2. #.PURPOSE
THE PURPOSE OF THIS PRESENTATION IS TO:
1. DEFINE OHM’S LAW
2. VERIFICATION OF OHM’S LAW
3. #.BACKGROUND
1. OHM'S LAW WAS CREATED IN 1827 BY GEORGE
OHM.
2. IT IS ONE OF THE MOST WIDELY USED AND
RECOGNIZED LAWS.
3. VERY IMPORTANT BASIS OF ALL ELECTRONIC AND
ELECTRICAL SYSTEMS.
4. IT HAS REMAINED UNCHANGED FOR ALMOST 200
YEARS.
4. #.OHM’S LAW DEALS PRIMARILY
WITH THE VALUES OF :
1. V = POTENTIAL DIFFERENCE (VOLTS)
2. I = CURRENT
3. R = RESISTANCE (OHMS)
4. Ω = UNIVERSAL SYMBOL FOR OHMS
5. 1. OHM’S LAW
* OHM’S LAW DEFINES THE RELATIONSHIPS
BETWEEN
(P) POWER, (E) VOLTAGE, (I) CURRENT, AND
(R) RESISTANCE.
* ONE OHM IS THE RESISTANCE VALUE THROUGH
WHICH ONE VOLT WILL MAINTAIN A CURRENT
OF
ONE AMPERE.
6. #. OHM’S LAW STATES THAT:
• THE CURRENT FLOWING THROUGH A CONDUCTOR IS
DIRECTLY PROPORTIONAL TO THE POTENTIAL DIFFERENCE
BETWEEN ITS ENDS PROVIDED ITS TEMPERATURE
REMAINS CONSTANT.‟
• V/I=CONSTANT OR V/I=R
WHERE R IS A CONSTANT CALLED RESISTANCE FOR A GIVEN METALLIC
WIRE AT A GIVEN TEMPERATURE.
7. 2.VERIFICATION OF OHM’S LAW
* SET UP THE CIRCUIT AS SHOWN IN THE CIRCUIT
DIAGRAM. FIRST USE ONE CELL AND NOTE THE
CURRENT (I) IN THE AMMETER AND THE POTENTIAL
DIFFERENCE (V) IN THE VOLTMETER ACROSS THE
NICHROME WIRE AB.
* REPEAT BY USING TWO CELLS, THREE CELLS AND
FOUR CELLS AND NOTE THE READINGS IN THE
AMMETER AND VOLTMETER. THEN PLOT A GRAPH
BETWEEN THE CURRENT (I) AND POTENTIAL
DIFFERENCE (V). THE GRAPH WILL BE A STRAIGHT
LINE.
* THIS SHOWS THAT THE CURRENT FLOWING THROUGH
A CONDUCTOR IS DIRECTLY PROPORTIONAL TO THE
POTENTIAL DIFFERENCE ACROSS ITS ENDS.
V/I=R
* WHERE R IS A CONSTANT CALLED RESISTANCE OF
THE CONDUCTOR.
8. #. SUMMARY
* THE PURPOSE OF THIS PRESENTATION WAS TO
VERIFY, EXPLAIN, AND DEMONSTRATE OHM‟S
LAW. IN THE FIRST SECTION OHM‟S LAW DEALS
PRIMARILY WITH THE VALUES OF POTENTIAL
DIFFERENCE, CURRENT AND RESISTANCE AND
THEN WHAT OHM‟S LAW STATES.
* IN THE SECOND SECTION THE OHM‟S LAW
VERIFIED BY AN EXPERIMENT BY SETTING
CIRCUIT IN ONE CELL AND THEN USING TWO,
THREE, AND FOUR CELLS AND READINGS
THROUGH VOLTMETER AND AMMETER, THEN
PLOTTING OF GRAPH.
11. * KIRCHHOFF’S LAWS PROVIDES A MEANS OF
OBTAINING ENOUGH INDEPENDENT
EQUATIONS TO SOLVE ELECTRICAL CIRCUITS
* HIS CIRCUIT LAWS STANDS FOR TWO
EQUALITIES THAT DEAL WITH THE CURRENT
AND POTENTIAL DIFFERENCE
* TWO TYPES OF KIRCHHOFF’S LAW.
12. #. KIRCHHOFF’S CIRCUIT LAW
:
~ A SINGLE EQUIVALENT RESISTANCE, (R) CAN BE FOUND WHEN TWO OR MORE RESISTORS ARE CONNECTED
TOGETHER IN EITHER SERIES, PARALLEL OR COMBINATIONS OF BOTH, AND THAT THESE CIRCUITS OBEY OHM’S LAW.
~ HOWEVER, SOMETIMES IN COMPLEX CIRCUITS SUCH AS BRIDGE OR T NETWORKS, WE CAN NOT SIMPLY USE OHM’S
LAW ALONE TO FIND THE VOLTAGES OR CURRENTS CIRCULATING WITHIN THE CIRCUIT. FOR THESE TYPES OF
CALCULATIONS WE NEED CERTAIN RULES WHICH ALLOW US TO OBTAIN THE CIRCUIT EQUATIONS AND FOR THIS WE
CAN USE KIRCHHOFF’S CIRCUIT LAW
13. #.KIRCHHOFF’S FIRST LAW - THE
CURRENT LAW (KCL)
KIRCHHOFF’S CURRENT LAW OR KCL, STATES THAT THE “TOTAL CURRENT OR
CHARGE ENTERING A JUNCTION IS EXACTLY EQUAL TO THE CHARGE
LEAVING THE JUNCTION AS IT HAS NO OTHER PLACE TO
GO EXCEPT TO LEAVE, AS NO CHARGE IS LOST WITHIN THE NODE.
* IN OTHER WORDS THE ALGEBRAIC SUM OF ALL THE CURRENTS ENTERING
AND
LEAVING A NODE MUST BE EQUAL TO ZERO.
* THIS IDEA BY KIRCHHOFF IS COMMONLY KNOWN AS THE CONSERVATION OF
CHARGE.
14. #.KIRCHHOFF’S SECOND LAW –
THE VOLTAGE LAW, (KVL)
1.KIRCHHOFF’S VOLTAGE LAW OR KVL, STATES THAT IN ANY CLOSED LOOP NETWORK,
THE TOTAL VOLTAGE AROUND THE LOOP IS EQUAL TO THE SUM OF ALL THE VOLTAGE
DROPS WITHIN THE SAME LOOP WHICH IS ALSO EQUAL TO ZERO.
~ IN OTHER WORDS THE ALGEBRAIC SUM OF ALL VOLTAGES WITHIN THE LOOP MUST BE
EQUAL TO ZERO. THIS IDEA BY KIRCHHOFF IS KNOWN AS THE CONSERVATION OF
ENERGY.
15. #.APPLICATION OF KIRCHHOFF’S CIRCUIT
LAWS:
THESE TWO LAWS ENABLE THE CURRENTS AND VOLTAGES IN A CIRCUIT TO BE
FOUND, IF, THE CIRCUIT IS SAID TO BE “ANALYZED, AND THE BASIC
PROCEDURE FOR USING KIRCHHOFF’S CIRCUIT LAWS IS AS FOLLOWS:
1. ASSUME ALL VOLTAGES AND RESISTANCES ARE GIVEN. (IF NOT LABEL THEM
V1, V2,
R1, R2, ETC.)
2. LABEL EACH BRANCH WITH A BRANCH CURRENT (11, 12, 13 ETC.)
3. FIND KIRCHHOFF’S FIRST LAW EQUATIONS FOR EACH NODE. (KCL)
4. FIND KIRCHHOFF’S SECOND LAW EQUATIONS FOR EACH OF THE
INDEPENDENT LOOPS OF THE CIRCUIT. (KVL)
5. USE LINEAR SIMULTANEOUS EQUATIONS AS REQUIRED TO FIND THE
UNKNOWN CURRENTS
16. #CONCLUSION :
*BY KNOWING AND USING KIRCHHOFF’S LAWS WE CAN SIMPLIFY OUR
CALCULATIONS AND REDUCE MORE AMOUNT OF MATHEMATICS IN SOLVING
FOR CIRCUITS.
