Radia

tion

Radia

tion

Pre

pa

red

by

Ma

ry F

lore

nce

CG

PIT

Uka

Ta

rsa

dia

Un

ive

rsity

Ba

rdo

li.

Unit 1

Introduction to Radiation

Rad

iatio

n

Aho

tobj

ecti

na

vacu

umch

ambe

rlo

ses

heat

byra

diat

ion

only

.

The

mec

hani

sm in

volv

ing

the

emis

sion

of i

nter

nal e

nerg

y of

the

obje

ct is

cal

led

radi

atio

n.

3

Pro

pert

ies

of R

adia

tion

Rad

iatio

ndi

ffers

from

the

othe

rtw

ohe

attr

ansf

er

mec

hani

sms

inth

atit

does

not

requ

ireth

epr

esen

ceof

a

mat

eria

lmed

ium

tota

kepl

ace.

Ene

rgy

tran

sfer

byra

diat

ion

isfa

stes

t(a

tth

esp

eed

oflig

ht)

and

itsu

ffers

noat

tenu

atio

nin

ava

cuum

Sol

arra

diat

ion

4

Sol

arra

diat

ion

reac

hes

the

eart

h

afte

rpa

ssin

g

thro

ugh

cold

air

laye

rsat

high

altit

udes

.

Fun

dam

enta

l Con

cept

TS>

Tsu

r

No

conduction

or

convection

-still

solid

will

cool

So

lidgets

coo

led

–e

mis

sio

nof

therm

alra

dia

tion

form

the

surf

ace

ofth

esolid

Ra

dia

tio

n

5

Ra

dia

tio

n

coo

ling

of

a

heate

d

solid

Jam

esC

lerk

Max

wel

lpr

opos

edth

atth

eac

cele

rate

d

char

ges

orch

angi

ngel

ectr

iccu

rren

tsgi

veris

eto

elec

tric

and

mag

netic

field

s.T

hese

rapi

dly

mov

ing

field

sar

eca

lled

elec

trom

agne

ticw

aves

orel

ectr

omag

netic

radi

atio

n

Ele

ctro

-mag

netic

Rad

iatio

nen

ergy

emitt

edby

mat

ter

asa

resu

ltof

the

chan

ges

inth

eel

ectr

onic

conf

igur

atio

nsof

the

atom

sor

mol

ecul

es

Ele

ctro

mag

netic

wav

esar

ech

arac

teriz

edby

thei

r 6

Ele

ctro

mag

netic

wav

esar

ech

arac

teriz

edby

thei

r

freq

uenc

y,ʋ

orw

avel

engt

h,λ

In V

acuu

m C

o= 2

.998

x 1

08 m/s

n =

Inde

x of

ref

ract

ion

c =

spe

ed o

f pro

poga

tion

of w

ave

in th

at m

ediu

m

Ele

ctro

mag

netic

radi

atio

nis

the

prop

agat

ion

ofa

colle

ctio

n

ofdi

scre

tepa

cket

sof

ener

gyca

lled

phot

ons

orqu

anta

Pro

pose

dby

Max

Pla

nck

inco

njun

ctio

nw

ithhi

squ

antu

m

theo

ry

each

phot

onof

freq

uenc

y,ʋ

isco

nsid

ered

toha

vean

ener

gyof

7

h =

6.62

56 x

10-3

4J

� s

is P

lanc

k’s

cons

tant

Ele

ctro

mag

netic

wav

e sp

ectr

um

8

Ene

rgy

ofa

phot

onis

inversely

proportional

toits

wav

elen

gth.

Sho

rter

-wav

elen

gth

radi

atio

npo

sses

ses

larg

erph

oton

ener

gies

.

Itis

now

onde

rth

atw

etr

yto

avoi

dve

ry-s

hort

-wav

elen

gth

radi

atio

nsu

chas

gam

ma

rays

and

X-r

ays

sinc

eth

eyar

e

high

lyde

stru

ctiv

e

The

type

ofel

ectr

omag

netic

9

The

type

ofel

ectr

omag

netic

radi

atio

nth

atis

pert

inen

tto

heat

tran

sfer

isth

ethermalradiation.

Eve

ryth

ing

arou

ndus

cons

tant

ly

emits

ther

mal

radi

atio

n.

ALLBODIESEMITRADIATION

Thermal

radiation

:R

ate

atw

hich

ener

gyis

emitt

edby

mat

ter

asa

resu

ltof

itsfin

itete

mpe

ratu

re

Mechanism

ofem

ission:

Ene

rgy

rele

ased

asa

resu

ltof

osci

llatio

nsof

man

yel

ectr

ons

that

cons

titut

em

atte

r

Rad

iatio

nat

abso

lute

zero

tem

p–

zero

Rad

iatio

nis

avo

lum

etric

phen

omen

a

Rad

iatio

nis

cons

ider

edas

surf

ace

phen

omen

a

10

Rad

iatio

nis

cons

ider

edas

surf

ace

phen

omen

a

Rad

iatio

n–in

terio

rm

olec

ules

–abs

orbe

dby

adjo

inin

g

mol

ecul

es

gam

ma

rays

are

prod

uced

bynu

clea

r

reac

tions

X-r

ays

byth

ebo

mba

rdm

ent

ofm

etal

s

with

high

-ene

rgy

elec

tron

s,

Mic

row

aves

bysp

ecia

lty

pes

ofel

ectr

on

tube

ssu

chas

klys

tron

san

d

mag

netr

ons,

11

mag

netr

ons,

radi

ow

aves

byth

eex

cita

tion

ofso

me

crys

tals

orby

the

flow

ofal

tern

atin

g

curr

entt

hrou

ghel

ectr

icco

nduc

tors

Sur

face

em

issi

on p

rope

rtie

s

Rat

eof

emis

sion

depe

nds

onth

efo

llow

ing

prop

ertie

s

The

tem

pera

ture

ofth

esu

rfac

e

Nat

ure

ofth

esu

rfac

e

Wav

elen

gth

and

freq

uenc

yof

the

radi

atio

n

12

Reg

ular

and

Diff

used

ref

lect

ion

13

AB

SO

RP

TIV

ITY

, RE

FLE

CT

IVIT

Y

AN

D T

RA

NS

MIS

SIV

ITY

14

AB

SO

RP

TIV

ITY

, RE

FLE

CT

IVIT

Y

AN

D T

RA

NS

MIS

SIV

ITY

15

Bla

ck b

ody

radi

atio

n

Blackbody

isde

fined

asa

perf

ect

emitt

eran

dab

sorb

erof

radi

atio

nat

asp

ecifi

edte

mpe

ratu

rean

dw

avel

engt

h.

Pro

pert

ies

ofBlackbody

1.A

blac

kbod

yab

sorb

sal

lin

cide

ntra

diat

ion,

rega

rdle

ssof

wav

elen

gth

and

dire

ctio

n.

16

wav

elen

gth

and

dire

ctio

n.

2.B

lack

body

isa

diffu

seem

itter

3.A

ta

spec

ified

tem

pera

ture

and

wav

elen

gth,

nosu

rfac

e

can

emit

mor

een

ergy

than

abl

ackb

ody.

Bla

ck b

ody

radi

atio

n

17

••Opaque body

Opaque body:

if n

o in

cide

nt r

adia

tion

is tr

ansm

itted

thro

ugh

the

body

.

••White Body

White Body:

if a

ll th

e in

cide

nt r

ay fa

lling

on

the

body

is

refle

cted

.

••Grey body

Grey body:

if a

ll th

e th

ree

are

assu

med

to b

e un

iform

then

it

is c

alle

d gr

ey b

ody. Black body

Opaque

White

18

Black body

Opaque

White

Reflectivity,

ρ0

1

1

Absorp

tivity,

α1

0

Tra

nsm

itiv

ity,

τ0

00

••Thermal

Thermal

emissive

emissive

power

power

:th

eto

tal

amou

ntof

radi

atio

n

emitt

edby

abo

dype

run

itar

eaan

dtim

e.

••Monochromatic

Monochromatic

emissive

emissive

power

power

:th

era

teof

ener

gy

radi

ated

per

unit

area

ofth

esu

rfac

epe

run

itw

avel

engt

h.

••Emissivity

Emissivity

:ab

ility

ofth

esu

rfac

eof

body

tora

diat

ehe

at.(

or)

the

ratio

ofem

issi

vepo

wer

ofan

ybo

dyto

the

emis

sive

pow

erof

the

blac

kbo

dyof

equa

ltem

pera

ture

,(E

/Eb)

.po

wer

ofth

ebl

ack

body

ofeq

ualt

empe

ratu

re,(

E/E

b).

19

Ste

phan

Bol

tzm

ann

law

••The

The

emissive

emissive

power

power

of

of

aablack

black

body

body

isisdirectly

directly

proportional

proportional

totothe

the

fourth

fourth

power

power

of

of

its

its

absolute

absolute

temperature

temperature

E EEEb bbb

=

=

=

= � ���

T TTT4 444

20

Kirc

hhof

f’s la

wA

tan

yte

mpe

ratu

reth

era

tioof

tota

lem

issi

vepo

wer

Eto

the

tota

l

abso

rptiv

eα

isa

cons

tant

for

all

subs

tanc

ew

hich

are

inth

erm

al

equi

libriu

mw

ithth

eir

envi

ronm

ent

21

Pla

nk’s

law

22

Wei

n’s

law

•A

sth

ete

mpe

ratu

rein

crea

ses,

the

peak

ofth

ecu

rve

inF

igur

e

shift

sto

war

dsh

orte

r

wav

elen

gths

.The

wav

elen

gth

at

whi

chth

epe

akoc

curs

for

a

spec

ified

tem

pera

ture

isgi

ven

23

spec

ified

tem

pera

ture

isgi

ven

byWien’s

displacementlaw

as

Num

eric

al 1

Con

side

ra

20cm

diam

eter

sphe

rical

ball

at80

0K

susp

ende

din

air

assh

own

inF

igur

e.A

ssum

ing

the

ball

clos

ely

appr

oxim

ates

a

blac

kbod

y,de

term

ine

a.th

eto

talb

lack

body

emis

sive

pow

er

b.th

eto

tala

mou

ntof

radi

atio

nem

itted

byth

eba

llin

5m

in

c.th

esp

ectr

albl

ackb

ody

emis

sive

pow

erat

aw

avel

engt

hof

3m

. 24

c.th

esp

ectr

albl

ackb

ody

emis

sive

pow

erat

aw

avel

engt

hof

3m

.

Inte

nsity

of R

adia

tion

••Intensity

Intensity

ofofRadiation

Radiation::

the

rate

ofen

ergy

leav

ing

asu

rfac

e

ina

give

ndi

rect

ion

per

unit

solid

angl

epe

run

itar

eaof

the

emitt

ing

surf

ace

norm

alto

the

mea

ndi

rect

ion

insp

ace.

25

Inte

nsity

of R

adia

tion

••Solid angle:

Solid angle:

port

ion

of s

pace

insi

de a

sph

ere

encl

osed

by

a

coni

cal s

urfa

ce w

ith th

e ve

rtex

of t

he c

one

at th

e ce

nter

of

the

sphe

re. T

he s

olid

ang

le is

den

oted

by

ωan

d its

uni

t is

the

ster

adia

n(s

r).

26

slice of a pizza is plane angle

slice of a water melon is solid

angle

Inte

nsity

of R

adia

tion

Rad

iatio

nin

tens

ityis

used

tode

scrib

eho

wth

eem

itted

radi

atio

nva

ries

with

the

zeni

than

daz

imut

han

gles

.

27

Pro

ject

ed A

rea

The

area

,dA

1,as

seen

from

the

pros

pect

ive

ofa

view

er,

situ

ated

atan

angl

eθ

from

the

norm

alto

the

surf

ace,

will

appe

arso

mew

hats

mal

ler,

asco

sθ�

dA1.

Thi

ssm

alle

rar

eais

term

edth

epr

ojec

ted

are

a

28

29

Let,

dA1

will

cor

resp

ond

to th

e em

ittin

g su

rfac

e or

the

sour

ce.

dA2

will

cor

resp

ond

to th

e re

ceiv

ing

surf

ace

or th

e ta

rget

.

The

are

a pr

oscr

ibed

on

the

hem

isph

ere

dA2

ca

n be

writ

ten

as

Relationship Between Emissive Power and

Intensity

30

31