# Physics GK Quiz-12

## Physics GK Quiz-12

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

### 221. Fog is an example of

(1) Gas dispersed in gas
(2) Liquid dispersed in gas
(3) Solid dispersed in gas
(4) Solid dispersed in liquid
221. (2) Fog is a collection of liquid water droplets or ice crystals suspended in the air at or near the Earth’s surface. While fog is a type of stratus cloud, the term “fog” is typically distinguished from the more generic term “cloud” in that fog is low-lying, and the moisture in the fog is often generated locally (such as from a nearby body of water, like a lake or the ocean, or from nearby moist ground or marshes). Fog is distinguished from mist only by its density, as expressed in the resulting decrease in visibility.

### 222. A concave lens always forms an image which is

(1) real and erect
(2) virtual and erect
(3) real and inverted
(4) virtual and inverted
222. (2) Concave lens possesses at least one surface that curves inwards. It is a diverging lens, spreading out those light rays that have been refracted through it. A concave lens is thinner at its centre than at its edges, and is used to correct short-sightedness (myopia). After light rays have passed through the lens, they appear to come from a point called the principal focus. The image formed by a concave lens is virtual, upright, and smaller than the object, and it cannot be projected onto a screen.

### 223. The modulus of rigidity is the ratio of

(1) longitudinal stress to longitudinal strain
(2) Volume stress to volume strain
(3) shearing stress to shearing strain
(4) tensile stress to tensile strain
223. (3) In materials science, shear modulus or modulus of rigidity, denoted by G, or sometimes S , is defined as the ratio of shear stress to the shear strain. The shear modulus describes the material’s response to shearing strains (like cutting it with dull scissors).The shear modulus is concerned with the deformation of a solid when it experiences a force parallel to one of its surfaces while its opposite face experiences an opposing force (such as friction). In the case of an object that’s shaped like a rectangular prism, it will deform into a parallelepiped.

### 224. The propagation of sound waves in a gas involves

(2) isothermal compression and rarefaction
(3) isochoric compression and rarefaction
(4) isobaric compression and rarefaction
224. (1) Sound is a mechanical wave that is an oscillation of pressure transmitted through a solid, liquid, or gas, composed of frequencies within the range of hearing. During propagation, waves can be reflected, refracted, or attenuated by the medium. Sound is transmitted through gases, plasma, and liquids as longitudinal waves, also called compression waves. Through solids, however, it can be transmitted as both longitudinal waves and transverse waves. Longitudinal sound waves are waves of alternating pressure deviations from the equilibrium pressure, causing local regions of compression and rarefaction, while transverse waves (in solids) are waves of alternating shear stress at right angle to the direction of propagation.

### 225. Which of the following is not a property of heavy water ?

(1) Boiling point of heavy water is lower than that or ordinary water
(2) Density of heavy water is higher than that of ordinary water
(3) Freezing point of heavy water is higher than that of ordinary water
(4) It produces corrosion
225. (1) Heavy water, formally called deuterium oxide or 2H 2O or D2O, is a form of water that contains the hydrogen isotope deuterium, rather than the common protium isotope. The colloquial term heavy water is often also used to refer a highly enriched water mixture that contains mostly deuterium oxide but also contains some ordinary water molecules as well: for instance heavy water used in CANDU reactors is 99.75% enriched by hydrogen atom-fraction. In comparison, in ordinary water, there are only about 156 deuterium atoms per million hydrogen atoms). In its pure form, it has a density about 11% greater than water, but otherwise, is physically and chemically similar. Heavy water is 10.6% denser than ordinary water, a difference which is not immediately obvious.

### 226. In which of the following processes is energy released ?

(1) Respiration
(2) Photosynthesis
(3) Ingestion
(4) Absorption
226. (1) Cellular respiration is the set of the metabolic reactions and processes that take place in the cells of organisms to convert biochemical energy from nutrients into adenosine triphosphate (ATP), and then release waste products. The reactions involved in respiration are catabolic reactions, which break large molecules into smaller ones, releasing energy in the process as they break high-energy bonds. Respiration is one of the key ways a cell gains useful energy to fuel cellular activity. Chemically, cellular respiration is considered an exothermic redox reaction.

### 227. If input frequency of a full wave rectifier be n, then output frequency would be

(1)n/2
(2) n
(3)3n/2
(4) 2n
227. (4) The frequency of a full-wave rectifier is double that of the input, if the input is a sine wave. A fullwave rectifier converts the whole of the input waveform to one of constant polarity (positive or
negative) at its output. Full-wave rectification converts both polarities of the input waveform to DC (direct current), and yields a higher mean output voltage. Two diodes and a centre tapped transformer, or four diodes in a bridge configuration and any AC source (including a transformer without center tap), are needed. Single semiconductor diodes, double diodes with common cathode or common anode, and fourdiode bridges, are manufactured as single components.

### 228. Heat transfer horizontally within the atmosphere is called

(1) Conduction
(2) Convection
(3) Absorption
228. (4) Convection transfers heat vertically into the atmosphere. In order for heat to be transferred to
other regions, it must be transferred horizontally by the wind. The horizontal transfer of heat by the wind is called advection. Advection is a transport mechanism of a substance or conserved property by
a fluid due to the fluid’s bulk motion. An example of advection is the transport of pollutants or silt in a
river by bulk water flow downstream.

### 229. Noise is measured in

(1) Watt
(2) REM
(4) Decibel
229. (4) The decibel (dB) is a logarithmic unit that indicates the ratio of a physical quantity (usually power or intensity) relative to a specified or implied reference level. A ratio in decibels is ten times the logarithm to base 10 of the ratio of two power quantities.

### 230. The bats can fly in the dark because

(1) they can see the objects in darkness
(2) they have weak legs and are likely to be attacked by predators
(3) they generate flashes of light
(4) they generate ultrasonic sound waves
230. (4) Bats use echolocation to navigate and forage, often in total darkness. They generally emerge from their roosts in caves, attics, or trees at dusk and hunt for insects into the night. Their use of echolocation allows them to occupy a niche where there are often many insects (that come out at night since there are fewer predators then) and where there is less competition for food, and where there are fewer other species that may prey on the bats themselves. Microbats generate ultrasound via the larynx and emit the sound through the open mouth or, much more rarely, the nose.

### 231. What changes will happen to a bowl of ice and water kept at exactly zero degree Celsius ?

(1) All ice will melt
(2) All water will become ice
(3) No change will happen
(4) Only some ice will melt
231. (3) Fresh water cooled to zero (0) degree Celsius and subjected to additional loss of heat energy normally will freeze. A mixture of fresh water and ice has an equilibrium temperature of zero (0) degree Celsius. Adding heat to the mixture causes ice to melt whereas removing heat causes water to freeze. For that reason, 0 (zero) degree Celsius is called the freezing point of fresh water. Cloud droplets can cool well below the usual freezing point while remaining liquid. Such cloud droplets are composed of super cooled water.

### 232. Curie point is the temperature at which

(2) A metal loses magnetic properties.
(3) A metal loses conductivity
(4) Transmutation of metal occurs.
232. (2) In physics and materials science, the Curie temperature (Tc), or Curie point, is the temperature
at which a ferromagnetic or a ferromagnetic material becomes paramagnetic on heating; the effect is
reversible. A magnet will lose its magnetism if heated above the Curie temperature. The term is also used in piezoelectric materials to refer to the temperature at which spontaneous polarization is lost on heating.

### 233. Angle of friction and angle of repose are

(1) equal to each other
(2) not equal to each other
(3) proportional to each other
(4) None of the above
233. (1) The angle of repose or the critical angle of repose, of a granular material is the steepest angle of descent or dip of the slope relative to the horizontal plane when material on the slope face is on the verge of sliding. This angle is in the range 0°–90°.When bulk granular materials are poured onto a horizontal surface, a conical pile will form. The internal angle between the surface of the pile and the horizontal surface is known as the angle of repose and is related to the density, surface area and shapes of the particles, and the coefficient of friction of the material. For certain applications it is more useful to define static friction in terms of the maximum angle before which one of the items will begin sliding. This is called the angle of friction or friction angle. The tangent of the angle of friction is equal to the coefficient of friction. Angle of friction is equal to the angle of repose.

### 234. If a boy sitting in a train, which is moving at a constant velocity, throws a ball straight up into the air, the ball will

(1) fall in front of him
(2) fall behind him
(3) fall into his hand
(4) None of the above
234. (3) If a person throws a ball vertically upwards in a moving train, it comes back to his hand. The moment the ball was thrown, the ball was also in motion alone with the person who had thrown the ball and the train. This is due to inertia of motion. So when the ball remains in the air, both the person and the ball move ahead by the same distance. This makes the ball to come back to his hand on its return.

### 235. Intensity of gravitational field of earth is maximum at

(1) Poles
(2) Equator
(3) Centre of earth
(4) Surface
235. (1) A perfect sphere of spherically uniform density (density varies solely with distance from centre) would produce a gravitational field of uniform magnitude at all points on its surface, always pointing directly towards the sphere’s centre. However, the Earth deviates slightly from this ideal, and there are consequently slight deviations in both the magnitude and direction of gravity across its surface. Furthermore, the net force exerted on an object due to the Earth, called “effective gravity” or “apparent gravity”, varies due to the presence of other factors, such as inertial response to the Earth’s rotation. A scale or plumb bob measures only this effective gravity. The major reason for the difference in gravity at different latitudes is that the Earth’s equatorial bulge (itself also caused by inertia) causes objects at the Equator to be farther from the planet’s centre than objects at the poles. Because the force due to gravitational attraction between two bodies (the Earth and the object being weighed) varies inversely with the square of the distance between them, an object at the Equator experiences a weaker gravitational pull than an object at the poles.

### 236. The spokes used in the wheel of a bicycle increase its

(1) Moment of inertia
(2) Velocity
(3) Acceleration
(4) Momentum
236. (1) A spoke is one of some number of rods radiating from the center of a wheel (the hub where the axle connects), connecting the hub with the round traction surface. Since bicycle and wheelchair wheel spokes are only in tension, flexible and strong materials such as synthetic fibers, are also occasionally used. Metal spokes used in bicycles also increase the moment of inertia.

### 237. A transformer works on the principle of

(1) Self induction
(2) Mutual induction
(3) Generator
(4) Inverter
237. (2) A transformer is a power converter that transfers electrical energy from one circuit to another through inductively coupled conductors—the transformer’s coils. A varying current in the primary winding creates a varying magnetic flux in the transformer’s core and thus a varying magnetic field through the secondary winding. This varying magnetic field induces a varying electromotive force (EMF), or “voltage”, in the secondary winding. This effect is called inductive coupling. The transformer is based on principle of mutual induction in which, firstly, that an electric current can produce a magnetic field (electromagnetism) and second that a changing magnetic field within a coil of wire induces a voltage across the ends of the coil (electromagnetic induction). Changing the current in the primary coil changes the magnetic flux that is developed. The changing magnetic flux induces a voltage in the secondary coil.

### 238. The sky appears blue because

(1) all colours interfere to produce blue
(2) in white light, the blue component dominates
(3) the atmosphere scatters blue colour more than the others
(4) it is actually blue
238. (3) Diffuse sky radiation is solar radiation reaching the Earth’s surface after having been scattered from the direct solar beam by molecules in the atmosphere. Of the total light removed from the direct solar beam by scattering in the atmosphere (approximately 25% of the incident radiation when the sun is high in the sky, depending on the amount of dust and haze in the atmosphere), about two-thirds ultimately reaches the earth as diffuse sky radiation. The sunlit sky is blue because air scatters short-wavelength light more than longer wavelengths. Since blue light is at the short wavelength end of the visible spectrum, it is more strongly scattered in the atmosphere than long wavelength red light. The result is that the human eye perceives blue when looking toward parts of the sky other than the sun.

### 239. When a ship enters the sea from a river

(1) it rises a little
(2) it sinks a little
(3) it remains at the same level
(4) it rises or sinks depending on the material it is made of
239. (1) On average, seawater in the world’s oceans has a salinity of about 3.5% (35 g/L, or 599 mM). Seawater is denser than both fresh water and pure water (density 1.0 g/ml ) because the dissolved salts add mass without contributing significantly to the volume. The density of sea water is high due to impurities and salts compared to river water as a result; the upthurst produced by the sea water on the ship is more than that of river water. When a ship enters a sea from a river ,the ship is elevated or uplifted due to the density of sea water and during the buoyant motion of the ship, as it would gain both potential and kinetic energy when rising in the fluid.

### 240. Two stones of unequal masses are thrown vertically up with the same velocity. Which of the following will happen?

(1) The heavier mass will reach greater height
(2) The lighter mass will reach greater height
(3) Both will reach the same height
(4) Any of them may reach greater height