A meter scale is held vertically in front of a plane mirror of length 15cm. A student peeps through a hole at 40cm mark. Sir you can refer to nso class 8th achiever section of 2014 question paper. The range of the scale of the meter ruler that can be seen? If the hole is at 80cm mark of the scale, then the range of the meter ruler that can be seen in mirror is?

For student's eye to see the range of the ruler i.e. the maximum reading and the minimum reading, the eye must look at the two extreme ends of the 15 cm mirror. Here, we use the fact that angle of incidence is equal to angle of reflection to show the range that can be seen by the eye through the mirror. If the student and the object is at the same perpendicular distance away from the mirror, the image seen through the mirror is twice as much as the size of the mirror. For this case a 15 cm mirror can see a range of 30 cm.
 

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The Answer for the 46th question is (c) because since form the hole the plane mirror is at a height of 10 cm, since the angle of incidence is equal to angle of reflection, hence if there would be a hole at 30 cm then the angle of reflection of 20 cm will be seen through the eye and if the hole is at 45 cm then according to the law of reflection the reflection of 50 cm would be seen.....hence the answer for the 46th question is 20cm-50cm..

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