HEAT - POST 12

HEAT - BLOG POST 12

      Radiation - PART 1


IMPORTANT REMINDER-

*We at St Columba's School, are ready to take the next step - and move towards using Google Classroom as a tool to enhance the teaching learning environment.

*This shift involves the school giving each student a unique email address, which he will need to setup ( the teachers will assist him in doing the same). This email will facilitate each student to interact with his teachers.

* The student should use this email ID only for:

-interacting with  teachers on school /subject related matters

-keep the words and expressions as he would- if he  were interacting with us as a Columban student

-use the facilities connected to this email ID only for google meets organised with the permission of a teacher 

-he should have a copy of the permission given ( when and by which teacher and for what purpose)

-do not access any of the other facilities connected with this email address unless he first seeks the permission of a teacher

(He should have a copy of the permission given - when and by which teacher and for what purpose).

*Please note that Google and St Columba's have legal obligations by giving you access to this email address and hence,

you will need to sign an agreement when creating this email ID. 

*Be informed that the history of use of this ID shall have a digital footprint !

Good morning Boys ! In the last class we discussed about convection. Today we will learn about radiation.
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 At the end of this lesson you will be able to:

DEFINE : RADIATION

Explain : How radiation takes place.

Understand and Explain that black bodies radiate heat faster

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      Q31)Defn: Radiation is the direct transfer of heat from a hot body to a cold body having no contact between them and without the help of any medium.


To understand the concept of radiation I’ll give you a real life example.

We feel warm when we sit in the sun , in front of the fire or in front of a heater. How does heat travel from the sun to us?

There is no direct contact between us and the source of heat. The air between us and the source of heat is a bad conductor of heat. Therefore heat can’t be transferred through conduction. It cannot be transferred  by convection because the hot air rises upwards and not towards.us So heat from the sun is transferred to us by the radiation.






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Remember: Radiation needs no medium. Transfer of heat by radiation can occur even in a vacuum.
Thermal radiation is called infrared radiation.  This radiation travels with the speed of light. Thermal radiation can even travel through vacuum.








How does heat get transferred through radiation? 
Ans) Radiant heat consists of thermal radiation. When thermal radiation falls on a body, a part of it is absorbed by it. The absorbed radiation makes the molecules vibrate more vigorously. The increased molecular vibrations make the object hotter.

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A video on radiation please watch this before continuing
https://youtu.be/JRitlbbhvmg



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IMP:-
-The quantity of heat absorbed by a body depends on its distance from the source of heat
-Black bodies are better heat absorbers and better radiators than white coloured bodies.
-In simple words black bodies absorb more heat than white bodies and they also lose heat(radiate) faster than the white bodies.

An experiment to show that black bodies are better heat absorbers than white bodies.

https://youtu.be/_SiSDcN9TBE

 The  link below explains  that black bodies  radiate and absorb heat faster
https://www.youtube.com/watch?v=DIfzIXmGth0




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Now I’ll be asking you some questions on radiation. Try to solve them yourselves before seeing the answer.

1)    Why is it more comfortable to wear white or light coloured clothes in summer and dark coloured clothes in winter?
Ans) We wear light coloured clothes in summer and dark coloured clothes in winter because white or light coloured clothes absorb lesser amount of heat and keep us cool in summer. On the other hand, black or dark coloured clothes absorb more heat and keep us warm during winter.










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WRITTEN WORK

TEXT in GREEN


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ASSET Q   2018