Question

The resistance of a heating coil in a heating appliance operating at \(200\ \text{V}\) is \(60\ \Omega\).

• [(a)] Which alloy is used to make heating coil of heating appliances?
• [(b)] Calculate the amount of heat produced if electricity flows through this appliance for 5 minutes.
• [(c)] If another appliance with a resistance less than \(60\ \Omega\) is operated at the same voltage for 5 minutes, will the amount of heat produced increase or decrease? What is your justification?

Hint:

At constant voltage: Lower resistance → more current → more heat

Answer 1

(a) Alloy used
Concept: Heating elements
Heating coils are made of materials with high resistivity and high melting point. Answer: \[ \text{Nichrome (Nickel-Chromium alloy)} \] (b) Heat produced
Concept: Joule’s Law of Heating
\[ H = \frac{V^2}{R} \times t \] Step 1: Given data}
\[ V = 200\ \text{V}, \quad R = 60\ \Omega, \quad t = 5\ \text{min} = 300\ \text{s} \] Step 2: Substitute values}
\[ H = \frac{(200)^2}{60} \times 300 \] Step 3: Calculation}
\[ H = \frac{40000}{60} \times 300 = 666.67 \times 300 = 200000\ \text{J} \] Conclusion (b): \[ \text{Heat produced} = 2 \times 10^5\ \text{J} \] (c) Effect of decreasing resistance
Step 1: Formula relation}
\[ H = \frac{V^2}{R} \times t \] Step 2: Observation}
At constant voltage and time: \[ H \propto \frac{1}{R} \] Step 3: Conclusion}
If resistance decreases: \[ H \text{ increases} \] Final Answer (c): \[ \text{Heat produced will increase because heat is inversely proportional to resistance.} \]