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नवोदय विद्यालय समिति

Navodaya Vidyalaya Samiti

( An Autonomous Body Under MHRD ) Government Of India

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CHAPTER 4

HEAT

e-Content

PREPARED BY : ASSEEM A M

TGT SCIENCE

JAWAHAR NAVODAYA VIDYALAYA PATHANAMTHITTA

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Learning Outcomes

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1) Know and understand about transfer of heat energy from high hot region to low hot region.

2) Know and understand the term: kink, range, thermometric liquid, conduction, convection and radiation.

3) Compare different types of thermometers.

4) Compare different units of temperature.

5) Understand about different modes of transfer of heat.

6) Know and understand about the properties of dark and light colour on the absorption of Heat.

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HOT OR COLD

Ice cream

Spoon in a

tea cup

Fruit juice

Handle of a frying pan

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ACTIVITY

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

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THERMOMETER�

Temperature is measured by a device called thermometer

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DIFFERENT TYPES OF THERMOMETER

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CLINICAL THERMOMETER

Clinical thermometer is a thermometer used to measure human body temperature.

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DIFFERENT TYPES OF CLINICAL THERMOMETER

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A thermometer contains  

mercury for the measurement  of temperature. Mercury   thermometers works with the principle of expansion of metals on heating.

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MERCURY THERMOMETER�

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DIGITAL THERMOMETER�

�An instrument that measures the temperature of an object and shows as digital readout.  Digital thermometer works with the help of heat sensing diodes.

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INFRARED THERMOMETER�

Instrument that focuses and detects the infrared radiation emitted by an object in order to determine its temperature of that object.

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������� Precautions to be observed while reading a clinical Thermometer

  • Thermometer should be washed before and after use, preferably with an antiseptic solution.
  • Ensure that before use the mercury level is below 35°C.
  • Read the thermometer keeping the level of mercury along the line of sight.
  • Handle the thermometer with care. If it hits against some hard object, it can break.
  • Don’t hold the thermometer by the bulb while reading it.

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NORMAL HUMAN BODY TEMPERATURE 

The normal temperature of human body is 37°C.

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°C -degrees Celsius 37oC

F -degrees Fahrenheit 98.6 F

K -Kelvin 310 K

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LABORATORY THERMOMETER

Laboratory thermometer is used in Scientific Laboratories to measure the temperature of different substance.

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  • While measuring the laboratory temperature, it should be kept upright not tilted.
  • bulb should be surrounded from all sides by the substance of which the temperature is to be measured.
  • The bulb should not touch the surface of the container.

Precautions to be observed while reading a laboratory thermometer

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Difference between clinical and laboratory thermometers

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Clinical Thermometer

Laboratory Thermometer

Clinical thermometer is scaled from 35°C to 42°C or from 94°F to 108°F.

Laboratory thermometer is generally scaled from -10°C to 110°C.

Mercury level does not fall on its own, as there is a kink near the bulb to prevent the fall of mercury level.

Mercury level falls on its own as no kink is present.

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Temperature can be read after removing the thermometer from armpit or mouth.

Temperature is read while keeping the thermometer in the source of temperature, e.g. a liquid or any other thing.

Clinical thermometer is small in size.

Laboratory thermometer is large in size.

It is used for taking the body temperature.

It is used to take temperature in laboratory.

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TRANSFER OF HEAT

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TRANSFER OF HEAT�� THE MOVEMENT OF HEAT ENERGY FROM HIGH HOT REGION TO THE LOW HOT REGION.

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  • Conductors of heat

Materials which do allow heat to pass through them easily are known as conductors of heat.

Eg: Aluminum, Iron, Copper, etc

  • Insulators of heat�

Materials which do not allow heat to�pass through them easily are poor�conductors of heat (insulators of heat) Eg: plastic and�wood. �

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�CONDUCTION

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Conduction is a process in which transfer of heat takes place between objects by direct contact.

In solid materials

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CONVECTION

Convection refers to the form of heat transfer in which energy transition occurs within the fluid.

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RADIATION

Radiation is the mechanism in which heat energy got transmitted without any physical contact between objects.(with out any mediums) ie, solid liquid or gas.

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LAND BREEZE AND SEA BREEZE

Land and sea breezes are wind and weather phenomena associated with coastal areas.� A land breeze is a breeze blowing from land out toward a body of water. �A sea breeze is a wind blowing from the water onto the land.

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SEA BREEZE

During day time the land gets heated faster than the water. The air over the land becomes hotter and rises up. Then cooler air from the sea rushes in towards the land is called sea breeze.

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LAND BREEZE

At night time the water cools down more slowly than the land. So, the hot air over sea rise up and the cool air from the land moves towards the sea. This is called the land breeze.

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When heat radiation fall on dark(black) surface it absorbs more heat energy, thereby black surface becomes more hot.

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When heat radiation fall on white(light) surfaces, most of the heat energy get reflected back by white surface, so heat energy absorbed will be very less, thereby white surface get less hot.

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Cotton clothes are thin and do not have space in which air can be trapped thus cotton clothes do not prevent heat coming out of our body where as woollen clothes keep us warm during winter because it has air trapped in between the fibers, also it is thick layered and hence heat can't exhaust from our body and air present outside can't contact with body

Woollen clothes keep us warm�in winter

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���SUMMARY

  • Temperature is a measure of the degree of hotness of an object.
  • Thermometer is a device used for measuring temperatures.
  • Clinical thermometer is used to measure our body temperature.
  • The range of Clinical thermometer is from 35°C to 42°C.
  • The range of laboratory thermometers is usually from

–10°C to 110°C.

  • The normal temperature of the human body is 37°C.
  • The heat flows from a body at a higher temperature to a body at a lower temperature.
  • Transfer of heat are of three type conduction, convection and radiation.

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  • In solids, generally, the heat is transferred by conduction.
  • In liquids and gases the heat is transferred by convection.
  • No medium is required for transfer of heat by radiation.
  • The materials which allow heat to pass through them easily are conductors of heat.
  • The materials which do not allow heat to pass through them easily are called insulators.
  • Dark-coloured objects absorb radiation better than the light-coloured objects.
  • Woollen clothes keep us warm during winter because wool is a poor conductor of heat and it has air trapped in between the fibers.

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WEB LINKS

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