Question

The power of lens is 2.5D. What is the focal length and the type of lens

Answer 1

Explanation:

1. Power P = 1/f = 2.5D 

Power P = 1/f = 2.5D f = 1/P = 100/2.5 = 40cm

Power P = 1/f = 2.5D f = 1/P = 100/2.5 = 40cmHere f = 40cm which is positive, it means the lens is a convex lens.

 

 2. In case of a concave f is negative. So in the question f = -30cm

 2. In case of a concave f is negative. So in the question f = -30cmMagnification m = -v/u = 3.

 2. In case of a concave f is negative. So in the question f = -30cmMagnification m = -v/u = 3.It means v = -3u.

 2. In case of a concave f is negative. So in the question f = -30cmMagnification m = -v/u = 3.It means v = -3u.Mirror formula = 1/f = 1/v + 1/u

 2. In case of a concave f is negative. So in the question f = -30cmMagnification m = -v/u = 3.It means v = -3u.Mirror formula = 1/f = 1/v + 1/u1/ (-30) = 1/(-3u) + 1/u

 2. In case of a concave f is negative. So in the question f = -30cmMagnification m = -v/u = 3.It means v = -3u.Mirror formula = 1/f = 1/v + 1/u1/ (-30) = 1/(-3u) + 1/u-1/30 = 1/u – 1/3u

 2. In case of a concave f is negative. So in the question f = -30cmMagnification m = -v/u = 3.It means v = -3u.Mirror formula = 1/f = 1/v + 1/u1/ (-30) = 1/(-3u) + 1/u-1/30 = 1/u – 1/3u-1/30 = 3/(3u)

 2. In case of a concave f is negative. So in the question f = -30cmMagnification m = -v/u = 3.It means v = -3u.Mirror formula = 1/f = 1/v + 1/u1/ (-30) = 1/(-3u) + 1/u-1/30 = 1/u – 1/3u-1/30 = 3/(3u)u = -20cms

 2. In case of a concave f is negative. So in the question f = -30cmMagnification m = -v/u = 3.It means v = -3u.Mirror formula = 1/f = 1/v + 1/u1/ (-30) = 1/(-3u) + 1/u-1/30 = 1/u – 1/3u-1/30 = 3/(3u)u = -20cmsIt means the object is placed 20cms in front of the mirror. Since focal length is -30 cm ,it means the object is placed between focus and optical centre.

hope its helpful for you ✔✔✔✔✔

Answer 2

Answer:

Explanation:

P=2.5D

F=1/P

F=1/2.5

F=10/25

F=0.4m

F=40m

Here f = 40cm which is positive, it means the lens is a convex lens.