A. Choose the Correct Option

1. Mercury is used in a thermometer because

(a) It is non-toxic

(b)It is cheap

(c) It remains a liquid over a large range of temperatures.

(d) It is easy to dispose of
Answer. (c) It remains a liquid over a large range of temperatures.

Mercury does not adhere to the glass tube and expands evenly, making it ideal for measuring temperature.

2. A clinical thermometer is used to measure

(a) temperature of the clinic

(b) Body temperature

(c) temperature of hot water

(d) laboratory temperature
Answer. (b) Body temperature.
It is specially designed for humans and shows temperature in the range of 35°C to 42°C.

3. Heat energy flows from

(a)  one body to another. If their temperatures are the same

(b) a hot body to a cold body

(c) a cold body to hot body

(d) The temperature of a body has nothing to do with heat flow
Answer. (b) A hot body to a cold body.
This is a natural rule: heat always moves from something hot to something cooler until both become equal in temperature.

4. Conduction of heat happens between two objects

(a)Only when the two objects touch each other

(b) only when the two objects touch

(c) When there is a mass movement of the objects

(d) When two objects are  separated by a vacuum.
Answer (a) Only when the two objects touch each other.
Example: A metal spoon getting hot when placed in hot soup.

5. Land breeze and sea breeze are set up in coastal areas because of

(a) Uneven heating of land and water.

(b) lack of trees

(c) pollution in the air

(d) clouds preventing the sunlight reaching the land
Answer. (a) Uneven heating of land and water.
Land heats up and cools down faster than water, causing air movement.

6. Cooking utensils are provided with plastic or wooden handles because they are

(a) good conductors of heat 

(b) bad conductor of heat

(c) used to increase convection

(d) used to reduce convection

Answer. (b) Bad conductors of heat.
This prevents our hands from getting burnt.

7. Convection is the main method of heat transfer in

(a) air and water

(b) solids

(c) vacuum

(d) water, but not in air
Answer (a) Air and water.
Hot air or water rises, while cooler parts sink, creating a cycle of heat transfer.

8. A thermos flask is constructed to minimize heat loss due to

(a) Conduction

(b) Convection

(c) Radiation

(d) All of these
Answer (d) All of these (Conduction, Convection, Radiation).
That is why tea or coffee remains hot in a thermos for long hours.

B. Match the Following

Column A	Column B
1. Celsius	a. Clinical thermometer
2. Thermistor	b. Joule
3. kink	c. temperature scale
4. Conductor	d. digital thermometer
5. Heat	e. Copper

Column A	Column B
1. Celsius	(c) Temperature scale
2. Thermistor	(d) Digital thermometer
3. kink	(a) Clinical thermometer
4. Conductor	(e) Copper
5. Heat	(b) Joule

Q2. Express each of the following temperatures in ℉.

Formula: ℉ = (°C × 9/5) + 32

(a) 55°C = (55 × 9/5) + 32 = 131°F
(b) 100°C = (100 × 9/5) + 32 = 212°F
(c) 0°C = (0 × 9/5) + 32 = 32°F
(d) 20°C = (20 × 9/5) + 32 = 68°F

Q3. Express each of the following temperatures in °C.

Formula: °C = (℉ − 32) × 5/9

(a) 58°F = (58 − 32) × 5/9 = 14.4°C
(b) 75°F = (75 − 32) × 5/9 = 23.9°C
(c) 5°F = (5 − 32) × 5/9 = −15°C
(d) 140°F = (140 − 32) × 5/9 = 60°C

Q4. How many divisions are there between the melting point of ice and the boiling point of water on the –

(a) Celsius Scale → From 0°C (melting) to 100°C (boiling).
So, 100 divisions.

(b) Fahrenheit Scale → From 32°F (melting) to 212°F (boiling).
So, 180 divisions.

Q5. Explain the steps of reading a clinical thermometer correctly.

Answer.

1. Wash the thermometer with antiseptic or clean water.
2. Hold it firmly and shake it gently until the mercury level falls below 35°C.

• Place the thermometer bulb under the tongue (or armpit) for about 1 minute.
• Take it out and read the mercury level at eye level.
• Note the temperature shown in °C or °F.

The normal human body temperature is 37°C (98.6°F).

Q6. Define conduction, convection, and radiation and give two examples of each.

a) Conduction – Heat transfer by direct contact

1. Conduction is the process of heat transfer through solids when their particles are in direct contact.
2. In this method, the particles do not move from their position but pass on heat energy by vibrating faster and transferring it to the next particles.
3. Metals are good conductors of heat because they allow heat to pass quickly through them, while materials like wood or plastic are poor conductors (insulators).
4. Example 1: A metal spoon placed in hot soup becomes hot because heat is conducted from the soup to the spoon.
5. Example 2: When we iron clothes, the hot iron transfers heat directly to the fabric through conduction.

b) Convection – Heat transfer in liquids and gases

1. Convection is the transfer of heat by actual movement of particles in liquids and gases.
2. When a liquid or gas is heated, the warmer part becomes lighter and rises up, while the cooler, denser part sinks down. This sets up a circular movement called a convection current.
3. Convection plays an important role in weather, cooking, and heating systems.
4. Example 1: When water is boiled in a pot, the hot water rises while the cooler water sinks, creating convection currents.
5. Example 2: Sea breeze and land breeze are caused by convection currents in air near coastal areas.

c) Radiation – Heat transfer through waves

1. Radiation is the transfer of heat in the form of electromagnetic waves, without requiring any medium.
2. Heat energy travels directly in straight lines and can pass even through empty space (vacuum).
3. Unlike conduction and convection, radiation does not need contact or movement of particles.
4. Example 1: Heat from the Sun reaches the Earth through radiation.
5. Example 2: We feel warmth from a fire or heater without touching it, as heat travels through radiation.

Q7. Explain how the sea breeze and land breeze are set up in places near the sea.

Answer. Sea Breeze and Land Breeze

In coastal areas, people often experience a special kind of wind that changes direction between day and night. These winds are known as sea breeze and land breeze, and they are caused because land and water heat up and cool down at different rates.

Sea Breeze (Daytime):
During the daytime, the sun heats both the land and the sea. However, land gets heated up much faster than water. As a result, the air above the land becomes hotter and lighter, so it rises up. When this hot air rises, the cooler and denser air above the sea rushes in to take its place. This flow of cool air from the sea towards the land is called a sea breeze. It usually brings relief to people living near the coast during hot afternoons, as the breeze feels cooler and more refreshing.

Land Breeze (Nighttime):
At night, the situation is reversed. The land cools down much faster than the sea after sunset. The air above the land becomes cooler and denser, while the air above the sea remains relatively warmer. The warm air above the sea rises, and the cooler air from the land flows towards the sea to replace it. This movement of air from the land to the sea is known as a land breeze.

Importance:
Both sea breeze and land breeze play an important role in maintaining the temperature balance in coastal areas. They provide natural cooling during the day and help circulate air, making the coastal climate more pleasant and comfortable.

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