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Physics

Assertion (A) : For an object placed symmetrically when the angle θ between the mirrors is 72°, the number of images formed is 4.

Reason (R) : If n = 360°/θ is odd, the number of images for an object placed symmetrically is equal to n.

  1. both A and R are true and R is the correct explanation of A
  2. both A and R are true and R is not the correct explanation of A
  3. assertion is false but reason is true
  4. assertion is true but reason is false

Reflection of Light

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Answer

assertion is true but reason is false

Explanation

Assertion (A) is true because as n=360°θ−1\text n = \dfrac{360°}{\text θ} - 1

Where:

θ = angle between the mirrors

n = number of images formed (if object is placed symmetrically)

Substitute, θ = 72° :

𝑛=360°72°−1=5−1=4\text 𝑛 = \dfrac{360°}{72°} − 1 = 5 − 1 = 4

Reason (R) is false because if angle θ° between the mirrors is such that 360°θ°\dfrac{360°}{\text θ°} is odd, then

(i) the number of images is n, when the object is placed asymmetrically between the mirrors.

(ii) the number of images is n - 1, when the object is placed symmetrically (i.e., on the bisector of the angle) between the mirrors.

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