EXPT NO: 12. OHM'S LAW
Aim
: To determine resistance per
cm of a given wire by plotting a graph of potential difference versus current.
Apparatus : Uniform metal wire of
unknown resistance, voltmeter, ammeter, battery power supply, rheostat, meter scale, one way
key, connecting wires etc.
Circuit Diagram :
Formulae: Résistance of wire 
Resistance
per cm of a wire = 
Procedure :
Arrange the apparatus as
shown in the circuit diagram and make the connections.
Determine the least count
of voltmeter and ammeter.
Close the key (K) and
adjust the rheostat, such that a minimum current passes through the resistance
wire. Note down potential difference (V) and corresponding current (I)
Repeat the above step for
different values (V) and corresponding current (I).
Calculate the resistance in
each case.
Plot the graph of V versus
I. Determine the slope of a graph, which is the resistance (R) of wire.
Observations :1) Length of a given
wire = L = …………cm
2) Least count of ammeter = …………mA
3) Least count of voltmeter = …………V
To
determine resistance of wire (R).
|
Sr.No.
|
Current
I
(mA)
|
Current I
(A)
|
Potential
V
(volt)
|
Resistance
 |
Mean Resistance
R
|
|
01
|
|
|
|
|
|
|
02
|
|
|
|
|
|
|
03
|
|
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|
|
|
|
04
|
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|
|
|
|
|
05
|
|
|
|
|
Calculations :
|
Obs No
|
01
|
02
|
03
|
04
|
05
|
|
logV=a
|
|
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|
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logI=b
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a-b=c
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R=antilog c
|
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|
|
Graph:
Result:
1) Unknown Resistance of the wire by
calculation =…………..
2) Unknown Resistance of the wire by Graph =…………..
3) Resistance per cm of the wire by
calculation =………….. 
4) Resistance per cm of the wire by Graph =…………..
Precautions
:
1)
The connection should be neat and
tight .
2)
The key should be inserted only
while taking the observation to avoid the heating of resistance.
3)
If the deflection of the pointer
is in between the two division then adjust the rheostat such that the reading
should be exactly coincides with the division.
J K L
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