Question

Three boys A, B, and C are measuring the length of a block from three different positions as shown. Who will report the maximum value of measurement?

• A. Boy B
• B. Boy A
• C. Both boys A and B will report the same maximum value of measurement.
• D. Boy C

Answer 1

The correct option is D Boy C

All three boys A, B, and C will report different value of measurement.
The difference in the reading of scale is due to different angle of vision. Parallax error is apparent change in position of the reading as viewed from different angles.

The correct way of taking a measurement is when the observer's eye is directly in line with the marking, making 90 degrees with the scale as in B's case.

If we extend the line of vision of boy A, it will read the value less than the value read in case of boy B.

Also, If we extend the line of vision of boy C, it will read the value more than the value read in case of boy B.

So, among all the boys, boy C will report maximum value of measurement.