The phenomenon of rainbow formation by water droplets involves :
- A.single refraction of sunlight
- B.one internal reflection of sunlight
- C.two internal reflections of sunlight
- D.both refraction and internal reflection of sunlight
Correct answer
Explanation
The correct answer is D, both refraction and internal reflection of sunlight. A rainbow forms only because sunlight is refracted, dispersed and internally reflected inside raindrops.
When sunlight enters a water droplet it is refracted and split into its colours (dispersion), because each colour bends by a different amount. The light is then reflected from the back of the droplet and refracted again as it comes out. In a primary rainbow there is one internal reflection, red appears on the outer edge and violet on the inner edge; in the fainter secondary rainbow there are two internal reflections and the order of colours is reversed. A rainbow is always seen with the Sun behind the observer.
A is wrong: refraction alone, without reflection, cannot send the light back towards the observer.
B is wrong: internal reflection is part of the process, but without refraction there would be no splitting into colours.
C is wrong: two internal reflections explain only the secondary rainbow, and it still needs refraction.
Exam tip: rainbow = refraction + dispersion + total internal reflection; Sun behind you, rain in front.
Practice Questions
View allBronze is an alloy of copper and
- A.nickel
- B.iron
- C.tin
- D.aluminium
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Bronze is an alloy of copper and tin, usually about 88 parts copper to 12 parts tin. Adding tin makes copper harder, stronger and easier to cast, and bronze also resists corrosion well.
Read the full explanation →Which one of the following instruments is used for measuring moisture content of air?
- A.Hydrometer
- B.Hygrometer
- C.Hypsometer
- D.Pycnometer
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A hygrometer measures humidity, that is, the amount of water vapour or moisture in the air. The name comes from the Greek "hygros", meaning wet.
Read the full explanation →Which one of the following elements is present in the green pigment of leaves?
- A.Magnesium
- B.Iron
- C.Calcium
- D.Copper
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The green pigment of leaves is chlorophyll, and a magnesium atom sits at the centre of every chlorophyll molecule.
Read the full explanation →Consider the following actions :
1. Detection of car crash/collision which results in the deployment of airbags almost instantaneously
2. Detection of accidental free fall of a laptop towards the ground which results in the immediate turning off of the hard drive
3. Detection of the tilt of the smartphone which results in the rotation of display between portrait and landscape mode
In how many of the above actions is the function of accelerometer required?
- A.Only one
- B.Only two
- C.All three
- D.None
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An accelerometer measures acceleration, including the pull of gravity, and each of the three actions depends on reading it. An accelerometer is a small sensor, today usually a MEMS (micro-electro-mechanical system) chip, that senses changes in speed and the direction of gravity.
Read the full explanation →Consider the following statements :
1. Carbon fibres are used in the manufacture of components used in automobiles and aircrafts.
2. Carbon fibres once used cannot be recycled.
Which of the statements given above is/are correct?
- A.1 only
- B.2 only
- C.Both 1 and 2
- D.Neither 1 nor 2
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Carbon fibre is widely used in cars and aircraft for its strength and low weight, and it can be recovered and recycled.
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