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| Sign Conventions and Rules for Drawing Ray Diagrams |
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| These new cartesian sign conventions adopted during measurements are as follows: |
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 All distances are measured from the pole of spherical mirrors. |
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Distances measured in the direction of incidence of light are taken as positive, and when measured in a direction opposite to the direction of incidence of light is taken as negative. |
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The heights measured upwards to the principal axis are taken as positive and negative if measured downwards. |
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Any ray of light traveling parallel to the principal axis, after reflection pass through the focus or appears to diverge from the focus. |
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| Curvature Reflects |
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Any ray of light passing through the centre of curvature reflects along the same path. |
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A ray of light initially passing through the focus after reflection travels parallel to the principal axis. |
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