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Page No 361:

Question 1:

Out of 60 W and 40 W lamps, which one has a higher electrical resistance when in use?

Answer:

In general use, appliances are connected in parallel to each other. In that case, the resistance is indirectly proportional to the power of the appliance. Hence, the lamp with smaller power i.e. 40 W will have higher resistance. 

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Question 2:

Name the largest cell present in the human body.

Answer:

The largest cell present in human body is the female egg/ovum.

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Question 3:

What is an electromagnet? Draw a circuit diagram to show how a soft iron piece can be transformed into an electromagnet.

Answer:

An electromagnet is a rod of magnetic material (say soft iron) placed inside a solenoid coil. On passing current in the solenoid coil, the iron rod begins to behave as a magnet. The strength of magnetization can be increased by increasing the amount of current flow or by increasing the number of turns in the coil. 


 

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Question 4:

What is meant by water of crystallisation in a substance? How would you show that blue copper sulphate crystals contain water of crystallisation?

Answer:

The water of crystallization is the number of water molecules that combine chemically in definite molecular proportion with the concerned salt in the crystalline state. This water is responsible for the geometric shape and colour of the crystal. For eg: CuSO4.5H2O

Copper sulphate crystals are blue in colour. However, when copper sulphate is heated in a china dish for some time, the blue colour disappears and it becomes white-grey in colour. This white grey substance is the anhydrous copper sulphate. The reaction is written as follows:

CuSO4.5H2OCuSO4+5H2O
 

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Question 5:

(a) Name the tissue which transports soluble products of photosynthesis in a plant.
(b) Name the tissue which transports water and minerals in a plant.

Answer:

(a) The tissue which transports soluble products of photosynthesis in a plant is phloem.
(b)The tissue which transports water and minerals in a plant is xylem.

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Question 6:

What is the chemical formula for plaster of Paris? How is it prepared? State the common and the chemical names of the compound formed when plaster of Paris is mixed with water.

Answer:

The chemical formula for plaster of paris is calcium sulphate hemihydrate (CaSO4.12H2O).
Plaster of Paris is prepared by heating of gypsum at 373 K.

2CaSO4.2H2O373 K2CaSO4.12H2OPlaster of paris+3H2O

When we mix plaster of Paris with the appropriate amount of water, it will give gypsum chemically known as calcium sulphate dihydrate.

2CaSO4.12H2O+3H2O2CaSO4.2H2OGypsum


 



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Question 7:

Give reasons for the following observations:
(a) Th element carbon forms a very large number of compounds.
(b) Air holes of a gas burner have to be adjusted when the heated vessels get blackened by the flame.
​(c) Use of synthetic detergents causes pollution of water.

Answer:

(a) Carbon forms a large number of compounds because of the following reasons:
(i) Catenation property, i.e. self linking property of carbon to form long chains.
(ii) Small size, helps in forming double and triple bonds.
(iii) The tendency to form rings.
(iv) High valency, allows forming bonds with other atoms.

(b) Blackening of vessels is due to deposition of waste material in the holes of the burner. These depositions prevent complete combustion of fuel and create black soot. Thus, the holes of the burner need to be cleaned and unclogged to give the undisturbed flow of gas.

(c) Synthetic detergents are made up of chemical compounds like fatty acid salts (aliphatic) or aromatics like linear alkyl benzene. These are non-biodegradable compounds which cannot be degraded and result in polluting our environment.

 

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Question 8:

What is meant by 'rusting'? With labelled diagrams, describe an activity to find out the conditions under which iron rusts.

Answer:

Rusting of iron: When iron is exposed to air and moisture for a very long time, it gets covered with a brown flaky substance. This brown flaky substance is called rust and the process is called rusting.

4Fe+3O2+xH2O2Fe2O3.xH2O

Activity -

  • Take three boiling tubes and label them A, B, and C. Place three clean iron nails (free from rust) in each of the tube.
  • Add water to tube A in such a manner that some parts of the nails are exposed to air.
  • Add water to test tube B, in such a way that the nails are completely submerged in water. Then, pour some amount of oil in the tube.
  • Add anhydrous calcium chloride to test tube C and then seal it. Anhydrous calcium chloride absorbs all the moisture present inside the tube so that the nails are only exposed to oxygen and no moisture.
  • Seal all the tubes with the help of rubber corks. Leave the tubes undisturbed for a few weeks and observe the changes. 

Conditions for rusting of iron 

Itwill be observed after a few weeks that the nails in tube A have rusted, while those in test tubes B and C have not. 

Explanation:

In tube A, both moisture and oxygen were available and the nails started rusting after two weeks. 

In tube B, iron nails were only in contact with water, and oxygen was not allowed to dissolve in water because of the layer of oil. As nails did not rust even after two weeks when only water was available, it shows that rusting cannot take place if only water is available.

In tube C, only oxygen is present as anhydrous calcium chloride absorbed all the moisture present inside the boiling tube. As the nails did not rust even after two weeks when only oxygen was available, it shows that rusting cannot take place if only oxygen is available.

This shows that the presence of both oxygen and water is essential for rusting to take place.

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Question 9:

(a) What is the colour of ferrous sulphate crystals? How does this colour change after heating?
​(b) Name the products formed on strongly heating ferrous sulphate crystals. What type of chemical reaction occurs in this change? Write chemical equation of the reaction.

Answer:

(a) Ferrous sulphate is green in colour. On heating, the green crystals are converted into a dirty-yellow anhydrous solid as it loses water of crystallization.

(b) When ferrous sulphate is strongly heated anhydrous material loses sulphur dioxide and sulphur trioxide leaving a reddish-brown iron oxide.
2FeSO4Fe2O3+SO2+SO3
 

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Question 10:

(a) State four factors on which the resistance of a conductor depends.
​(b) A piece of wire of resistance 20 Ω is drawn out so that its length is increased to twice its original length. Calculate the resistance of the wire in the new situation.

Answer:

(a) The resistance of a conductor depends on the following factors:

(i) Shape of the conductor
(ii) Size of the conductor
(iii) Material of the conductor
(iv) Temperature of the conductor

(b) Initial resistance = 20 Ω

When the length of the resistance is increased, it's volume remains constant. 

According to relation,

RlAl2V V = Constant R  l2

RiRf=li2lf220 ΩRf=li2(2li)2=14Rf=80 Ω

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Question 11:

(a) A charged particle enters at right angles into a uniform magnetic field as shown. What should be the nature of a charge on the particle if it begins to move in a direction pointing vertically out of the page due to its interaction with the magnetic field?



(b) Between which two points of a concave mirror should an object be placed to obtain a magnification of, −3?
​(c) "The refractive index of carbon disulphide is 1.63". What is the meaning of this statement in relation to the speed of light?

Answer:

(a) When a charged particle enters at right angles into a uniform magnetic field, it feels a force, F=q(v × B), also known as Lorentz force. Here, q is the charge of the particle, v is it's velocity vector and B is the magnetic field strength vector in that region.

Clearly, the direction of the force is perpendicular to both, the velocity vector and the magnetic field strength vector. In the given case, the cross product of velocity and magnetic field points vertically out of the page. The direction of charge is also given the same. Hence, the charged particle is positive in nature.

(b) The object should be placed between the focus and radius of curvature of the concave mirror. Then it will form an inverted and enlarged image. In that case, a magnification of '-3' can be obtained.

(c) Refractive index of a medium is the measure of the speed of light in that, medium with respect to the vacuum. It is defined as the ratio of the speed of the light in a vacuum to the speed of the light in the given medium. So, "The refractive index of carbon disulphide is 1.63" means that the speed of light in carbon disulphide is 11.63 times the speed of the light in vacuum.

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Question 12:

(a) What is myopia (near-sightedness)?
(b) Draw a ray diagram to show an eye having myopia.
​(c) Draw another ray-diagram to show how myopia can be corrected by using a lens.

Answer:

(a) Nearsightedness (myopia) is a common vision defect, in which a person can see only nearby objects clearly, but distant objects appear to be blurry. This defect arises due to the decresed focal length of the eye lens or due to elongation of the eyeball.

(b) An eye having Myopia:

 

(c) Correction of myopia using a concave lens.

 
 

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Question 13:

(a) What are the two main components of our environment?
(b) What will happen to a plant if its xylem is removed?
(c) Name two tissues that provide control and coordination in multicellular animals.

Answer:

(a) Biotic and abiotic components are the two main components of our environment.
The living parts of the ecosystem are referred to as biotic components. For example: plants, animals humans etc.
The non-living parts of the ecosystem are referred to as abiotic components. For example: land, air etc.

(b) Xylem is the water-conducting tissue of plants. If the xylem of a plant is removed, then the conduction of water will not take place. As a result of which the plant will die.

(c) Neuron and muscular tissues are involved in control and coordination in multicellular organisms.

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Question 14:

What is rainwater harvesting? What is the need of rainwater harvesting? Mention any four rainwater harvesting structures.

Answer:

Collecting rainwater for future use by storing it in storage reservoirs is called rainwater harvesting. In rainwater harvesting, the rainwater that falls on the roof and other parts of a building is channeled through pipes to an underground reservoir. These collecting pipes run along the sides of the roof and join together at a point to form the main pipe. This pipe flows into the tank present in the ground. The collected water may be allowed to seep inside the ground to recharge ground water or can be stored in tanks for future use.

Rainwater harvesting is one of the methods to deal with water shortage and meet the demands of water for the growing population. It also ensures water conservation and all round availability of water for various purposes.

Rain water harvesting structures include - Khadins, Nadis, Tal and Kulhs.

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Question 15:

(a) What are natural resources? Name some of the important natural resources.
​(b) State two factors which work against an equitable distribution of natural resources.

Answer:

Natural resources are the resources present in nature, which can be used for our various needs. The examples of such resources are forests, wildlife, water, coal, petroleum, etc.

Two factors that work against the equitable distribution of these resources are:

(i) human greed

(ii) corruption and the lobby of the rich and the powerful

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Question 16:

(a) Name a device which helps to maintain a potential difference across the ends of a conductor.
(b) What is meant by saying that the potential difference between two points is 1 V?
(c) Define Ohm's law. Write an expression for it.
(d) What is the unit of resistance?
​(e) When the potential difference between the terminals of an electric heater is 110 V, a current of 5 A flows through it. What current will flow through the heater if the potential difference is increased to 220 V? What is the resistance of heater?

Answer:

(a) The potential difference across the ends of a conductor is maintained by connecting a battery or a dry cell at the ends of the conductor.

(b) When 1 Joule of work is done to move a 1 Coulomb charge from one point to another, then the potential difference between the two points is said to be 1 Volt (V).

(c) According to Ohm's Law, the current flowing in a circuit is directly proportional to the applied potential difference. 

Mathematical expression for Ohm's Law: V  I or V = IR (Where 'R' is the constant of proportionality and is known as the resistance of the circuit) 

(d) Unit of resistance is Ohm, denoted by the symbol Ω.

(e) According to Ohm's law, V = IR

R=VI=110 V5 A=22 Ω


Hence, the resistance of the heater is 22 Ω.

Now, if the potential difference is changed to 220 V, then the current in the circuit = I=VR=220 V22 Ω=10 A
 



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Question 17:

(a) How should the electric lamps in a building be connected so that switching on or off in a room has no effect on other lamps in the building? State one or more advantage of such an arrangement.
(b) Which effect of current is utilised in the working of an electric fuse? How does an electric fuse work?
(c) What is the usual colour of the insulation of (i) earth wire, and (ii) live wire?
(d) When does an electric short circuit occur? What harm can do it?
(e) Explain the purpose of earthing an electrical appliance.

Answer:

(a) Electric lamps should be connected in parallel so that every lamp gets its separate current. In that condition, switching on and off in a room will not affect the other lamps in the building. Advantage of this type of connection is, if any appliances fail in the circuit or stop working, then it won't affect the other appliances, as in parallel connected every appliance get their separate current from the main circuit. 

(b) Heating effect of current is utilized in the working of an electric fuse. A fuse is made such that it can allow only a particular amount of current to flow in the circuit. So, when a current more than the rating of the fuse starts flowing in the circuit, the wire of the fuse melts and it breaks the circuit. Therefore, no current flows further in the circuit, and no other appliances get any damage.

(c) (i)The usual colour of the earth wire is either green or yellow.
(ii) While the usual colour for the live wire is brown.

(d) An electric short-circuit occurs when the live wire comes in contact with the neutral in any circuit. A short-circuit can result in a flow of sudden high amount of current in the circuit, which may damage low rating appliances.

(e) The main purpose of earthing is to provide an immediate path to excess flow of current due to a fault in the circuit. This is done to prevent us from getting a shock. For this, the earthing wire is connected directly to the earth, so that whenever a high current flows in the circuit, it can be discharged directly to the ground. 

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Question 18:

(a) Give the electron configuration of magnesium and chlorine.
(b) Write the electron dot-structures of magnesium and chlorine atoms.
(c) Describe the formation of magnesium chloride from magnesium and chlorine by the transfer of electrons.
(d) What type of chemical bonds are present in the magnesium chloride formed?
​(e) Why do such compounds have high melting points?

Answer:

(a) Electronic configuration of magnesium is 2, 8, 2 and of chlorine is 2, 8, 7.

(b) Electron dot structure of magnesium and chlorine.


(c) Electronic configuration of magnesium is 2, 8, 2, so valence shell contains two electrons. To attain noble gas configuration magnesium will lose two electrons.
Electronic configuration of chlorine is 2, 8, 7, so valence shell contains seven electrons. To attain noble gas configuration chlorine will gain one electron.
So, the valency of magnesium is two while valency of chlorine is one. 

                                                      

(d) Ionic bond is formed in Magnesium chloride.

(e) Ionic compounds have a high melting point because of strong inter electronic attraction forces between them.

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Question 19:

In the following diagram for the first three periods of the periodic table, five elements have been represented by the letters a, b, c, d and e (which are not their chemical symbols):

(i) Select the letter which represents a halogen.
(ii) Select the letter which represents a noble gas.
(iii) What type of bond is formed between a and b?
​(iv) What type of bond is formed between c and b?
(v) Which element form a divalent anion?
Give reasons for your choices.

Answer:

(i) The letter "b" represents halogen as "b" belongs to 17 group where valence electrons are 7.

(ii) The letter "e" represents noble gas as "e" belongs to 18 group where valence electrons are 8 and their octet is full.

(iii) Electronic configuration of a is 2, 8, 4
Electronic configuration of "b" is 2, 8, 7.
Elements "a" and "b" will form a bond by sharing of the electron, so a covalent bond will be form between them.

(iv) Electronic configuration of a is 2, 8, 2.
Electronic configuration of "b" is 2, 8, 7.
Elements "c" and "b" will form a bond by transfer of electrons and thus will form an ionic bond.

(v) The letter "d" will form a divalent anion. 
Electronic configuration of d will be 2,8,6. It has 6 valence electrons in its outermost shell, so it will gain 2 electrons and become a divalent anion. 

 

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Question 20:

(a) Name two biodegradable and two non-biodegradable wastes.
(b) Name the biotic and abiotic components of ecosystem.
(c) What is the role of decomposers in the ecosystem?
(d) If the plants get 10000 J of energy from the sun, how much energy will be available to tiger in the following food chain?
      Plants → Deer → Tiger
​(e) A harmful chemical enters food chain comprising peacock, frog, grass, snake and grasshopper. Which of these organisms will have the maximum concentration of harmful chemical in its body? Why?

Answer:

(a) Biodegradable wastes - Paper, vegetable wastes
Non-biodegradable wastes - Plastic, glass objects

(b) Biotic components - Plants and animals
Abiotic components - Land and air

(c) Decomposers include microorganisms such as bacteria and fungi that obtain nutrients by breaking down the remains of dead plants and animals.

Role of decomposers -

  • They help in the breakdown of organic matter or biomass of dead plants and animals into simple inorganic raw materials such as CO2, H2O and nutrients.
  • They help in the natural replenishment of soil.
  • They help in keeping the environment clean.
(d) The energy is transferred according to the 10% law of energy transfer.
In this case, plants get 10000 J of energy.
Deer will get 10% of this energy i.e. 1000 J.   
The amount of energy tiger will get is = 10100×1000 = 100 J

(e)  The increase in the concentration of pollutants or harmful chemicals with the increase in trophic level is called biomagnification. 

The food chain formed by these organisms would be -
Grass→Grasshopper→Frog→Snake→Peacock

In this case, the peacock occupies the last trophic level which means the maximum concentration of harmful chemicals will be present in its body.



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Question 21:

Name the organs of the human female reproductive system. Draw a neat, labelled diagram of the human female reproductive system and describe its working. How much is the gestation period in humans?

Answer:

The human female reproductive system consists of ovary, oviduct, uterus and vagina.


Functioning of human female reproductive system is as follows -


Ovaries -The ovaries are located on each side of the lower abdomen. They produce thousands of eggs in the female body. They also produce a hormone called oestrogen, which brings about the development of secondary sexual characteristics in the female body. The eggs produced in the ovary start maturing on reaching puberty. 

Fallopian tube - One egg from each ovary grows and matures and is carried from the ovary to the uterus by a thin oviduct or the fallopian tube. Fertilisation of the egg also takes place in the oviduct.

Uterus - Once the fertilisation occurs, the developing embryo is implanted in the uterus/womb.

Vagina - Also known as the birth canal. It is the passage through which the baby passes out of the body after the completion of gestation period.

The gestation period in human females is 9 months.

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Question 22:

An organic compound A of molecular formula C2H6O is a constituent of wine and beer. This compound on heating with alkaline potassium permanganate forms another organic compound B which turns blue litmus to red. Identify the compounds A and B.

Answer:

An organic compound A of molecular formula C2H6O is a constituent of wine and beer, so it must be an alcohol containing molecule, i.e. ethanol (CH3CH2OH).

When ethanol is treated with alkaline potassium permanganate, it oxidizes ethanol and forms compound "B" which is ethanoic acid.

C2H5OH+KMnO4alkalineCH3COOH+H2O

Due to the formation of ethanoic acid, blue litmus turns red. 

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Question 23:

When dilute hydrochloric acid is added to a sodium compound A, then brisk effervescence of a gas B is produced. On passing this gas through lime-water, the lime-water turns milky forming an insoluble compound C. When excess of gas is passed, the insoluble compound dissolves forming a soluble compound D.
(a) What could be compound A?
(b) Name the gas B.
(c) Name the insoluble compound C.
(d) Name the soluble compound D.

Answer:

(a) Compound "A" must contain a carbonate as it gives brisk effervescence with hydrochloric acid. So, compound "A" must be sodium bicarbonate (Na2CO3).

(b) When dilute hydrochloric acid is added to a sodium compound A, then brisk effervescence of gas is produced which means carbon dioxide gas is released during the reaction. Carbon dioxide on passing through lime water, turns lime water milky.

Na2CO3+2HCl2NaCl+CO2+H2O

(c) When carbon dioxide is treated with lime water (calcium hydroxide), it forms insoluble compound "C" which is calcium carbonate.

Ca(OH)2+CO2CaCO3+H2O

(d) When an excess of carbon dioxide is passed through an aqueous solution of calcium carbonate, it forms compound "D" which is calcium bicarbonate.

CaCO3+H2O+CO2Ca(HCO3)2

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Question 24:

Draw the path of a ray of light passing through a triangular glass prism. Label the angle of incidence and the angle of deviation in the ray-diagram.

Answer:

A diagram of the path of a ray passing through a triangular glass prism:

Page No 364:

Question 25:

A student has been given 3 resistances of 3 ohms each.
(a) How should he connect these resistances so as to obtain a resultant resistance of 1 ohm?
(b) Draw a labelled diagram to show the combination of these resistances.

Answer:

(a) He should connect all the three resistances in a parallel connection. Then the net resistance of the parallel combination will be 1 ohm.

1Rnet=1R1+1R2+1R3=13+13+131Rnet=33=1 Ω Rnet=1 Ω

(b) All three given resistors connected in parallel:

 

Page No 364:

Question 26:

A student placed a potted plant growing in a glass pot horizontally (with the root and shoot, both being in the horizontal direction). After a few days, the student observed that the root of the plant bends downwards and the shoot (stem) of the plant bends upwards. Which scientific term is used to indicate:
(a) upward bending of shoot (or stem)?
(b) downward bending of root?

Answer:

(a) upward bending of shoot (or stem) - phototropism
(b) downward bending of root - geotropism

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Question 27:

A Mendelian experiment consisted of breeding tall pea plants bearing violet flowers with short pea plants bearing white flowers. The progeny all bore violet flowers, but almost half of them were short. This suggested that the genetic make up (or genotype) of the tall parent can be depicted as:
(a) TTWW   (b) TTww   (c) TtWW   (d) TtWw
Give reason for your choice.

Answer:

In this case there are two possibilities -

Possibility I - The genetic makeup of the tall parent can be TTWW.
Possibility II - The genetic makeup of the tall parent can be TtWW. 

According to possibility I, if the tall parent has the genotype TTWW, then all the offsprings that are obtained will be tall bearing white flowers.

According to possibility II, if the tall parent has gentotype TtWW, then half the offsprings will be short bearing white flowers.

oSo, we can say that, the genotype of the tall parent would be TtWW.



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