A rainbow is produced due to which one of the following phenomena ?
- A.Dispersion of light
- B.Interference of light
- C.Diffraction of light
- D.Scattering of light by atmospheric dust
Correct answer
Explanation
The correct answer is A, Dispersion of light. A rainbow forms when raindrops split white sunlight into its seven colours.
When sunlight enters a raindrop, it is refracted, and because each colour bends by a different amount, the colours spread apart. The light is then reflected from the back of the drop and refracted again as it leaves. Each drop acts like a tiny prism. A rainbow is seen only when the Sun is behind the observer and the rain is in front, and in the primary bow red is on the outer edge and violet on the inner edge.
B is wrong: interference produces coloured fringes, as in soap films and oil layers, not a rainbow. C is wrong: diffraction is the bending of light around small obstacles or slits. D is wrong: scattering by fine particles makes the sky blue and sunsets red, but it does not split light into a bow of colours.
Exam tip: Rainbow means dispersion plus internal reflection in raindrops; blue sky means scattering; soap-film colours mean interference.
Practice Questions
View allThe valency of phosphorus is
- A.2, 3
- B.3, 4
- C.4, 5
- D.3, 5
Show answer
Phosphorus has five electrons in its outer shell and shows two common valencies, 3 and 5. Phosphorus, atomic number 15, has the electronic configuration 2, 8, 5.
Read the full explanation →Which one of the following statements is NOT correct ?
- A.Single celled eukaryotes belong to Kingdom Protista
- B.Yeast, a fungus is multicellular
- C.The fungi constitute a unique kingdom of heterotrophs
- D.Ascomycetes, a saprophytic fungi is multicellular or rarely unicellular
Show answer
This statement is false, because yeast is one of the few fungi that are unicellular. In Whittaker's five-kingdom system, fungi form a separate kingdom.
Read the full explanation →Desalination of seawater is done by using reverse osmosis. The pressure applied to the solution is
- A.larger than osmotic pressure
- B.smaller than osmotic pressure
- C.equal to osmotic pressure
- D.equal to atmospheric pressure
Show answer
Only a pressure greater than the osmotic pressure of seawater can push pure water backwards through the membrane. In ordinary osmosis, water moves through a semipermeable membrane from the dilute side to the concentrated side.
Read the full explanation →Which one of the following does not form oxide on reaction with oxygen?
- A.Magnesium
- B.Lead
- C.Tin
- D.Silver
Show answer
Silver sits near the bottom of the reactivity series and does not combine with oxygen even when heated in air.
Read the full explanation →The foul smell of urine of a healthy man having healthy food, when spilled on floor, is mainly due to the bacterial decomposition of
- A.urea into sulphur dioxide
- B.sugar into carbon dioxide
- C.lipids into methane
- D.urea into ammonia
Show answer
Bacteria on the floor break down the urea in urine and release ammonia, which has a sharp, pungent smell. Urea, CO(NH2)2, is the main nitrogenous waste of humans.
Read the full explanation →