Electricity: Magnetic and Heating Effects MCQs for UPSC Prelims
110 practice questions covering Electricity: Magnetic and Heating Effects, organised into 2 topics.
110 questions include a written explanation.
Pick a topic below, or try the samples first.
An ordinary filament bulb feels hot after being on for a while, while an LED bulb of the same brightness feels only slightly warm. What does this suggest?
AThe LED bulb gives out no light at all
BHeat and light are the same form of energy
CThe filament bulb turns a much larger share of its electrical energy into heat
DThe filament bulb uses no electrical energy
Show answer and explanation
Correct answer: C - The filament bulb turns a much larger share of its electrical energy into heat
A filament has to be white hot before it gives light, so most of the energy it takes ends up as heat, while an LED produces light with far less heating. The LED is stated to be equally bright, the filament bulb obviously uses electrical energy, and heat and light are different forms of energy.
Q2
medium
Why is the filament of a bulb made very thin and quite long?
ASo that it can be seen easily from far away
BSo that it weighs less than the glass around it
CSo that the current cannot enter it at all
DSo that it offers a high resistance and becomes hot enough to glow
Show answer and explanation
Correct answer: D - So that it offers a high resistance and becomes hot enough to glow
A long thin wire resists the current strongly, so a large part of the electrical energy is turned into heat and the filament reaches glowing temperature. Its weight, how easily it is seen, and blocking the current are none of them reasons for its shape.
Q3
medium
Two wires of the same length and thickness, one of nichrome and one of copper, carry exactly the same current. Which becomes hotter, and why?
AThe copper wire, because copper is a metal
BThe nichrome wire, because it offers much more resistance to the current
CBoth become equally hot, because the current is the same
DNeither becomes hot, because metals do not heat up
Show answer and explanation
Correct answer: B - The nichrome wire, because it offers much more resistance to the current
A wire that resists the current more turns more electrical energy into heat, and nichrome resists far more than copper. Both are metals, so being a metal does not decide it, equal currents do not mean equal heating when the wires differ, and metals certainly do heat up.
Q4
medium
An electromagnet can just lift ten steel pins. Its maker then doubles the number of turns of wire and leaves everything else unchanged. The number of pins it can lift will most likely
Astay exactly the same
Bfall to zero
Cdepend only on the colour of the wire's covering
Dincrease
Show answer and explanation
Correct answer: D - increase
More turns give a stronger field for the same current, so the magnet holds more pins. Its strength cannot stay unchanged when the coil has been changed, the magnetism does not vanish, and the colour of the insulation has no effect whatsoever.
Q5
medium
A torch does not light. Which is the most efficient way to find the fault?
AReplace every part of the torch all at once
BShake the torch hard and hope that it works
CCheck the cells, the bulb and the contacts one at a time
DLeave the torch in bright sunlight for an hour
Show answer and explanation
Correct answer: C - Check the cells, the bulb and the contacts one at a time
Testing one part at a time shows which one is at fault, and that is what finding a fault means. Replacing everything is wasteful and teaches nothing, shaking may only loosen the contacts further, and sunlight does not recharge an ordinary dry cell.
Q6
medium
Fuse wire is usually made of a metal or alloy that has
Aa low melting point and a higher resistance than the circuit wiring
Ba strong magnetic property
Cno resistance to the current at all
Dthe highest melting point of all the metals
Show answer and explanation
Correct answer: A - a low melting point and a higher resistance than the circuit wiring
A fuse must heat up faster than the rest of the circuit and melt before anything else is damaged, so a low melting point together with a somewhat higher resistance is needed. A very high melting point would stop it ever melting, no resistance would mean no heating, and magnetism plays no part.
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