V

RI

120 V

V

1 s

1 s

40 m A

1 0 A

C O M

Ra ng eAuto ra ng eTo uc h/Ho ld

Fused

O FF V

V

Hz

m V

A

What is the (hot) resistance of the bulb? 138




22

Graph of Current versus Voltage

I (m

A)

V (V )

00

2 4

4

6 8

8

10

12

14

16

A student takes data for a resistor and fits the straight line shown to the data. What is the resistance and the conductance of the resistor?

The slope represents the conductance.

14.8 mA - 0 mA1.48 mS

10.0 V - 0 VG

The reciprocal of the conductance is the resistance:

1 1 676 Ω

1.48 mSR

G

VR

I




23

Graph of Current versus Voltage

Notice that the plot of current versus voltage for a fixed resistor is a line with a positive slope. What is the resistance indicated by the graph? 2.7 k

What is its conductance? 0.37 mS

Voltage (V)

Cur

rent

(m

A)

0 10 20 300

2.0

4.0

6.0

8.0

10




24

Graph of Current versus Resistance

If resistance is varied for a constant voltage, the current - resistance curve plots a hyperbola.

What is the curve for a 3 V source?

Resistance (k )

Cur

rent

(m

A)

0 1.0 2.0 3.00

2.0

4.0

6.0

8.0

10

V IR?




25

Application of Ohm’s law

26.8 mA

P o w er S u p p ly

+15 V- + - +5 V 2 A

D C A m m e te r

+-

G n d

V A




26

Linear

Ohm’s law

Troubleshooting

Characterized by a straight-line relationship.

A law stating that current is directly proportional to voltage and inversely proportional to current.

A systematic process of isolating, identifying, and correcting a fault in a circuit or system.

Selected Key Terms




27

1. Holding the voltage constant, and plotting the current against the resistance as resistance is varied will form a

a. straight line with a positive slope

b. straight line with a negative slope

c. parabola

d. hyperbola




28

2. When the current is plotted against the voltage for a fixed resistor, the plot is a

a. straight line with a positive slope

b. straight line with a negative slope

c. parabola

d. hyperbola




29

Quiz

3. For constant voltage in a circuit, doubling the resistance means

a. doubling the current

b. halving the current

c. there is no change in the current

d. depends on the amount of voltage




30

Quiz

5. If the current in a 330 resistor is 15 mA, the applied voltage is approximately

a. 5.0 V

b. 22 V

c. 46 V

d. 60 V




31

Quiz

7. The circuit with the largest current is

a. (a)

b. (b)

c. (c)

d. (d)

R 10 k

+12 V R 15 k

+15 V R 22 k

+18 V R 27 k

+24 V

(a) (b) (c) (d)




32

Quiz

8. The circuit with the smallest current is

a. (a)

b. (b)

c. (c)

d. (d)

R 10 k

+12 V R 15 k

+15 V R 22 k

+18 V R 27 k

+24 V

(a) (b) (c) (d)




33

Quiz

Answers:

1. d

2. a

3. b

4. b

5. a

6. c

7. a

8. c

9. d

10. c

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Chapter 2-3 Principles of Electric Circuits, Conventional Flow, 9 th ed., Floyd T. Elsarnagawy, mde207, 311 1