Name the instrument used to control current in an electric circuit.

Answer

**Step-by-Step Solution:**

1. **Understanding the Question**: The question asks for the name of the instrument used to control current in an electric circuit.

2. **Identifying the Instrument**: The instrument that is commonly used for this purpose is called a "rheostat."

3. **Definition of Rheostat**: A rheostat is a type of variable resistor. It allows the user to adjust the resistance in a circuit, which in turn controls the amount of current flowing through the circuit.

4. **Application of Ohm's Law**: According to Ohm's Law, the relationship between voltage (V), current (I), and resistance (R) is given by the formula:
\[ I = \frac{V}{R} \]
Here, if the voltage (V) is kept constant and the resistance (R) is varied using the rheostat, the current (I) will also change.

5. **Conclusion**: Therefore, by adjusting the resistance with a rheostat, we can effectively control the current in an electric circuit.

**Final Answer**: The instrument used to control current in an electric circuit is called a rheostat.

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