# Concave mirrors - where is the object

• danago
In summary, a concave mirror with a focal length of 1m is used to magnify an object by a factor of 4. The object is located at a distance of 0.75m from the pole of the mirror. The formula used is 1/do - 1/di = 1/f, and using this formula, the correct answer is 0.75m.
danago
Gold Member
"A concave mirror of focal length 1m is used to magnify an object by a factor of 4. Where is the object in relation to the pole of the mirror?"

Heres what i did:
$$\begin{array}{c} M = \frac{v}{u} \\ \therefore 4 = \frac{v}{u} \\ \therefore v = 4u \\ \end{array}$$

$$\begin{array}{c} \frac{1}{f} = \frac{1}{u} + \frac{1}{v} \\ \therefore 1 = \frac{1}{u} + \frac{1}{{4u}} = \frac{5}{{4u}} \\ \therefore u = 1.25m \\ \end{array}$$

Where am i going wrong? According to my textbook, the answer is 0.75m.

Dan.

You are forgeting that M = -di/do

Formula = (1/do + 1/di) = (1/f)

So 4do = - di

1/do - 1/4do = 1

1/4do - 4/4do = 1

3/4do = 1

do = .75

Last edited:
Alt+F4 said:
3/4do = 1

do = .75

Right.

3/(4do) = 1 so do = .75

Last edited:

## 1. Where is the object located in front of a concave mirror?

The object is located in front of a concave mirror between the center of curvature and the focal point.

## 2. Can the object be placed anywhere in front of a concave mirror?

No, the object must be placed within the radius of curvature for a clear image to form.

## 3. How does the distance of the object from the mirror affect the image?

The distance of the object from the mirror affects the size and position of the image. The closer the object is to the mirror, the larger and closer the image will be. The further away the object is, the smaller and further away the image will be.

## 4. What is the relationship between the object and image in a concave mirror?

The object and image are always located on the same side of the mirror. The image will be inverted and can be either real or virtual, depending on the position of the object.

## 5. How does the shape of a concave mirror affect the image?

The concave shape of the mirror allows for light rays to converge at the focal point, resulting in an enlarged and inverted image. The more curved the mirror, the larger the image will appear.

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