Which of the following is a vector quantity
Answer: A
Momentum is a vector.
It is mass times velocity, and velocity has direction, so momentum points the same way. Pressure, energy and work are all scalars - work is a dot product of two vectors, which yields a scalar.
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The working principle of a washing machine is
Answer: C
A washing machine's spin cycle works by centrifugation.
The drum spins fast, and water in the fabric, having no centripetal force to hold it in a circle, moves outward and escapes through the perforations while the clothes are held by the drum wall.
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In which among the following is alternating current not used?
Answer: B
Alternating current is not used in electroplating.
Electroplating needs the metal ions to travel consistently to one electrode and deposit there. Alternating current would reverse the direction every half cycle, plating and stripping in turn, so direct current is essential.
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The speed of light will be minimum while passing through
Answer: D
Light is slowest in glass.
Speed in a medium is \(c/n\), so the higher the refractive index the slower the light. Glass has \(n \approx 1.5\), water 1.33, air 1.0003 and vacuum exactly 1 - so the order of speeds runs the other way.
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Light from the laser is________.
Answer: D
Laser light is monochromatic.
All the photons come from the same atomic transition, so they share a single wavelength; they are also coherent, being in step in phase, and highly directional. Ordinary light contains many wavelengths with random phases.
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Let a thin capillary tube be replaced with another tube of insufficient length then, we find water
Answer: B
The water will not rise above the top of the tube, and it does not overflow.
If the tube is shorter than the calculated capillary height, the liquid rises to the top and stops. The radius of curvature of the meniscus adjusts itself so that \(hr\) stays constant, so the meniscus simply becomes flatter and the water stays put.
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What is Newton’s first law of motion?
Answer: A
Newton's first law states that every body maintains its state of rest or of uniform motion in a straight line unless acted on by an external force.
It defines inertia and identifies the inertial frames in which the second and third laws hold. It is not a special case of \(F = ma\) but a statement about which frames the second law applies in.
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Water kept in an earthen pot is less cool on rainy days than in summer because during the rainy days
Answer: C
Because the water that oozes out does not evaporate quickly, the air being already humid.
An earthen pot cools by evaporation of the water seeping through its pores, and evaporation draws latent heat from what remains. On a rainy day the air is close to saturation, so evaporation is slow and little heat is carried away.
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Einstein got the Nobel prize for?
Answer: D
Einstein received the Nobel Prize for the photoelectric effect.
The 1921 prize cited his services to theoretical physics and especially his discovery of the law of the photoelectric effect, \[h\nu = \phi + \tfrac{1}{2}mv^2_{max}\] Relativity was still thought too speculative by the committee to be honoured.
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Which one of the following is the softest?
Answer: B
Sodium is the softest of these.
It rates about 0.5 on the Mohs scale and can be cut with a knife. Alkali metals are soft because each atom contributes only one electron to the metallic bond, and the bond weakens further as the atom grows; sodium is softer than lithium for that reason.
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