Question

A rod AB of length 10 cm is placed in front of a concave mirror of focal length 20cm .the length of the image of AB formed by mirror is?

Answer 1

Answer:

hdjghvgjgvhcbcjgcfjwjshshhdydy dyyhh

Answer 2

Answer:

6.65 cm OR approx. 6.70 cm

Explanation:

Rod length = 10 cm

f = –20 cm

Radius of curvature, R= 2f= –40 cm

If $v_{1}$ = $\frac{fu_{1} }{u_{1} -f}$, with u1 = –40 cm,

then $v_{1} =\frac{(-20)(-40) }{-40-(-20)} = -40 cm$ ----------(1)

Similarly, $v_{2} =\frac{fu_{2} }{u-f}$, with u2 = -(40+10) = -50 cm,

then $v_{2} =\frac{(-50)(-20) }{-50-(-20)} = -33.35 cm$ ------------(2)

|$v_{1}$| – |$v_{2}$| = 40 - 33.35 = 6.65 cm is the length of the rod AB

NOTE: Do take care of using the sign conventions for f, u and v. For a concave mirror, f, u and v are always –ve.