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LPG stoves burn with a blue colour of the flame because in case of LPG the
fuel burns completely.

Supply of oxygen is one of the necessary condition for combustion. Hence, if
the supply of oxygen is not sufficient then the fuel will not burn completely.

Oxygen helps in combustion. Air contains about 29% of oxygen, thus supply of air makes the oxygen available which helps in combustion. Without oxygen, combustion will not take place.

The direction of magnetic field is from N-pole to S-pole; on applying Fleming's left-hand rule, the wire tends to move perpendicular to plane of paper upward.

Both the poles facing each other represent south pole in nature as the magnetic field lines outside the magnet move from North to South Poles.

The core of solenoid must be of some soft type magnetic material which can be strongly magnetized but does not retain induced magnetism.

The substances which react are called Reactants of a chemical reaction. The substances which are formed are called Products of a chemical reaction.

Substances which vapourise during burning, produce flames, such as wax in the candle, Kerosene.

Substances which do not vapourise during burning, do not produce flames. 

Example- coal and charcoal.

Water is not suitable for fires involving oil and petrol because water is heavier than oil and petrol. Hence, when we spray water on a fire involving oil and petrol the water sinks below the oil and petrol and the oil keeps on burning at the top.

Hint: 

• Water is not suitable for fires involving oil. 

• Manu should have switched off the flame of the burner and put a lid on the frying pan. By doing this the contact between fuel and oxygen is cut off and the flame will go off.

Charcoal does not vaporize and so does not produce a flame.

The temperature at which a substance catches fire and starts burning is called its ignition temperature.

Combustion is a chemical process in which a substance reacts with oxygen and gives out energy during the process in the form of either heat or light or both. Rusting of iron is an exothermic process as heat is released during rusting. Hence, it is a kind of slow combustion.

Molten wax(Solid), Kerosene oil(Liquid) and LPG(gas) are the substances which burn by producing flames.

The amount of heat energy produced on complete combustion of 1 Kg fuel is called its calorific value.

The force on the wire due to the interaction of magnetic fields of the bar magnet and current carrying wire can act only in upwards or downwards direction.

A small fire like a drum of kerosene on fire can be extinguished by throwing sand or soil over it. When sand is thrown over burning kerosene oil, the sand covers it like blanket. The sand cuts off the air supply to the burning kerosene oil due to which the fire gets extinguished.

As water is heavier than petrol therefore slips down permitting the petrol to rise to the surface and continue to burn. Besides, the existing temperature is so high that the water poured on the fire evaporates even before it can extinguisher the fire.

Hint: Pertrol will catch fire instantly because it is highly inflammable.

Flame is the zone of combustion of a combustible substance. Substances which vapourise during burning produce flames. 

Eg:- kerosene, wax etc.

A goldsmith blows air into the kerosene lamp flame with a blow pipe so that complete combustion of fuel takes place and the temperature of the flame increases. He blow the outermost zone of a flame with a metallic blow pipe for melting gold and silver because this is the hottest part of the flame.

Calorific Value is the term which is used to express the efficiency of a fuel.

c) Due to water the ignition temperature of paper is not reached

The substances which have very low ignition temperature and can easily catch fire with a flame are called inflammable substances.

Due to the burning of coal, the available oxygen gets depleted and it leads to incomplete burning of coal. Incomplete combustion of coal gives carbon monoxide gas. It is a very poisonous gas. It is dangerous to burn coal in a closed room. The carbon monoxide gas produced can kill persons sleeping in that closed room.

Iron wire will become red hot and glow. It will not produce a flame.

Hint: calorific value.

C. three zones 

It has three zones.

Carbon dioxide is the best fire extinguisher to put out fire caused by inflammable materials like oil and petrol and electrical equipments. Carbon dioxide is heavier than air and it covers the fire and cuts off the supply of oxygen and puts out the fire. Carbon dioxide is stored at high pressure as liquid in cylinders.

To put an electrical fire out, we need to unplug or de-energise the equipment on fire. That will eliminate the electricity that is causing the fire. If one cannot unplug what is burning there is a special type of fire extinguisher.

As it is a closed tank full of petrol, there will be no supply of air. Hence the petrol will not catch fire as air is necessary for the combustion of petrol.

True.

If we put a current carrying wire in a magnetic field perpendicular to its length, then it neither gets attracted or repelled by that field and hence these concentric circles neither have a starting point nor an ending point and the compass points tangential to the circles at every point.

Electric Generator.

There are mainly five types of fire extinguisher – Water, Foam, Dry Powder, CO₂ and Wet Chemical. 

Water is one of the best, cheapest and most common fire extinguishers.

1. Water fire extinguisher 

2. Foam fire extinguisher 

3. Dry Powder fire extinguisher 

4. CO₂ fire extinguisher and, 

5. Wet Chemical fire extinguisher.

Water is one of the best, cheapest and most common fire extinguishers.

Out of all these, the Water fire extinguisher is one of the best, cheapest and most common fire extinguishers.

Due to insufficient availability of oxygen in the closed room carbon monoxide gas is produced which can kill persons sleeping in that room.

Hint: Sudden formation of large amount of gas due to chemical reactions.

(a)–(iii)–(x), (b)–(ii)–(z), (c)–(i)–(y)

B. it is lighter than air 

Carbon dioxide is lighter than air and forms a layer around the burning substance. It covers the fire like a blanket due to which fresh air cannot reach the burning substance.

i. The burning of any fuel releases carbon dioxide into the environment.

ii. This increased concentration of carbon dioxide above the normal level is believed to cause global warming.

C. carbon dioxide 

Burning of fuels releases carbon dioxide in air in the environment. Increased percentage of carbon dioxide in air is causing global warming. Carbon dioxide gas in the air trap sun’s heat rays by producing green house effect.

B. baking soda 

To obtain carbon dioxide for extinguishing a fire is to release a lot of dry powder of chemicals like sodium bicarbonate(baking soda) or potassium bicarbonate over the fire.

False.

An electric generator is a device used to convert mechanical energy, which is used to rotate the coil between magnets, into electrical energy which is obtained by the phenomena called electromagnetic induction.

(a) False – A chemical process in which a substance reacts with oxygen to give off heat is called combustion. 

(b) False – Carbon dioxide is the best extinguisher for fires involving electrical equipment. 

(c) True. 

(d) False – Increased concentration of carbon dioxide in air is believed to cause global warming. 

(e) True. 

(f) False – outer zone is the hottest zone of a flame. 

(g) True.

(a)–(iv), (b)–(vi), (c)–(v), (d)–(iii), (e)–(i), (f)–(ii)

Global warming is the rise in temperature of earth atmosphere caused by the excessive amount of carbon dioxide in the air. Due to rise in the temperature of atmosphere, the ice in polar regions will melt very fast, producing a lot of water. Burning of fuels releases carbon dioxide in air in the environment. Increased percentage of carbon dioxide in air is causing global warming. Carbon dioxide gas in the air trap sun’s heat rays by producing green house effect. Rise in water may cause a rise in the sea level leading to floods in coastal areas. The low-lying areas may be completely submerged under water leading to loss of life and property.

Hint: CNG, because the calorific value of CNG is higher than that of petrol. Therefore CNG will be more economical. At the same time it produces the least air pollutants.

Hint: 

• At high temperature, some times dry grass catches fire which spreads through out the forest. 

• Camp fire may also be a reason. 

• Human negligence. 

• Lightening.

(i) On reversing the terminals of the battery, the deflection of the rod will be in opposite direction. 

(ii) When the direction of current is perpendicular to the direction of the magnetic field, then the rod will experience a maximum force.