Lecture 12a

Question 1

Radiation does not require

Answer 1

a medium to take place

Question 2

radiation occurs in

Answer 2

solids, liquid and gases

Question 3

Radiation can occur between

Answer 3

two bodies even when they are separated by a medium colder than both

Question 4

radiation is

Answer 4

electromagnetic waves

Question 5

type of electromagnetic relevant to heat transfer

Answer 5

thermal radiation, wavelength 10^2 mirco metres to 10^-1 micro metres

Question 6

what emits thermal radiation

Answer 6

all matter about absolute zero

Question 7

thermal radiation increases with

Answer 7

temperature

Question 8

What is a light source

Answer 8

a body that emits radiation in visible range ie the sun

Question 9

at room temperature thermal radiation is

Answer 9

infrared region of the spectrum

Question 10

radiation is a

Answer 10

volumetric phenomenon, but we treat it as a surface

Question 11

a blackbody emits

Answer 11

the maximum amount of radiation by surface at a given temperature
and absorbs all incident radiation

Question 12

a blackbody is

Answer 12

a perfect emitted and absorber of radiation, idealized body to serve as standard

Question 13

Radiation energy emitted by a blackbody =

Answer 13

Eb = sigma *T^4

Question 14

what is important to remember when dealing with radiation equation

Answer 14

always do in kelvin

Question 15

What is spectral blackbody emissive power

Answer 15

amount of radiation energy emitted by a blackbody at a thermodynamic temperature T per unit time per unit surface area and per unit wavelength, about the wavelength lander

Question 16

wavelength at which peak occurs for a specified tempearture is given by

Answer 16

wiens displacement law

lander *T = 2897

Question 17

observation from variation of the blackbody emissive power with wavelength figure

Answer 17

emitted radiation is a continuous function of wavelength
amount of emitted radiation increases with temperature
as temperature increases curve shifts left to shorter wavelength, larger fraction of radiation is short wavelengths at high temps

Question 18

Area under a Eblander lander chart represents

Answer 18

total radiation energy emitted by blackbody at that temperature

Question 19

How to use Eblander lander chart to find energy emitted in wavelength band

Answer 19

find area under graph between wavelengths

Question 20

what does blackbody radiation functions equal

Answer 20

fraction of radiation emitted from a blackbody at temperature T in the wavelength band from lander = 0 to lander

Question 21

What does intensity describe

Answer 21

magnitude of radiation emitted or incident in a specified direction in space denoted by I

Question 22

if opaque what can we consider radiation

Answer 22

a surface phenomenon

Question 23

what is emissivity

Answer 23

ratio of radiation emitted by the surface at a given temperature to radiation emitted by a blackbody at the same temperature
how closely a surface approximates a blackbody

Question 24

what will we always consider emissivity

Answer 24

constant grey and diffuse

emissivity equal to the value in the normal direction

Question 25

if a surface is diffuse

Answer 25

properties are independent of direction

Question 26

if surface is grey

Answer 26

properties are independent of wavelength

Question 27

absorptivity =

Answer 27

alhpa = Absorbed radiation / Incident radiation = Gabs /G

Question 28

What is G

Answer 28

irradiation G radiation flux incident on a surface

Question 29

reflectivity

Answer 29

pho = Reflected radiation/G = Gref/G

Question 30

Tranmissivity

Answer 30

tau = Transmitted radiation/G = Gtr/G

Question 31

Draw a diagram of how incident radiation is split

Answer 31

see book

Question 32

for opaque surfaces

Answer 32

tau = 0 therefore alpha + rho = 1

Question 33

G =

Answer 33

Gabs + Gref + Gtr

alpha + rho + tau = 1

Question 34

Specular reflection

Answer 34

angle of reflection equals angle of incidence (mirrorlike)

Question 35

Diffuse reflection

Answer 35

radiation is reflected equally in all direction

Question 36

What is reflection generally assumed

Answer 36

diffuse or specular

Question 37

Kirchoffs law

Answer 37

Gabs = alhpa G = alpha *sigma*T^4
Eemit = em*sigma*T^4
As*em*sigma*T^4 = As*alpha*sigma*T^4

Question 38

relationship between emissivity and absorptivity

Answer 38

epsilon (T) = alpha (T) for all cases

spectral form of kirchoffs law