Heating Effect of Electric Current (Joule's Law) MCQs

Q1. Which appliance does NOT primarily use the heating effect of current?

• A.an electric iron
• B.a room heater
• C.an electric fan
• D.an electric geyser

Answer: C. an electric fan

Q2. Why is the heating effect undesirable in a computer or TV?

• A.the heat can damage components and wastes energy
• B.it improves picture quality
• C.it increases the supply voltage
• D.it makes them work faster

Answer: A. the heat can damage components and wastes energy

Asked for computer or TV?; data is laid out in the stem. By Joule's law of heating: H = I^2*R*t (or equivalently H = V*I*t = V^2*t/R). Joule's law of heating: H = I^2*R*t (or equivalently H = V*I*t = V^2*t/R). substitute the given current, resistance and time into this expression. Therefore option A) the heat can damage components and wastes energy. Others fail: option B) 'it improves picture quality' fails since Overheating degrades, not improves, performance; option C) 'it increases the supply voltage' is wrong because Heat does not raise the voltage.

Q3. Why are the heating coils of electric toasters and electric irons made of an alloy (like nichrome) rather than a pure metal?

• A.Because alloys like nichrome have high resistivity and do not oxidise (burn) easily at high temperatures
• B.Because alloys have lower resistivity than pure metals
• C.Because alloys are cheaper than pure metals
• D.Because alloys conduct electricity better than pure metals

Answer: A. Because alloys like nichrome have high resistivity and do not oxidise (burn) easily at high temperatures