Exercises: Temperature And Heat | Class 7 Oxford Science: Chapter Notes, Worksheets & Tests PDF Download

I. Objective type Questions

Q.1. The terms 'hot' and 'cold' are relative.

True
The terms 'hot' and 'cold' are relative because they depend on the temperature of the surroundings or reference point. What may be considered hot in one context may be cold in another.

Q.2. On the Fahrenheit scale, the difference between the boiling point of water and the melting point of ice is divided into 100 degrees.

False
On the Fahrenheit scale, the difference between the boiling point of water and the melting point of ice is divided into 180 degrees. The Fahrenheit scale has 180 equal divisions between the melting and boiling points of water, which makes each degree Fahrenheit smaller than a degree Celsius.

Q.3. Digital thermometers use mercury to measure temperature.

False
Digital thermometers use electronic sensors such as thermistors or thermocouples to measure temperature. They do not use mercury or any other liquid.

Q.4. Mercury is used in thermometers because it is relatively easy to see because of its red colour.

False
Mercury is used in thermometers because it expands uniformly with temperature and can be easily seen in a glass tube. Mercury is a silver-white liquid at room temperature and does not have a red color.

Q.5. Heat energy is measured in degree centigrade.

False
Heat energy is measured in units of Joules (J) or calories (cal), not in degrees centigrade. Temperature is measured in degrees Celsius (°C) or Fahrenheit (°F) and indicates the level of hotness or coldness of an object or substance.

B. Choose the Correct Option.

II. Very Short Answer type Questions

Give one word for the following.
Q.1. The scale in which the melting point of ice and the boiling point of water are taken as 0 and 100, respectively

Celsius

Q.2. The silvery grey liquid used in clinical thermometers

Mercury

Q.3. The breeze that flows from the land to the sea during night time

Land breeze

Q.4. The type of waves via which heat and light energy travel

Electromagnetic

Q.5. A unit for measuring heat energy

Joule

III. Short Answer type Questions

Heat flows from a hot body to a cold body by conduction when the two bodies are in direct contact with each other and there is a temperature difference between them.

Q.2. Give one advantage of using alcohol as the liquid in a thermometer as compared to using mercury.

One advantage of using alcohol as the liquid in a thermometer as compared to using mercury is that alcohol has a lower freezing point than mercury. This means that alcohol thermometers can be used to measure temperatures below the freezing point of mercury (-38.8°C), such as in cold climates or in laboratory experiments involving low temperatures.

Q.3. List two characteristic features of a mercury clinical thermometer.

Two characteristic features of a mercury clinical thermometer are:

• The mercury inside the thermometer expands when heated and contracts when cooled, which causes the mercury level to rise or fall in the thermometer tube, indicating the temperature.
• The thermometer has a narrow glass tube with a bulb at one end, which contains the mercury. The tube is marked with a scale that shows the temperature in degrees Celsius or Fahrenheit.

Q.4. Why wool is a bad conductor of heat?

Wool is a bad conductor of heat because it has a structure that traps air between its fibers. Air is a poor conductor of heat, so when heat is applied to wool, the air pockets between the fibers act as an insulator, reducing the rate of heat transfer through the material. This property of wool makes it useful for making warm clothes and blankets, as it helps to retain body heat and keep us warm in cold weather.

IV. Long Answer type Questions

Experiment to show that 'hot' and 'cold' are relative terms:

Take two containers of water, one at a temperature of 50°C and the other at 10°C. Put your right hand in the container with hot water and your left hand in the container with cold water. Keep them there for about a minute. Now, without removing your hands, put both hands into a third container of water at room temperature, which is neither hot nor cold. You will feel that the same water feels hot to your left hand and cold to your right hand. This shows that the terms 'hot' and 'cold' are relative, and depend on the temperature of the body they are being compared to.

Q.2. What are temperature scales? Explain how Celsius and Fahrenheit scales are defined. 

Temperature scales:

Temperature is a measure of the degree of hotness or coldness of a body. There are different temperature scales used to measure temperature. The most commonly used temperature scales are Celsius, Fahrenheit and Kelvin.

Celsius scale:
The Celsius scale, also known as the centigrade scale, is based on the freezing and boiling points of water. On the Celsius scale, the freezing point of water is defined as 0°C and the boiling point of water is defined as 100°C. The interval between these two points is divided into 100 equal parts or degrees.

Fahrenheit scale:
The Fahrenheit scale is also based on the freezing and boiling points of water. On the Fahrenheit scale, the freezing point of water is defined as 32°F and the boiling point of water is defined as 212°F. The interval between these two points is divided into 180 equal parts or degrees.

Q.3. With the help of diagram, explain the working of a thermos flask.

Thermos flask:
A thermos flask is a device that is used to keep hot liquids hot and cold liquids cold for a long period of time. It consists of two glass walls with a vacuum between them. The vacuum acts as a good insulator and prevents the transfer of heat by conduction or convection. The outer glass wall is silvered to reduce heat loss by radiation. The flask has a stopper made of plastic or cork, which also acts as an insulator.
When hot liquid is poured into the flask, the heat from the liquid is trapped inside the flask due to the vacuum between the glass walls. Similarly, when cold liquid is poured into the flask, the heat from the surroundings is prevented from entering the flask due to the insulating properties of the vacuum and the silvered surface. This allows the liquid to remain hot or cold for a long period of time. The stopper prevents any heat transfer through the opening of the flask.
The following diagram shows the working of a thermos flask:

V. Numerical-based Questions

Express the following temperatures in the Fahrenheit scale:

a. 110°C = 230°F

b. 85°C = 185°F

c. 225°C = 437°F

d. 30°C = 86°F

e. 0°C = 32°F

2. Express the following temperatures in the Celsius scale.
(a) 131°F
(b) 77°F
(c) 149°F
(d) 32°F
(e) 23°F

Express the following temperatures in the Celsius scale:

a. 131°F = 55°C

b. 77°F = 25°C

c. 149°F = 65°C

d. 32°F = 0°C

e. 23°F = -5°C