Applied Physics I: Chapter 3: Properties of Matter - Thermal Physics
Bimetallic strips
Definition, Fabrication, Applications - Thermal Physics
As the name itself implies that Bimetallic strips are made up of two thin metal strips with different co‒efficient of thermal expansion.
BIMETALLIC
STRIPS
Definition
As the name itself
implies that Bimetallic strips are made up of two thin metal strips with
different co‒efficient of thermal expansion.
Fabrication
Let
us consider two metals viz.
1.
Brass of higher co‒efficient of thermal expansion
2.
Steel of lower co‒efficent of thermal expansion
These
two metals are welded as shown in Fig. 3.4.
While Heating
When
the bimetallic strip is heated then the strip will start expanding and
therefore the
brass,
which has large co‒efficient of thermal expansion expands more than the steel
and hence the bimetallic strip bends like an arc as shown in Fig. 3.5.
While cooling
Now,
when the bimetallic strip is cooled then the strip will start contracting and
therefore the brass which has large co‒efficient of thermal expansion contacts
more than the steel and bends dag like an arc as shown in Fig. 3.6.
Applications
Bimettalic
strips are commonly used in water heaters as temperature controller as detailed
below.
A
water heater consists of a heater coil connected to the bimetallic strip as
shown in Fig. 3.7. At room temperature the bimetallic strip remains straight
and the knob attached to the bimetallic strip helps the circuit to be in the
closed condition as shown in Fig. 3.7.
When
the power supply is switched ON, then the current starts flowing through the
bimettalic strip to the heater coil as shown in Fig. 3.7 and the water is
heated. Due to increase in temperature of the water, the heater coil becomes
hot and in turn the bimetallic strip also becomes hot. Now, due to thermal
expansion, the bimetallic strip starts bending and at a particular temperature
the knobs get detached and hence, the circuit becomes open circuit as shown in
Fig. 3.8.3
Again,
when the water becomes cool, the temperature of the bimetallic strip decreases,
and in turn the strip contracts and the circuit is closed as shown in Fig. 3.7.
This process continues and hence the bimetallic strip act as a temperature
controller (or) as a switch to maintain the temperature of the water.
Applied Physics I: Chapter 3: Properties of Matter - Thermal Physics : Tag: Applied Physics : Definition, Fabrication, Applications - Thermal Physics - Bimetallic strips
Applied Physics I: Chapter 3: Properties of Matter - Thermal Physics
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