Question

ravi made a makeshift heater at home during winters by coiling a nichrome wire around a core and passing an electric current through it. When he switched the heater on he realized that the heating wasn’t much. So, he decided to add more coils onto the core and got more nichrome wire to do so.


1. Do you think his decision was right in adding more coils to increase the heating?


2. Give a reason for your answer.

Answer 1

Yes, his decision of adding more coils was correct.

But why ??

• Heat produced in a coil is essentially due to resistance of current flow through the nichrome wire.

• As current flows through the wire, heat is generated, hence higher the resistance, higher will be the heat produced.

$\boxed{ \bf H = {i}^{2} \times r \times t}$

• So, when current and time is constant, we can say:

$\boxed{ \bf H \propto r}$

• Now, resistance is written as :

$\boxed{ \bf H \propto \dfrac{ \rho \times l}{a} }$

• For constant area of cross-section of wire and $\rho$, we can say:

$\boxed{ \bf H \propto l }$

• So, higher length of nichrome wire, higher will be the heat produced.

So, his decision was correct.