Question

The least count of vernier calipers is 0.01cm, and if the zero mark of the vernier scale is to the right of zero of the main scale and the vernier coincides with 7 when the jaws are in contact, then the zero error is_______cm.
$
  {\text{A}}.{\text{ + 6}} \times {\text{0}}{\text{.01}} \\
  {\text{B}}{\text{. + 7}} \times {\text{0}}{\text{.01}} \\
  {\text{C}}{\text{. - 7}} \times {\text{0}}{\text{.01}} \\
  {\text{D}}{\text{. - 6}} \times {\text{0}}{\text{.01}} \\
$

Answer 1

Hint: The zero error can be found by multiplying the least count of the vernier with the number of divisions which is coinciding with the zero of the main scale. It depends on whether it is to the left or right that zero error needs to be added or subtracted from a reading.

Step by step solution:

Vernier calipers are an instrument used to accurately measure lengths. This precision up to which certain length can be measured using it is called least count. The least count of given vernier calipers is 0.1 cm.
Zero error is the situation when the instrument gives a measurement when the jaws are closed and actual measurement should be zero.

Zero errors are of two types:

a.)Positive zero error: When the instrument gives a positive value when its jaws are closed, it is called the positive zero error. It needs to be deducted from the final reading.

b.)Negative zero error: When the instrument gives a negative value when its jaws are closed, it is called the negative zero error which needs to be added to the final value.

The zero error of vernier calipers equal to the product of least count with the value of division with which the zero coincides when jaws are closed.

For the given instrument,
$L.C. = 0.01cm$
Division coinciding with zero = 7

The zero of the vernier scale is to the right of the zero of the main scale, this means it is positive zero error and must be subtracted from the final reading.

Therefore, the zero error

$ = - 7 \times 0.01cm$

And the correct answer is option C.

Note: The type of zero error needs to be calculated carefully. If zero vernier calipers are to the right of zero of the main scale then zero error needs to be added to the final reading. It is necessary to find zero error to ensure accuracy of measurement.