Physics GK Quiz-10

Physics GK Quiz-10

Physics Multiple Choice Questions (MCQs) Quiz for State and UPSC Civil Services Examinations. Objective Questions on Physics for competitive examinations.

181. Which of the following circuit elements is used to ‘block’ DC in an electronic circuit ?

(1) Resistances
(2) Capacitance
(3) Inductance
(4) Diode
181. (2) A capacitor (originally known as condenser) is a passive two-terminal electrical component used to store energy in an electric field. Capacitors are widely used in electronic circuits for blocking direct current while allowing alternating current to pass, in filter networks, for smoothing the output of power supplies, in the resonant circuits that tune radios to particular frequencies, in electric power transmission systems for stabilizing voltage and power flow, and for many other purposes. The capacitance is greatest when there is a narrow separation between large areas of conductor; hence capacitor conductors are often called plates, referring to an early means of construction.

182. Spectacles used for viewing 3D films have

(1) Bifocal lens
(2) Convex lens
(3) Concave lens
(4) Polaroids
182. (4) A polarized 3D system uses polarization glasses to create the illusion of three-dimensional images by restricting the light that reaches each eye, an example of stereoscopy. To present stereoscopic images and films, two images are projected superimposed onto the same screen or display through different polarizing filters. The viewer wears low-cost eyeglasses which contain a pair of different polarizing filters. As each filter passes only that light which is similarly polarized and blocks the light polarized in the opposite direction, each eye sees a different image. This is used to produce a three-dimensional effect by projecting the same scene into both eyes, but depicted from slightly different perspectives.

183. A boy sitting in an open car moving with the constant speed throws a ball straight up into the air. The ball falls

(1) behind him
(2) in front of him
(3) into his hand
(4) by his side
183. (1) The moment ball is thrown, it is moving with the velocity of the car. According to the inertia of motion it will continue to move in the same direction with the same velocity. As the ball is moving up and the down it will maintain its forward motion but practically it is not possible to neglect the resistance caused by air friction. So, the ball will fall behind him. Inertia is the resistance of any physical object to a change in its state of motion or rest, or the tendency of an object to resist any change in its motion.

184. The process involved in making soap is

(1) saponification
(2) hydrolysis
(3) condensation
(4) polymerisation
184. (1) Saponification is a process that produces soap, usually from fats and lye. In technical terms,
saponification involves base (usually caustic soda NaOH) hydrolysis of triglycerides, which are esters
of fatty acids, to form the sodium salt of a carboxylate. In addition to soap, such traditional saponification processes produces glycerol. “Saponifiable substances” are those that can be converted into soap. Vegetable oils and animal fats are the main materials that are saponified. These greasy materials, triesters called triglycerides, are mixtures derived from diverse fatty acids. Triglycerides can be converted to soap in either a one- or a two-step process.

185. A kilowatt-hour is unit of

(1) Energy
(2) Power
(3) Electric charge
(4) Electric current
185. (1) Work is defined as a force acting through a distance (a length of space), energy is always
equivalent to the ability to exert pulls or pushes against the basic forces of nature, along a path of a certain length. In the International System of Units (SI), energy is measured in joules, but in many fields other units, such as kilowatt-hours and kilocalories, are customary. All of these units translate to units of work, which is always defined in terms of forces and the distances that the forces act through.

186. Ventilators are provided near the ceiling of the room because

(1) the exhaled warmer air rises up and goes out
(2) these provide cross ventilation in the room
(3) these provide some sunlight in the room
(4) these do not look nice in the lower part
186. (1) Ventilation is a room air distribution strategy where conditioned outdoor air is supplied at floor level and extracted above the occupied zone, usually at ceiling height. A typical displacement ventilation system, such as one in an office space, supplies conditioned cool air from an air handling unit (AHU) through a low induction diffuser. The cool air spreads through the floor of the space and then rises as the air warms due to heat exchange with heat sources in the space (e.g., occupants, computers, lights). The warmer air has a lower density than the cool air, and thus creates upward convective flows known as thermal plumes. The warm air then exits the zone at the ceiling height of the room.

187. The hair of shaving brush clings together when removed from water due to

(1) Surface tension
(2) Viscosity
(3) Elasticity
(4) Friction
187. (1) Surface tension is a contractive tendency of the surface of a liquid that allows it to resist an external force. It is revealed, for example, in the floating of some objects on the surface of water, even though they are denser than water, and in the ability of some insects (e.g. water striders) to run on the water surface. This property is caused by cohesion of similar molecules, and is responsible for many of the behaviors of liquids. In the present case, because the forces inside the molecules of water also pulls in the hair on the shaving brush as they have less mass, due to this tension in the surface of the water the hair sticks together.

188. In severe winter, in cold countries water pipes burst because

(1) water expands on freezing
(2) contraction of water pipes
(3) high atmospheric pressure
(4) combined effect of all the above three
188. (1) Most liquids have a quite simple behavior when they are cooled (at a fixed pressure): they shrink. The liquid contract as it is cooled; because the molecules are moving slower they are less able to
overcome the attractive intermolecular forces drawing them closer to each other. Then the freezing
temperature is reached, and the substance solidifies, which causes it to contract some more because
crystalline solids are usually tightly packed. Water is one of the few exceptions to this behavior. When
liquid water is cooled, it contracts like one would expect until a temperature of approximately 4 degrees
Celsius is reached. After that, it expands slightly until it reaches the freezing point, and then when it freezes it expands by approximately 9%.

189. In the process of magnetisation of a bar

(1) The entire bulk of the bar gets magnetised
(2) Only the surface of the bar gets magnetised
(3) Only the ends of the bar get magnetised
(4) Only some parts of the outer layers of the bar get magnetised
189. (1) In classical electromagnetism, magneti-zation or magnetic polari-zation is the vector field that
expresses the density of permanent or induced magnetic dipole moments in a magnetic material. The
origin of the magnetic moments responsible for magnetization can be either microscopic electric
currents resulting from the motion of electrons in atoms, or the spin of the electrons or the nuclei. In
the process of magnetization of a bar, the entire bulk of the bar gets magnetized. The magnetization of a
material is done by electric current. By the process of magnetization, the formed pieces develop North
polarity on one end or side and South polarity on the other end or side, in a very short period of time.

190. A falling drop of rain water acquires the spherical shape due to

(1) Viscosity
(2) Surface Tension
(3) Atmospheric pressure
(4) Gravitational force
190. (2) Raindrops start out as round high in the atmosphere as water collects on dust and smoke
particles in clouds. But as raindrops fall, they lose their rounded shape. A raindrop falling through the
atmosphere forms as a roughly spherical structure due to the surface tension of water. This surface
tension is the “skin” of a body of water that makes the molecules stick together. The cause is the weak
hydrogen bonds that occur between water molecules. On smaller raindrops, the surface tension is stronger than in larger drops. The reason is the flow of air around the drop. Air flow on the bottom of the water drop is greater than the airflow at the top.

191. The weakest of all fundamental forces is

(1) Gravitational force
(2) Electrostatic force
(3) Magnetic force
(4) Nuclear force
191. (1) In particle physics, fundamental interactions (sometimes called interactive forces or fundamental forces) are the ways that elementary particles interact with one another. An interaction is fundamental when it cannot be described in terms of other interactions. The four known fundamental interactions are electromagnetism, strong interaction (“strong nuclear force”), weak interaction (“weak nuclear force”), and gravitation. All are non-contact forces. Gravitation is by far the weakest of the four interactions. The weakness of gravity can easily be demonstrated by suspending a pin using a simple magnet (such as a refrigerator magnet). The magnet is able to hold the pin against the gravitational pull of the entire Earth.

192. Velocity of sound in air does not change with the change of

(1) Temperature of air
(2) Pressure of air
(3) Moisture content in air
(4) Wind in the direction of propagation of sound
192. (2) The speed of sound in an ideal gas is independent of frequency, but it weakly depends on frequency for all real physical situations. It is a function of the square root of the absolute temperature, but is independent of pressure or density for a given ideal gas. Sound speed is slightly dependent on pressure only because air is not quite an ideal gas. In addition, for different gases, the speed of sound is inversely dependent on square root of the mean molecular weight of the gas, and affected to a lesser extent by the number of ways in which the molecules of the gas can store heat from compression, since sound in gases is a type of compression.

193. The density of a gas is maximum at

(1) Low temperature, low pressure
(2) Low temperature, high pressure
(3) High temperature, low pressure
(4) High temperature, high pressure
193. (2) The density of gases depends upon the temperature. The higher the temperature, the more
the molecules are spread out and the lower the density. The result is that warm gases rise and cool
gases sink. The same concept helps to explain the weather resulting in high and low pressures. High
pressure means high density, cooler, sinking air. Low pressure means low density, warmer, rising air. In
general, density can be changed by changing either the pressure or the temperature.

194. The cause for the Tsunami, as deduced by the seismologists, is

(1) gravitational pull of the moon
(2) low pressure trough in the ocean
(3) deformation of sea floor and vertical displacement of water
(4) sudden change in the monsoon wind
194. (3) Earthquakes, volcanic eruptions and other underwater explosions (including detonations of
underwater nuclear devices), landslides, glacier calvings, meteorite impacts and other disturbances
above or below water all have the potential to generate a tsunami. Tsunami can be generated when the sea floor abruptly deforms and vertically displaces the overlying water. Tectonic earthquakes are a particular kind of earthquake that are associated with the Earth’s crustal deformation; when these earthquakes occur beneath the sea, the water above the deformed area is displaced from its equilibrium position. More specifically, a tsunami can be generated when thrust faults associated with convergent or destructive plate boundaries move abruptly, resulting in water displacement, owing to the vertical component of movement involved.

195. Which one of the following wavelengths of light is most effective in photosynthesis ?

(1) Blue
(2) Green
(3) Orange
(4) Yellow
195. (1) Photosynthesis, process by which green plants and certain other organisms use the energy of light to convert carbon dioxide and water into the simple sugar glucose. The wavelength most effective in conducting photosynthesis is 420nm. Actually, 420nm is on the blue side of the spectrum, which makes up between 1 and 10% of the light needed for photosynthesis. There is a plateau on the blue side
when comparing blue wavelength effects on photosynthesis, and 420nm is right on the edge of it. 430nm would be more in the middle of the plateau, making it the safer bet. Plants need red light, and
lots of it. Red light contributes to over 90% of photosynthesis.

196. Why is it difficult to breathe at higher altitudes?

(1) Due to low air pressure
(2) Due to low temperature
(3) Due to ozone
(4) Due to high humidity
196. (1) Low air pressure is usually the most significant limiting factor in high mountain regions. The
percentage of oxygen in the air at 3.2 km is essentially the same as at sea level (21%). However, the air
pressure is 30% lower at the higher altitude due to the fact that the atmosphere is less dense—that is,
the air molecules are farther apart. At high altitudes, the lower air pressure makes it more difficult for
oxygen to enter our vascular systems. The result is hypoxia, or oxygen deprivation. In serious cases,
pneumonia-like symptoms (pulmonary edema) due to hemorrhaging in the lungs and an abnormal
accumulation of fluid around the brain (cerebral edema) develop. Pulmonary and cerebral edema
usually results in death within a few days if there is not a return to normal air pressure levels. There is
also an increased risk of heart failure due to the added stress placed on the lungs, heart, and arteries at high altitudes.

197. The strongest force in nature is

(1) electrical force
(2) gravitational force
(3) nuclear force
(4) magnetic force
197. (3) The nuclear force (or nucleon–nucleon interaction or residual strong force) is the force between two or more nucleons. It is responsible for binding of protons and neutrons into atomic nuclei. The energy released causes the masses of nuclei to be less than the total mass of the protons and neutrons which form them; this is the energy used in nuclear power and nuclear weapons. The force is powerfully attractive between nucleons at distances of about 1 femtometer (fm) between their centers, but rapidly decreases to insignificance at distances beyond about 2.5 fm.

198. According to the theory of relativity, which of the following always remains constant ?

(1) Length of an object
(2) Time
(3) Space
(4) Velocity of light
198. (4) The theory of relativity, or simply relativity, generally encompasses two theories of Albert
Einstein: special relativity and general relativity. Concepts introduced by the theories of relativity
include: Measurements of various quantities are relative to the velocities of observers. In particular,
space and time can dilate. Space time: space and time should be considered together and in relation to
each other. The speed of light is nonetheless invariant, the same for all observers.

199. The spoon dropped by an astronaut in a satellite will

(1) fall to the floor
(2) remain stationary
(3) continue to follow the motion of the satellite
(4) move tangentially away
199. (3) An orbiting satellite is a projectile in the sense that the only force acting upon an orbiting satellite is the force of gravity. A satellite is acted upon by the force of gravity and this force does accelerate it towards the Earth. In the absence of gravity a satellite would move in a straight line path tangent to the Earth. In the absence of any forces whatsoever, an object in motion (such as a satellite) would continue in motion with the same speed and in the same direction. The force of gravity acts upon a high speed satellite to deviate its trajectory from a straight-line inertial path. Indeed, a satellite is accelerating towards the Earth due to the force of gravity. As far as spoon dropped by astronaut in a satellite is concerned, it continues to follow the motion of the satellite as there is inertia of motion acting upon it.

200. A colour-blind person cannot

(1) see distant objects
(2) see black colour
(3) distinguish between certain colours
(4) have persistence of vision