PHYSICS [2 Mark Question Answer]

The bottom part of the cooking utensil or pan is painted black. The reason is that the black surface absorbs more heat and so the contents of utensil or pan get cooked rapidly if its bottom part is painted black.

Tea kettles are provided with wooden or ebonite handles. The wood or the ebonite being the insulators of heat, does not pass heat from the utensils to our hand. Thus, we can hold the hot utensils or pans comfortably by their handles.

An oven is made of double walls and the space between them is filled with wool, cork etc. because the wool and cork are the insulator of heat. They prevent the heat of the oven to escape.

Gases expand much more than the liquids and the solids. Like liquids, the gases do not have a definite shape, so they also have only the cubical expansion.

When the bottle is heated, bubbles of air are seen escaping into the water. This happens because the air present in glass bottle expands on heating and tries to escape out through the tube into the 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.

The wooden wheels of a bullock-cart are fitted with iron tyres. To ensure a tight fit, the tyre is made slightly smaller in diameter than the wheel. The tyre is first heated due to which it expands. The heated tyre is then fitted on the wheel. When the tyre cools, it contracts and makes a tight fit on the wheel.

The expansion of a substance when, heated, is called thermal expansion.
Or
Thermal expansion is the tendency of matter to change .in shape, area and volume in response to a change in temperature.

When we bring two objects of different temperature together, energy will always be transferred from hotter to the cooler object.
Here, also heat will flow from hot milk tumbler to tub of cold water.

On Kelvin scale of temperature zero mark is when no molecular motion occurs. Ice point is at 273 and steam point is at 373 K. Thus 0 K = – 273°C and one degree on Kelvin scale is same as one degree on Celsius scale.

Heat is a form of energy which flows. It is the energy of motion of molecules constituting the body.
The unit of heat is same as that of energy, The S.I. unit of heat is joule (abbreviated as J) and other common units of heat are calorie and kilo calorie, where 1 kcal = 1000 cal.