To determine resistance per cm of a given wire by plotting a graph of potential difference versus current.
A metallic conductor (coil or a resistance wire), a battery, one way key, a voltmeter and an ammeter of appropriate range, connecting wires and a piece of sand paper, a scale.
The resistance (R) of the given wire (resistance coil) is obtained by Ohm’s Law V/I=R
Where, V : Potential difference between the ends of the given resistance coil. (Conductor)
I: Current flowing through it.
If ι is the length of resistance wire, then resistance per cm of the wire = R/ι
S.No. | Ammeter Reading I (A) | Ammeter Reading I (A) | Voltmeter Reading, V(v) | Voltmeter Reading, V(v) | V/I=R |
Observed | Value | Observed | Value | ||
1 | 50 | 500 mA | 16 | 16 x 0.05=0.8 | 1.6Ω |
2 | 35 | 350 mA | 11 | 0.55 | 1.57Ω |
3 | 32 | 320 mA | 10 | 0.50 | 1.56Ω |
4 | 19 | 190 mA | 6 | 0.30 | 1.58Ω |
5 | 10 | 100 mA | 3 | 0.15 | 1.5Ω |
Mean R = 1.56
Length of resistance wire: 28 cm
Scale: X – axis : 1 cm = 0.1 V of potential difference
Y – axis: 1 cm = 0.1 A of current
The graph comes out to be a straight line.
It is found that the ratio V/I is constant, hence current voltage relationship is established i.e. V ∝ I or Ohm’s Law is verified.
Unknown resistance per cm of given wire = 5.57 x 10^{2}Ωcm^{-1}
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