Heat Energy Transfer by Radiation 
Heat Energy Transfer by Radiation
by Prof. Miller
Video Lecture 24 of 46
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Date Added: February 5, 2015

Lecture Description

In conduction and in convection we need some STUFF. In this mechanism called RADIATION things go better with nothing in between! Which is a strange business.

A. We energize an incandescent lamp. Nearly INSTANTLY we FEEL
the heat energy on the arm a foot or so away — but the lamp bulb
still is unheated. The radiation passes through the glass envelope
- falls on the flesh - is absorbed - and this is commuted to
thermal energy IN THE FLESH. The mechanism is very complicated.

B. The classical RADIOMETER: Here is a device that nearly every¬
body has seen. Strangely enough - even physicists do not thoroughly understand it! Radiation falls upon the vanes. The black
faces retreat. A good inquiry to investigate is this: How would
this enchanting device work if placed between two big cakes of
ice? Try it.

C. THE CASE OF THE THREE CANS: One is shiny - one is black -
one is covered with a thin layer of asbestos. Thus we would say
that this one is insulated. We fill them equally with hot water.
They cool at different rates - obviously. And we can hardly believe it: the asbestos covered can — the insulated can - cools
off the fastest! HINT: The surface of this can is very very rough
thus exposing very much area for radiation losses!

D. THE CASE OF TWO THERMOMETERS: The bulb of one is black -
the bulb of the other is white. We place them in the Sun. What
do we see AT ONCE? Answer: The black one rises faster -
sooner — but in due course they both come to read the same. These
ideas are very important.

E. THE CASE OF THE TWO THERMOMETERS: The bulb of one is
wrapped with cotton batting LIGHTLY - LOOSELY — the bulb
of the other is wrapped with the same mass - the same weight -
the same amount - of batting - but tightly. How do they be-
have in the Sun? Answer: The tightly wrapped one climbs higher
sooner - faster - quicker — but in due course they come to the
same reading. The air lodged in the loose wrapping is a good ther¬
mal insulator.

F. A Dewar flask - which is a thermos bottle — utilizes this mechanism. Quiet air is a good insulator — but better still - NO
air at all is a good insulator. So the thermos bottle has two glass
walls - an inner one and an outer one - and the space between
evacuated - mostly. Also: The outer wall and the inner wall are

both shiny - for good reflection.
G. An interesting problem:* THE CASE OF THE BLACK COFFEE AND
CREAM:
a. We pour a cup of hot coffee black.
b. We are on the verge of adding cream when the phone rings.
c. We wish to answer the phone and return to find the coffee
as hot as possible.
d. QUESTION: Do we add the cream before going to the phone
or after?
e. ANSWER: We add the cream BEFORE! See why? And do
not say that the cream holds the heat in or some such worth¬
less phrase.

H. We show a chart of ELECTROMAGNETIC RADIATIONS - the E-M SPECTRUM. Of the entire range we know the visible light is but a tiny part. Human vision, although a wonderful mechanism, utilizes only a small - very small - part of the whole thing. And what lies beyond we can not now say. There may be wavelengths yet undiscovered.

Course Index

  1. The Idea of the Center of Gravity
  2. Newton's First Law of Motion: Inertia
  3. Newton's Second Law of Motion: The Elevator Problem
  4. Newton's Third Law of Motion: Momentum
  5. Energy and Momentum
  6. Concerning Falling Bodies & Projectiles
  7. The Simple Pendulum and Other Oscillating Things
  8. Adventures with Bernoulli: Bernoulli's Principle
  9. Soap Bubbles and Soap Films
  10. Atmospheric Pressure
  11. Centrifugal Force and Other Strange Matters
  12. The Strange Behavior of Rolling Things
  13. Archimedes' Principle
  14. Pascal's Principle: The Properties of Liquids
  15. Levers, Inclines Planes, Geared-wheels and Other Machines
  16. The Ideas of Heat and Temperature
  17. Thermometric Properties and Processes
  18. How to Produce Heat Energy
  19. Thermal Expansion of Stuff: Solids
  20. Thermal Expansion of Stuff: Gases & Liquids
  21. The Strange Thermal Behavior of Ice and Water
  22. Heat Energy Transfer by Conduction
  23. Heat Energy Transfer by Convection
  24. Heat Energy Transfer by Radiation
  25. Evaporation, Boiling, Freezing: A Dramatic Adventure
  26. Miscellaneous Adventures in Heat
  27. The Drama in Real Cold Stuff: Liquid Nitrogen
  28. The Physics of Toys: Mechanical
  29. The Physics of Toys: Acoustic and Thermal
  30. Waves: Kinds of Properties
  31. Sound Waves: Sources of Sound & Pitch and Frequency
  32. Vibrating Bars and Strings: The Phenomenon of Beats
  33. Resonance: Forced Vibrations
  34. Sounding Pipes
  35. Vibrating Rods and Plates
  36. Miscellaneous Adventures in Sound
  37. Electrostatic Phenomena: Foundations of Electricity
  38. Electrostatic Toys, Part 1
  39. Electrostatic Toys, Part 2
  40. Adventures with Electric Charges
  41. Adventures in Magnetism
  42. Ways to "Produce" Electricity
  43. Properties and Effects of Electric Currents
  44. Adventures in Electromagnetism
  45. Further Adventures in Electromagnetism
  46. Miscellaneous and Wondrous Things in E&M

Course Description

Demonstrations in Physics was an educational science series produced in Australia by ABC Television in 1969. The series was hosted by American scientist Julius Sumner Miller, who demonstrated experiments involving various disciplines in the world of physics. The series was also released in the United States under the title Science Demonstrations.

This program was a series of 45 shows (approximately 15 minutes each) on various topics in physics, organized into 3 units: Mechanics; Heat and Temperature / Toys; and Waves and Sound / Electricity and Magnetism.

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