When a body falls in viscous medium, its velocity first increases and finally becomes constant. The constant velocity is called
Answer: D
This constant speed is the terminal velocity.
The body accelerates until the viscous drag and buoyancy together balance the weight, after which the net force is zero. For a sphere obeying Stokes' law, \[v_t = \frac{2r^2(\rho - \sigma)g}{9\eta}\]
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The orbital speed of a satellite depends on its mass.
Answer: B
False. Orbital speed does not depend on the satellite's mass.
Equating gravitational and centripetal force, \[\frac{GMm}{r^2} = \frac{mv^2}{r} \Rightarrow v = \sqrt{\frac{GM}{r}}\] The satellite's mass \(m\) cancels, so it depends only on the earth's mass and the radius of the orbit.
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Why does the sea appear blue in colour?
Answer: C
The sea looks blue because of scattering of sunlight by water molecules.
Scattering follows \(I \propto 1/\lambda^4\), so short blue wavelengths are scattered far more than red ones. Water also absorbs red light strongly within a few metres, which deepens the effect.
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Which of following in not a property of cathode ray
Answer: C
Cathode rays do not make materials cool - they heat them.
Being fast electrons, they give up kinetic energy on striking a target, which appears as heat and, from a heavy target, as X-rays. They do ionise gases, penetrate thin metal foil, and travel in straight lines while remaining invisible themselves.
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Which of the following terms is not used in the field of physics?
Answer: D
Stock value is not a term in physics.
It belongs to finance. Latent heat is the energy absorbed in a change of state, nuclear fusion the joining of light nuclei, and refractive index the ratio \(c/v\) for a medium.
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Metals are good conductors of electricity because:
Answer: A
Because metals contain free electrons.
In the metallic bond, the valence electrons are delocalised over the whole lattice rather than bound to individual atoms. An applied field sets this electron sea drifting, which is the current. The same electrons also carry heat, which is why good electrical conductors are good thermal ones.
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A parsec is the unit of
Answer: A
A parsec is a unit of distance.
It is the distance at which one astronomical unit subtends an angle of one arcsecond - the name is short for parallax-second. One parsec is about \(3.26\) light years, or \(3.086\times10^{16}\) m.
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The I.C Chip used in a computer is made up of_______.
Answer: C
The IC chip is made of silicon.
Silicon is a semiconductor whose conductivity can be controlled precisely by doping, it is abundant as sand, and it forms a stable insulating oxide, \(\mathrm{SiO_2}\), that makes the layered fabrication of integrated circuits possible.
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On a rainy day, small oil films on water show brilliant colours. This is due to
Answer: B
This is due to interference.
Light reflected from the top of the oil film and light reflected from the oil-water boundary travel different distances and interfere. The path difference depends on the film's thickness and on the wavelength, so different colours reinforce at different thicknesses, giving the shifting bands.
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Electric Motor converts
Answer: C
An electric motor converts electrical energy into mechanical energy.
A current-carrying coil in a magnetic field experiences a force \(F = BIL\), and the resulting couple turns the armature. A generator is the same machine run backwards, converting mechanical energy into electrical.
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