Chapter 4

Heat

 

Introduction

In our daily lives, we come across various things, some of which are hot while others are cold, such as when a frying pan placed on a hot gas burner gets heated while the pan's handle remains cool. We frequently need to contact various items, some of which are cold and some of which are hot, while completing our regular chores. Even amongst hot things, some may be hotter than others. In the same way, amongst the cold items, some may be colder than others. So, if I ask you how you determine the relative hotness or coolness of items, you might say "by just feeling the objects." However, our sense of touch is insufficient for determining if an object is truly hot or cold. Thus, this may be accomplished with a thermometer.

An iron rod exposed to the sun for an extended time grows heated, yet ice cream stored in the refrigerator remains cool. We continually switch between heat and cold without even realizing it. The temperature now fluctuates based on the circumstances and the items. So, how can we identify which items are hotter than others? Naturally, it is feasible to figure out by feeling the thing, but finding precision in temperature can be difficult. In class 7 science chapter 4, "Heat," we will be dealing with all such phenomena.

Heat is transferred from a hotter body to a colder body. Heat may transfer from one thing to another in three ways. Conduction, convection, and radiation are the three types. Conduction is the most common mode of heat transport in solids. Heat is transmitted by convection in liquids and gases. There is no need for a medium for heat transmission by radiation. Heat conductors are materials that allow heat to travel through them readily. Insulators are materials that do not enable heat to travel through them easily. Light-coloured items absorb more heat than dark-coloured objects. That is why we feel more at ease in light-coloured clothing in the summer.

Heat is a type of energy that causes a substance to become heated. For example, it is usual for us to feel cold inside the home in the winter and warm when we go outside into the sun's rays. How do we experience this sense of warmth or cold now that we know that? So, what will be our response? Think. This class 7 chapter 4 in science will attempt to discover a solution to such a question.

1. Explain the differences and similarities between a laboratory and a clinical thermometer.

2. Give two instances of heat conductors and heat insulators.

3. Fill in the blanks with the following information:

(a) The temperature of an item is governed by its __________.

(b) _____________ thermometer cannot be used to determine the temperature of boiling water.

(c) The temperature is expressed in degree ______________.

(d) In a cup of hot milk, a cold steel spoon is immersed. The process of convection transfers heat from one end to the other by the process of______________.

(e) Clothes in ______________ absorb more heat than dark-coloured clothing.

4. Match the following:

(i) During this time, a land wind blows. (a) summer

(ii) During this time, a sea wind blows. (b) winter

(iii) During this time, dark-coloured clothing is preferable. (c) day

(iv) Light-coloured clothing is recommended. During (d) night

5. Discuss why wearing many layers of clothes keeps us warmer in the cold than wearing just one thick layer.

6. Mark where the heat is transmitted through conduction, convection, and radiation in Fig. 4.13.

7. It is recommended that the exterior walls of dwellings be painted white in hot climates. Explain.

8. One litre of 30 °C water is combined with one litre of 50°C water. The mixture's temperature will be:

(a) 80°C.

(b) More than 50°C but less than 80°C.

(c) 20°C.

(d) Between 30°C and 50°C.

9. A 40°C iron ball is put into a cup filled with 40°C water. The temperature will rise:

(a) From the iron ball to the water.

(b) There is no flow from the iron ball to the water or from the water to the iron ball.

(c) From the water to the iron ball.

(d) Both of their temperatures should be raised.

10. In a cup of ice cream, a wooden spoon is dipped. What will happen to its opposite end?

(a) The process of conduction causes the object to get chilly.

(b) The mechanism of convection causes the room to get cool.

(c) Radiation causes it to become frigid.

(d) It does not become chilly.

11. Copper bottoms are commonly included with stainless steel cookware. This may be because:

(a) The pan's bottom is made of copper, which makes it more durable.

(b) Such pans look to be vibrant.

(c) Copper conducts heat more efficiently than stainless steel.

(d) Stainless steel is more difficult to clean than copper.

Solutions

1. Similarities:

  • Both are composed of glass and consist of a series of long, thin glass tubes.
  • They both have a bulb on one end.
  • Both thermometers utilize a Celsius scale, and their bulbs are constructed of mercury.


Differences:

 

Clinical Thermometer

Laboratory thermometer

Temperatures vary from 35 to 42 degrees Celsius.

The temperature ranges from -10 to 110 degrees Celsius.

It is used to determine the temperature of a person's body.

In the laboratory, it is used to measure temperature.

It has a kink in it that prevents mercury from flowing backwards.

There is no kink in it.

 

2. Conductors: Iron and Copper

    Insulators: Plastic and wood

3. (a) temperature.

    (b) clinical

    (c) Celcius.

    (d) radiation.

    (e) conduction.

    (f ) dark

4. 

Column-I

Column-II

(i) During this time, the land breeze blows.

(d) night

(ii) During this time, the sea air blows.

(c) day

(iii) Dark-coloured clothing is preferable at this time.

(b) winter

(iv) Light-coloured clothing is preferable at this time.

(a) summer

 

  1. Because air is trapped between layers, more layers of clothing keep us warmer in the cold than just one thick piece of clothing. Heat does not escape from the body because air is a poor conductor of heat. Air acts as a heat insulator. Our body heat is kept from leaking into the environment by this layer. More layers of light clothes will trap more air, and we will not feel chilly. Wearing many layers of clothing instead of just one hefty article of clothing keeps us warmer in the cold. Clothes do not transfer heat well. As a result, they limit heat loss by keeping the air around the body warm. As a result, we are not bothered by the cold. Because the former technique preserves more layers of warm air around our body, wearing numerous thin layers of clothes keeps us warmer than wearing a single heavy one. Because they are further removed from our bodies' heat centres, some body parts, such as the arms, legs, and feet, require more heating than others. 

  2. Figure.

  3. Because white is a poor heat absorber, it is advised that the outer walls of homes be painted white in hot regions. White reflects the bulk of the heat that is incident on it. The deeper the hue, the more heat is trapped. White, on the other hand, as the lightest hue, is ineffective at trapping heat. The house will stay cool as a result of this.

  4. Because hot water loses heat and cold water absorbs heat at the same time, the temperature of the mixture will be between 30°C and 50°C.

  5. Because both the iron ball and the water have the same temperature of 40°C, the answer is (b) Neither the iron ball nor the water flow from the iron ball to the water.

  6. The answer is (d) Because wood is a poor heat conductor, it does not become cold.

  7. The answer is (c) Copper is a superior heat conductor to stainless steel.

The class 7 science chapter “Heat” is an essential topic demands pupils to pay close attention to every concept. This chapter teaches us: Our sense of touch is not always a trustworthy indicator of an object's degree of hotness. Temperature is a measure of an object's degree of hotness. A thermometer is a device that measures temperature.

Our body temperature is measured with a clinical thermometer. This thermometer has a temperature range of 35°C to 42°C. We use laboratory thermometers for numerous reasons. These thermometers typically have a temperature range of –10°C to 110°C. The average human body temperature is 37°C. Heat is transferred from a hotter body to a colder body. Heat may transfer from one thing to another in three ways. First, heat is transferred from a hotter body to a colder body. Heat may transfer from one thing to another in three ways. Conduction, convection, and radiation are the three types.

Conduction is the most common mode of heat transport in solids. Heat is transmitted by convection in liquids and gases. There is no need for a medium for heat transmission by radiation. Heat conductors are materials that allow heat to travel through them readily. Insulators are materials that do not enable heat to travel through them easily. Light-coloured items absorb more heat than dark-coloured objects. That is why we feel more at ease in light-coloured clothing in the summer.

Students may learn more about heat, how it is conducted, the process of heat transmission, including radiation and convection, by downloading the msvgo app.

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