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The steps of constructions are: (i) Draw a line segment  = 10.3 cm (ii) Taking X and Y as centres and radius more than half of AB, draw two arcs which intersect each other at C and D. (iii) Join CD. Then CD is the required perpendicular bisector of . Now: (a) Take any point P on the bisector drawn. With the help of divider, we can check that =. (b) If M is the mid-point of , then ???????
Given that the water is pouring into a cuboidal reservoir at the rate of 60 litres per minute. Volume of reservoir is , then The number of hours it will take to fill the reservoir will be: As we know . Then  = 108,000 Litres ; Time taken to fill the tank will be: or   .  
The outermost part of the flame is the hottest region of the flame. Hence, water kept near it will get heated faster i.e in shorter time. Therefore, the water in Ramesh's beaker will get heated in a shorter time.
No, it cannot be considered as combustion because in rusting no heat or light is produced and in combustion a substance reacts with oxygen or air and gives out energy in the form of heat or light  
The calorific value of the fuel is the amount of heat produced by the complete combustion of 1 kg of fuel. Given, Heat produced by 4.5 kg of fuel  = 180000 kJ  Heat produced by 1 kg of fuel = 180,000 kJ/4.5 Kg = 40,000 kJ   The calorific value of the fuel is 40,000 kJ/kg.
The goldsmith uses the outermost non-luminous (blue) zone for melting gold and silver. This is because it is the hottest part of the flame and hence melts the metals easily.
It is difficult to burn a heap of green leaves but dry leaves catch fire easily because green leaves have moisture present in them. Hence the heat gets absorbed by water to provide energy to evaporate. But, the dry leaves have no moisture and hence the heat is not lost. That is why it catches fire easily.
  is heavier than . Therefore, it acts as a blanket over the substance and cuts off the oxygen supply required for combustion. This way  is able to control fires. 
  The calorific value of a fuel is expressed in kilojoules per kilogram (kJ/kg).  
Following is the labelled diagram of a candle flame:  
Paper has a low ignition temperature and hence catches fire easily. But when it is wrapped around an aluminium pipe, heat is transferred to the metal and hence the ignition temperature of the paper is not reached. That is why paper by itself catches fire easily whereas a piece of paper wrapped around an aluminium pipe does not.
  Wood produces lots of smoke and unburnt carbon particles, which cause respiratory problems. But LPG does not produce these. Thats why LPG is a better domestic fuel than wood. 
Water is not used to control fires involving electrical equipment because water being a good conductor of electricity may lead the electric current to spread causing electric shocks or short-circuits.
LPG Wood                     It does not produce smoke. It produces smoke. It is easy to store and can be easily transported using pipelines. It takes a lot of space to store. It has low ignition temperature It has a high ignition temperature It does not cause environmental pollution It leaves un-burnt carbon particles causing air pollution Calorific value is...
Fuels like petroleum and coal release toxic gases like carbon monoxide, carbon dioxide, and sulphur dioxide during combustion. These harmful gases cause pollution and respiratory problems. Whereas CNG (Compressed Natural gas) is a clean fuel and produces these harmful gases in very small quantity.  (CNG is methane stored at high pressure!)
(a) Burning of wood and coal causes pollution of air. (b) A liquid fuel, used in homes is LPG(Liquified Petroleum Gas) . (c) Fuel must be heated to its ignition temperature before it starts burning. (d) Fire produced by oil cannot be controlled by water .
The conditions required for the combustion to take place are: (a) Presence of oxygen (b) Presence of inflammable substance (fuel) (c) Maintain Ignition Temperature (the minimum temperature at which substance catches fire).
The paper should be saved because to make one-tonne paper we need to cut approximately seventeen fully grown tree. Therefore, to save trees and prevent the impact of their loss on living organisms. we need to save the papers. Paper can be saved by following ways- by collecting used paper and recycle it use both sides of the paper  Spread the awareness about paper Use paper efficiently  
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