How long does light take to reach the Earth from the Sun ?
- A.About 4 minutes
- B.About 8 minutes
- C.About 24 minutes
- D.About 24 hours
Correct answer
Explanation
The correct answer is B, About 8 minutes. Sunlight takes about 8 minutes and 20 seconds, roughly 500 seconds, to travel from the Sun to the Earth. The average distance between the Sun and the Earth is about 150 million kilometres, a distance called one astronomical unit. Light travels at about 3 lakh kilometres per second, so dividing 150 million km by 3 lakh km per second gives about 500 seconds. This also means we always see the Sun as it was about eight minutes earlier. The time varies slightly over the year because the Earth's orbit is an ellipse, being a little shorter at perihelion in early January and a little longer at aphelion in early July. Option A is wrong because 4 minutes would put the Earth only about half as far from the Sun. Option C is wrong because 24 minutes is three times too long. Option D is wrong because in 24 hours light covers about 26 billion kilometres, far beyond the planets of the solar system. Exam tip: Sun to Earth light ≈ 8 min 20 s (500 s); Moon to Earth light ≈ 1.3 s.
Practice Questions
View allWhich one of the following is not used as fertilizer?
- A.Ammonium nitrate
- B.Ammonium sulphide
- C.Ammonium phosphate
- D.Ammonium sulphate
Show answer
Ammonium sulphide is an unstable, foul-smelling compound that breaks down to release ammonia and toxic hydrogen sulphide, so it is not used as a fertiliser.
Read the full explanation →The focal length of the objective lens of a telescope is 50 cm. If the magnification of the telescope is 25, then the focal length of the eye-piece is
- A.12.5 cm
- B.5 cm
- C.2 cm
- D.10 cm
Show answer
For an astronomical telescope in normal adjustment the magnifying power equals the focal length of the objective divided by that of the eyepiece, so the eyepiece focal length is 50 ÷ 25 = 2 cm.
Read the full explanation →The major source of vitamins and minerals for vegetarians is
- A.black gram and wheat.
- B.rice and mustard.
- C.vegetables and fruits.
- D.soya bean and milk.
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Vegetables and fruits supply most of the vitamins and minerals in a vegetarian diet, which is why they are called protective foods.
Read the full explanation →Which one of the following compounds is used in black and white photography?
- A.AgF
- B.AgBr
- C.AgCl
- D.Ag2SO4
Show answer
Silver bromide is the light-sensitive compound coated on black and white photographic film and paper, because light breaks it down into tiny grains of silver metal.
Read the full explanation →Which one of the following statements about speed and velocity is correct?
- A.Speed and velocity both are vector quantities.
- B.Speed and velocity both are scalar quantities.
- C.Speed is vector quantity and velocity is scalar quantity.
- D.Speed is scalar quantity and velocity is vector quantity.
Show answer
Speed tells only how fast a body moves, while velocity also tells the direction of motion, and a quantity with both magnitude and direction is a vector.
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