Question

21. A student holding a mirror in his hand, directed the reflecting surface of the mirror towards the Sun. He
then directed the reflected light on to a sheet of paper held close to the mirror.
a) What should he do to burn the paper?
b) Which type of mirror does he have?
c) Will he be able to determine the approximate value of focal length of this mirror from this activity? Give
reason and draw ray diagram to justify your answer in this case.
22. What is meant by power of a lens? Write its SI unit. A student uses a lens of focal length 40 cm and
another of - 20 cm. Write the nature and power of each lens.
23. State the cause of dispersion of white light by a glass prism. How did newton, using two identical glass
prisms show that white light is made of seven colours? Draw a ray diagram and explain.
24. What is 'che difference between Displacement and Double displacement reaction? Write equations for these
reactions.
25. State vvhat happens when
a) Hydrated copper sulphate is heated?
b) Gypsum is heated at 373 K.
C) Chlorine gas is passed through dry slaked lime.
26. A non-metal X exists in two different forms Y and Z. Y is the hardest natural substance, where as z is a
good conductor of electricity. Identify X,Y,and Z
27. Mention two ways in which food gets oxidized in organisms.
28. Define phototropism and give one example,
29. What is the importance of DNA copying in reproduction?
30). How will an organism be benefited if it reproduces through spores?
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Answer 1

Answer:

21 (1)need a lens for burn the paper

(2)Plane mirror