Q4 of 46 Page 268

________ surface absorbs more heat than any other surface under identical conditions.

Black body’s are known for their ability to absorb every radiation, there are theories on black body radiations which you will study in higher classes, due to these reasons black body are used in solar cookers and solar heaters because they absorb all the heat radiation and do not let them escape easily, the other colors white or any other color cannot be more efficient in absorbing radiations than black body or black color.

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2

Two electric bulbs have resistances in the ratio 1 : 2. If they are joined in series, the energy consumed in these are in the ratio _________. (1 : 2, 2 : 1, 4 : 1, 1 : 1)

 3

Kilowatt-hour is the unit of __________.

 5

The atomic number of natural radioactive element is _________.

 6

Which one of the following statements does not represents Ohm’s law?

(i) current / potential difference = constant


(ii) potential difference / current = constant


(iii) current = resistance x potential difference