state and verify ohms law by plotting graph lab manual practical
Answers
Answer:
Aim
To study the dependence of potential difference (V) across a resistor on the current (I) passing through it and determine its resistance. Also plot a graph between V and I.
Theory
Ohm’s Law: The potential difference, V across the ends of a given metallic wire in an electric circuit is directly proportional to the current flowing through it, provided its temperature is the same. This is Ohm’s law.
V ∝ I
.’. V = IR, (Here R = Constant for the given metallic wire)
The SI unit of resistance is Ohm (Ω).
R=\frac { V }{ I }
One Ohm: If the potential difference across the ends of a conductor is 1 volt and the current flowing through it is 1 ampere, then the resistance of the conductor R is 1 ohm.
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Factors affecting resistance:
The nature of resistor (a conductor having some resistance.)
The length of the resistance. (R ∝ l)
(Resistance increases as the length of the wire is increased)
The area of cross-section of the resistor. R\propto \frac { 1 }{ A }
(Resistance decreases with the increase in the cross-section area of the wire)
Circuit Diagram:
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In a circuit ammeter is always connected in series and voltmeter is connected in parallel across the points between which potential difference is to be measured.
A straight line graph obtained between V and I verifies the Ohm’s law.
Least Count: It is very important to find the least count of ammeter and voltmeter before using them.
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If in the ammeter, there are 10 divisions from 0 to 0.1 A then each division indicates 0.01 A.
A. To calculate the least count of ammeter.
Range of ammeter = AR…………………….
Number of divisions in ammeter = AN…………………………..
.’. Least count of ammeter = \frac { { A }_{ R } }{ { A }_{ N } }= …………….. ampere.
B. To calculate the least count of voltmeter.
Range of voltmeter = VR……………………
Number of divisions in voltmeter = VN
.’. Least count of voltmeter = \frac { { V }_{ R } }{ { V }_{ N } } = ………………. volt.
Materials Required
A battery, an insulated copper wire (cut into 10 pieces), a key, an ammeter, a voltmeter, a rheostat, a resistor and a piece of sand paper.
Procedure
Keep the devices as shown in the circuit diagram.
Connect them with the connecting wires and keep the key open.
Positive terminal of the battery is connected to the positive terminal of the ammeter.
Check the +ve and -ve terminals of voltmeter before connecting it in the circuit.
Once the circuit is connected, insert the key and check the rheostat, adjust its slider and see whether the ammeter and voltmeter readings are shown.
By using the slider of rheostat take three different readings of current 1 and voltmeter V.
Record your observations in the observation table.
Calculate resistance of a given resistor by formula R=\frac { V }{ I }.
Plot a graph of voltmeter reading and current reading. On x axis take V and on y axis take I.
Resistance increases with increase in temperature of pure metals.