Question

Nichrome wire is used as the heating element because it has
A. Low specific resistance
B. Low melting point
C. High specific resistance
D. High conductivity

Answer 1

Hint: The rate of heat produced with time in a conducting material is given as $P={{i}^{2}}R$. Specific resistance of a material is its resistance when its length is of one unit and its cross sectional area is also of one unit. With this information figure out the correct option.

Formula used:
$P={{i}^{2}}R$

Complete step by step answer:
Heating elements used electric appliances work on the principle of Joule’s law of heating. According to the law, when a current passes through a material, the material heats up. This is due to the resistance of the given material.
One of these types of materials is nichrome wire.
Resistance is the ability of the material to oppose the flow of charges when a potential difference is applied across the material.
Suppose a conducting material of length l and uniform cross sectional area A, connected in a circuit in such a way that a potential difference is created across the material. Then according to Ohm’s law, there is current in the circuit. The material continuously consumes energy and converts the energy into heat.
The rate of heat produced with time (power of heat) in the material is given as $P={{i}^{2}}R$.
Here, i is the current flowing in the material and R is the resistance of the material.
This means that the heat generated in a conducting material is directly proportional to the resistance of the material.
Specific resistance is the resistance of the material for one unit length and one unit cross sectional area of the material.
Therefore, to produce more heat, the specific resistance of the material must be high.
Hence, the nichrome wire is used as a heating element because it has high specific resistance.
Thus, the correct option is C.

Note: A nichrome wire is used as a heating element because of its high melting point and high resistivity (low conductivity) also.
Having a high melting does not allow the nichrome wire to melt easily when a large amount of heat is produced.
Resistance of a material is directly proportional to the resistivity of the material. Resistivity of the material is reciprocal of its conductivity. Hence, nichrome has high resistivity and low conductivity.