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4. All the above

a. Starting from Portugal, they had to sail down the west coast of Africa, round the Cape of Good Hope, across the Indian ocean, and then reach the western coast of India.

b. Vasco da Gama

c. Portugal

d. England

e. Portugal, Dutch (Holland); France, and England.

i. Combustion and redox reaction
ii. Double displacement and precipitation reaction
iii. Combination reaction
iv. Displacement reaction

(i) CH4(g) + 2O₂ (g) → CO₂ (g) + 2H₂O (g): This is an example of Exothermic reaction because it leads to release of HEAT as can be seen water is given in gaseous form. 

(ii) 2NaCI (l) \(\overset{Electric \,current}\longrightarrow\) 2Na (s) + Cl₂ (g) : This is the example of Decomposition reaction of common salt using electricity. This reaction is also called Electrolysis of Bryn solution. 

(iii) MnO₂ + 4HCI → MnCl₂ + 2H₂O+ Cl₂ 

This reaction is the example of a redox reaction. Because MnO₂ has donated its oxygen atoms and hence got reduced. Also, Chlorine is converted into Clto form Cl₂ and hence get oxidised. Since both oxidation and reduction has taken place. This is a redox reaction.

a. C + O₂ → CO₂

CH₄ + 2O₂ → CO₂ + 2H₂O

CaCO₃ → CaO + CO₂

b. N₂ + O₂ → 2NO

H₂ + I₂ → 2Hl

Fe + HCl → FeCl₂ + H₂

CO₂ + C → 2CO

C) endoscopy

1. The patient’s stomach can be viewed by inserting one end of a light pipe into the stomach through the mouth. 

2. Light is sent down through one set of fibres in the pipe. 

3. This illuminates the inside of the stomach. 

4. The light from the inside travels back through another set of fibres in the pipe and the viewer gets the image at the outer end.

Applications oruses of optical fibres : 

1. Light pipes using optical fibres may be used to see places which are difficult to reach things such as inside of a human body. 

2. The other important application of fibre optics is to transmit communication signals through light pipes.

An optical fibre is very thin fibre made of glass or plastic having radius about a micrometer. 

A bunch of such thin fibres forms a light pipe. 

Working : 

1. Because of the small radius of the fibre, light going into it makes a nearly glancing incidence on the wall. 

2. The angle of incidence is greater than the critical angle and hence total internal reflection takes place. 

3. The light is thus transmitted along the fibre.

The light ray bends away from normal.

The light ray undergoes total internal reflection.

B) Lateral shift

1. On a hot sunny day, a driver may see a pool of water on the road before him. It is the phenomenon of mirage which is often observed in desert.

2. An empty test tube placed in a beaker with mouth outside the water surface shines like a mirror. 

3. A crack in a glass vessel often shines like a mirror. 

4. A piece of diamond sparkles when viewed from certain directions. 

5. An optical fibre is used to transmit a light signal over a long distance with negligible loss of energy.

1. When the angle of incidence is greater than the critical angle, the light ray is reflected into denser medium at interface. This phenomenon is called total internal reflection. 

2. Total internal reflection is the main reason for brilliance of diamonds. The critical angle of a diamond is very low. So if a light ray enters a diamond it is very likely to undergo total internal reflection which makes the diamond shine. 

3. Total internal reflection is the basic principle behind working of optical fibre. Because of the small radius of the fibre light going into it makes a nearly glancing incidence is greater than the critical angle and hence total internal reflection takes place. The light is thus transmitted along the fibre.

Correct option is: C) denser to rarer medium

Procedure : 

1. Place the semi-circular glass disc in such a way that its diameter coincides with interlace line MM and its center coincides with point O’. 

2. Now send light from the curved side of the semicircular glass disc. 

3. The light travels from denser medium to rarer medium.

4. Start with angle of incidence (i), equals to 0° and observe for refracted on other side of the disc. 

5. It does not deviate into its path when entering rarer medium. 

6. Send laser light along angles of incidence 5°, 10°, 15°, etc. and measure the angle of refraction. 

7. And tabulate the results in the given table. 

Observation : 

• Make a table shown below and note the values ‘i’ and ‘r’.

• At particular angle of incidence, the refracted ray does not come out but grazes the interface separating the air and glass. This angle is called critical angle. 
• When the angle of incidence is greater than critical angle, the light ray gets reflected into denser medium at the interface, i.e. light never enters rarer medium. This phenomenon is called total internal reflection.

1. Optical fibres are used to transmit communication signals through light pipes. 

2. For example, about 2000 telephone signals, approximately mixed with lightwaves, may be simultaneously transmitted through a typical optical fibre.

3.  The clarity of the signals transmitted in this way is much better than other conventional methods.

B) The ray does not deviate from its path

Application of total internal reflection : 

1. Brilliance of diamonds, 

2. Optical fibres.

Correct Answer is: (a) R = r 

Let ℰ = emf of the cell, i = current in the circuit

i = ℰ / R + r.

Power delivered to R = P = i²R =  ℰ²R/(R + r)² = f(R).

For P to be maximum, dP/dR = 0 = ℰ² [1 / (R + r)² - 2R / (R + r)³]

or 2R = R + r 

or R = r

Correct Answer is: (b, c, & d)

Correct Answer is: (b)

When we move in the direction of the current in a uniform conductor, the potential decreases linearly. When we pass through the cell, from its negative to its positive terminal, the potential increases by an amount equal to its potential difference. This is less than its emf, as there is some potential drop across its internal resistance when the cell is driving current. 

Correct Answer is: (a, b, c, & d)

Correct Answer is: (a, c & d)

Hint: Write briefly about (i) shearing, (ii) scouring, (iii) sorting (iv) picking out of burrs from the hair, (v) dyeing of fibres, (vi) straightening, combing of fibres and rolling into yarm

A pile of cocoons is used for obtaining silk fibres. The Cocoons are kept under the sun or boiled or exposed to steam. The silk fibres separate out. The process of taking out threads from the cocoon for use as silk is called reeling the silk. Reeling is done in special machines, which unwind the threads or fibres of silk from the cocoon. Silk fibres are then spun into silk threads, which are woven into silk cloth by weavers.

The types of silks are mulbery silk, tassar, silk, eri silk, mooga silk etc.,

Sorting is the process of separating the different textures of hair.

The female silk moth lays eggs from which hatch larvae which are called Caterpillars or silkworms. They grow in size and when the caterpillar is ready and enter pupa stage. The caterpillar secretes fibre made of a protein, soon the caterpillar completely covers itself by silk fibres and turns into pupa. This covering is known as Cocoon. The further development of the pupa into moth continues inside the cocoon. The silk yarn (thread) is obtained from the cocoon of the silk moth.

In Jammu and Kashmir, Himachal pradesh, Uttaranchal, Arunachal pradesh, sikkim, the plains of Haryana, Punjab, Rajasthan, Gujarat etc., the shepherds taking their herds of sheep for grazing. Sheep are herbivores and prefer grass and leaves. Apart from grazing, reares also feed them on a mixture of pulses, com, Jowar, oil cakes etc., In winter Sheep are kept indoors and fed on leaves grain and dry footder.

There are two types of fibres from sheep fleece. 

They are 

1. the coarse beard hair 

2. the fine soft under-hair close to the skin.

(a) Plant fibres are obtained from Jute and cotton

(b) Animal fibres are Silk and wool

1. Wool is obtained from the fleece (hair) of sheep or Yak. 

2. Parhmina shawls are woven from the soft wool of kashmiri goat 

3. Yak wool is common in Tibet and Ladakh 

4. Mohair is obtained from angora goats. 

5. Llama and Alpaca found in South America. 

6. The rearing of silk worms for obtaining silk is called Sericulture. 

7. The soft silk yarn (thread) is as strong as the thread of steel. 

8. The most common silk moth is the mulberry silk moth.

(a) Woollen shawl 

(d) Moth,Answer is correct

(a) – True, 

(b) – False, 

(c) – False

Answer is (c) cocoon

Coir : Ropes, floor covering , stuffing in mattresses and pillows. 

Jute : Jute bags, hat, slipper, rope, matand sack 

Hemp : Ropes , carpets, nets, clothes and paper 

Flax : Used to make a fabric called linen, rope and quality paper

Given, 2P(B) = P(A) = 6/13

2P(B) = 6/13; P(B) = 3/13 again, P(A) = 6/13

According to question,

P(A/B) = 1/3; P(A ∩ B)/P(B) = 1/3; P(A ∩ B)/(3/13) = 1/3

P(A ∩ B) = (1/3) x (3/13) 

P(A ∩ B) = 1/3

P(A ∪ B) = p(A) + P(B) - P(A ∩B) 

= (6/13) + (3/13) - (1/13) 

= (6 + 3)/13 - (1/13) 

= (9/13) - (1/13)

= 8/3   

d.The chances of contacting bird flu from a properly cooked (above 100°C) chicken and egg are non

Correct Answer is: (b) 20 Ω 

Correct Answer is: (b) all the cells should be joined in parallel

For series connection, I_max = ℰN/Nr =  ℰ / r .

For parallel connection, I_max = ℰN / r/n = Nℰ / r .

Correct Answer is: (c) 1/0.693

Q = Q₀(1 - e ^-t/τ ) = 0.9Q₀

or e ^-t/τ = 0.1 or e^t/τ = 10.

Correct Answer is: (b) t = τ ln η

Q = Q₀ e ^-t/τ = Q₀/η

or e ^-t/τ 1/η

or e^t/τ = η

or t/τ = ln η. 

Correct Answer is: (c) τ In (10/9) 

Q = Q₀(1 - e ^-t/τ ) = 0.1Q₀

or e ^-t/τ = 0.9 or e^t/τ = 10/9.

Correct Answer is:(c) τ In (10/9) 

Q = Q₀e ^-t/τ and potential difference across C is proportional to Q. For the p.d. to fall by 10%, Q must fall by 10%.

Q = 0.9Q₀ = Q₀e ^-t/τ 

or e^t/τ = 10/9 

or t/τ = In (10/9).

i' = 2 μA, t = 5 min = 5 x 60 sec.

q = i t = 2 x 10^–6 x 5 x 60

= 10 x 60 x 10^–6 c = 6 x 10^–4 c