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CBSE Class 10 Science Solved Question Paper 2018

Short Answer Type

11.
a) Write Joule’s law of heating.
b) Two lamps, one rated 100 W; 220 V, and the other 60 W; 220 V, are connected in parallel to the electric mains supply. Find the current drawn by two bulbs from the line, if the supply voltage is 220 V

a) Joule's Law of Heating states that the amount of heat produced in a conductor is directly proportional to the square of current passing through it, directly proportional to the resistance of the conductor, directly proportional to the time for which current passed i.e

$H \propto I^{2} . . . (i) H \propto R . . . (i i) H \propto t . . . . (i i i) c o m b i n i n g (i), (i i) a n d (i i i) H \propto I^{2} R t J o u l e$

b) Resistance of first lamp = R₁
Resistance of second lamp =R₂

$R = \frac{V^{2}}{P}, R_{1} = \frac{220 x 220}{100} = 48 Ω R_{2} = \frac{220 x 220}{60} = \frac{2420}{3} Ω T h e y a r e c o n n e c t e d i n p a r a l l e l \frac{1}{R} = \frac{1}{R_{1}} + \frac{1}{R_{2}} = \frac{1}{484} + \frac{3}{2420} R = \frac{484 x 2420}{3 (484 + \frac{2420}{3})} = \frac{605}{2} Ω$

12.

Name the hormones secreted by the following endocrine glands and specify one function of each :

(a) Thyroid
(b) Pituitary
(c) Pancreas

13.

2 mL of sodium hydroxide solution is added to a few pieces of granulated zinc metal taken in a test tube. When the contents are warmed, a gas evolves which is bubbled through a soap solution before testing. Write the equation of the chemical reaction involved and the test to detect the gas. Name the gas which will be evolved when the same metal reacts with a dilute solution of a strong acid.

14.

The pH of a salt used to make tasty and crispy pakoras is 14. Identify the salt and write a chemical equation for its formation. List its two uses.

15.

(a) Why are most carbon compounds poor conductors of electricity?

(b) Write the name and structure of a saturated compound in which the carbon atoms are arranged in a ring. Give the number of single bonds present in this compound.

16.

Decomposition reactions require energy either in the form of heat or light or electricity for breaking down the reactants. Write one equation each for decomposition reactions where energy is supplied in the form of heat, light and electricity.

17.

What is a dam? Why do we seek to build large dams? While building large dams, which three main problems should particularly be addressed to maintain peace among local people? Mention them.

18.

Students in a school listened to the news read in the morning assembly that the mountain of garbage
in Delhi, suddenly exploded and various vehicles got buried under it. Several people were also injured
and there was traffic jam all around. In the brain- storming session, the teacher also discussed this issue and asked the students to find out a solution to the problem of garbage. Finally, they arrived at two main points - one is self-management of the garbage we produce and the second is to generate lee
garbage at the individual level.

(a) Suggest two measures to manage the garbage we produce.
(b) As an individual, what can we do to generate the least garbage ? Give two points.
(c) List two values the teacher instilled in his students in this episode.

19.

(a) List the factors on which the resistance of a conductor in the shape of a wire depends.
(b) Why are metals good conductors of electricity whereas glass is a bad conductor of electricity? Give reason.
(c) Why are alloys commonly used in electrical heating devices ? Give reason.