When light enters from air to water, then its
Answer: B
The frequency is the same but the wavelength is smaller in water.
Frequency is fixed by the source and cannot change at a boundary. Since \(v = f\lambda\) and light slows to \(c/1.33\) in water, the wavelength must shrink in the same proportion - which is exactly why the ray bends.
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A Step-Up Transformer Increases
Answer: D
A step-up transformer increases voltage.
The secondary has more turns than the primary: \[\frac{V_s}{V_p} = \frac{N_s}{N_p}\] Power is conserved apart from losses, so the current falls in the same proportion, and the frequency is unchanged. Stepping voltage up for transmission is what cuts \(I^2R\) losses in the line.
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The information of brilliant colors in a thin soap film is a consequence of the phenomena of
Answer: D
The colours arise from multiple reflection and interference.
Light reflected from the front surface of the film and light reflected from the back travel different distances and interfere. The path difference depends on both thickness and wavelength, so different colours cancel or reinforce at different points, giving the shifting bands.
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If a body weighs 12N on the surface of the earth, how much will it weigh on the surface of the moon where acceleration due to gravity is only one-sixth of that on earth's surface?
Answer: B
It will weigh 2 N.
Weight is \(W = mg\), and the mass is unchanged, so the weight falls in the same proportion as \(g\): \[W_{moon} = \frac{12}{6} = 2\ \mathrm{N}\] The mass remains \(12/9.8 \approx 1.22\) kg on both bodies.
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What is Newton’s second law of motion?
Answer: B
Newton's second law states that the rate of change of momentum of a body is directly proportional to the applied force, and takes place in the direction of the force.
\[F = \frac{dp}{dt} = \frac{d(mv)}{dt} = ma\] for constant mass. The law gives force its quantitative meaning and defines the newton as the force that gives 1 kg an acceleration of \(1\ \mathrm{m\,s^{-2}}\).
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Lightning heats the surrounding air to
Answer: C
Lightning heats the air to about 30,000 °C.
That is roughly five times the temperature of the sun's surface. The air expands explosively at that heat, and the shock wave it sends out is what we hear as thunder.
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Suitable impurities are added to a semiconductor depending on its use. This is done in order to
Answer: C
Impurities are added to increase the semiconductor's electrical conductivity.
Doping with a pentavalent element such as phosphorus adds free electrons, giving n-type material; a trivalent one such as boron adds holes, giving p-type. Either raises the carrier concentration by orders of magnitude, and putting the two together makes the p-n junction.
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Identify the vector quantity from the following
Answer: B
Angular momentum is the vector.
It is \(\vec{L} = \vec{r} \times \vec{p}\), a cross product, so it has a direction - along the axis of rotation, by the right-hand rule. Heat, time and work are all scalars.
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Which one has the highest specific heat?
Answer: D
Water has the highest specific heat of these.
It is \(4186\ \mathrm{J\,kg^{-1}\,K^{-1}}\), against about 2400 for alcohol and 2100 for kerosene - among the highest of any common substance, because much of the energy goes into breaking hydrogen bonds. This is why water is used as a coolant and why coastal climates are mild.
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Mica is used in electrical appliances such as electric iron because mica is
Answer: A
Because mica is a good conductor of heat but a bad conductor of electricity.
That combination is exactly what an iron needs: the heating element must be electrically isolated from the sole plate while passing its heat through. Mica also splits into thin sheets and withstands high temperature without decomposing.
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