Fog is an example of a
Answer: A
Fog is a liquid dispersed in a gas.
It is an aerosol of tiny water droplets suspended in air, formed when moist air is cooled below its dew point. Smoke is a solid in a gas, an emulsion a liquid in a liquid, and foam a gas in a liquid.
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Stars which appear single to the naked eye but are double when seen through a telescope are
Answer: B
Such stars are binaries.
A binary is a pair of stars bound by gravity and orbiting their common centre of mass, too close together to be separated by the eye but resolved in a telescope. More than half the stars in the sky are thought to belong to multiple systems.
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A telescope and microscope differ in that______.
Answer: A
A telescope has an objective of large focal length and an eyepiece of small focal length.
Its magnification is \(f_o/f_e\), so a long objective focal length helps. A microscope is the other way round: its objective has a very short focal length, of a few millimetres, to give a large magnified real image which the eyepiece then magnifies again.
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Lightning conductors are made up of _________.
Answer: C
Lightning conductors are made of copper.
Copper conducts almost as well as silver at far less cost, so it carries the enormous discharge current to earth without melting, and it resists corrosion out of doors. The conductor runs from a pointed rod above the roof to a plate buried in moist earth.
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A piece of ice is floating in water kept in a beaker. When all the ice melts the level of water will
Answer: C
The level will remain the same.
Floating ice displaces its own weight of water; on melting it becomes exactly that weight of water, which occupies exactly the volume it had been displacing. This is why melting sea ice does not raise sea level, whereas melting land ice does.
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Who discovered X-Rays?
Answer: B
Wilhelm Roentgen discovered X-rays, in 1895.
He noticed a fluorescent screen glowing while he worked with a covered cathode-ray tube, and called the unknown radiation X. He received the first Nobel Prize in Physics in 1901, and the first X-ray photograph was of his wife's hand.
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Isotopes of an element contain
Answer: A
Isotopes have the same number of protons but different numbers of neutrons.
The proton count fixes the element and its chemistry; the differing neutron count changes only the mass. Carbon-12, carbon-13 and carbon-14 are examples, all with six protons.
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The energy possessed by a body in motion is called
Answer: B
The energy of a body in motion is its kinetic energy.
\[KE = \tfrac{1}{2}mv^2\] Note that it varies as the square of the speed, so doubling the speed quadruples the energy - which is why stopping distances grow so sharply with speed.
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What is refractive index ?
Answer: C
Refractive index is the ratio of the speed of light in vacuum to its speed in the medium.
\[n = \frac{c}{v}\] It is always greater than one, since nothing travels faster than light in vacuum, and it measures how much the medium slows and hence bends the light. For water \(n = 1.33\) and for glass about 1.5.
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A hunter on the ground wishes to shoot a bird on a tree at a distance with his rifle. He has to point the rifle
Answer: B
He must point at a higher elevation than the bird.
The bullet begins to fall under gravity the moment it leaves the barrel, so it follows a parabola and drops below the line of sight. Aiming slightly high compensates for that fall over the flight time - which is why rifle sights are zeroed for a particular range.
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