Answer to Question #211230 in Optics for Tawanda

Question

A tarantula of height h sits cautiously before a spherical mirror whose focal length has

absolute value | f | = 40 cm. The image of the tarantula produced by the mirror has the

same orientation as the tarantula and has height hꞌ= 0.20h.

(a) State with reasons, the image location and determine whether it is real or not.

(b) Determine the focal length f (sign included) of the mirror and hence deduce whether it

is a concave or convex mirror. [3,3]

Answer 1

(a)

• Location: Behind the mirror. The image is virtual. Reasons: The reflected image is upright. This means that the mirror is convex. Once we know this, it is clear that convex mirrors always produce virtual, upright images which are located behind the mirror and are smaller than the object.

(b).

• -40cm. The mirror is convex.
• Note that the focal length for a convex mirror is negative.