§ 3. Kß'ict of boniiilarici^. litfltvtion and ll( fntcliun. 



When a wave, wlutlii'v iiciiiiimI m- tniiisvcrsc, iiU'ut.-^ a siirfiict' svparatiiiLC tin' 

 nii'iliiiiii in wliicli it is travi'lliiii;- iVnni aiiotluT n\i'iliiiin, it will in nvncral siilVcr 

 icllii'tinn an<l retraction. Tlio lines tit' transit dl' the nllceled and ref'raeleil 

 \\a\e-- will lie in (lie [ilaiie wliieli eonliins the line nt'tiansil dl'tiie incident wave 

 and the nurnial tu the separatinj:; siiil'ace. 



The .-iniplest fitsi; is that in which Imth media are thiiil, and eiinseiiiieiiily 

 I 111- incident, the rcHected and the rel'racte«! waves are all nCthc normal ty|ie. In 

 till- lifijliro, let All lie the liiiiindin;; snrl'ace hefween two llnid nitdia. and ''l' 

 the direction "f |»r(ijiairatiiin nf the inciduit wave. MX is diawn MMinial 1^ 

 the .■-iirt'ace Ali. 



B 



A wave is reflected liacl< iiii i the first medium aloni:; tiic line PQ, and 

 anidher wave is tnni-mitted intu the .second nii'dinm alonu: a ceitain line J'(j,. 

 'I'hi' an^^lc 0PM >n- H i> called th ■ an;ile ol' iM.i.lcncM', ',',/'A' or ", i.- c:i!l<d the 

 an;rle cf refraction and ('I'M the ;,iiude of rclicclion. <tl\]/ i- ■■ |nai to (/I'M, 

 \\ hilc il^ and » are conned cd liy tic e [nation 



sill It sin '/, 

 where V i- the vcjocitv of transit of the inciihnl wave, and V, i~ the velocity of 

 tian-it of the wave tran-mllt"d into th'.' second medinm. 



In the ca-e re|ire.scnlcd in the tiirnrc \, is less than V, and there will lie a 

 refnicli'd wave whatcvei' l»' the .-uij^le of incidence. II tie- \clociiv in ihi' -I'concl 

 mi'dium were tin- greater of iln- two, the refrac|ci| wave wonhl he licnl away fmm 

 in-lead oi towards the normal, and hy increa.-iiij; the anjjle of iinidiMice snlli- 

 ciciiilv we .-hoiild have l'(i^ coincidini; with I'/l. 'I'hi- would occui- when 

 V 



II -- -\\\ 



At ihi- or aii\- irrc.ii'i' .iii^Ii- df iiK'ide loi.d icili-.tion woul 



take |i!ac<' ; the incident wave would he re.-tored to the lower medinm without 

 loxs of eiicrjry, mid with no otiii-r rlian(j;e than a ehanne of direction and a ciiaiiKc 

 of |iii:is4-. 



