Point A is at a lower electrical potential than point B. An electron between them on the line joining them will
Answer: B
The electron moves towards B.
Conventional current and positive charge move from high to low potential; an electron, being negative, is attracted the other way, towards the higher potential. B is at the higher potential, so the electron accelerates towards it.
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The ozone layer protects us from
Answer: C
The ozone layer protects us from ultraviolet rays.
Ozone absorbs strongly between about 200 and 320 nm, screening out almost all UV-C and most UV-B - the wavelengths that damage DNA and cause skin cancer and cataract. Visible light and infrared pass through freely.
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Which law states, "the effect produced by a moving source of waves in which there is an apparent upward shift in frequency for observers towards whom the source is approaching and an apparent downward
Answer: B
This is the Doppler effect.
The observed frequency shifts because successive wavefronts have less distance to travel when source and observer approach: \[f' = f\left(\frac{v \pm v_o}{v \mp v_s}\right)\] It explains the falling pitch of a passing horn and the redshift of receding galaxies.
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No current will flow between two charged bodies if they have the same
Answer: C
No current flows if the two bodies are at the same potential.
Charge flows in response to a potential difference, not to a difference in charge. A large body may hold much more charge than a small one and still sit at the same potential, since \(V = Q/C\).
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Which of the following is Not a form of Energy?
Answer: D
Pressure is not a form of energy.
It is force per unit area, with dimensions \(\mathrm{ML^{-1}T^{-2}}\), while energy is \(\mathrm{ML^2T^{-2}}\). Heat, sound and motion are all energy in different forms; pressure times volume, however, does give energy.
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Rolling friction is caused by ____ from the following?
Answer: A
Rolling friction arises from non-elastic effects.
The wheel and the surface deform slightly at the contact, and the deformation does not recover all its energy as the contact moves on - the hysteresis loss. This is why rolling friction is far smaller than sliding friction, and why hard, well-inflated tyres roll more easily.
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Which of the following physical quantities have the same dimensions
Answer: A
Momentum and impulse share dimensions.
Impulse is force times time and momentum is mass times velocity: \[[\mathrm{Ft}] = \mathrm{MLT^{-2}\cdot T} = \mathrm{MLT^{-1}},\qquad [\mathrm{mv}] = \mathrm{M\cdot LT^{-1}} = \mathrm{MLT^{-1}}\] They must agree, since the impulse–momentum theorem says one equals the change in the other.
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The number of base SI units is
Answer: B
There are seven base SI units.
They are the metre, kilogram, second, ampere, kelvin, mole and candela, for length, mass, time, electric current, temperature, amount of substance and luminous intensity. Every other SI unit is derived from these.
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