Year 12s: what will be the first way you research your future options? >>

Image Distance calculation?

Converging lens of focal length 5 cm with the following object distance 15cm.

The answer given is 7.5 cm, but I am at a total loss how they got that figure.

I am also asked to describe the image produced.

I said it would be Diminished, Imagined and Real; because Distance >2f.

I am also asked for Converging lens of focal length 5 cm with the following object distance 2cm.

I said this would be Magnified, Upright and Virtual because Distance <f

The image distance is given as 3.3cm

Can someone help me please, show me the technique for calculating image distance correctly :frown:

Reply 1

Joinedup

Original post by apronedsamurai

o=object distance
i=image distalce
f=focal length

thin lens equation
1/f = 1/o + 1/i

e.g.

1/i = 1/f - 1/o
1/i = 1/5 - 1/15
1/i =3/15 - 1/15
1/i = 2/15
i= 15/2 = 7.5

see also http://www.physicsclassroom.com/class/refrn/Lesson-5/The-Mathematics-of-Lenses