Question

A Wheatstone bridge is used to measure ________.

• A. unknown resistances
• B. direct current
• C. alternating current
• D. electric power
• E. voltage

Hint:

Balanced condition: $R_1/R_2 = R_3/R_4$.

Answer 1

The Correct Option is A

Step 1: Understanding the Concept
This question asks for the primary application of a Wheatstone bridge circuit. A Wheatstone bridge is a specific type of electrical circuit consisting of four resistive arms arranged in a diamond or bridge shape.
Step 2: Detailed Explanation
A Wheatstone bridge is an electrical circuit used for the precise measurement of an unknown electrical resistance. It works by balancing two legs of a bridge circuit, one leg of which includes the unknown component.
How it works:
The circuit consists of four resistors. Three of these resistors have known values (one of which is often variable), and the fourth is the unknown resistance (\(R_x\)). A galvanometer is connected between the middle points of the two legs of the bridge to detect any current flow.
The variable resistor is adjusted until the galvanometer reads zero current. This is the "balanced" condition. When the bridge is balanced, the ratio of resistances in one leg is equal to the ratio of resistances in the other leg.
The balance condition is given by:
\[ \frac{R_1}{R_2} = \frac{R_3}{R_x} \] By knowing the values of the three known resistors (\(R_1, R_2, R_3\)), the unknown resistance (\(R_x\)) can be calculated accurately.
Evaluating the options:
(A) unknown resistances: Correct. This is the primary and classic use of the Wheatstone bridge.
(B) direct current: Incorrect. A galvanometer measures current, but the bridge circuit itself is a tool for measuring resistance, not the current itself. It typically operates with a DC source.
(C) alternating current: Incorrect. While bridge circuits can be adapted for AC (like the Wien bridge), the standard Wheatstone bridge is a DC circuit for measuring resistance.
(D) electric power: Incorrect. Power is measured with a wattmeter.
Step 4: Final Answer
A Wheatstone bridge is used to measure unknown resistances.