[3 Mark Questions]

Question 13 Marks

i. Several electric bulbs designed to be used on a 220V electric supply line are rated 10W. How many lamps can be connected in parallel with each other across the two wires of 220V line if the maximum allowable current is 5A?
ii. Calculate the cost of seeing 2 movies on colour T.V. daily for the month of September. Given wattage of colour T.V. = 60 W, duration of each movie is 2 hours 30 min and 1kWh costs Rs. 4

Answer

i. Let current through each bulb be I.
P = VI, 10 = 220 I
$I =\frac{1}{22} A$
Let n such bulbs be connected in series
Current through n bulbs = 5A
n (current in 1 bult) = 5
$n \frac{1}{22}=5$
n = 110
110 such bulbs can be lighted within allowable limit of 5A.
ii. Wattage of colour T.V. = 60 W
Number of hours for which colour T.V. is on during September = $2 \times 2 \frac{1}{2} \times 30=150 h$
Energy consumed = $\frac{\text { watt } \times \text { hour }}{1000}=\frac{60 \times 150}{1000}=9 kWh$
Cost of seeing 2 movies per day for 30 days =$9 \times 4$=Rs. 36 only

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Question 23 Marks

A heater coil connected to 200 V has a resistance of 80$\Omega$ . If the heater is plugged in for the time t such that 1 kg
of water at 20°C attains a temperature of 60°C. Find
i. the power of heater.
ii. the heat absorbed by water and the value of t in seconds.

Answer

i. $\therefore$ Power of heater,
$P=\frac{V^2}{R}=\frac{200 \times 200}{80}=500 W$
ii. $\therefore$ Heat absorbed by water,$H=m C \theta_R$
$=1 \times 4200 \times 40\left[\because \theta_R=60^{\circ}-20^{\circ}=40^{\circ} C , C=4200 J / kg ^{\circ} C \right]$
= 168000J
= 168kJ
iii. $H=P \times t$
$168000=500 \times t$
$\Rightarrow t=\frac{168000}{500}=336 s$

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Question 33 Marks

What should be the position of an object with respect to focus of a convex lens of focal length 20cm, so that its real and magnified image is obtained?

Answer

Given focal length f of lens 20 cm
To obtain real and magnified image, the object should be placed between F1 and 2F1,So the range will be from 20 cm to 40 cm of convex lens.

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Question 43 Marks

An individual inherits different traits from his parents. On what basis classification of traits as dominant and recessive is done?

Answer

A trait which is able to express itself both in homozygous condition as well as heterozygous conditions is called a dominant trait. A trait which expresses itself only in homozygous condition is called recessive trait.

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Question 53 Marks

i. Why is nutrition necessary for the human body?
ii. What causes the movement of food inside the alimentary canal?
iii. Why is the small intestine in herbivores longer than in carnivores?
iv. What will happen if the mucus is not secreted by the gastric glands?

Answer

i. A healthy diet throughout life promotes healthy pregnancy outcomes, supports normal growth, development, and aging, helps
to maintain healthy body weight, and reduces the risk of chronic disease leading to overall health and well-being of human
beings.
ii. Peristalsis mainly causes the movement of food inside the alimentary canal.
iii. Digestion of cellulose takes a longer time. Hence, herbivores need a longer small intestine to allow the complete digestion of
cellulose. Carnivorous animals cannot digest cellulose, hence they have a shorter intestine.
iv. Mucus is the inner lining of the digestive system which helps in the movement of food through the digestive system.
Moreover, mucus in the stomach protects the inner lining from damage by hydrochloric acid which is secreted by oxyntic cells
of the gastric gland to make the environment acidic for pepsin to function. So, the lack of mucus will damage the inner lining
of the stomach by acid activity. It may result in gastric ulcers.

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Question 63 Marks

i. Predict the reaction, if any, between
a. zinc and silver nitrate solution,
b. magnesium and iron (II) chloride solution,
c. copper and magnesium sulphate solution.
Write the equations, with its physical form symbols, for the reaction.
ii. A lump of element X can be cut by a knife. During its reaction with water, X floats and melts. What is X? Explain.

Answer

i. a. Zinc is more reactive than silver. It will displace silver from silver nitrate solution and will form zinc nitrate in the
solution.
$Zn ( s )+2 AgNO _3( aq ) \rightarrow Zn \left( NO _3\right)_2( aq )+2 Ag ( s )$
b. Magnesium is more reactive than iron. It will displace iron from iron (II) chloride solution and will form magnesium
chloride in the solution.
$Mg ( s )+ FeCl _2( aq ) \rightarrow MgCl _2( aq )+ Fe ( s )$
c. Copper is less reactive than magnesium. It will not displace magnesium from magnesium sulphate solution and, hence, no
reaction will take place.
$Cu ( s )+ MgSO _4( aq ) \rightarrow$ No reaction
ii. X is potassium (K). Potassium is a soft metal that's why it can be cut with a knife and it is lighter than water that's why it floats
on the surface of water and the heat produced melts the potassium.

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Question 73 Marks

i. a. Write two properties of gold which make it the most suitable metal for ornaments.
b. Name two metals which are the best conductors of heat.
c. Name two metals which melt when you keep them on your palm.
ii. Explain the formation of ionic compound CaO with electron-dot structure. Atomic numbers of calcium and oxygen are 20 and 8 respectively.

Answer

i. a. Malleability and ductility are the two properties of gold that make it the most suitable metal for ornaments
b. Silver and Copper are the best conductors of heat.
c. Gallium and Cesium are mostly known as metals that dissolve easily when held on a palm. Gallium basically melts when
held on the palm due to the fact that it has a very low melting point.

ii. (2, 8, 8, 2) (2, 6)
Calcium atom, Oxygen atom, Calcium oxide

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Question 83 Marks

(i) Name a metal for each case:
(a) It does not react with cold as well as hot water but reacts with steam.
(b) It does not react with any physical state of water.
(ii) When calcium metal is added to water the gas evolved does not catch fire but the same gas evolved on adding sodium metal to water catches fire. Why is it so?

Answer

(i) (a) Aluminium, (b) Copper
(ii) In both cases, the gas evolved is $H _2$ . When calcium reacts with water the heat evolved is not sufficient for hydrogen to catch fire. On the other hand, sodium metal reacts with water violently and in this case a lot of heat is evolved which is sufficient for hydrogen to catch fire.

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Science [3 Mark Questions]

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