Consider the following statements about visible light, UV light and X-rays: 1. The wavelength of visible light is more than that of X-rays. 2. The energy of X-ray photons is higher than that of UV light photons. 3. The energy of UV light photons is less than that of visible light photons. Which of the statements given above is/are correct?
- A.1, 2 and 3
- B.1 and 2 only
- C.2 and 3 only
- D.1 only
Correct answer
Explanation
The correct answer is B, 1 and 2 only. In the order visible light → ultraviolet → X-rays, the wavelength falls and the photon energy rises, so statements 1 and 2 are true and 3 is false.
The energy of a photon is E = hc/λ, so a shorter wavelength means more energy. Visible light runs from about 400 to 700 nm, ultraviolet from about 10 to 400 nm, and X-rays below about 10 nm. That is why UV photons can cause sunburn and break chemical bonds that visible light cannot, and X-rays pass through soft tissue.
A is wrong because statement 3 reverses the truth: UV photons carry more energy than visible photons.
C is wrong because it includes the false statement 3 and leaves out the true statement 1.
D is wrong because statement 2 is also correct.
Exam tip: across the spectrum from radio to gamma rays, wavelength falls while frequency and photon energy rise.
Practice Questions
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- A.has high thermal conductivity
- B.has low coefficient of expansion
- C.has high chemical stability
- D.is extremely hard
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- A.Cavity of tooth
- B.Erosion of nail
- C.Deformation of bone
- D.Mottling of tooth
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- A.1 and 3 only
- B.2 and 3 only
- C.1 and 2 only
- D.1, 2 and 3
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- A.Auxin
- B.Cytokinin
- C.Gibberellin
- D.Abscisic acid
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Read the full explanation →Which one of the following is considered as the basic structural element of all life forms?
- A.Phosphorus
- B.Carbon
- C.Oxygen
- D.Nitrogen
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