Transcript Ohm's Law and Resistors in Series and in Parallel

Ohm's Law and Resistors
in Series and in Parallel
Presented by
Mahmud AbdurRahman
&
Nazim Uddin
Physics 2.3 honor Class
DR. Roman Kezerashvili
Objectives:
1. Verify law by observing the dependence
of the electric current as a function of voltage
and as a function of resistance.
• 2. Determine the equivalent resistance of
series and parallel combination of resistors
and compare the results with the theoretical
predictions.
• 3. Study currents flow and voltages in series
and parallel circuits.
Equipment
• 1
Resistance box
• 2. Digital Multmeter
• 3. DC power supply with adjustable
voltage (0-20 V)
• 4. Resistors board
• 5. Connecting wires
• 6. Switch
Theory
What is the Ohm’s Law
•
Ohm’s law States that current through a resistor is directly proportional to
the applied voltage V and inversely proportional to the resistance R of the
resistance
•
Ohm’s law is not a fundamental law of nature
•
An empirical relationship that is valid for certain material
•
at constant temperature
Electric current
I=Q/T
Ohm’s Law
I=V/R
Procedure
• Part1
• 1.Investigate the variation of the current with
potential difference when the resistance is constant
• 2. Investigate the variation of the current with
resistance when the voltage is constant.
• Part II
• 1.Resistors in series
• 2. Resistors in Parallel
Ohm’s Law( The relationship among current,voltage
and resistance)
Resistors in Series
Resistors in Parallel
Data:
»
Table 1. The Voltage Dependence of Current (Constant resistance)
•
Power supply , V
•
Voltage V,
R1= 1000 
R2= 1200 
V Current I, A
Voltage V,V
•
4
4.02 0.0040
4.02 0.0033
•
5
5.02 0.0049
5.02 0.0041
•
6
6.02 0.0060
6.03 0.0049
•
7
7.02 0.0070
7.04 0.0058
•
8
8.01 0.0079
8.01 0.0066
•
9
9.01 0.0090
9.00 0.0074
10
10.03 0.0099
10.02 0.0082
Data
•
Resistance R,  1/R, -1
•
700
0.00143
•
800
0.00125
0.01490
•
900
0.00111
0.01320
•
1000
0.00100
0.01190
•
1100
0.00091
0.01084
•
200
0.00083
0.00994
Current I, A
0.01700
Voltage Power supply
V,V=12
V from Slope,V 11.874
%Difference 1.06%
» Table 3. Resistors in Series
Continuation
R = 4950 
•
I = 0.0024 A,
V = 12 V,
•
Resistors
Current I, A
Voltage V, V
Resistance R, 
•
RA
0.0024
8.74
3620
•
RB
0.0024
2.63
1090
•
RC
0.0024
0.57
230
Equivalent resistance from equation (9) R = 4940 ;
% difference = 0.20%
Total voltage from equation (5)
% difference = 0.50%
–
V = 6 V,
V = 11.94 V;
Table 4. Resistors in Parallel
R = 185.6 
•
I = 0.032 A,
•
Resistors
Current I, A
Voltage V, V
Resistance R, 
•
RA
0.0018
6
3620
•
RB
0.0054
6
1090
•
RC
0.026
6
230
GRAPH
the Current I Versus the Voltage V
0.012
y = 0.001x - 1E-05
the Current I, (A)
0.01
0.008
0.006
y = 0.0008x - 2E-05
0.004
0.002
0
0
2
4
6
the Voltage V, (V)
8
10
12
Graph 2
the Current I Versus the 1/R
y = 11.874x + 4E-05
0.01800
0.01700
the Current I, (A)
0.01600
0.01500
0.01400
0.01300
0.01200
0.01100
0.01000
0.00900
0.00800
0.00060
0.00070
0.00080
0.00090
0.00100
0.00110
the 1/R
0.00120
0.00130
0.00140
0.00150
Calculation and Analysis:
1. Use data from Table 1 and plot a graph of the current I us the
voltage V for both values of the resistance. Determine the slope
of the graph. From the slope of the graph find the resistance
using
» R=1/slope
•
and compare it to the actual value of resistance by calculating
a percent difference.
– 2. Use data from Table 2 and plot a graph of the current I versus
the 1/R. Determine the slope of the graph. Compare the slope of
the graph with the output voltage of power supply by computing
a percent difference.
– 3. Resistors in series.
– Using the resistors value compute the equivalent resistance R
of the circuit by using equation (9). Compare this value with
your experimental measurement by finding a percent
difference.
– Using the measured voltages compute the total voltage V by
using equation (5). Compare this value with your experimental
measurement by finding a percent difference.
Continue Calculations
R  RA  RB  RC  3620 1090 230  4940
%difference
 0.20%
R1  R2
( R1  R2 ) / 2
100% 
4950 4940
(4950 4940) / 2
100%  0.002022100%
Continue Calculations
1
1
1
1
1
1
1






 0.005542
R RA RB RC 3620 1090 230
1
 180.46
0.005542
R1  R2
185.6  180.46
%difference
100% 
100%  0.02808100%
( R1  R2 ) / 2
(185.6  180.46) / 2
R
 2.81%
I  I A  I B  I C  0.0018 0.0054 0.026  0.0332A
%difference
 3.68%
I1  I 2
( I1  I 2 ) / 2
100% 
0.0332 0.032
(0.0332 0.032) / 2
100%  0.03681100%
• According to the experiment we observed
that the electric current through a
resistor is directly proportional to the
applied voltage and inversely
proportional to the resistance of the
resistor and verified Ohm’s law.
• We also observed the difference between
series and parallel connections.
I LOVE
PHYSICS
THANKS TO
PROFESSOR DR. ROMAN
FOR MAKING PHYSICS SO ENJOYABLE