15. Fill in the blanks.

(i) In a heat engine, heat energy is changed into _________ (mechanical energy, magnetic energy, light energy)

(iii) Deficiency of vitamin B causes _________ (rickets, beriberi, night blindness)

(iv) Cheapest source of producing electricity is _________ (coal, natural gas, water)

(v) The smallest unit of measurement of wavelength is _________ (micrometer, angstrom, manometer)

(vi) The chemical generally used in refrigerators is _________ (ethylene, glycofreon, methyl alcohol)

(viii) Unit of electricity ‘KILOWATT HOUR’ is the unit of (force, work, power)

(ix) Period of famous Muslim scientists is _________ (3rd – 5th century, 6th – 7th century, 7th – 13th century A.D.)

(x) Heat radiation travels at a speed equal to _________ (half the speed of light, speed of light, speed of wind)

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Marwatone.