Page 14 - Physics - XII

Graph and Calculations
1. From the observation table fi nd the ratio of Graph between Potential Diff erence and Current
V and I. Scale :
2. Plot a graph between potential diff erence V and X-axis: 1cm = 0.5 of potential diff erence
Y-axis: 1 cm = 0.25 A of current
current I, taking V along X-axis and I along Y
Y-axis. The graph comes to be a straight line
passing through the origin. The resistance can be 1.5
calculated from the following graph: A

AB I
In ∆ABC, tanθ = …(1)
CB V 1.0
V CB
or cotθ …(2) Current (I) in amperes
I AB
V CB 0.5 C θ B
So, R = cot …(3)
I AB

R = ____ Ω.
0
Length of the wire, L = ____ m O 0 1.0 2.0 3.0 X
Diameter of the wire, D = ____ m Potential diff erence (V) in volts

πDR
2
So, resistivity of the wire, ρ = = ____ Ω m Fig. 1.3: Graph between potential diff erence and
4 L current. It is a straight line.
Repeat the experiment for second and third wire.

Result

1. Resistivity of wire 1 is _____ Ω m.
2. Resistivity of wire 2 is _____ Ω m.
3. Resistivity of wire 3 is _____ Ω m.
4. The graph between V and I is a straight line, passing through the origin.

Precautions
1. All the connection should be neat, clean, and tight.
2. Thick wires should be used for the connections after removing the insulations near their ends by
rubbing with sand paper.

3. Voltmeter and ammeter should be of proper range.
4. A low resistance rheostat should be used.
5. The key should be inserted only while taking observations to avoid heating of resistance.

Sources of Error
1. The instrument screws may be loose.
2. Thick connecting wires may not be available.

3. Rheostat may have high resistance.

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