Text section 28.3 Kirchhoff’s circuit rules

Text section 28.3 Kirchhoff's circuit rules

Practice: Chapter 28, problems 17, 19, 25, 26, 43

Junction Rule: total current in = total current out at each junction (from conservation of charge).

Loop Rule: Sum of emfs and potential differences around any closed loop is zero (from conservation of energy).

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Junction Rule: conservation of charge.

I1

I2

I3 or

I1 = I2 + I3

I1'

I2' (= -I2)

I1' + I2' + I3' = 0

I3' (= -I3)

Loop Rule: conservation of energy. Follow a test charge q around a loop:

around any loop in

circuit.

R

R - + -Q +Q

C

I I

changes going from left to right V = -IR

V = +IR V =

V = Q/C

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18 b

9 V I1 a

I2 6

3 V d

c 3

I3

Find the current through each battery.

The junction rule will give:

A) I1 + I2 + I3 = 0 B) -I1 + I2 + I3 = 0 C) I1 - I2 + I3 = 0 D) I1 + I2 - I3 = 0 E)none of these

18 b

9 V I1 a

I2 6

3 V d

c 3

I3

3

18 b

9 V I1 a

I2 6

3 V d

c

Find the current

3

through each battery.

I3 = - (I1 + I2)

The junction rule will give:

A) I1 + I2 + I3 = 0 B) -I1 + I2 + I3 = 0 C) I1 - I2 + I3 = 0 D) I1 + I2 - I3 = 0 E)none of these

18 b

9 V I1 a

I2 6

3 V d

c 3

I3

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18 b

c

The loop rule applied to 9 V

I2 6

3

loop abcda will give:

I1

3 V

I3

a

d

A) 9A - 18I1 -3I3 = 0 B) 9A + 18I1 -3I3 = 0 C) 9A + 18I1 +3I3 = 0 D) 9A - 18I1 +3I3 = 0 E)none of these

18 b

c

The loop rule applied to 9 V

I2 6

3

loop abda will give:

I1

3 V

I3

a

d

A) 12A - 18I1 + 6I2 = 0 B) 12A - 18I1 - 6I2 = 0 C) 6A - 18I1 - 6I2 = 0 D) 6A + 18I1 + 6I2 = 0 E) 6A - 18I1 + 6I2 = 0

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