Question

an object is situated at a distance of 0.1m from the pole of a mirror such that a virtual image is produced by the mirror at 0.3 m state nature of mirror and find focal length​

Answer 1

Answer :-

→ The mirror is a concave mirror.

→ Focal length of the mirror is 0.15 m .

Explanation :-

We have :-

→ Distance of the object (u) = 0.1 m

→ Distance of the image (v) = 0.3 m

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According to sign convention :-

• u = -0.1 m

Now, from the formula of magnification of a spherical mirror :-

m = -(v/u)

⇒ m = -(0.3/-0.1)

⇒ m = -(-3)

⇒ m = +3

Since magnification is postive and image formed is virtual [larger than object], so we can say that the mirror is concave .

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According to mirror formula, we have :-

1/v + 1/u = 1/f

⇒ 1/0.3 + (-1)/0.1 = 1/f

⇒ 10/3 - 10 = 1/f

⇒ (10 - 30)/3 = 1/f

⇒ -20/3 = 1/f

⇒ -20f = 3

⇒ f = 3/-20

⇒ f = -0.15 m

[We got value of 'f' as negative, as focal length is always negative for a concave mirror.]

Answer 2

Answer:

1. concave mirror
2. 0.15m

Explanation:

Solution:

Distance from the object(u)=0.1m

Distance from the image(v)=0.3m

By using the formula of magnification of a spherical mirror we can say this mirror is of what kind

Sign convention-u=-0.1

m=-(v/u)

m=-(0.3/-0.1)

m=-(-3)

m=3

So the answer is in postive and image is virtual so it is a concave mirror.

Now, using the mirror formula we find the focal length-

1/v+1/u=1/f

1/0.3+1/-0.1=1/f

10/3-10=1/f

10-30/3=1/f

-20/3=1/f

f=-3/20

f=-0.15

It is always negative for convex not for concave so answer is in positive-0.15m