KIRCHHOFF’S LAW

Lecture 2

Maha K. Omar

OVERVIEW

Ohm’s Law

R the circuit resistance

V the potential difference across R

I is the current flowing through R

RIV

Electric power P

Electric Energy W

R

V

RI

VIP

2

2

tPW

SERIES CIRCUIT

Two Elements are said to be in series if they are

connected at a single point and if there are no

other current carrying connections at this point.

Current is the same everywhere in a series circuit.

KIRCHHOFF’S VOLTAGE LAW

The summation of voltage rises and voltage drops around a closed loop is equal to zero

0V

0321 VVVE

PROBLEM

Verify Kirchhoff’s voltage law

SERIES TOTAL RESISTANCE

321

321321

321 0

RRRR

RIE

RIRIRIVVVE

VVVE

tot

tot

PROBLEM Find

Total resistance

Current (direction and magnitude)

Potential across each resistor

Power dissipated by each resistor

Power delivered by the voltage source

Compare the last two quantities

PARALLEL CIRCUIT

Elements or branches of elements are said to be in a parallel connection when they share exactly the same two nodes.

The voltage across all parallel elements is the same.

KIRCHHOFF’S CURRENT LAW

The summation of currents entering a node is equal to the summation of currents leaving the node

leavingentering II

43251 IIIII

PROBLEM

Verify Kirchhoff’s current law

PARALLEL TOTAL RESISTANCE

321

321

321

1111

RRRR

R

E

R

E

R

E

R

E

IIII

T

T

T

PROBLEM

Find

total resistance

Total current

Power delivered by the voltage source

Current in each resistance

Power dissipated by each resistance

QUIZ

Find vab when:

Rx=0

Rx=15 KΩ

Rx=∞