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Question

An object is placed between two plane mirrors inclined at angle of 30° to each other. How many images do you expect to see?

The correct answer is

11

Understanding Image Formation by Inclined Plane Mirrors

When an object is placed between two plane mirrors that are inclined at a certain angle to each other, multiple images are formed due to successive reflections. The number of images formed depends on the angle between the two mirrors.

Calculating the Number of Images

The formula used to calculate the number of images (\(n\)) formed by two plane mirrors inclined at an angle \(\theta\) is generally given by:

\(n = \frac{360^\circ}{\theta} - 1\)

This formula is applicable when the object is placed symmetrically or asymmetrically, provided that \(\frac{360^\circ}{\theta}\) is an integer. If \(\frac{360^\circ}{\theta}\) is not an integer, the number of images is often taken as the integer part of \(\frac{360^\circ}{\theta}\), depending on the object's position, but for integer results, the formula \(\frac{360^\circ}{\theta} - 1\) is standard and represents the total distinct images visible, excluding the object itself.

Applying the Formula for 30 Degrees

In this question, the angle between the two plane mirrors is given as \(30^\circ\).

Here, \(\theta = 30^\circ\).

First, let's calculate the value of \(\frac{360^\circ}{\theta}\):

\(\frac{360^\circ}{30^\circ} = 12\)

Since 12 is an integer, we can use the formula \(n = \frac{360^\circ}{\theta} - 1\) to find the number of images.

Substituting the value into the formula:

\(n = 12 - 1\)

\(n = 11\)

Therefore, you can expect to see 11 images when an object is placed between two plane mirrors inclined at an angle of 30 degrees to each other.

Let's summarize the calculation:

Quantity Value Formula Step
Angle between mirrors (\(\theta\)) \(30^\circ\) Given
Calculate \(\frac{360^\circ}{\theta}\) \(\frac{360^\circ}{30^\circ} = 12\) Step 1
Number of images (\(n\)) \(12 - 1 = 11\) Step 2 (\(\frac{360^\circ}{\theta} - 1\))

The calculation confirms that 11 images are expected to be seen.

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Important Questions from Mirrors and Images

  1. Which one of the following telescopes contains only mirrors?

  2. The correct relation between the radius of curvature R and focal length f of a spherical mirror is

  3. Spherical mirror formula relating an object distance ‘u’, image distance ‘v’ and focal length of mirror ‘f’ may be applied to a plane mirror when

  4. The image of an object formed by a plane mirror is

  5. The image we see in plane mirror is

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