Question

6) consider a double convex thick lens in air with radiu curvature of 30cm and 40cm for front and back surfaces, respectively, and q thickness of 10cm. calculate the lens power. use n=1.5 for the glass.

a) 0.46D

b) 3.13D

c) 3.04D

d) 2.78D

e) 2.92D

Answer 1

we have been given a double conves lens=>

radius of curvature of front surface = R1 = + 30 cm = 0.3 m

radius of curvature of back surface = R2 = - 40 cm = - 0.4 m as back side is also convex.

the refractive index n = 1.5

Thickness d = 10 cm = 0.1 m

the power P is given as :=>

P = ( n -1 )( 1/R1 - 1/R2 + ( n-1 )d/(nR1R2) )

so we put in the values=>

P = ( 1.5 -1 )( 1/0.3 - ( 1/(-0.4) + 0.5x0.1/( 1.5 x 0.3 x (-0.4) ) )

P = 0.5 x ( 10/3 + 10/4 - 5/18 )

P = 0.5 x ( (120 + 90 - 10) /36 ) = 2.777 D

OPTION D is correct.

-=-=

Hope it helps!

Have a nice day!