Question

Collect information about bimetallic strips and discuss in your class how a fire alarm is made using it.

Answer 1

Key Features of Bimetallic Strips:

1. Materials Used: Usually two metals with different coefficients of thermal expansion, such as brass and steel.
2. Working Principle: When heated, the strip bends due to unequal expansion of the two metals.
3. Applications: Used in devices like thermostats, thermometers, and fire alarms.

Fire Alarm Using Bimetallic Strips

1. Setup:

   • A bimetallic strip is fixed at one end, while the other end is free to move.
   • An electrical circuit, including a bell or buzzer, is placed such that the bimetallic strip completes the circuit when it bends.

2. Operation:

   • When the surrounding temperature rises due to a fire, the bimetallic strip is heated.
   • The strip bends because the two metals expand at different rates.
   • Once the strip bends enough to touch a contact point, it closes the circuit.
   • This triggers the alarm, alerting people to the fire.

3. Advantages:

   • Simple design.
   • Cost-effective.
   • Does not require continuous power supply until triggered.

4. Enhancements:

   • Sensitivity can be adjusted by choosing metals with appropriate coefficients of thermal expansion.
   • Additional components like temperature thresholds can be added for accuracy.