To determine the equivalent resistance of two resistors when connected in series - Science Practicals

Aim
To determine the equivalent resistance of two resistors when connected in series.

Theory
Two resistors are said to be in series if they are connected in such a way that one end of one resistor is connected to the starting end of the other. In such a case same current flows through all the resistors. The equivalent resistance Rs in series combination is given as Rs = R1 + R2 where R1 and R2 are the individual resistances of the respective resistors used in series combination. If there are n resistors connected in series, then the above equation becomes: Rs = R1 + R2 + R3 ... Rn

Materials Required
A dc voltmeter (0-5 volt), dc ammeter (0-15A), a rheostat, two resistence wires, one way key, sand paper, connecting wires, a battery or eliminator (0-4V)

Procedure
Step 1: The resistance R1 and R2 of two given resistors are found separately by repeating the second experiment of finding the resistance across resistors.
Step 2: The two resistors having resistance R1 and R2 are connected respectively in series as per the circuit diagram shown.
Step 3: The key is plugged in and set rheostat for minimum value in the ammeter.
Step 4: The value of the current is increased in the ammeter with the help of rheostat and the corresponding value of potential difference in the voltmeter is noted. The voltmeter and ammeter readings are recorded in a tabular form.
Step 5: The steps are repeated for 4 to 5 more values of current and voltages.

Verification
(i) R1 + R2 =  ohms (theoretical)   Rs =  ohms(practical)
(ii) (R1 × R2)/(R1 + R2) =  ohms (theoretical)  Rp =   ohms(practical)

Results
Within experimental errors Rs = R1 + R2 and  Rp = (R1 × R2)/(R1 + R2) in series and in parallel the equivalent resistance i.e. combination respectively are verified.

Precautions
1. The connections should be tight and clean.
2. The wires should only be connected at the terminals and not in between.
3. Clean the ends of connecting wire with a sand paper.
4. Take the voltmeter and ammeter of proper range.
5. The rheostat should be used of low resistance (about 100).
6. The positive terminals of ammeter and voltmeter should be connected to the positive pole of the battery.
7. The ammeter and voltmeter should be checked, if necessary, adjust for zero setting.

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