Which of the following happen to the wire within a Wheatstone bridge when it is exposed to oxygen concentrations higher than room air?

1. Its resistance decreases.
2. Its resistance increases.
3. It cools down.
4. It heats up.
a. 1 and 4 c. 1 and 4
b. 2 and 3 d. 1 and 3

ANS: D
The Wheatstone bridge contains two parallel wires that receive current flow from an external power source, usually a battery. One of these wires, which serves as the reference, is exposed to room air. The other wire is located in the sample chamber and is exposed to the gas being ana-lyzed. If the sample gas contains a higher oxygen-to-nitrogen ratio than is present in room air, the sample wire cools and its resistance decreases, because oxygen is a better conductor of heat than nitrogen.