An object 20 cm high is placed at a distance of 90 cm from a plane mirror, the size of image will be :

Options

A. 20 cm
B. 90 cm
C. 180 cm
D. 40 cm

Answer

To solve the problem of finding the size of the image formed by a plane mirror when an object of height 20 cm is placed at a distance of 90 cm from the mirror, we can follow these steps:

### Step-by-Step Solution:

1. **Identify the Object Height**:
The height of the object (h_o) is given as 20 cm.

2. **Understand the Properties of Plane Mirrors**:
A plane mirror has the property that the image formed is of the same size as the object. This means that the height of the image (h_i) will be equal to the height of the object.

3. **Determine the Image Height**:
Since the image formed by a plane mirror is of the same height as the object, we can conclude:
\[ h_i = h_o = 20 \text{ cm} \]

4. **Consider the Orientation of the Image**:
The image formed by a plane mirror is also erect (upright) and virtual. This means it appears to be behind the mirror and cannot be projected onto a screen.

5. **Final Answer**:
Therefore, the size of the image is 20 cm.

### Summary:
The size of the image formed by the plane mirror is **20 cm**.

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