Question

What is a Wheatstone bridge?

Answer 1

A Wheatstone bridge is a simple electrical circuit used to measure an unknown electrical resistance by balancing two legs of the bridge. It was invented by Samuel Hunter Christie in 1833 and later popularized by Sir Charles Wheatstone, which is why it is known as the Wheatstone bridge.

The basic Wheatstone bridge consists of four resistors arranged in a diamond shape, with a voltage source applied across the top and bottom points of the diamond. The unknown resistor whose value you want to find is connected between two of the points, and the other three resistors have known values.

Here's the configuration:

javascript
Copy code
       R1       R3
   ----/\/\/\----/\/\/\----
  |                       |
  |                       |
  |                       |
  |                       |
  |                       |
   ----/\/\/\----/\/\/\----
       R2       RX


The bridge is considered balanced when there is no current flowing through the galvanometer (G) or voltmeter connected between the midpoints of the two resistor branches. In this balanced condition, the ratio of the resistances on one side of the bridge equals the ratio of the resistances on the other side:

Copy code
R1 / R2 = R3 / RX


By measuring the known resistances R1, R2, and R3 and adjusting the value of RX (usually done using a variable resistor), you can determine the unknown resistance RX when the bridge is balanced. The balancing is often achieved by adjusting RX until the galvanometer reads zero or the voltmeter shows no voltage difference.

Wheatstone bridges are commonly used for accurate resistance measurements, and they find applications in various fields, including electronics, physics, and engineering. Nowadays, there are more sophisticated electronic measurement devices available, but the Wheatstone bridge remains an essential concept in electrical engineering education and theory.