Question

the focal length of david's lens is 50 cmcm . if rebecca stands in front of david at a distance of dodo and david perceives the position of rebecca at didi , what does dodo equal if the magnification is -0.50?

Answer 1

The distance of dodo is 150 cm.

What is focal length of lens?

The distance between a lens's center and its focal point is its focal length. A focal point is a location on the principal axis where, following refraction via the lens, light rays parallel to the principal axis either actually meet or appear to meet.

Given parameters:

the focal length of David's lens is: f = 50 cm.

magnification is: m = -0.50

We have to find: distance of dodo, that is, object's distance : u = ?

We know that:

u =f( 1/m -1)

⇒ u = 50(-1/0.50-1) = - 150 cm.

Hence, distance  is 150 cm.

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