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1. Due to air conditioners, air becomes cool so its density increases and it becomes heavy. So it goes down and warm air with less density comes up and take the place of cold air. This cycle goes on and on and the whole room becomes cool.

2. If it is fitted near the floor then cool air of high density can’t go up and upper air with low density cannot come down and cooling of the room does not take place properly so air conditioners are fitted near the ceiling of a room.

3. Heaters are fitted near the floor. Due to heating, air becomes hot which is lighter than cold air. So it goes up and upper air with high density comes down.

4. This cycle goes on and on and the full room becomes warm. So heaters are fitted near the floor.

1. The heat from the sun is reached to the Upper layers of the lakes first. 

2. We know that heat transfers in convectional mode in water. . 

3. Convectional currents take more time to reach the lower layers as there are in deep. 

4. This means it takes more time to transfer of heat to the bottom of the lake or pond. 

5. The water of the surface layer is evaporated by absorbing heat and does not heat up quickly. 

6. As a result heat does not reach the lower layers of the lake. It is another reason.

In case ‘B’ the pin P will fall before the pin Q because the heat will reach pin P first. In case ‘A’, the heat travels in both the directions and pins P and Q will fall simultaneously.

Correct option is  D) 10⁶ cal

The specific heat of a substance is the amount of heat required to raise the temperature of the unit mass of the substance by one unit.

S = \(\frac a{m\Delta T}\)

The principle of heat exchange is used to measure the specific heat capacity of a substance. This principle is as follows: If a system of two objects is isolated from the environment by keeping it inside a heat resistant box, then no energy can leave the box or enter the box. In this situation, heat energy lost by the hot object = heat energy gained by the cold object.

Correct option is  A) lead

A) Specific heat of B is less than that of A

Cooking utensils are made of metals such as copper, aluminium, brass, steel etc., so that heat is easily conducted through the base to their contents. But they are provided with handles of bad conductors (such as ebonite or wood) to hold them easily as handles will not conduct heat from the utensil to our hand.

When wet clothes dry, the water molecules from wet clothes, after evaporation, change into water vapour and mix with water molecules present in surrounding air, in the form of water vapour.

1. Boiling point of liquid increases with external pressure. 

2. Pressure cooker gives external pressure to the water in it. 

3. So, while cooking in pressure cooker it increases boiling point of water more than 100°C. 

4. So that, cooking is fast in pressure cooker compared to open vessel.

Once water starts boiling, all the heat supplied to it is used in conversion of water into steam at the boiling point of water. Hence, there is no rise in its temperature.

1. Water at 100°C takes additional heat energy to convert from liquid state to vapour (steam) state. This energy is called latent heat of vapourisation. 

2. Hence, steam at 100°C contains more heat energy than that of water at 100°C. 

3. So, burns caused by steam at 100°C are more painful than that of water at 100°C.

1. A given quantity of steam contains more heat than the same quantity of boiling water at the same temperature.

2. When steam comes in contact with one’s body, it releases extra heat of 540 calories per gram and causes a more serious burn than that caused by boiling water.

The rails of railway track are made of steel. While laying the railway track, a small gap is left between the two successive length of rails. The reason is that the rails expand in summer. The gap is provided to allow for this expansion. If no gap is left, the expansion in summer will cause the rails to bend sideways. This may result in a train accidents.

Correct option is  B) Brass

Correct Answer is: (c) 70 m

Correct Answer is: (b) first increases and then remains constant

Correct Answer is: (d) 3/2 pV in all cases

Correct Answer is: (c) 2v 

c = √(3RT/M)

Here, T becomes double and M becomes half.

Correct Answer is: (c) 0.048

The correct option is A) 100.

Using of a laboratory thermometer: 

1. Place the mercury bulb of the thermometer in a liquid, so that the bulb immerses in it. 

2. Wait for some time till the mercury level shows a constant reading. 

3. And take the reading at the level of the mercury.

Using of a clinical thermometer: 

1. Wash the clinical thermometer properly with an antiseptic solution. 

2. To lower the mercury level, hold the thermometer firmly and give some jerks. 

3. Ensure that it falls below 35 °C.

4. Now place the bulb of the thermometer under your friend’s tongue. 

5. After one or two minutes, take the thermometer out and note the reading. 

6. This is your body temperature. 

7. Don’t hold the thermometer by the bulb while reading it.

At constant temperature the heat energy required to change one gram of liquid into gaseous state.