Substances that allow heat energy to flow through them are called good conductors of heat. e.g., metals. Substances that do not allow heat energy to flow through them are insulators. e.g., wood, plastic, glass, etc.
(a) Practical applications of good conductors of heat:
(i) Cooking utensils are made of metals so that heat can easily get transferred to food.
(ii) Coils of refrigerators and air conditioners are made of copper to conduct away heat.
(iii) Mercury is used as a thermometric liquid in thermometers.
(b) Practical applications of insulators:
(i) Handle of cooking utensils are made of insulators like bakelite, wood, etc.
(ii) Woollen clothes are insulators and keep us warm in winter.
(iii) Hair and fur in animals are insulators. So they keep them warm during winter.

Thermo flask is a special kind of flask for keeping liquids. It prevents loss or gain of heat by any of the three methods. It keeps liquid warm or cold for a long time. It was invented by Sir James Dewan in 1893.
It consists of a double-walled glass-cylinder. A vacuum is created in the space between the double walls. The two inner surfaces of glass walls are silvered. The flask is placed on a spring within a non-conducting cylindrical case to protect it from jerks and breakages. The gaps between flask and outer casing is packed with felt pads. The mouth of the flask is finally closed with a cork.

Since the container is made of glass which is a bad conductor of heat and therefore, the loss or gain of heat due to conduction is prevented. As there is vacuum between the double walls, it prevents transmission of heat by convection. Due to silvering of the inner surfaces, the heat loss by radiation is prevented. The cork and the felt pads also help to preserve the heat inside the flask. So, the hot liquids like tea, coffee, etc., remain hot and cold liquids like water, juice, etc., remain cold for a long time.

The solar energy cannot reach to us by the process of conduction or convection as there is no medium such as air, in most part of the space between the earth and the sun. This process of heat transfer is called radiation. The transfer of heat by radiation does not require any medium. When you sit in front of a room heater or bonfire you feel warm. We get heat by radiation because air is a poor conductor of heat, heat is not transferred through conduction. Convection is also not possible in this case as convection current rise upwards and not sideways. Further if we put an insulating material like a cardboard between the fire and ourselves, we no longer feel hot. This shows air around us remains cold and is not involved in transferring heat to us from the heat source. Further heat is transferred to us by radiation only in the straight path.
All hot bodies radiate heat when the heat falls on some object, it divides into three parts:
(i) a part of it is reflected.
(ii) a part of it gets absorbed.
(iii) a part of it may be transmitted.
The temperature of the object rises due to the absorbed part of the heat.

At sea-shore during the day cold air from the sea moves towards the beach because the land gets more heated than the sea water. Hot air above the land rises up, and cold air from the sea moves towards the land beach. This is called sea breeze as shown in fig. (a).
During the night, cold air from the land moves towards the sea because the land cools more quickly than the sea water. So hot air above the sea rises up and cold air from the land moves towards the sea. This is called land breeze as shown in fig.(b).
       

Since, it is a fact that the water present in the ocean (near the equator) is heated by the sun to a very higher temperature than the water near the poles of the earth. It is due to the falling of the sun rays perpendicularly in the equatorial region. So, in the equatorial region, the ocean water expands and becomes lighter.
While on the other side, the water in the polar region remains cold and heavy. It leads to the flow of convection currents of heat of warm water from the equator towards the poles.
Heat of the cold water flow from the poles towards the equator just below the surface of ocean. So, these types of currents are known as oceanic currents.

(a) As we know that plastic is a bad conductor of heat which does not allow the heat to pass through itself. So, heat from the fry pan does not flow to the handle due to which we can hold it easily. So that's why, the fry pans are provided with the plastic handles.
(b) The value showed by Pooja here is a great concern and careness towards her five years old small daughter.

(a) The following precautionary measures while checking the fever through a clinical thermometer are
(i) While reading the clinical thermometer, it should never be held by the bulb.
(ii) The clinical thermometer should be washed properly (before and after use).
(b) The values showed by the elder brother of Pankaj, Vishwas, are concern towards the way of using the clinical thermometer and the importance of money as well.

First of all, take a flat bottom flask and fix a rubber stopper having two holes in the mouth of the flask. Shift a thermometer through one hole and a glass tube with stopper through the other hole. Now, with the help of a vacuum pump, remove the air from the flask and try to record the temperature from the thermometer. Put a flask in the bright sunlight and we will observe that the thermometer records a rise in temperature. So, on this basis, we can say that this experiment proves that the heat radiation can travel through vacuum.

The particles of water become more lighter and rise up in the middle. Due to this, the cold particles of water which are heavier come down along the sides of the vessel. So, the convection currents of heat are setup and water becomes hot. The moment, when the heat is applied at the top, then the water present in the upper portion becomes hot and these hot water molecules get fixed over the surface. Since, water is a bad conductor of heat, due to which water present at the lower end (or bottom) of the vessel remains.

The differences between heat and temperature are given as below