NCERT Solutions Std 7 Science Heat

Heat

Exercise:

1). State similarities and differences between the laboratory thermometer and the clinical thermometer.

Similarities:

i). both consists of long, narrow, uniform glass tube.

ii). both have mercury in the bulb.

iii). both has Celsius scale on the glass tube

Differences:

 

Laboratory thermometer Clinical thermometer
1. The laboratory thermometer is designed to measure the temperature of other things.

 

1. The clinical thermometer is designed to measure the temperature of human body only.
2. this thermometer has temperature range between -100 C to 1100 C

 

2. This thermometer has temperature range between 350C to 420 C

2). Give two examples each of conductors and insulators of heat.

Conductors of heat: aluminium, copper

Insulators of heat: wood, plastic

3). Fill in the blanks:

(a) The hotness of an object is determined by its temperature.

(b) Temperature of boiling water cannot be measured by a

clinical thermometer.

(c) Temperature is measured in degree Celsius.

(d) No medium is required for transfer of heat by the process of radiation.

(e) A cold steel spoon is dipped in a cup of hot milk. Heat is transferred to its other end by the process of conduction.

(f) Clothes of dark colours absorb more heat better than clothes of light colours.

 

4). Match the following:

(I) Land breeze blows during                              (a) summer

(ii) Sea breeze blows during                                  (b) winter

(iii) Dark coloured clothes are preferred during     (c) day

(iv) Light coloured clothes are preferred during     (d) night

Answer:

(i) Land breeze blows during – night

(ii) Sea breeze blows during – day

(iii) Dark coloured clothes are preferred during – winter

(iv) Light coloured clothes are preferred during – summer

5). Discuss why wearing more layers of clothing during winter keeps us warmer than wearing just one thick piece of clothing.

          Wearing more layers of clothing during winter keeps us warmer than wearing just one thick piece of clothing because the air is trapped between the two layers of the woollen clothes. This air prevents the flow of heat from our body to the cold surroundings.

6). Look at Fig. 4.13. Mark where the heat is being transferred by conduction, by convection and by radiation.

7). In places of hot climate it is advised that the outer walls of houses be painted white. Explain.

          White colour reflects most of the heat that falls on them and, therefore, we feel more comfortable wearing them in the summer.

8). One litre of water at 30°C is mixed with one litre of water at 50°C. The temperature of the mixture 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

Answer: between 30°C and 50°C

9). An iron ball at 40°C is dropped in a mug containing water at 40°C. The heat will

(a) flow from iron ball to water.

(b) not flow from iron ball to water or from water to iron ball.

(c) flow from water to iron ball.

(d) increase the temperature of both.

Answer: not flow from iron ball to water or from water to iron ball.

10). A wooden spoon is dipped in a cup of ice cream. Its other end

(a) becomes cold by the process of conduction.

(b) becomes cold by the process of convection.

(c) becomes cold by the process of radiation.

(d) does not become cold.

Answer: does not become cold.

11). Stainless steel pans are usually provided with copper bottoms. The reason for this could be that

(a) copper bottom makes the pan more durable.

(b) such pans appear colourful.

(c) copper is a better conductor of heat than stainless steel.

(d) copper is easier to clean than stainless steel.

Answer: copper is a better conductor of heat than stainless steel.

 

Additional Questions:

Write True or False.

1). A laboratory thermometer reads temperature from 35°C to 42°C.

False.

2). Body temperature of every person is 370 C.

False.

3). Mercury is a toxic substance.

True.

4). The heat flows from hotter object to cooler object.

True.

5). During the day, the water gets heated faster than the land.

False.

6). The transfer of heat by radiation does not require any medium.

True.

Fill in the blanks.

1). A reliable measure of the hotness of an object is its temperature.

2). Temperature is measured by a device called a thermometer.

3). The air from the sea is called the sea breeze.

4). All hot bodies radiate heat.

Answer the following in one sentence.

1). Name the types of thermometer?

          Clinical thermometer, laboratory thermometer and maximum-minimum thermometer are the types of thermometers.

2). What is a clinical thermometer?

          The thermometer that measures our body temperature is called a clinical thermometer.

3). What is the normal temperature of human body?

          The normal temperature of human body is 37°C.

4). What is the range of clinical thermometer?

          This thermometer has temperature range between 350C to 420 C.

Answer the following

1). Write Precautions to be observed while using a clinical thermometer.

i). Thermometer should be washed before and after use, preferably with an antiseptic solution.

ii).  Ensure that before use the mercury level is below 35°C.

iii). Read the thermometer keeping the level of mercury along the line of sight.

iv).  Handle the thermometer with care. If it hits against some hard object, it can break.

v).  Don’t hold the thermometer by the bulb while reading it.

2). Write a note on clinical thermometer.

          The thermometer that measures our body temperature is called a clinical thermometer. A clinical thermometer consists of a long, narrow, uniform glass tube. It has a bulb at one end. This bulb contains mercury. Outside the bulb, a small shining thread of mercury can be seen. The clinical thermometer is designed to measure the temperature of human body only. This thermometer has temperature range between 350C to 420 C.

3). What are conductors of heat.

          The materials which allow heat to pass through them easily are conductors of heat. For examples, aluminium, iron and copper.

4). What are insulators.

          The materials which do not allow heat to pass through them easily are poor conductors of heat such as plastic and wood. Poor conductors are known as insulators. The water and air are poor conductors of heat.

Define

1). Conduction

The process by which heat is transferred from the hotter end to the colder end of an object is known as conduction.

2). Convection

          The process of heat transfer by the movement of molecules in the fluids like liquids and gases is known as convection.

3). Temperature

          A reliable measure of the hotness of an object is its temperature.

Distinguish between

1). Conductors and insulators

Conductors Insulators
1. The materials which allow heat to pass through them easily are conductors of heat. 1. The materials which do not allow heat to pass through them easily are insulators of heat.

 

2. Example, aluminium, iron and copper. 2. Example Plastic and wood

 

Click here for the solutions of

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2). Nutrition in Animals

3). Fibre to Fabric

4). Heat

5). Acids, Bases and Salts

6). Physical and Chemical Changes

7). Weather, Climate and Adaptations of Animals to Climate

8). Winds, Storms and Cyclones

9). Soil

10). Respiration in Organisms

11). Transportation in Animals and Plants

12). Reproduction in Plants

13). Motion and Time

14). Electric Currents and its Effects

15). Light

16). Water: A Precious Resource

17). Forests: Our Lifeline

18). Wastewater Story

 

 

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