Question

TA
plane mirrors?
2. To get 3 multiple images, what should be the angle between two
(A) 120° (B) 60° (C) 90° (D) 30°​

Answer 1

Required Answer:

→ Option C (90°)

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Let's understand briefly!

$\boxed { \large \bf \red { Concept : }}$

Here, the concept of multiple reflections has been used. To calculate the number of images of an object placed between two mirrors can be found from the formula:

$\boxed { \sf \pink { No. \: of \: images \: formed = \dfrac{{360}^{\circ} }{\theta} -1 }}$

Where,

$\theta$ is the angle between the mirrors.

So, let us substitute the values of the angles given in the options and check out which one is correct.

Now, 1st option: (120°)

$\rm { No. \: of \: images \: formed = \dfrac{{360}^{\circ} }{{120}^{\circ} } -1 }$

$\rm {No. \: of \: images \: formed = 3 -1 }$

${\underline {\boxed {\bf \gray { 2 \: images } }}}$

So, this option is incorrect.

2nd option: (60°)

$\rm { No. \: of \: images \: formed = \dfrac{{360}^{\circ} }{{60}^{\circ} } -1 }$

$\rm {No. \: of \: images \: formed = 6 -1 }$

${\underline {\boxed {\bf \gray { 5 \: images } }}}$

So, this option is incorrect.

3rd option: (90°)

$\rm { No. \: of \: images \: formed = \dfrac{{360}^{\circ} }{{90}^{\circ} } -1 }$

$\rm {No. \: of \: images \: formed =4 -1 }$

${\underline {\boxed {\bf \green { 3 \: images } }}}$

So, this option is correct.

Therefore, option C is the correct.

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Note:

• The number of images formed by the two plane mirrors increases when the angle between the two mirrors decreases.

• When the angle between two mirrors are parallel to each other, infinite images are formed.

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