What is the maximum value of deforming force upto which a material shows elastic property and above which the material loses it ?
Answer: D
This is the elastic limit.
Up to it the body returns exactly to its original shape when the load is removed; beyond it a permanent set remains. It should not be confused with the breaking stress, which lies further along the stress-strain curve.
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A car parked in the sun with its windows closed gets terribly hot inside. This is due to
Answer: B
This is the greenhouse effect.
Short-wavelength sunlight passes through the glass and is absorbed by the seats and dashboard, which then re-radiate at much longer infrared wavelengths. Glass is opaque to that infrared, so the heat is trapped, and the closed windows also prevent it escaping by convection.
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Electrical Pressure is also called
Answer: B
Electrical pressure is another name for voltage.
The analogy is with a water circuit: voltage is the pressure that drives the flow, current the rate of flow, and resistance the constriction opposing it. The relation is Ohm's law, \(V = IR\).
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Which liquid is the most viscous?
Answer: D
Oil is the most viscous of these.
Viscosity measures resistance to flow, and it rises with the size of the molecules and the strength of the forces between them. Lubricating oil has long hydrocarbon chains that tangle, while water and milk flow freely.
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What is displacement ?
Answer: C
Displacement is the shortest distance covered in a definite direction.
It is the straight-line vector from start to finish, so it has both magnitude and direction, and can be zero even after a long journey if the body returns to where it began. Distance is the scalar length of the actual path and can only increase.
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Large astronomical telescopes always use as objective a
Answer: C
Large astronomical telescopes use a mirror as the objective.
A big lens can be supported only at its rim, so it sags under its own weight, and it also suffers chromatic aberration. A mirror can be supported across its whole back, is free of chromatic aberration, and needs only one surface figured. The largest refractor ever built is 1 m across; mirrors now exceed 10 m.
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Which of the following uses a Non Renewable Energy Source?
Answer: C
A nuclear power plant uses a non-renewable source.
Uranium ore is a finite mineral resource. Wind, hydroelectric and tidal plants all draw on flows driven continuously by the sun and the moon, and are not depleted by use.
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The cover of a solar cooker is made of glass because
Answer: C
Because it retains the heat inside by the greenhouse effect.
Glass transmits the short-wavelength sunlight that heats the food, but is opaque to the long-wavelength infrared the food then re-radiates. The cover also stops the hot air escaping by convection.
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On a clean glass plate a drop of water spreads to form a thin layer whereas a drop of mercury remains almost spherical because
Answer: D
Because the cohesion of mercury is greater than its adhesion to glass.
A liquid spreads when its adhesion to the surface exceeds its own cohesion, as water does on clean glass. Mercury's cohesive forces are far stronger, so it pulls itself into the shape of least surface area - a sphere - and its meniscus curves the opposite way to water's.
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The intensity of sound at a point is ______ its distance from the source.
Answer: D
Intensity is inversely proportional to the square of the distance.
A point source spreads its power over a spherical wavefront of area \(4\pi r^2\), so \[I = \frac{P}{4\pi r^2}\] Doubling the distance therefore cuts the intensity to a quarter.
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