Question

Imagine that a sphericalMirror gives an Image magnified 5times at a distance 5cm. If so ditermine WhetherThe mirror is concave Or convex? Calculate the focal length? ​

Answer 1

Answer:

Explanation:

Given:-

v = 5 cm

To Find :-

focal length, f = ??

Formula to be used:-

Mirror formula, 1/v + 1/u = 1/f

Magnification = - v/u

Solution:-

The  mirror is concave because image is magnified 5 times the object.

Putting the formula, we get

m = - v/u

⇒ 5 = -5/u

⇒ u = - 1 cm

Now, 1/v + 1/u = 1/f

⇒ 1/5 + 1/- 1 = 1/f

⇒ 1/5 - 1 = 1/f

⇒ 1/f = - 4/5

⇒ f = - 5/4

⇒ f = - 1.25 cm

Hence, the focal length of the concave mirror is 1.25 cm.

Answer 2

Explanation:

Given -

v = 5 cm (image distance)

m = 5 (magnification)

To Find -

The focal length

As we know that :-

• m = -v/u

» 5 = -(5)/u

» u = -5/5

• » u = -1

Now,

As we know that :-

• 1/f = 1/v + 1/u

here,

f = focal length

v = image distance

u = object distance

» 1/f = 1/5 + 1/(-1)

» 1/f = 1/5 - 1

» 1/f = 1-5/5

» 1/f = -4/5

» f = -5/4

• » f = -1.25 cm

Hence,

The focal length of the mirror is -1.25 cm

And

The mirror is concave.