Consider the following pairs : Objects in space : Description 1. Cepheids : Giant clouds of dust and gas in space 2. Nebulae : Stars which brighten and dim periodically 3. Pulsars : Neutron stars that are formed when massive stars run out of fuel and collapse How many of the above pairs are correctly matched?
- A.Only one
- B.Only two
- C.All three
- D.None
Correct answer
Explanation
The correct answer is A, Only one. Only pair 3 is right; the descriptions of Cepheids and nebulae have been swapped.
Cepheid variables are pulsating stars that brighten and dim on a regular cycle. Henrietta Leavitt found in 1912 that their period is tied to their true brightness, which made them 'standard candles' that Edwin Hubble used to measure the distance to other galaxies. Nebulae are huge clouds of gas and dust in which new stars are born, like the Orion Nebula. A pulsar is a fast-spinning neutron star, left behind when a massive star runs out of fuel, collapses and explodes as a supernova; its beams sweep past Earth like a lighthouse.
Pair 1 is wrong because a giant cloud of dust and gas is a nebula, not a Cepheid. Pair 2 is wrong because a star that brightens and dims periodically is a Cepheid, not a nebula. So B (two), C (three) and D (none) are wrong.
Exam tip: Cepheid = pulsating star (distance yardstick); nebula = star nursery; pulsar = spinning neutron star.
Practice Questions
View allWith reference to polyethylene terephthalate, the use of which is so widespread in our daily lives, consider the following statements :
1. Its fibres can be blended with wool and cotton fibres to reinforce their properties.
2. Containers made of it can be used to store any alcoholic beverage.
3. Bottles made of it can be recycled into other products.
4. Articles made of it can be easily disposed of by incineration without causing greenhouse gas emissions.
Which of the statements given above are correct?
- A.1 and 3
- B.2 and 4
- C.1 and 4
- D.2 and 3
Show answer
PET fibre (polyester) is blended with wool and cotton, and PET bottles are widely recycled into new products. Polyethylene terephthalate is a polyester made from ethylene glycol and terephthalic acid.
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- A.Observation and understanding of the Universe
- B.Study of the solar and the lunar eclipses
- C.Placing satellites in the orbit of the Earth
- D.Origin and evolution of living organisms on the Earth
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- A.F is maximum when v and B are parallel to each other.
- B.F is maximum when v and B are anti-parallel to each other.
- C.F is maximum when v and B are perpendicular to each other.
- D.The force F is independent of the angle between v and B.
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Read the full explanation →In Sun-Earth system, the Sun, the Earth and the Lagrange point L4 form :
- A.an isosceles triangle
- B.an equilateral triangle
- C.a straight line
- D.a scalene triangle
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L4 lies on Earth's orbit 60° ahead of the Earth, so it is as far from the Sun as from the Earth.
Read the full explanation →Which one of the following is the most characteristic property of an element?
- A.Density
- B.Boiling point
- C.Mass number
- D.Atomic number
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The number of protons in the nucleus defines an element, and no two elements share it. The atomic number (Z) is the number of protons in an atom's nucleus, and in a neutral atom it also equals the number of electrons, which decide chemical behaviour.
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