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## Friday, October 26, 2012

### 8th Mensuration CBSE Enrichment questions

1. A rectangular tank can hold 650 litres of milk . if it is 130cm long & 250cm wide , find the height of the tank.

Solution: Volume of rectangular tank = 650 litres = 650 × 1000 cm 3 = 650000 cm 3

We know that Volume of a cuboid = l × b × h

650000 = 130 × 250 × h

h = (650000)/( 130 × 250 )= 20 cm

Therefore, height of the tank = 20 cm

2. a hall is of length 16m , breadth 14m & height 5m . Calculate the no: of persons that can be accommodated in the hall , assuming 3.5m3 of air is required for each person.

Solution: Volume of the hall = length × breadth × height

= 16 × 14 × 5

= 1120 m3

Volume occupied my 1 man = 3.5 m3

3.5 m3  of air occupied my 1 man

1120 m3  of air occupied my ( 1/3.5)x 1120= 320 man

Therefore, number of men that can be accommodated = 32 0 men

2. A cylinder container with diameter 48cm contains sufficient water to submerge a rectangular solid of iron with dimensions 33cm x 18cm x 12cm.find the rise in the level of water when solid is completely submerged.

Solution:  Diameter of cylinder = 48 cm      Radius of cylinder (r) = 24 cm

Now, when the Cuboid  is completely submerged

Then, Volume of cylindrical portion formed by original water level and after increase in water level = volume of cuboid

πr 2 h = 33 cm × 18 cm × 12 cm

22/7 x 24 x 24 x h = 33 cm × 18 cm × 12 cm

h = (33 cm × 18 cm × 12 cm x7)/ 22 x 24 x 24=3.94cm

Hence, the required increase in water level is 3.94 cm

3. The difference between the circumference and radius of a circle is 74 cm. Find the circle diameter.

Solution: circumference - radius = 74 Þ      pd- d/2 =74 Þ  22d/7  - d/2 =74

Þ  (44d-7d)/14 =74 Þ 37d = 74x14 Þ d= (74x14)/37 Þ d  = 28cm

4. Find the area of the rhombus if the length of each side be 7 cm. and  corresponding altitude is 8 cm

Solution:  area of rhombus = base × height = 7 cm × 8 cm = 56 sq cm

5. A solid cubical block of fine wood costs rupees 256 at rupees 500/m3. Find its volume and the length of each side.

Solution: Let the edge of the cubical box be “a” m.

Rs. 500 is the cost of 1 m3 wood

Rs. 256. is the cost of 1x256/500 m3 wood=0.512m3
So, Volume of total wood = 0.512m3
a x a x a = 0.512m3
a x a x a = 0.8 x 0.8 x0.8x

The length of each side = 0.8m=80cm

6. What will be the volume of the cylinder in which area of the base is 45 sq.cm and height is 6 cm?

Solution: The volume of the cylinder = Area of base x height =45 sq.cm x 6 cm =270cm3

7. Area of 4 walls of a room is 108 m2 .If height and length of room is in ratio 2: 5 and height and breadth in ratio 4: 5. Find the area of floor of the room.

Solution: Given: L : H = 5 : 2 Þ  H : B = 4 : 5

L : H : B = 20 : 8 : 10

Area of four walls of a room is =2(l + b) h = 108 Þ (l + b) h = 54

(20 x + 10x) x 8x = 54

240x2 = 54

x2 = 54 / 240

x2 = 0.225

The area of floor of the room = l x b =l × b = 20x × 10x =200x2 =200x 225= 45m2

8. If Area of the square inscribed in a semicircle is 2cm2 .Find the area of the Square Inscribed In a full circle.

Solution: Area of square = 2cm2

Side of square = square root of 2

Let r be the radius of the circle and adjust it like that it forms a right angle triangle

then

r2 = (square root of 2)2 + (square root of 2 / 2)2

r2 = 2 + ( 2 / 4)

r2 = 5 / 2

r = square root of ( 5 / 2)

In a full square the diagonal of square will be the diameter of the cirlcle.

r = square root of ( 5 / 2) is this so diameter = 2 * square root of (5 / 2)

Diagonal of square = side * square root of 2

side * square root of 2 = 2 * square root of 5 / square root of 2

side * 2 = 2 * square root of 5

side = square root of 5

Area of square = r2

= (square root of 5)2

= 5 cm2

9. A cylinder tube open at boyh ends is made of metal. The internal diameter of the tube is 11.2 cm and its length is 21 cm .The metal everywhere is 0.4 cm thick . Calculate the volume of the metal correct to 1 place of decimal.

Solution: Internal diameter = 11.2 cm

Internal radius= 11.2/2 = 5.6 cm  Length of the tube = 21 cm

Volume of the internal cylinder π r 2 h = 22x 5.6x5.6x21/7 =2069.76cm 2

External radius, R = (5.6 + 0.4) cm = 6 cm

Volume of the external cylinder = πR2 h =22x6x6x21/7=2376cm2

Now, volume of the metal = Volume of the external diameter – Volume of the internal diameter  = (2376 – 2069.76) cm3 = 306.24 cm3 = 306.2 cm3

10.  The dimension of an oil tin are 26 m x 26 cm x 45 cm .Find the area of the tin sheet required for making 20 such tins. If 1 square meter sheet costs Rs. 10 , find the total cost for making 20 such tins.

Solution : Area of the tin sheet required =  Area of 20 oil tins

= 20 × 2 (lb + bh + hl)   = 20x2(26x26+26x45+45x26)=12.06m2
Cost of 1 m2 tin sheet = Rs.10

Cost of  12.064 m2 tin sheet = Rs.10 2.064  = Rs.120.64

So, total cost for making 20 such tins = Rs.120.64

## Tuesday, October 23, 2012

### X CBSE NCERT Chapter Tangent of Circle Questions Bank

1. If radii of the two concentric circles are 15cm and 17cm , then find the length of each chord of one circle which is tangent to one other.

Ans. 16cm

2. If two tangents making an angle of 120 with each other , are drawn to a circle of radius 6cm, then find the angle between the two radii, which are drawn to the tangents.
Ans. 600

3. PQ is a chord of a circle and R is point on the minor arc. If PT is a tangent at point P such that < QPT = 60 degree  then find <PRQ.
Ans. 1200

4. If a tangent PQ at a point P of a circle of radius 5cm meets a line through the centre O at a point Q such
that OQ = 12 cm then find the length of PQ.
Ans. √119cm

5. From a point P, two tangents PA and PB are drawn to a circle C(O,r) . If OP =2r ,then what is the type
of Triangle APB.
Ans. Equilateral triangle

6. If the angle between two radii of a circle is 130,then find the angle between the tangents at the end of the radii.
Ans. 500

7. ABCD is a quadrilateral. A circle centred at O is inscribed in the quadrilateral. If AB = 7cm , BC = 4cm , CD = 5cm then find DA.   '                        Ans. 8 cm

( 2 Mark Questions )

9. Two tangents PA and PB are drawn from an external point P to a circle with centre O. Prove that OAPB is a cyclic quadrilateral.

10. If PA and PB are two tangents drawn to a circle with centre O , from an external point P such that PA=5cm and < APB = 60, then find the length of the chord AB.
Ans. 5cm

X Chapter : Circle Questions Bank for CBSE EXAMS

10th Chapter : Tangent of Circle Solved CBSE Test Paper

 10th Maths SA-2 Chapter Quick links

## Monday, October 22, 2012

### Electricity and Electric Circuits for Class VI(CBSE)

Quest Time CBSE NCERT VI Chapter: Electric currents, Circuits, Cell.

For Questions 1 to 10 visit link: Class VI Physics By Jsunil

11. What conductors and insulators?

Ans: The materials which allow electric current to pass through them are called conductors. Examples: All metals like Copper,Iron, Silver and Human body.
INSULATORS: The materials which do not allow electric current to pass through them are called bad conductors or insulators. Examples: Plastic, Wood, Rubber and Glass.

12. Why do electricians wear rubber gloves and shoes while at work?

Ans: It because rubber gloves are an insulator and prevent current to flow in body .Thus saves electricians from electric shock.

13. What do you mean by heating effect of current?

Ans: Electric current is actually the flow of electrons in the conducting material. Now,
when these electrons flow, they encounter some resistance in the structure of the conductor, which accounts for the "resistance" of materials. As the electrons collide or vibrate, heat energy is generated depending on the resistance of the conductor. This overall effect is called heating effect of electrical current.

14. Name a few appliances that work on the heating effect of current?

Ans: Electric kettle: Used for boiling water to make tea or coffee
Electric bulb : The filament of the bulb is heated when current flows and becomes white hot to emit brilliant light.
Electric iron: Used for ironing or pressing clothes.
Electric toaster: Used to toast bread

15. Name a special material used for heating component?

Ans: It is a coil of wire made of a special material called nichrome which becomes very hot when current is passed. This heat is used to cook food (as in an electric stove), heat water ( as in an electric kettle, electric heater) etc

16. Name the elements used to make an alloy nichrome?

Ans: Nickel and Chromium.

17 Why are electric wire are made up of copper through silver is best conductor?

Ans: Silver is an expensive metal. Material needed for conductor should be cheap as wires are used extensively in almost every appliance. That is why silver can't be used to make wires.

18. Why do you apply a tap over the joint of electric wire?

Ans: Tap is an insulator and save us from electric shock.

19. If you connect a battery cell to the bulb through a wooden stick, the will not glow. Why?

Ans: No, wooden stick is an insulator that cannot conduct electricity

20. Do not handle the electric appliances when your hands are wet. Why?

Ans: Tap water is good conductor and we may get electric shock.

21. There will be three colored wires normally used while connecting any electric equipment. What are those colors? Tell which coloured wire gives us electric shock?

Ans: Red (Live wire that give us electric shock), Black (Neutral) , and Green(Earth wire)

### Light, Shadows And Reflections Quest Time for class VI

Brain Teaser Quest Time For Class 6th Light, Shadows And Reflections

1. How can you determine the length of the shadow of an object?

Ans: We cannot correctly determine the length of the shadow of an object. The length of shadow depends on the angle at which light fall on a body and varies at different time of day. This principal helps us to make sun dial for calculating time.

2. How can you make sundial at home?

Ans: We take a pencil and place it into the whole of the empty spool of thread.This work as sundial.

Making the Sundial:

1. Using the pencil, poke a hole on the side of the paper / Styrofoam cup pproximately 2 inches below its top (rim).
2. Place the pebbles in the cup so to give it some weight and hold it upright.3. Cover the cup with the plastic lid.
4. Put the straw through the hole on the side of the cup and its lid while letting about half an inch of the straw stick out from the side.
4. Secure the straw to the cup by taping it down on the side.

3. How do you make a pinhole camera?

Ans: Take two rectangular boxes that fit into one another without leaving any gap.
Cut open one side of each box.

Make a small hole in the larger box at the centre of the closed end opposite the side that has been cut open.

Cut a square of side five centimetres in the smaller box in the closed end opposite the side that has been cut open. Cover this square with tracing paper.
Finally, slide the smaller box into the larger box, ensuring that the pinhole and the tracing paper are in line with one another, but at the opposite ends.

Slide the smaller box to adjust the focus so that you can capture the image of any object you want.

Look through the open face of the smaller box. you can see the image of the object and inverted on the screen.

4. Explain with the help of an activity that light travels in a straight line.

Ans: Place a candle at one corner of the room
Now look through the pipe, you can see the candle
Now bend the pipe and look. you cannot  see the candle
This shows that light travel in straight line called rectilinear propagation of light

5. What is meant by reflection of light ?

Ans: When light fall on smooth or rough surface return back after hitting these surface this phenomenon is called reflection of light

6. What types of image form in pinhole camera?

Ans: Inverted (upside-down)

7. Why is the image formed by a pinhole camera upside down?

Ans: It is because there is no refracting or reflecting optical element to change the path of the rays of light.

8. What happens if we place an opaque object in coloured light?

The colour of light will not affect the shadow, because shadow is the dark patch formed when an object obstructs the path of light

9. On a sunny day, does a bird or an aeroplane flying high in the sky cast its shadow on the ground? Under what circumstances can we see their shadow on the ground?

Ans: when the bird is flying very low close to the ground.

10. You are given a transparent glass sheet. Suggest any two ways to make it translucent without breaking it

Ans:
(i) By applying oil, grease, butter on it or pasting a butter paper on it.
(ii) Grinding (rubbing) the surface of the glass by any abrasive material.

11. Suggest a situation where we obtain more than one shadow of an object at a time.

Ans: We can obtain more than one shadow of an object if light from more than one source falls on it. [For example during a match being played in a stadium, multiple shadows of players are seen].

12. Three identical towels of red, blue and green colour are hanging on a clothes line in the sun. What would be the colour of shadows of these towels?

Ans: The colour of shadows of all three towels will be the same

13. Using a pinhole camera a student observes the image of two of his friends, standing in sunlight, wearing yellow and red shirt respectively. What will be the colours of the shirts in the image?

Ans: The colours of the image of the shirts will be the same as the colour of the shirt.

14. A football match is being played at night in a stadium with flood lights ON. You can see the shadow of a football kept at the ground but cannot see its shadow when it is kicked high in the air. Explain.

Ans: We can see the shadow of football lying on the ground because the ground acts as a screen for it. However, when the football is kicked high, the ground, which is acting as a screen is away from the football, hence no shadow of the football will be formed on the ground

15. . A student had a ball, a screen and a torch in working condition. He tried to form a shadow of the ball on the screen by placing them at different positions. Sometimes the shadow was not obtained. Explain.

Ans: Possible reasons  (i) The screen away from the ball.
(ii) The beam of light from the torch is falling parallel to the screen on the ball.
(iii) The torch is kept away from the ball.

Lesson 11: Light, Shadows And Reflections.

6th Chapter Light CBSE Test paper-1                            View/Download
6th Chapter Light CBSE Test paper-2                            View/Download

### CBSE Class 6th Light Shadow and Reflections

Answer the following in one word

1. Light is form of what?

Ans: Energy

2.What is the speed of light?

Ans: 3 x10 m/s

3. Name the dark part of shadow?

Ans: Umbra

4.What is lighter part of shadow known as?

Ans: Penumbra

5. Are stars luminous or non luminous?

Ans: Luminous _Objects that give out or emit light of their own are called luminous objects like the sun

6. Do shadow depends on colour of objects?

Ans: No

7. Which types of object allow light to pass partially?

Ans: Translucent

Answer the following in detail

8.What are transparent, translucent and Opaque objects. Give at least two example of each?

Ans: If we cannot see through an object we call it Opaque like wood, plastic. Opaque object cannot allow
light to pass through. If we can see through an object we call it transparent like glass, water and air .

Transparent objects allow  light to pass through . If we can see through an object but not very clearly we call it translucent like milk, wax paper, ground glass .
Translucent objects allow light to pass partially through.

9. Why shadow of object like aero plane or bird cannot visible on Earth?

Ans: It is because umbra region cannot able to reach earth and finish above the earth.

10. What is shadow .What are condition essential for the formation of shadow?

Ans: The dark patch that formed when opaque object come in the path of light is called shadow.
Condition essential for the formation of shadow are:

(a)Source of light (b) Opaque object (c) Screen on which shadow form

LIGHT , SHADOWS AND REFLECTIONS Hots Questions

1. In a completely dark room, can you see your face in a mirror? Why?

Ans: Due to absence of light In a dark room. Light is the source that illuminates our face by reflection.

2. Why cannot we see upside down image of the sun?

Ans: Object like sun is in infinity whose image form point sized or highly demised.

3. Why shadows are black in colour?

Ans: It is because no light reaches on screen in area where shadow form. The colour of object is colour components of light that reflect and reach our eyes.

4. Can you see an object through a “T” shaper pipe? If, no, Why?

Ans: No, it is because light always travel in straight path that is known as rectilinear properties of light.

5. Can you see a reflected light directly? If, no Why?

Ans No, the path of the ray of light is itself invisible but make the things visible only when fall on our eyes.

## Sunday, October 21, 2012

### Carbon and its Compounds class 10 CBSE | NCERT Solutions

NCERT Solution, MCQs, Study Notes, Q & A

1.Define the term, functional group and give two examples for it.

Ans:
An atom or a group of atoms on which properties of the carbon compound depends is known as functional group. Eg: -
OH-            Alcoholic
- CHO        Aldehydic
- CO           Ketonic
- COOH     Carboxylic

2. Name the functional groups present in the following compounds.

CH3CH2CH2-OH;  CH3CH2CH2COOH ; CH3-CH2-CHO;CH3COCH2CH2CH3
Ans:
CH3CH2CH2-OH          Alcoholic
CH3CH2CH2COOH     Carboxylic
CH3-CH2-CHO              Aldehydic
CH3COCH2CH2CH3      Ketonic

3. Describe the preparation of ethanol by the fermentation process.

Ans:Fermentation of sugar is a process in which the sugar molecules are broken down in the ethylalcohol and carbon dioxide by the action of enzymes called invertage and zymase which are present in yeast. Molasses the bi-product of the sugar industry is mixed with suitable quantity of water and yeast powder. This mixer is kept in a huge steel tank at 250C to 300C for about 10 to 12 days, during this time fermentation takes place to form C2H5OH and CO2 gas. C2H5OH is recovered from this mixture by distillation.
Invertase
C12 H22 O11 + H2O  -------------->        C6H12O6           +          C6H12O6
(From yeast)            Glucose                          fructose
Zymase
C6 H22 O16                                       ----------------->  2C2H5OH + 2CO2
Glucose & Fructose                   (from yeast)                        Ethanol

4. What is meant by denaturated alcohol ? How is it prepared?

Ans:
Ethyl alcohol (ethanol) made into unfit for drinking is called denaturated alcohol.
It is prepared by adding poisonous substances like menthol, pyridine,  copper sulphate etc., to ethanol.

5. Give the names of the following :
i) an aldebyde derived from ethane
ii) A ketone derived from butane
iii) The compound obtained by oxidation of ethanol by chromic anhydride (CrO3); and
iv) The substance formed on catalytic hydrogenation of methanal

Ans
(i) Ethanal (Or)Acetaldehyde CH3CHO
( ii) 2-Butanone (Or) Butanone-2 CH3COCH2CH3
(iii) Ethanal (Or)Acetaldehyde CH3CHO
(iv) Methane CH4

5. How is ethanoic acid prepared commercially from methanol ?

Ans:  Ethanoic acid is prepared commercially by reaction between methanol and carbon monoxide in the presence of Iodine - rhodium catalyst.
I2-Rh
CH3OH + CO   ------------------> CH3COOH

6. Explain the follwing terms: (i)Esterification (ii)saponification (iii) decarbodylation

Ans: Esterification:- The reaction of carboxylic acid with an alcohol to form ester in the presence of conc. H2SO4 know as Esterifilation reaction.
CH3COOH + C2H5OH --------------à CH3COOC2H5 + H2O
Saponification : oil or a fat on heating with sodium hydroxide (NaOH) Solution forms sodium salt of carboxylic acid (soap)and glycerol, this reaction is know as saponification reaction.
CH2 – O COR                         CH2OH
|                                                  |
CH – O COR + 3NaOH       CHOH + 3RCOO Na
|                                                  |
CH2 – O COR       --------->        CH2OH

Decarboxylation: Sodium salt of ethanoic acid and soda lime on heating forms methane gas. This reaction is known as Decarboxylation reaction.
CH3COONa + NaOH         ------------->      CH4 + Na2CO3

7. Write chemical equations of the reactions of ethanoic acid with i)sodium (ii) sodium carbonates (iii) ethanol in presence of conc. H2SO4 and (iv) soda lime

Ans: (i) 2 CH3COOH + 2Na ------------------>2CH3COONa + H2­
(ii) 2CH3COOH + Na2CO3  --------------------------->  2CH3COONa + CO2 + H2O
(iii) CH3COOH + C2H5OH  -------------------------->     CH3COOC2H5 + H2O
(iv) CH3COOH + NaOH   ---------  ----------------------> CH4 + Na2CO3

8. “Saturated hydrocarbons burn with a blue flame while unsaturated hydrocarbons burn with a sooty flame”. Why?

Ans: It is because a saturated hydrocarbon undergoes complete combustion due to high amount of carbon.
C2H6 (CNG) + 7O2 ---------------> 4CO2 + 6H2O + Heat

9. How ethanoic acid got its name as glacial acetic acid?

Ans: Ethanoic acid  has melting point is 290K so it often freezes during winter and looks like glacier. Therefore, it is also known as glacial acetic acid.

10. Name the products obtained on complete combustion of ethanol.

Ans: Carbon dioxide water and Heat

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