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Why is red light used as a danger signal...

Why is red light used as a danger signal ?

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BINA LIBRARY-Optics-I-EXERCISE
  1. Explain the origin of the blue colour of sky.

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  2. Explain why the setting sun looks red?

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  3. Why is red light used as a danger signal ?

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  4. Explain why yellow head-lights are used in cars in foggy weather.

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  5. In order to take colour photograph of a planet, what kind of telescope...

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  6. Why should a simple magnifying glass be placed closer to the eye ?

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  7. What is the best position for eye viewing an object through microscope...

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  8. Define beam of light.

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  9. Find the position of an object which when placed in front of a concave...

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  10. When an object is placed at a distance of 60 cm from a convex mirror, ...

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  11. An object is kept at 0.2 m from a convex lens of focal length 0.15 m. ...

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  12. A double convex lens made of glass of refractive index 1.5 has both ra...

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  13. Calculate the focal length of the combination of a convex lens of foca...

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  14. A converging lens has focal length of 20 cm in air. It is made of a ma...

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  15. Two lenses of powers, 15D and +5D are in contact with each other formi...

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  16. The refractive index of a prism of angle 60 degree is 1.62 for sodium ...

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  17. A ray of light incident on an equilateral glass prism shows minimum de...

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  18. A ray of light passes through an equilateral prism such that the angle...

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  19. An astronomical telescope of magnifying power 10 consists of two thin ...

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  20. A near point of hypermetropic person is 50 cm from the eye. What is th...

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