Physics
On a cold day when the room temperature is 15°C, the metallic cap of a pen becomes much colder than its plastic body, though both are at the same temperature of 15°C, because :

Metals are good conductors of heat
Plastics have a higher thermal conductivity than metals
Metals have higher thermal capacity than plastics
Plastics have a lower density than metals

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Physics
What is refractive index ?

It is defined as the ratio of speed of light in vacuum to the speed of light in the medium.
It is defined as the product of speed of light in medium and in vacuum.
None of above
It is defined as the ratio of speed of light in the medium to the speed of light in vacuum.

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Physics
A photon of X-ray has energy of 1 keV. A photon of visible radiation has energy of 3 eV. In this context, which one of the following statements is not correct?

Both the photons have different energies.
The speeds of both the photons in vacuum are different
The wavelength of X-ray photon is less than the wavelength of visible radiation photon.
The frequency of X-ray photon is higher than the frequency of visible radiation photon.

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Physics
'Mirage' is an example of

Dispersion of light only
Refraction of light only
Total internal reflection of light only
Refraction and total internal reflection of light

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