An object is placed 10 cm from a diverging lens which forms an image 6.5 cm from the lens. What is the focal length of the lens?

Asked by RAHUL rd | 22nd Nov, 2014, 10:33: PM

Expert Answer:

Given that:
The object distance,u = -10cm
The image distance ,v= -6.5 cm
Let f be the focal length of the lens.
According to lens formula we know that:

begin mathsize 14px style 1 over straight f equals 1 over straight v minus 1 over straight u 1 over straight f equals fraction numerator 1 over denominator minus 6.5 end fraction minus fraction numerator 1 over denominator minus 10 end fraction 1 over straight f equals fraction numerator minus 10 minus minus 6.5 over denominator minus 6.5 cross times minus 10 end fraction equals fraction numerator minus 3.5 over denominator 65 end fraction straight f space equals minus 18.6 space cm end style

Given that it is a diverging lens ,i.e. concave lens.The focal length of a concave lens is - ve.
So the focal length of the lens =-18.6 cm

Answered by Jyothi Nair | 22nd Nov, 2014, 11:59: PM