Physics
What is refractive index ?

None of above
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.
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?

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

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