Mirage is an illustration of
- A.only dispersion of light.
- B.only reflection of light.
- C.only total internal reflection of light.
- D.both refraction and total internal reflection of light.
Correct answer
Explanation
The correct answer is D, both refraction and total internal reflection of light. On a hot day the air just above a road or desert sand is much hotter, and so optically rarer, than the air higher up. Light from the sky or a distant tree, travelling downward, passes from denser to rarer layers and keeps bending away from the normal; this is refraction. When the angle of incidence at a layer exceeds the critical angle, the light is totally internally reflected and curves back upward into the observer's eye. The observer sees an inverted image, as if it were reflected by a sheet of water on the ground. Option A is wrong because dispersion is the splitting of white light into colours, as in a prism or a rainbow, and plays no part here. Option B is wrong because ordinary reflection from a surface is not involved; there is no mirror-like surface, only layers of air. Option C is wrong because total internal reflection alone does not explain it; the gradual bending by refraction is equally essential. Exam tip: mirage and looming = refraction plus total internal reflection in air layers of different density.
Practice Questions
View allChlorophyll in photosynthetic prokaryotic bacteria is associated with
- A.plastids
- B.membranous vesicles
- C.nucleoids
- D.chromosomes
Show answer
Photosynthetic bacteria have no chloroplasts; their pigments sit on infoldings of the cell membrane that form vesicles or sacs, often called chromatophores.
Read the full explanation →Fat in human body is stored in
- A.Adipose tissue
- B.Red blood cells
- C.Muscle tissue
- D.Epithelial tissue
Show answer
Adipose tissue is a loose connective tissue whose cells, called adipocytes, are built to store fat. Each cell holds a large droplet of fat that pushes the nucleus and cytoplasm to one side.
Read the full explanation →Which one of the following is a metalloid ?
- A.Germanium
- B.Coke
- C.Iodine
- D.Sugar
Show answer
Germanium is a metalloid, an element whose properties lie between those of metals and non-metals. It is a hard, shiny, grey-white solid like a metal, yet it is brittle and conducts electricity far less well than a metal, which makes it a semiconductor.
Read the full explanation →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.
Show answer
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.
Read the full explanation →Which of the following substances cause temporary hardness in water?
1. Mg(HCO3)2
2. Ca(HCO3)2
3. CaCl2
4. MgSO4
Select the correct answer using the code given below.
- A.3 and 4
- B.2 and 3
- C.1 and 4
- D.1 and 2
Show answer
Temporary hardness is caused by the bicarbonates of magnesium and calcium, Mg(HCO3)2 and Ca(HCO3)2. It is called temporary because simple boiling removes it: on heating, the soluble bicarbonates break down into insoluble carbonate or hydroxide, carbon dioxide and water, and the solid settles out.
Read the full explanation →