Chapter 11 · Question 4

What is a rheostat? Explain how it can be used to regulate the current in a circuit without changing the voltage source.

Answer Revealed

Direct Answer:

A rheostat is a variable resistance device. By changing the effective length of the resistance wire introduced into the circuit (through a sliding contact), the total resistance of the circuit changes. Since

I = V / R

from Ohm's law, increasing resistance reduces current and decreasing resistance increases current, all while keeping the voltage source unchanged.

Simple Explanation

A rheostat is like an adjustable obstacle in the path of current. By sliding a contact along a resistance wire, you can include more or less of the wire in the circuit. More wire means more resistance and less current. Less wire means less resistance and more current. The battery stays the same throughout.

Exam-Ready Structure

A rheostat is a component that provides variable resistance and is used to regulate current in a circuit: 1. Purpose: A rheostat is a device that changes the resistance in a circuit without changing the voltage source. 2. Working principle: By changing the effective resistance introduced into the circuit, the rheostat changes the total circuit resistance. 3. Current regulation: According to Ohm's law, the current

I = V / R

. When the resistance (

R

) is increased, the current (

I

) decreases for the same applied voltage (

V

). When the resistance is decreased, the current increases. 4. In experiments such as verifying Ohm's law, a rheostat is used to vary the current through the conductor while the readings of the ammeter and voltmeter are observed. 5. The key point is that current can be controlled by changing resistance rather than changing the voltage source.

Key Points

A rheostat is a variable resistance (component that can change resistance continuously)
It works by varying the effective length of resistance wire in the circuit
Longer wire in circuit = more resistance = less current ( $I = V / R$ )
Shorter wire in circuit = less resistance = more current
Regulates current without changing the voltage source

What is a rheostat? Explain how it can be used to regulate the current in a circuit without changing the voltage source.