Question

6
30 (a) How does the thermal expansion of a metal strip depend on various
factors ? Why does a bimetallic strip bend on heating? With the
help of a diagram explain the principle of working of bimetallic
thermostat used in automatic heating devices.
ch
Explain why soft
i​

Answer 1

[a]Bimetallic strips

[b]When the strip gets hot, one of the metals expands more than the other so the whole strip bends very slightly. Eventually, it bends so much that it breaks open the circuit

Answer 2

Question 1:

How does the thermal expansion of a metal strip depend on various factors ?

Answer:

The factors on which thermal expansion of a metal strip depends are :

• Initial length of strip

• Linear expansion coefficient $\alpha$

• Change in temperature of strip

Question 2:

Why does a bimetallic strip bend on heating?

Answer:

• Bi-metallic strip consists of two different metallic strips with different coefficient of linear expansion.

• Now, the metal strip with higher $\alpha$ undergoes higher change in length as compared to the other metal with lower $\alpha$.

• As a result, the bimetallic strip bends with one side being concave and the other side being convex.

Question 3:

With the help of a diagram explain the principle of working of bimetallic thermostat used in automatic heating devices.

Answer:

• From the diagram , we can see that with change in temperature of the system there is differential increase in length of the the metal strips.

• This causes bending of the metal strips and causes removal of contact of the metal from the rest of the circuit.

• This breaks the circuit and stops current flow.