# CBSE Class 7 Science Revision Notes Chapter 4

## CBSE Class 7 Revision Notes Science Chapter 4 – Heat

Extramarks’ concise Class 7 Science Chapter 4 Notes are recommended for quick revisions before exams. These notes, curated as per the latest CBSE guidelines, help students gain a clear understanding of various concepts in this important chapter while studying for the exam.

Chapter 4 of Class 7 Science discusses heat. The chapter provides a deeper understanding of the changes caused due to heat, the process of transfer of heat involving radiation and convection, etc., and interesting facts related to different coloured substances absorbing different amounts of heat. Class 7 Science Chapter 4 Notes explain all of these concepts in detail and are a dependable resource for quick exam revisions.

### Access Class 7 Science-Chapter 4 – Heat

Heat:

• Many things in our surroundings can be hot, like tea or boiling water, or cold, like ice or ice cream.
• Heat is not just a sense but a form of energy. Heat can be called a form of energy as there is a shift of energy from a hotter to a cooler object when it occurs.
• Hot and cold can be differentiated based on the differences in their temperatures. Therefore, the temperature is a measure of the hotness or coldness of an object represented in terms of degrees.

Measuring Temperature:

• A thermometer is a device used to measure temperature.The different types of thermometers are categorised according to how they are used.
• Here are the various types of thermometers:

Clinical Thermometer:

• A clinical thermometer usually consists of a long, narrow glass tube with a bulb that consists of mercury at one end. The scale indicated on the thermometer as well as a thread of shining mercury is visible, which aids in getting the reading.
• The body temperature is solely measured by this type of thermometer. It is widely used in hospitals by doctors as well as at home.
• The Celsius scale is the scale used in India and ℃ is the symbol used to indicate it.
• Since the body’s normal temperature is 37°C, the clinical thermometer temperature range is 35°C to 42°C. One end of the thermometer is placed for a minute under the tongue or in the underarms of any person to obtain a reading.
• Nowadays, digital thermometers are favoured since they don’t contain mercury and are less harmful as mercury has a toxic nature and the leakage of mercury from broken thermometers causes severe problems.

Maximum-Minimum Thermometers:

These are used to calculate the daily minimum and maximum temperatures.

They are parallel glass tubes with a U-shape. It is used to keep track of a place’s temperature.

Laboratory Thermometer:

All items other than human bodies can have their temperatures measured using this thermometer.

It consists of an extended, straight glass tube with a mercury-filled bulb at the end.

This is typically used in laboratories to test freezing and boiling points, among other things. As a result, the temperature range of this thermometer is 10 degree to 110 degree C.

Transfer of Heat:

• Heat is the transmission of energy from a hotter commodity to a cooler commodity. For example, if a spoon is kept in a bowl of hot soup for a long time,  the heat from the soup is passed on to the spoon, and it turns hot.
• Heat transfer can take place in various ways. They are as follows:
1. Conduction:
• This is a procedure of heat transfer where the heat is transmitted from the hot section to the cold section of the articles. Example – When the pan is heated, then the handle of the pan also becomes hot. Therefore, the handles of most utensils are made of plastic or wood.
• The substances that let the heat penetrate through them are known as conductors. Examples of the most common conductors are iron and copper.
• The substances that do not let the heat penetrate through them are called insulators or poor conductors. Examples of the most common insulators are wood and plastic.

2.Convection:

• This is one of the ways of heat transfer in liquids and gases, where the heat is transmitted by the shifting of the heated molecules in them. One example is when bubbles rise to the top from the bottom of a vessel while boiling water.
• The molecules of any liquid or gas close to the source of heat turn hot and rise, and rise and this in turn is swapped by the colder molecules in the liquid or air. They get warmed up and proceed until the entire fluid or air is heated up.
• This is the concept behind the interesting characteristics found in the coastal areas, termed the sea and land breeze.

A.Sea Breeze:

• In coastal regions, the land becomes warmer faster during the day and as the land gets hotter, the hot air rises up.
• At that moment, the cool air from the sea bursts into occupy its place. The warm air from the land moves to the sea. This completes a cycle. The cool breeze that flows from the sea to the land is called the sea breeze.

B.Land Breeze

• The land cools quicker in comparison to the water at night. Therefore, the warm air from the sea shifts towards the land, while the cool air from the land shifts towards the sea.
• The cool air shifting towards the sea from the land is called the land breeze.

• Mediums such as air or liquid are not required to transfer the heat energy in the process of radiation. For example, heat from the sun.
• Heat can be radiated by all the hot bodies.

One feels warm when standing under the sun. The heat from the sun cannot reach the earth by means of conduction or convection. The vacuum is the only medium in the majority of the region of space between the Earth and the Sun. The process through which the earth receives heat from the sun is known as radiation. No medium is required for the transfer of heat by radiation.

The transfer of heat can take place even if a medium is present or not. For example, one can feel the heat from a room heater in cold regions, a hot utensil removed from the flame cools down as it transmits heat to the surroundings by the process of radiation, and living bodies transfer heat to their surroundings while absorbing heat from the surroundings as well. This is done through the process of radiation. When heat falls on certain articles, a portion of it is radiated, a portion is reflected, a portion is absorbed, and a portion may be transferred. The temperature of any article increases due to the portion of the article that absorbs heat.

Absorption of Heat:

• The radiation of heat by objects is either reflected or absorbed.
• The temperature of the object increases based on the heat it is exposed to.
• Heat is absorbed faster by dark colours. Therefore, it is recommended to wear dark-coloured clothes during winter to feel warm and use a black umbrella while in the sun.
• The heat is reflected by light colours, which is why light-coloured clothes are preferable in summer.
• Even though wool is a poor conductor of heat, it can trap air (as it is a bad conductor of heat) within the fibres, which does not let the heat from the body escape into the surroundings. This is why woollen clothes are worn in winter.

Highlights of Class 7 Science Chapter 4 Notes

• Temperature
• Different types of thermometers
• Land Breeze and Sea breeze
• Conduction
• Convection
• Heat transfers

How Do Different Colours Absorb Different Amounts of Heat?

Class 7 Science Chapter 4 Notes explain the absorption of heat by different colours based on varying amounts of heat. One of the important experiments is stated in this chapter. The steps mentioned to conduct this experiment are below:

• Take two same-sized tin cans.
• You can paint both the cans in two dissimilar colours. You can take black and white.
• Both cans should be filled with an equivalent volume of water.
• The cans should be left in the mid-afternoon sun for around an hour. Students must precisely follow these instructions.
• The temperature of the water present in the cans can be measured after an hour.

The result of this experiment is that the water in the black can would be hotter than the water in the white can.

Production of Biogas in a Biogas Plant

Biogas can be generated in a biogas plant from raw materials such as municipal waste,  agricultural waste, plant waste, food waste, etc. It mainly comprises carbon dioxide and methane.

A biogas plant is a facility that provides oxygen-free conditions where anaerobic digestion can occur. Simply put, it’s an artificial system where you can turn waste into sustainable energy and fertilisers, with positive effects on the environment

The four essential elements that are needed for the formation of biogas are as follows:

1. Hydrogen sulphide
2. Methane
3. Carbon dioxide
4. Water vapour

What is the Difference Between Heat and Temperature?

Heat is the energy reserved in an object, whereas the measurement of the hotness or coldness of an object is based on temperature. The heat of an object is dependent on its mass, temperature, and material, while the temperature of an object is based on the kinetic energy of its molecules. These differences are clearly explained in the Cass 7 Science Chapter 4 Revision Notes.

What Do You Understand by Radiation?

Heat energy from the sun is received through a process known as radiation. It is capable of travelling through space, therefore, there is no need for a medium for transmission. Students can gain an in-depth understanding of radiation through heat and temperature in Class 7 Science Chapter 4 Notes. In addition, radiation constantly travels in the form of electromagnetic energy waves like radio and light waves.

What are the Disadvantages of the Celsius Scale Mentioned in Class 7 Science Chapter 4 Notes?

There are high chances of temperature going below zero degrees Celsius on the celsius scale. The volume and pressure of gases do not modify or change in proportion to the temperature.

### 1. What are conductors and insulators?

The substances that let heat pass through them easily are called conductors of heat. For example, aluminium, iron, and copper.  Substances that do not let heat pass through them easily are known as poor conductors of heat. These poor conductors are also called insulators. For example, plastic and wood.

### 2. What is a clinical thermometer?

When you or someone in your family has a fever, their body temperature is always measured by a thermometer. The temperature of each person may vary. Every human’s body temperature may not be 37°C. It can be a little higher or lower. The average body temperature of a large number of healthy individuals is called normal temperature. A body’s temperature is measured by a thermometer that is named a clinical thermometer.  The clinical thermometer was invented to measure the temperature of only the human body. The human body’s temperature usually does not go below 35°C or above 42°C. That is the main reason why the thermometer has a range of 35°C to 42°C.

### 3. What is a laboratory thermometer?

We measure the temperature of other objects, including the human body. For different purposes, different types of thermometers are used. One such thermometer is termed the laboratory thermometer. They are mainly used in laboratories. It has different highest and lowest temperatures that it can measure. This thermometer typically has a temperature range of -10 °C to 110 °C.

### 4. What is the “maximum and minimum thermometer”?

The measure the past day’s maximum and minimum temperatures for reporting in the weather reports, are measured by a thermometer known as the maximum-minimum thermometer.