Practice Test General Science- 8 - BPSC (Bihar) PDF Download

Ques 51. A liquid rises in a capillary tube when the angle of contact is________ 

Ans: an acute angle

The liquid wets the tube walls when the angle of contact is acute; adhesive forces between liquid and glass exceed cohesive forces within the liquid, causing rise by capillarity.

Ques 52. The hydraulic brakes used in automobiles is a direct application of________ 

Ans: Pascal's Law

Pascal's law states that pressure applied to a confined fluid is transmitted undiminished in all directions. Hydraulic brakes multiply force by transmitting pressure through brake fluid to larger-area pistons.

Ques 53. A periscope works by the principle of________ 

Ans: reflection

A periscope uses plane mirrors (or prisms) to reflect light from one end to the viewer's eye, enabling observation from a concealed position. Refraction is not required for the basic periscope.

Ques 54. Super conductors are those materials which________ 

Ans: lose all electrical resistance when cooled below a certain critical temperature

Below their critical temperature superconductors show zero electrical resistance and expel magnetic flux (Meissner effect); this allows lossless current flow and applications such as MRI magnets and maglev trains.

Ques 55. Bat can fly in the dark because they are guided by______ waves produced by them. 

Ans: ultrasonic waves

Bats emit ultrasonic pulses and listen to echoes (echolocation) to determine distance, direction and size of obstacles or prey; ultrasonic frequencies are above human hearing range.

Ques 56. A solid piece of iron sinks in water but floats in mercury. This is because the________ 

Ans: density of iron is more than that of water but less than that of mercury

Whether an object floats depends on comparing its density with the fluid's density. Iron (≈7.87 g·cm⁻³) is denser than water (≈1 g·cm⁻³) so it sinks in water, but is less dense than mercury (≈13.6 g·cm⁻³) and therefore floats in mercury.

Ques 57. A red object, when seen through a thick blue glass, appears________ 

Ans: black

Blue glass transmits blue wavelengths and absorbs red. A red object reflects red light, which the blue filter removes; no visible light of appropriate wavelength reaches the eye, so the object appears black.

Ques 58. ________ is the cause of weightlessness experienced while orbiting around earth on a spaceship. 

Ans: free fall (apparent zero gravity)

Objects in orbit are in continuous free fall towards Earth while moving tangentially fast enough to keep missing it; both spacecraft and occupants fall together, producing apparent weightlessness (microgravity).

Ques 59. If two bodies are completely covered with water, they have________ 

Ans:the same buoyant force per unit volume of displaced water (i.e., the same fluid pressure distribution for the same shape and immersion depth)

If two different bodies are completely submerged in the same liquid and displace the same volume, the buoyant force on each equals the weight of displaced liquid. Complete immersion alone does not make densities equal; density is mass per unit volume and may differ between bodies.

Ques 60. In a reactor, Cadmium rods are used for________ 

Ans: absorbing neutrons

Cadmium has a high neutron-absorption cross-section and is used as control rods to absorb neutrons, thereby regulating the chain reaction and controlling reactor power.

Ques 61. Radar is based on the principle that________ 

Ans: radio waves are reflected by objects

Radar systems transmit radio waves and detect echoes returned by objects; the time delay gives distance and the Doppler shift gives relative speed. Reflection of radio waves from targets is the key principle.

Ques 62. For a given velocity of projection, the maximum range of a projectile can be achieved if the angle of projection is________ 

Ans: 45°

Neglecting air resistance and assuming level ground, the range R = (v² sin 2θ)/g is maximised when sin 2θ = 1, i.e., 2θ = 90°, so θ = 45°.

Ques 63. Detergents dissolved in water help in cleaning clothes by________ 

Ans:reducing the surface tension of water and emulsifying grease

Detergent molecules have hydrophilic and hydrophobic ends; they reduce water's surface tension, penetrate fabric, and form micelles around oily dirt, allowing it to be rinsed away.

Ques 64. An aeroplane rises because________ 

Ans: the pressure above its wings is less than the pressure below them (producing lift)

Wing shape and angle of attack cause a pressure difference: faster airflow over the wing produces lower pressure above. The net upward force (lift) overcomes weight to raise the aircraft.

Ques 65. An ordinary clock loses time during summer because the length of the pendulum________ 

Ans: increases and therefore the time period increases

Thermal expansion of the pendulum rod increases its effective length in summer; the period T = 2π√(L/g) increases, so the clock runs slow and loses time.

Ques 66. The apparent weight of a man in a lift is less than his real weight________ 

Ans: when the lift is going down with acceleration (or uniform downward acceleration)

Apparent weight = m(g - a). If the lift accelerates downward (a > 0), apparent weight decreases; for free fall (a = g) apparent weight becomes zero.

Ques 67. Light from the Sun reaches us in nearly________ 

Ans:8 minutes

Sunlight takes about 8 minutes 20 seconds to travel the average Sun-Earth distance (1 astronomical unit ≈ 1.496×10¹¹ m) at the speed of light (≈3×10⁸ m·s⁻¹).

Ques 68. A boat loaded with rocks floats in the middle of a swimming pool and a man in the boat throws rocks over board in water. The water level of the pool will___

Ans:be lowered

While rocks are in the boat they cause displacement equal to their weight (larger volume of water displaced). When thrown overboard and sunk, they displace water equal to their volume, which is less (rocks are denser than water), so overall water level falls.

Ques 69. A tennis ball will bounce higher on_____than on plains. 

Ans: higher on hills than on plains

Air pressure and density vary slightly with altitude; a less dense atmosphere at high altitude reduces air resistance, so a ball may travel faster and bounce higher. Note: surface hardness and ground conditions also affect bounce.

Ques 70. The leaning tower of Pisa does not fall because______ 

Ans: the vertical line through the C.G. of the tower falls within its base

An object remains stable as long as its centre of gravity (C.G.) projects vertically within its base; the leaning tower's C.G. still lies over the base, providing a restoring torque that prevents toppling.

Ques 71. A man carrying a load on his back bends forward because of one of________ 

Ans:To adjust the C.G. of the system such that the vertical line through the C.G. passes within the base.

Bending forward shifts the combined centre of gravity of man + load so that the vertical projection falls within his feet, maintaining balance and preventing tipping backward.

Ques 72. When milk is churned cream gets separated due to__ 

Ans: centrifugal force

Churning applies rotational motion; fat globules experience centrifugal effects and coalesce into butter/cream, separating from the liquid (buttermilk).

Ques 73. Production of beats is a result of the phenomenon of__ 

Ans:interference

Beats occur when two sound waves of slightly different frequencies interfere; the amplitude varies at the beat frequency equal to the frequency difference, producing periodic loudness fluctuations.

Ques 74. The internal resistance of ____ of the instruments is the highest. 

Ans:Voltmeter

A voltmeter is connected in parallel and must have a very high internal resistance so that it draws negligible current and does not appreciably change the circuit conditions being measured.

Ques 75. Siphon will fail to work if the level of the liquid in the two vessels are at the________height. 

Ans: same

A siphon transfers liquid from a higher level to a lower level by atmospheric pressure and gravity; if both vessels are at the same height, there is no net driving head and the siphon will not operate.

Ques 76. The nature of light waves is similar to________rays. 

Ans: gamma rays

Light and gamma rays are both electromagnetic waves; they differ only in wavelength/frequency and energy. All are transverse electromagnetic radiation obeying the same basic laws.

Ques 77. If the radius of the earth were to shrink by one per cent, its mass remaining the same, the acceleration due to gravity on earth's surface would________ 

Ans: increase

Surface gravity g = GM/R². If R decreases by 1% (R → 0.99R), g increases by factor 1/(0.99)² ≈ 1.0203, i.e., about a 2.03% increase.

Ques 78. A dental plate clings to the roof of the mouth because________ 

Ans: adhesion between the plate and the moist mucous membrane and the formation of a partial seal (suction)

Adhesive forces between the denture surface and the wet tissues, together with slight pressure differences (suction) and surface tension of saliva, help the plate remain in place.

Ques 79. At absolute zero of temperature the molecular energy is________ 

Ans: minimum (ground-state energy) but not zero for quantum systems

Classically one would expect zero motion, but quantum mechanics requires zero-point energy; molecular (and vibrational) energy attains its minimum allowable quantum value, not absolute zero kinetic energy.

Ques 80. The half life of a substance is 10 days. How much of the substance will be left after 40 days if initial mass is 2 gm________ 

Ans: 0.125 gm

After 40 days = 4 half-lives, remaining fraction = (1/2)^4 = 1/16. Remaining mass = 2 g × 1/16 = 0.125 g.

Ques 81. Angstrom is equal to________nanometer. 

Ans: 10^-1 nanometre

1 ångström (Å) = 10⁻¹ nanometre = 10⁻¹⁰ metre. It is commonly used for atomic-scale distances such as interatomic spacings.

Ques 82. A cricketer lowers his hand while catching the ball. This saves him from injury because of________ 

Ans:conservation of momentum together with increasing time of impact (reducing force)

Lowering the hands and moving them backward increases the time over which the ball's momentum changes, thereby reducing the average force on the hands and lowering the chance of injury.

Ques 83. One litre of cool air weighs heavier than one litre of dry air because of the________ 

Ans: higher density at lower temperature (molecules are closer together)

At the same pressure, cooler air has greater density since molecules have less kinetic energy and occupy less volume per molecule; hence one litre of cool air contains more mass than one litre of warm air. (Note: moist air can be lighter than dry air because water vapour has lower molecular mass than dry air.)

Ques 84. A piece of rock was brought from moon to earth. Then its weight________ 

Ans: alone changed

Mass of the rock remains the same; its weight changes because weight depends on local gravitational acceleration, which is larger on Earth than on the Moon.

Ques 85. Diamond is harder than graphite because of difference of________

Ans: crystalline structure (bonding arrangement)

Carbon atoms are bonded differently: diamond has each carbon tetrahedrally bonded to four others in a 3D network (strong covalent bonds), while graphite has planar hexagonal layers with weaker interlayer forces, making graphite soft and lubricious.

Ques 86. Four identical kettles with the same amount of water have bases made of brass, copper, steel and aluminium metals of the same thickness. If these kettles are placed on identical flames in an identical manner, water will boil first in the kettle the base of which is made of________ 

Ans: copper

Copper has the highest thermal conductivity among the listed metals, so it transfers heat most rapidly from the flame to the water, causing it to reach boiling point sooner.

Ques 87. The principle underlying a microwave oven is________ 

Ans: microwaves vibrate water molecules in food thereby generating heat

Microwave ovens use electromagnetic waves (microwaves) that are absorbed primarily by polar molecules such as water; molecular rotation and collisions convert this energy into heat, heating the food from the inside out.

Ques 88. ________is a good conductor of heat and electricity. 

Ans: graphite

Graphite conducts electricity along its planar carbon layers due to delocalised electrons and also conducts heat relatively well; it is used in electrodes and as a lubricant.

Ques 89. Why ________is platinum wire used inside very narrow glass rods?

Ans:Platinum and glass have nearly the same linear coefficients of expansion

When both materials expand similarly with temperature changes, thermal stress at the glass-metal junction is minimised, preventing breakage of the narrow glass tubes containing the platinum wire.

Ques 90. Grass looks green because________ 

Ans:it absorbs most colours in the visible spectrum and reflects/transmits green wavelengths

Chlorophyll in plant leaves absorbs red and blue light strongly for photosynthesis and reflects green light, which is why grass appears green to our eyes.

Ques 91. Persistence of vision is the principle behind________ 

Ans:cinema

Persistence of vision means an image remains on the retina for a short time after the stimulus ends; a rapid sequence of still images (frames) appears as continuous motion, the basis of film and cinema.

Ques 92. Television signals cannot be received ordinarily beyond a particular distance due to________ 

Ans:curvature of the Earth (line-of-sight limitation)

Television broadcasts at VHF/UHF propagate largely line-of-sight; the Earth's curvature obstructs reception beyond the radio horizon unless relay transmitters or satellites are used.

Ques 93. Cones in the retina of eyes (about 6 million) are concerned with________ 

Ans: colour discrimination and acute discrimination of detail

Cones are photoreceptor cells concentrated in the fovea; they provide high visual acuity and colour vision under bright-light (photopic) conditions.

Ques 94. A fisherman sitting on the bank of a pond trying to spear a fish should aim________ 

Ans:a little below where he sees the fish

Light refracts when passing from water to air; the apparent position of the fish is raised. To hit the actual fish, the fisherman must aim a bit below the apparent image to compensate for refraction.

Ques 95. The comic mirrors seen in amusement parks have reflecting surfaces that are________ 

Ans: irregularly curved

Distorting mirrors use convex and concave curved surfaces in varying patterns to produce enlarged, reduced or otherwise distorted images for amusement.

Ques 96. The total internal reflection occurs when the angle of incidence is________than the critical angle. 

Ans: greater

Total internal reflection happens when light travels from a denser to a rarer medium and the angle of incidence exceeds the critical angle; all light is reflected back into the denser medium.

Ques 97. After rains if the sun is shining brightly in one part of the sky, ________rainbows are observed. 

Ans: two

Primary and secondary rainbows can appear: the primary is formed by one internal reflection inside raindrops, and the secondary (fainter) by two internal reflections, producing reversed colour order.

Ques 98. In cold countries glycerol is added to water in car radiators as it helps to________ 

Ans: lower the freezing point of the coolant (antifreeze)

Glycerol (or ethylene glycol) reduces the freezing point and raises the boiling point of the coolant, preventing freezing in winter and overheating in summer.

Ques 99. You can hear the roar of the sea on holding a sea shell to your ear because________ 

Ans: the shell amplifies and modifies ambient sounds by multiple reflections and resonance of air inside it

Ambient environmental noise and the shell's resonant cavity produce a complex, low-frequency "roar" amplified by multiple reflections within the shell.

Ques 100. A tape-recorder's tape is coated with a________

Ans: ferromagnetic powder (magnetic oxide) layer

The tape surface is coated with a fine magnetic material (e.g., iron oxide or other magnetic particles) bound to a plastic base; magnetic patterns on this coating store audio information read by the playback head.