Potentiometer is used for:

• Potentiometer: The instrument designs for measuring the unknown voltage by comparing it with the known voltage, such type of instrument is known as the potentiometer.
• In other words, the potentiometer is the three-terminal device used for measuring the potential differences by manually varying the resistance. The known voltage is drawn by the cell or any other supply sources.

CHARACTERISTICS OF POTENTIOMETER

• The potentiometer is very accurate because it works on the comparing method rather than the deflection pointer method for determining the unknown voltages.
• It measures the null or balance point which does not require power for the measurement.
• The working of the potentiometer is free from the source resistance because no current flows through the potentiometer when it is balanced.

WORKING OF POTENTIOMETER

• The working principle of the potentiometer is explained through the circuit shown below.
• consider S is the switch used for connecting or disconnecting the galvanometer from the potentiometer. 
• The battery through the rheostat and slide wire supply the working current.
• The working current may vary by changing the setting of the rheostat.

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• The method of findings the unknown voltage depends on the sliding position of the contact at which the galvanometer shows the zero deflection. 
• The Zero or null deflection of galvanometer shows that the potential of the unknown source E and the voltage drops E₁ across the sliding wires are equal. Thus the potential of the unknown voltage drops across the ac portion of the sliding wire.
• The slide wire has the uniform cross-section and resistance across the entire length. As the resistance of the sliding wire is known, then it is easily controlled by adjusting the working current. 
• The process of equalising the working voltage drop is known as the standardisation.
• Hence option 1 is correct.