Geometric Optics- Two Questions

[_Pistolkisses]

1.Determine the magnification of a 5cm object that has been placed 20 cm in front of a lens with a power of -2.5 d?

2. Light strikes a rectangular piece of crown glass with an angle of incidence of 30 degrees. If the block of glass is 10cm, determine the measure of lateral displacement.

Can anyone give me the steps to solving these? I'm kind of having a hard time.

It would really be appreciated.:shy:

 

[Chi Meson]

1. use the thin-lens equation to find the image distance, then use the magnification equation to determine the magnification. The "5 cm" is extraneous information.

2. Draw the ray as it refracts through the glass. Find the angle of refraction. Do a little trig.

 

[ghulam]

p=-2.5d
f=-1/2.5=-0.4
i/f=i/v-i/u
-2.5=1/v-(-1/(20/100))
-2.5=1/v+5
1/v=-7.5
m=v/u
(1/-7.5)/(-20/100)
(1/-7.5)*-5
2/3
thus, it is a concave lens