Question

The material of heating element in an electric press has :
A) High melting point and high specific resistance
B) High melting point and low specific resistance
C) Low melting point and high specific resistance
D) Low melting point and high specific resistance

Answer 1

Any heating element is an element that converts electrical energy into heat through the process of joule heating. According to joule’s law total energy produced within some timespan is proportional to time and applied voltage’s square and inversely proportional to the resistance of the material.

Formula used:
Heat energy generated within some timespan through current flow is given by:
$E = {I^2}Rt = VIt = \dfrac{{{V^2}t}}{R}$ ……………………….(1)
Where,
E is total energy (mostly in terms of heat) produced,
I is current through the material,
R is resistance of the material,
t is the timespan of current passing through the circuit.

Complete step by step answer:
From eq.(1) we can see that to increase the amount of heat produced in the material one must increase the current flow through the circuit by decreasing the resistance assuming that the applied voltage is kept constant. Also, the material must have a high melting point and shouldn’t oxidize easily with a low expansion coefficient. Otherwise, the material might burn or get distorted in shape and cause problems.

Correct answer:
The material of the heating element in an electric press has (b) High melting point and low specific resistance.

Note: So we got the relation that to increase heat obtained from the material by joule heating effect the resistance of the material must be minimized. Practically, the materials that have less resistivity (like copper and silver) don’t have higher melting points and easily get oxidized. So, for practical purposes nichrome wires are used as heating material which has a very high melting point and very less reactive, but has moderately higher resistance.