Critical angle for glass (n=1.5) to air: MCQ with Answer and Explanation

Critical angle for glass (n=1.5) to air:
A. 42°
B. 90°
C. 30°
D. 60°
Answer: Option A
Solution (By JKSSB Mock Tests)
sinθ_c = n₂/n₁ = 1/1.5 = 2/3 ⇒ θ_c = sin⁻¹(0.667) ≈ 42°. Total internal reflection condition. Memory tip: 'θ_c = sin⁻¹(1/n) for denser to air'. Optics calculation frequently tested in competitive exams with standard refractive indices.

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Question #1
What is the equivalent capacitance when three capacitors of 3 microfarads each are connected in series?
A. 0.33 microfarads
B. 1 microfarad
C. 9 microfarads
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Correct Answer: Option B


Explanation:
The formula for capacitors in series is exactly the opposite of resistors. 1/C_eq = 1/C1 + 1/C2 + 1/C3. Here, all are 3 uF. So, 1/C_eq = 1/3 + 1/3 + 1/3 = 3/3 = 1. Therefore, C_eq = 1 microfarad. When identical capacitors are in series, you simply divide the capacitance by the number of capacitors (3/3 = 1).

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Question #2
The working of a rocket is based on
A. Conservation of linear momentum
B. Newton's first law
C. Law of gravitation
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Correct Answer: Option A


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A wire of resistance 9 Ω is bent to form an equilateral triangle. The resistance across any two vertices is
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Correct Answer: Option B


Explanation:
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