Optical Instruments — Flashcards
NIOS · Class 12 · Physics
40 flashcards for Optical Instruments (NIOS Class 12 Physics) to test yourself on key terms and facts. Sample: "State the formula for magnifying power"
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State the formula for magnifying power of a simple microscope when the final image is formed at the least distance of distinct vision (D = 25 cm).
Answer
Formula: M = 1 + D/f Where: • M = magnifying power • D = least distance of distinct vision = 25 cm • f = focal length of the convex lens Key point: Smaller the focal length f, greater the magnifying…
A simple microscope has a focal length of 2.5 cm. Calculate its magnifying power. (D = 25 cm)
Answer
Given: • f = 2.5 cm • D = 25 cm Formula: M = 1 + D/f Step 1: M = 1 + 25/2.5 Step 2: M = 1 + 10 Step 3: M = 11 Answer: The magnifying power = 11 Verification: The lens with shorter focal length giv…
What is the magnifying power of a simple microscope in normal adjustment (image at infinity)?
Answer
Formula for normal adjustment: M = D/f Where: • D = least distance of distinct vision = 25 cm • f = focal length of the lens Note: In normal adjustment, the image is formed at infinity. • This is mo…
Why does a simple microscope use a convex lens of SHORT focal length?
Answer
Reason: Magnifying power M = 1 + D/f • As focal length f decreases, D/f increases, so M increases. • A lens with very short focal length gives a much larger magnified image. Real-world connection: •…
Define the following terms: (i) Near Point (ii) Least Distance of Distinct Vision (iii) Angular Magnification
Answer
(i) Near Point: The closest distance from the eye at which an object can be seen clearly. For a normal adult eye, it is approximately 25 cm. (ii) Least Distance of Distinct Vision (D): The minimum di…
What is 'Normal Adjustment' in an optical instrument? Why is it preferred?
Answer
Normal Adjustment: The condition where the final image is formed at infinity. For Simple Microscope: Object is placed at the focal point of the lens. For Telescope: The image formed by the objective …
Describe the construction and working of a Compound Microscope. What is the role of each lens?
Answer
Construction: • Two convex lenses mounted coaxially in a tube • Objective lens: Short focal length, small aperture, faces the object • Eyepiece: Short focal length, large aperture, faces the eye Work…
Write the formula for magnifying power of a compound microscope when the final image is at D. Explain each symbol.
Answer
Formula: M = (v₀/u₀) × (1 + D/fₑ) Or in approximate form (when u₀ ≈ f₀ and v₀ ≈ L): M = (L/f₀) × (1 + D/fₑ) Where: • v₀ = image distance from objective • u₀ = object distance from objective • f₀ = f…
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