A convex lens is dipped in a liquid whose refractive index

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A convex lens is dipped in a liquid whose refractive index is equal to the refractive index of the lens. Then its focal length will

1. remain unchanged
2. become zero
3. become infinite
4. become small, but non-zero

Correct Option: C

1	= (_ℓμ_g - 1)		1	-	1
f			R₁		R₂

where , _ℓμ_g = 1 is given

⇒	1	= (1 - 1)		1	-	1		= 0 ⇒ f = ∞
	f			R₁		R₂