Question

A boy uses vernier calipers to measure the thickness of his pencil. He measures it to be 1.4 mm. if the zero error is +0.02 cm, what is the correct thickness of the pencil?
(A) 1.3 mm
(B) 1.2 mm
(C) 1.02 mm
(D) 1.20 mm

Answer 1

Hint We know that if we have to find the correct thickness of an object then we will have to add or subtract the zero error in the measured value.
We can formulate it as follows:
Actual reading $$\text{ = }$$Observed reading $$\text{ - }$$Excess reading (zero error)

Complete step by step answer
Given:
Observed reading: 1.4 mm
Excess reading (zero error): +0.02 cm (here the positive sign indicates positive zero error) i.e., 0.2 mm
To find:
Actual reading: _______
Here, we will use the formula,
Actual reading $$\text{ = }$$Observed reading $$\text{ - }$$Excess reading (zero error)
$$\Rightarrow$$actual reading 1.4 – 0.2
$$\Rightarrow$$actual reading = 1.2 mm

Hence, the correct answer is option (b.).

Note It is important to convert the values into the same units. As you can see in the above solution, the units of zero error and measured value were different. In this case we cannot apply any operation on them. Also, the zero error can be both positive and negative, so one needs to be careful while substituting the values in the formula. As the formula also contains a minus sign.