Question

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Answer 1

Explanation:

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Answer 2

Question 1:

Explain how heat is conducted from the heated end of a rod to its cold end.

ANSWER:

Heat is conducted from the heated end of a rod to its cold end through the effective vibration of its molecules. Molecules of the rod starts vibrating as heat is supplied to it. When one end of the rod heats up, the molecules of that end starts vibrating and colliding with the nearby molecules to make them unstable. These molecules further hit their neighbouring molecules to transfer the heat. In this way, heat is transferred from one end of the rod to its other end.

Question 2:

With an example of each, explain the uses of good and bad conductors of heat.

ANSWER:

Good conductors of heat are used where we want to transfer heat faster from one point to the other. For example, cooking utensils are made of metals like brass, steel and aluminium, which are good conductors of heat. Though silver and copper are best conductors of heat but not usually used in cooking utensils as they are expensive.

Bad conductors of heat are used where we want to stop the heat from getting transferred or where we do not want the heat to be lost or gained from the surroundings. For example, handles of cooking utensils are made of wood or plastic, which are bad conductors of heat. Hence, the handles don't heat up during cooking, thereby allowing us to hold the utensils comfortably.

Question 5:

Sea and land breezes

(a) are caused by currents set up in air due to conduction.

(b) are caused by currents set up in air due to convection

(c) are caused by currents set up in air due to radiation

(d) have no relation to conduction, convection or radiation

ANSWER:

(b) are caused by the currents build in air due to convection

Due to convection, the hot air from the land moves towards the sea during the day and vice versa during the night. This causes land and sea breezes.

Question 6:

A thermos flask prevents loss or gain of heat by

(a) conduction only

(b) convection only

(c) radiation only

(d) all of the above

ANSWER:

(d) all of the above

The empty space between the two glass walls prevent the loss of heat through conduction and convection, as both of these processes need a medium to transfer heat. Also, the silvery wall of flask reflects back the heat and prevents its loss through radiation.

Question 7:

Which of these is the best conductor of heat?

(a) iron

(b) water

(c) nitrogen

(d) alcohol

ANSWER:

(a) iron

The molecules of iron transfer heat from the hotter region to the colder ones by hitting the surrounding molecules through vibration, without moving themselves from one end to the other. But water and alcohol are liquids, and nitrogen a gas; therefore, they cannot conduct heat.

Question 8:

Which of these is the best insulator of heat?

(a) iron

(b) water

(c) nitrogen

(d) alcohol

ANSWER:

(c) nitrogen

Gases are bad conductors to heat, and nitrogen being a gas can be considered as the best insulator among the given options.

Question 9:

The transfer of heat from molecule to molecule, without movement of molecules from one place to another is

(a) conduction

(b) convection

(c) radiation

(d) either of these

ANSWER:

(a) Conduction

In conduction, heat is transferred from one place to another without the movement of molecules. However, in convection and radiation, heat energy is transferred through the movement of molecules.