Interesting Questions in Physics

IAS PRELIMS-PHYSICS-I

The racing cars are driven only on dry tracks because
a) they can run faster only on dry tracks.
b) they may not skid in dry tracks.
c) the racing car tyres are not grooved.
d) the racing cars tyres are having wide base.

Answer: c
Explanation: Ordinary car tyres have grooves at their bottom so that it will not skid on wet roads and since the racing car tyres are not grooved it has to be driven only on dry roads

Out of the following, the one that is not a unit of length
a) angstrom.
b) micron.
c) parsec.
d) radian.

Answer: d
Explanation: Parsec is the unit of length used in astronomy 1 parsec=3.2616 light year

The equation E = mc2 gives the amount of energy released as a result of nuclear fission. What does the term 'm' stands for
a) the original mass of the nuclei
b) the final total mass of the nuclei
c) the increase in total mass of the nuclei
d) the decrease in total mass of the nuclei

Answer: d
Explanation: It is a good question. Many of them think that the term ‘m’ in the equation as the total mass. But actually, during fission reaction, there is a decrease in mass and this decrease in mass is referred as m in that equation. In fact this decrease in mass is released as energy in the fission reaction.

A ballet dancer can increase her angular velocity by folding her arms as this
a) increases the moment of inertia.
b) decreases the moment of inertia.
c) makes the MI to be zero.
d) makes the MI to be constant.

Answer: b
Explanation: The angular velocity is inversely proportional to the moment of inertia and hence Iw = constant.

A block of ice in a room at normal temperature.
a) does not radiate.
b) radiates less but absorbs more.
c) radiates more than it absorbs.
d) radiates as much as it absorbs.

Answer: b
Explanation: Ice is at a temperature of 0 C and so it radiates less. Since the room temperature is very much more than the temperature of ice it absorbs more.

The number of images of an object held between the parallel plane mirrors.
a) infinity.
b) one.
c) three.
d) Zero

Answer: a
Explanation: The formula for number of images formed when two mirrors are fixed with an angle = [(360/angle between the mirrors) –1], In this case the mirrors are kept with an angle of zero and so the number of images formed = [(360/0) –1] = infinity

Two lenses of power +12 and –2 dioptres are placed in contact. The focal length of the combination is.
a) 7.14 cm.
b) 10 cm
c) 12 cm
d) 14 cm

Answer: b
Explanation: The total power of the combination = 12-2 = 10. The power = reciprocal of focal length. Focal length = 1/10 metre = 10 cm

A converging lens is used to form an image on the screen. When the lower half of the lens is covered by an opaque screen then.
a) half of the image will disappear.
b) Complete image will be formed
c) No image is formed
d) Intensity of the image is high.

Answer: b
Explanation: The image formation not based on the size of the lens, but it is based on where the object is kept.

A man of 1.80 metre tall standing in front of a plane mirror. What is the minimum size of the mirror required to see his complete image.
a) 0.90 metre.
b) 1.80 metre
c) 0.45 metre
d) 1 metre

Answer: a
Explanation: Based on the laws of reflection, it has been calculated that the minimum size of the mirror required to view the full size of man is half of his height.

Which one of the following statement is not a feature of dry cell.
a) small size and easily portable
b) chemical reactions and irreversible
c) internal resistance is small
d) easily rechargeable

Answer: d
Explanation: The only disadvantage of the dry cell is that it cannot be recharged like a secondary batter or alkaline battery.

Nichrome which is used as heating element it has
a) low specific heat
b) low melting point
c) high specific heat
d) high conductivity

Answer: c
Explanation: Nichrome is an alloy; combination of metals of nickel and chromium and Nichrome will not get oxidized so easily, it has high melting point and high specific heat capacity.

Of the following devices which has small resistance
a) moving coil galvanometer
b) ammeter of range 0-1 A
c) ammeter of range 0-10 A
d) voltmeter

Answer: c
Explanation: The instrument which has a very small resistance can only measure a large current and in that principle, the ammeter which can measure a maximum current of 10 A must have a small resistance

Electromagnetic induction is not used in
a) transformer
b) room heater
c) ac generator
d) choke coil

Answer: b
Explanation: The room heater is operated on the principle of electrical energy is converted into heating energy by a coil of wire made of nichrome.

Transformer works on
a) ac only
b) dc only
c) both ac and dc
d) ac more effective than dc

Answer: a
Explanation: A transformer works on the principle of mutual induction and hence it can operate only on ac. It is a suitable example for the static induction.

Which of the following cannot be stepped up in transformer
a) input current
b) input voltage
c) input power
d) all the above

Answer: c
Explanation: The input power cannot be stepped up in the transformer. In transformer input power is equal to the output power.

Radio carbon dating is done by estimating in the specimen
a) the amount of ordinary carbon still present
b) the amount of radio carbon still present
c) the ratio of amount of radio and ordinary carbon still present
d) the ratio of amount of ordinary and radio carbon still present

Answer: c
Explanation: Radio carbon dating is used to determine age of fossils, which will stop absorbing radiocarbon once they are dead. So the age of fossils can be determined based on the ratio of amount of ordinary and radiocarbon present in them.

The rate of cooling of two different liquids in exactly similar calorimeters and kept in identical surroundings are the same if
a) the masses of the liquids are the same
b) equal masses of the liquids at the same temperature are taken
c) different volumes of the liquids at the same temperature are taken
d) equal volumes of the liquids at the same temperature are taken

Answer: d
Explanation: Newton’s law of cooling states that the rate of cooling of two different liquids put in exactly similar calorimeters and kept in identical surroundings are the same if equal volumes of the liquid at the same temperature are taken.

Which are the following statement is not true about thermal radiation
a) all bodies emit thermal radiation at all temperature
b) thermal radiation are electromagnetic waves
c) thermal radiations are not reflected from mirror
d) thermal radiations travel in free space with velocity of 3x108 m/s

Answer: c
Explanation: Thermal radiations have the properties of light and so it can be reflected from mirror.

A hollow metallic sphere filled with water is hung from a support by a long thread a small hole is made at the bottom of the sphere and it is oscillated. how will the time period of oscillations be affected as water slowly flows out of the hole
a) the time period will remain unchanged as water is flowing out.
b) The time period will keep increasing until the sphere is empty
c) The time period will keep decreasing until the sphere is empty.
d) The time period will increase at first then decrease until the sphere is empty. Initially the period will be the same as that when the sphere was full of water

Answer: d
Explanation: The length of the pendulum is the distance between the point of support and the center of gravity of the sphere. The center of gravity of the sphere is at the center when it is empty and completely filled with water. The center gravity falls below the center of the sphere as the water flows out until the sphere is half full and after which the center of gravity begins to raise, hence the effective length of the pendulum. Hence its time period will increase at first and decrease until the sphere is empty when it becomes equal to the time period when the sphere was full of water.

Which of the following is connected to a galvanometer to convert galvanometer as an ammeter
a) a low resistance in series
b) a high resistance in series
c) a high resistance in parallel
d) a low resistance in parallel

Answer: d
Explanation: If a galvanometer to be converted into an ammeter it has to be connected with a low resistance in parallel and if the galvanometer to be converted into a voltmeter it has to be connected with a high resistance in series.

A bird sitting on an uninsulated wire carrying a current feels quite safe because
a) the bird is a non conductor of electricity
b) resistance of the bird is very large
c) there is a large potential difference between the bird and wire
d) there is no potential difference between the bird and the wire

Answer: d
Explanation: Since the bird is sitting on the live wire, there is no potential difference maintained between the bird and the live wire. Suppose a person catches the live wire by standing on earth, there is potential difference between the live wire and the earth (earth is zero potential) and so current passes through the person.

The process responsible for the beautiful colours produced when white light is incident on a thin soap film is
a) scattering of light
b) interference of light
c) dispersion of light
d) refraction of light

Answer: b
Explanation: When light passes through the soap film, there shall be two light rays, which are coherent, but they have a phase difference and they form an interference pattern

Which of the following statement is wrong
a) visible region lies between ir and uv region
b) the sensitivity of eye is maximum for light of wavelength 600 nm
c) microwaves used in radar
d) X rays are used in the study of crystal structure

Answer: b
Explanation: The sensitivity of eye is highest for light of wavelength 560 nm, which is green colour.

When you stand in base feet with one foot on the stone floor and the other on a carpet .The stone floor foot feels colder than the carpet, what is the most likely explanation
a) the stone floor is at a lower temperature than carpet
b) air is unable to circulate through the carpet fibers
c) more energy flows from your foot to stone floor than from the foot with the carpet
d) more energy flows from your foot to carpet floor than from the foot with stone

Answer: c
Explanation: Stone is a good conductor of heat and conducts heat away and foot feels colder on the stone floor. Carpet is bad conductor of heat and does not conduct heat and the foot feels warmer.

An unlit match is held near to an extremely hot Bunsen flame, the match does not get hot enough to light because
e) the flame is not hot enough
f) the flame does not radiate any heat sideways
g) a match can only be lit striking it on a rough surface
h) air is a bad conductor of heat

Answer: d
Explanation: Air being bad conductor does not help the heat to travel to the match to heat up.

A spanner is used to loosen a nut. The turning effects depend on the force applied and the perpendicular distance from the force to the nut. What name given to the turning effect
i) moment
j) couple
k) torque
l) pressure

Answer: a
Explanation: The turning effect of a force is called a moment. That is why the moment of a momentum is called angular momentum.

A sound wave from violin has a larger amplitude than that from a flute. The sound wave from the flute has a higher frequency than that from the violin. Which instrument produces louder sound and which produces the sound of higher pitch.
m) flute and flute
n) flute and violin
o) violin and flute
p) violin and violin

Answer: c
Explanation: The amplitude is related to the loudness and the frequency is related to the pitch of a sound

Many houses have electricity meter that is read so that the cost of electricity used by the customer may be calculated. What does the electricity meter record?
q) voltage
r) current
s) power
t) energy

Answer: b
Explanation: The meter in our houses measures the electrical energy in terms of units. I unit =1000 Watt of electrical energy

In a cream separator the heavier particles of skimmed milk move away from the center and move towards the wall of the container. This is because of
u) Centripetal force.
v) Centrifugal force
w) Surface tension
x) viscosity

Answer: b
Explanation: The centrifuge machine consists of a vessel rotated with a high speed by using an electrical motor. When the vessel is filled with liquid, the particles experience the centrifugal force and try to fly away from the center. The centrifugal force is mrw2 and as w is the same for all the particles, centrifugal force is greater

On what does the quality of a sound wave depend
y) the loudness of the sound
z) the pitch of the sound
aa) the shape of the sound
bb) the speed of the sound

Answer: c
Explanation:
The shape of the sound wave decides the quality of the sound.