What is the function of rheostat in the circuit?
A. It limits the current
B. It increases the current
C. It makes the current constant in the circuit
D. It increases the voltage

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Hint: Rheostat is an electrical device which is used as a variable resistor. It can vary the resistance through a circuit without causing any interruption in its working. It is very similar to potentiometers in its construction.

Complete step by step answer:
A rheostat is a variable resistor which is used as a current controlling device in a circuit. It is made up of two terminals of which one is fixed and the other one can move. This moving terminal helps in varying the resistance of the whole circuit and hence it can control the current or the voltage through the circuit.
We know that there are three main parameters in an electric circuit that are: applied voltage, current through the circuit and the resistance offered by the circuit and all of them are interdependent on each other. That means if we change the resistance either the current or the voltage of the circuit will vary.
Therefore, we can say that a rheostat can limit the current, increase or decrease the current, keep it constant and also control the voltage.
Hence the correct answers are all the options A. B. C. D .

Note: The resistance of resistor depends on the length of the wire, area of cross section and the material. So, when the sliding part of the resistor is moved the effective length of the wire increases or decreases. The net resistance in a circuit is directly proportional to the length of the resistive path.