Muchidzidzo fundoyetsimba, rupambuko rwechiedza (refraction of light in English) zvinoreva kubhenda nokushanduka kwakanangwa kunoitika kana masaisai achipfuura muhwendedzo (medium) hwakasiyana. Panoshanduka hwendedzo, muchacha wesaisai unoshanduka asi frequency yemasaisai haishanduke. Rupambuko rwechiedza runoonekwa kana masaisai achisvika pahwendedzo negonyo risiri 90o kana 0o. Rupambuko runonyanya kuonekwa pamasaisai echiedza, asi unoitikawo kana masaisai emuriro achipfuura muhwendedzo hwakasiyana. Rupambuko runoitika kana masaisai emvura achipfuura mumvura yakadzika zvakasiyana. Chiitiko chekukombamiswa kana kutsaudzwa kwechiedza pakati pehwendedzo huviri chinotsanangurwa nemutemo waSnell unonyorwa sezvinotevera: Pane hwendedzo huviri huri kudarikwa nesaisai rine dendera pa mineti rakafanana, rheshiyo yemasine egonyo rokusvika θ1 negonyo rerupambuko θ2 yakaenzana nerheshiyo yemuchacha muhwendedzo mbiri (v1 / v2). Zvakare rheshiyo idzi dzakaenzana nemusunamiswa werheshiyo dzemutendeki werupambuko, (n2 / n1): sin ⁡ θ 1 sin ⁡ θ 2 = v 1 v 2 = n 2 n 1 . {\displaystyle {\frac {\sin \theta _{1}}{\sin \theta _{2}}}={\frac {v_{1}}{v_{2}}}={\frac {n_{2}}{n_{1}}}.}