PHYSICS [2 Mark Question Answer]

Substances that allow heat energy to flow through them easily are called good conductors of heat or thermal conductors. Some good conductors of heat are copper, aluminium, gold and iron. On the other hand, substances that do not allow heat energy to flow through them easily are called bad conductors of heat or thermal insulators. Glass, mica, cotton, cork, wood, asbestos, plastics and ebonite are some of the bad conductors of heat.

Applications of convection currents in air are as follows :
(a) In nature, sea breeze and land breeze are examples of convection currents set up in air in coastal areas. .
(b) Chimneys are fitted in factories to remove undesirable smoke and fumes. Being hot, and thus lighter, these gases rise up and escape through the chimneys.

Differences between conduction and convection are :
Conduction :

• It is the process of transfer of heat from one particle to the other, without the actual movement of the particles.
• Conduction takes place in solids only.

Convection:

• It is the process of transfer of heat wherein the particles actually move from one part to the other.
• Convection takes place in fluids, i.e., liquids and gases.

Heat can be transmitted in three ways :

• Conduction.
• Convection.
• Radiation.
  Fastest mode is Radiation.

Effects of heat are :

• Change in temperature.
• Change in dimensions.
• Change in state.

Some precautions that need to be taken while handling fire are as follows:
(a) Any inflammable object such as plastics, wood, clothes and paper should not be left close to fire/electrical switches.
(b) LPG gas pipes/cylinders/regulators should be checked regularly for any leakage.

Electricity gives off heat in many ways. For example, an induction plate produces heat to cook food, a tea or coffee maker provides heat to boil water, a room heater or convector produces heat to warm up the air in a room and so on.

In the Fahrenheit scale, the lower fixed point is 32 °F, the upper fixed point is 212 °F, and the length of the thermometer between the lower fixed point and the upper fixed point is divided into 180 equal parts.

The silvered surfaces reflect the heat back, thus reducing the heat exchange due to radiation and liquid in the thermos flask stays hot or cold for a longer duration.

It is because water is a bad conductor of heat. It does not easily conduct heat from the top to the bottom of the test tube.

Two thin blankets trap air in between our body and themselves. The trapped air, being a bad conductor of heat does not allow heat from our body to escape to the surroundings and thus we stay warm.

The base of cooking utensils is made black to increase the intake of heat from the flame. The inside of cooking utensils is generally kept shiny to minimize the loss of heat by radiation.

It is due to conduction. This happens because heat energy is transmitted from the heated end of the spoon to the other end without actual movement of the particles of the spoon.

SI unit of temperature is kelvin (K).
K = C + 273 = 40 + 273 = 313 K