( ( When ( ( ( the ( parallel rays ) ) ( of ( a ( light source ) ) ) ) ( strike ( a ( convex lens ) ) ) ) ) ( ( the rays ) ( ( will ( ( ( concentrate or ) focus ) ( at ( ( ( a ( specific point ) ) , ) ( the ( focal point ) ) ) ) ) ) . ) ) )
(ROOT (S (SBAR (WHADVP (WRB When)) (S (NP (NP (DT the) (JJ parallel) (NNS rays)) (PP (IN of) (NP (DT a) (JJ light) (NN source)))) (VP (VBP strike) (NP (DT a) (NN convex) (NN lens))))) (NP (DT the) (NNS rays)) (VP (MD will) (VP (VB concentrate) (CC or) (VB focus) (PP (IN at) (NP (NP (DT a) (JJ specific) (NN point)) (, ,) (NP (DT the) (JJ focal) (NN point)))))) (. .)))
When the parallel rays of a light source strike a convex lens the rays will concentrate or focus at a specific point, the focal point .
(ROOT (S (NP (NNP Convex) (NNS lenses)) (VP (VBP are) (NP (NP (JJR thicker)) (PP (IN in) (NP (DT the) (NN middle)))) (PP (IN than) (PP (IN at) (NP (DT the) (NNS edges)))) (SBAR (IN so) (S (NP (PRP they)) (VP (VBP cause) (S (NP (NP (NNS rays)) (PP (IN of) (NP (NN light)))) (VP (TO to) (VP (VB converge) (, ,) (CC or) (VB meet) (, ,) (PP (IN at) (NP (NP (DT a) (NN point)) (VP (VBN called) (NP (NN focus)))))))))))) (. .)))