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?
- A.The wavelength of X-ray photon is less than the wavelength of visible radiation photon.
- B.Both the photons have different energies.
- C.The speeds of both the photons in vacuum are different.
- D.The frequency of X-ray photon is higher than the frequency of visible radiation photon.
Correct answer
Explanation
The correct answer is C, The speeds of both the photons in vacuum are different. This statement is wrong because every photon, whatever its energy, travels in vacuum at the same speed of light, about 3 × 10^8 metres per second. X-rays and visible light are both electromagnetic waves and differ only in frequency and wavelength. The energy of a photon is E = hν, where h is Planck's constant and ν the frequency, and since c = νλ, a higher energy means a higher frequency and a shorter wavelength. Here the X-ray photon, at 1 keV or 1000 eV, carries about 330 times the energy of the 3 eV visible photon. Option A is wrong to choose because the X-ray photon's higher energy does give it the shorter wavelength, so A is a correct statement. Option B is wrong to choose because 1 keV and 3 eV are plainly different energies. Option D is wrong to choose because higher energy means higher frequency, so D is also correct. Exam tip: all electromagnetic waves share the speed c in vacuum; energy rises with frequency and falls with wavelength.
Practice Questions
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1. Mg(HCO3)2
2. Ca(HCO3)2
3. CaCl2
4. MgSO4
Select the correct answer using the code given below.
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- B.twice the focal length of the convex lens
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