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# A bird in air is diving vertically over a tank with speed 5cm/s Base of the tank is silvered A fish in the tank is rising upward along the same line with speed 2cm/s Water level is falling at a rate of 2cm/s Speed of the image of fish formed after reflection in the mirror as seen by the bird in cm/s

- 8
- 6
- 3
- 4

## The correct answer is: 3

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### A bird in air is diving vertically over a tank with speed 5cm/s Base of the tank is silvered A fish in the tank is rising upward along the same line with speed 2cm/s Water level is falling at a rate of 2cm/s Speed of the image of fish as seen by the bird directly in cm/s is

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### Spherical aberration in spherical mirrors is a defect which is due to dependence of focal length ‘f’ on angle of incidence ‘ q ’ as shown in figure is given by where R is radius of curvature of mirror and q is the angle of incidence The rays which are closed to principal axis are called paraxial rays and the rays far away from principal axis are called marginal rays As a result of above dependence different rays are brought to focus at different points and the image of a point object is on a point For paraxial rays, focal length approximately is

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