CBSE Guess > Papers > Question Papers > Class X > 2009 > Science > Science
Q. 6. Name the gas usually liberated when a dilute acid reacts with a metal. What happens when a burning candle is brought near this gas? 1
Ans. When a dilute acid reacts with a metal, usually hydrogen gas is liberated. When a burning candle is brought near this gas, it burns with a ‘pop’ sound.
Q. 7. What is the basis of Mendeleev’s periodic table? Write two achievements of Mendeleev’s periodic table. 2
Ans. Basis. See Q.4 (S.A.T.), Chapter 5. [Page 50
Achievements of Mendeleev’s periodic table. See Q.5 (S.A.T), Chapter 5. [Page 50
Q. 8. State Mendeleev’s periodic law. Write two achievements of Mendeleev’s periodic table. 2
Ans. See Q.4 and Q.5 (S.A.T), Chapter 5. [Page 50
Q. 9. What is meant by spectrum? How can we recombine the components of white light after a prism has separated them? 2
Ans • When a beam of white light is passed through a glass prism, a band of seven colours is formed on a white screen. This band of seven colours is called spectrum of white light.
• Newton showed that the seven coloured lights of the spectrum can be recombined to give back white light.
• First he tried to split the colours of the spectrum of white light using a prism.
• He then placed a second identical prism in an inverted position with respect to the first prism. This allowed all the colours of the spectrum to pass through the second prism. He found a beam of white light emerging from the other side of the second prism.
Q.10. Give reasons for the following. 2
(i) The sun appears reddish at sunrise or sunset.
(ii) The sky appears dark instead of blue to an astronaut.
Ans. (i) The Sun at the time of sunrise and sunset is more near the horizon,
and near the horizon most of the blue light of shorter wavelengths is
scattered away by the particles and gases of the atmosphere. Light
from the Sun near the horizon passes through thick layers of air and
larger distance in the Earth’s atmosphere before reaching our eyes.
Therefore, the light that reaches our eyes is of longer wavelength that
gives rise to the reddish appearance of the sun.
(ii) The sky appears dark instead of blue to an astronaut because there is
no atmosphere containing air in the outer space to scatter sunlight.
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