32 practice questions on properties-of-materials from the Materials Around Us section of the UPSC Prelims syllabus. 32 come with a written explanation. Try the sample set below - the answer stays hidden until you ask for it.
Which of these is a lustrous material?
Correct answer: B - Freshly cut iron
A freshly cut piece of iron shines brightly, so it is lustrous. Chalk, wood and cardboard all have dull surfaces that do not reflect light in this way.
Which of these is opaque?
Correct answer: B - A wooden door
A wooden door stops light completely, so nothing behind it can be seen. A clean glass window and clear water are transparent. Butter paper lets some light through with a blurred view, which makes it translucent.
Two coins are placed side by side. One shines and the other looks dull. Which property is being compared?
Correct answer: C - Appearance
Shine and dullness are noticed simply by looking, so appearance is the property being compared. Hardness would need a scratch test, solubility would need a glass of water, and floating would need a tub of water.
Why can a huge steel ship float although a small steel nail sinks?
Correct answer: A - The ship is hollow and holds a great deal of air, so it is light for its size
A ship encloses a large volume of air inside its hull, so the whole ship is light for the space it takes up and it stays afloat. Metals do sink in sea water. Ships are built of ordinary steel. The last statement reverses what is seen every day.
A sheet of butter paper is held in front of a lit candle and only a blurred glow is seen. Butter paper is therefore
Correct answer: D - translucent
Light passes through but the image is not clear, which is exactly what translucent means. A transparent sheet would show the flame sharply. An opaque sheet would show no light at all. Lustre describes a shiny surface, not what passes through.
A steel plate floats when placed flat and gently on water, but the same plate sinks when dropped in edge first. What does this show?
Correct answer: B - Whether an object floats can depend on how it is placed in the water
The same plate behaves differently in the two trials, so the way it is placed matters as well as the material it is made of. The steel itself does not change. The water is the same in both trials. Since it sank in one trial, it does not always float.
Which of these sinks when placed in water?
Correct answer: A - A stone
A stone is heavy for its size, so it sinks. A hollow plastic ball, a dry leaf and a piece of thermocol are all very light for their size and stay on the surface.
Which of these is insoluble in water?
Correct answer: A - Sand
Sand settles at the bottom and can still be seen, so it is insoluble. Common salt, sugar and glucose powder all dissolve and vanish into the water, leaving it clear.
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