Explain why you cannot measure the focal length directly for a diverging lens. Using no more than four sentences, explain why the technique of placing the diverging lens touching another converging lens with the the light reaching the converging lens first, allows you to determine the focal length of the diverging lens.

Diverging lense can not find a real image because, when you extend the light rays, they diverse and never meet. To produce a real image the outgoing rays must converge. A convex lens acts as a converging lens when the object is beyond the near focal point which is when it forms real image, hence there is no image form and we can not Measure the focal length directly.

To measure the focal length of a diverging lens, we will first use a converging lens to create a real image. This real image will then become the object for the diverging lens. We will place the diverging lens such that the image formed by the converging lens is on the diverging lens’s back side

This two-lens system, one converging and one diverging lens, allows us to make a real image that can be viewed on a screen. Using the object and image distances from the diverging lens, the focal length of the diverging lens can be calculated by following equation

1       =   1     +       1

F               p               q

Where

f = focal length

p = object distance and

q = image distance