DC Circuits Sums

24
• Series and parallel resistors • Kirchhoff’s Rules for network problems • Electrical meters and household circuits • R-C circuits DC CIRCUITS: Chapter 26 C 2012 J. Becker

Transcript of DC Circuits Sums

Page 1: DC Circuits Sums

• Series and parallel resistors• Kirchhoff’s Rules for network problems• Electrical meters and household circuits• R-C circuits

DC CIRCUITS: Chapter 26

C 2012 J. Becker

Page 2: DC Circuits Sums

Learning Goals - we will learn:• How to simplify resistors connected in a circuit in series and in parallel. • How to simplify and analyze more

complicated networks using Kirchhoff’s Rules.

• R-C circuits

Page 3: DC Circuits Sums

Series connection

Parallel connection

Resistors connected in a circuit in series or parallel can be simplified using the

following:

Page 4: DC Circuits Sums

C 1998 McDermott, et al., Prentice Hall

Calculate the total resistance of each box if each bulb has a resistance of 1000 Ohms ().

Page 5: DC Circuits Sums

Method of simplifying the circuit in (a) below to get the equivalent resistance. We can then calculate the power P = I2 R

dissipated in each resistor.

Page 6: DC Circuits Sums

Exercise 26.13: Four equivalent light bulbs R1 = R2 = R3 = R4 = 4.50 , emf = 9.00

Volts.Find current and power in each light bulb.

Which bulb is brightest?

Later, if bulb #4 is removed which bulbs get brighter? Dimmer?

Page 7: DC Circuits Sums

On the course website, see old Test #1

from previous semesters for typical DC circuit problems

AND other typical problems on tests…

Seewww.physics.sjsu.edu/Becker/physics51

Page 8: DC Circuits Sums

These complex circuits cannot be reduced to series – parallel combinations.

So use Kirchhoff’s Rules:1. Ij = 0 junction rule

(valid at any junction); conservation of charge

2. (Vj ) = 0 loop rule(valid for any closed loop); conservation of energy

Page 9: DC Circuits Sums

At node A, Iin = IoutI1 + I3 = I2

Vrises = VdropsLoop #1:I2R2 +4+ I1R1 = 1 + 2

Loop #2:3 + 2 = I2R2 + I3R3

• Label: 3 I’s; +/- on R’s; loops.

• Write equations.

Page 10: DC Circuits Sums

Figure 26.66

5.00 A = I44.0

0B

I3 I2

Label the 3 branch currents I2, I3, and I4.Since VAB across all 3 branches is the same

and is known: V4 = I4R4 = 5A (4) = 20 Volts, the currents and can be readily solved.

A

Page 11: DC Circuits Sums

V4 = I4R4 = 5A (4) = 20 Volts I3 = V3 / R3 = 4V / 3= 1.33 A

At junction B, I in = I outI4 = I2 + I3 ; I2 = I4 – I3 = 5A - 1.3A

I2 = 3.7ALoop #1: V rises = V drops = I2R2 + I4R4 = 3.7A (2) + 5A(4)

= 27.4 V

Page 12: DC Circuits Sums

V4 = I4R4 = 5A (4) = 20 Volts I3 = V3 / R3 = 4V / 3= 1.33 AAt junction B, I in = I out

I4 = I2 + I3 ; I2 = I4 - I3 = 5A - 1.3A = 3.7ALoop #1: V rises = V drops

= I2R2 +I4R4 = 3.7A (2) + 5A(4) =27.4 V

5.0 A4.0

0B

I3 I2

Page 13: DC Circuits Sums

Figure 26.11

Typo on top of page 890 (12th Edition), 2nd line from top of page:“right side” should read “bottom”

(See Figure 26.11 which is rotated 90o from figure in the 11th Edition.)

Page 14: DC Circuits Sums

ELECTRICAL MEASURING INSTRUMENTS – METERS

A d’Arsonval galvanometer meter movement

Page 15: DC Circuits Sums

AMMETERS have a very small shunt resistor in them to reduce the effect of introducing the meter resistance into the circuit being measured.VOLTMETERS (V) have a very large series resistor in them to reduce the amount of current drawn from the circuit being measured.

Page 16: DC Circuits Sums
Page 17: DC Circuits Sums

•DISCHARGING: CHARGING:

•An RC circuit that can be

used to charge and discharge

a capacitor (through a resistor).

Page 18: DC Circuits Sums

•CHARGING A CAPACITOR:current vs time

•CHARGING A CAPACITOR:

charge vs time

Page 19: DC Circuits Sums

•DISCHARGING A CAPACITOR:current vs time

•DISCHARGING A CAPACITOR:charge vs time

Page 20: DC Circuits Sums

o

o

Page 21: DC Circuits Sums

•A battery, a capacitor, and a resistor are connected in series. Which of the following affect(s) the maximum charge stored on the capacitor?

•Q26.26

•A. the emf of the battery

•B. the capacitance C of the capacitor

•C. the resistance R of the resistor

•D. both and C

•E. all three of , C, and R

Page 22: DC Circuits Sums

House wiring circuits

Page 23: DC Circuits Sums

Hand drill circuit with ground wire for safety

Page 24: DC Circuits Sums

see www.physics.sjsu.edu/Becker/physics51

Review

C 2012 J. F. Becker