Question

Accuracy is defined as:
(A) A measure of how often an experimental value can be repeated.
(B) The closeness of a measured value to the real value.
(C) The number of significant figures used in a measurement.
(D) None of these

Answer 1

Hint: To answer this question, we have to elucidate each of the three statements given in the options by considering an example from a particular experiment. From there we will be able to choose the correct option.

Complete step-by-step solution:
In an experimental data, we measure a number of values corresponding to a particular quantity. From these values we prepare a set of the experimental values. In this set, a particular experimental value may or may not repeat. A value which is not repeated at all in the experimental data can also be the most accurate value. So the accuracy has nothing to do with the repetition of an experimental value.
Therefore the option A is incorrect.
Now, the number of significant figures is used to measure the degree of the accuracy of the experimental values, not the accuracy itself. For example, let us consider an experiment for calculating the time period of a pendulum. Let us pick up two values from the set of observations, one equal to $1.1s$, and the other equal to $1.10s$.
We see that there are three significant figures in the first value, but four significant figures in the second value. The first value is only telling us that the time period is $1.1s$. But there may be a possibility that this value has been written after rounding off the actual value. So we do not get any idea about the digit at the second place after the decimal.
But the second value tells us that the time period is $1.10s$. So we are sure that the actual value at the second place after the decimal is equal to zero. There is no question of rounding off here, up to the first decimal place.
But again, the significant figure does not give us any idea about the accuracy of the measured value. It only tells us to what decimal place the given value is trustable.
Therefore, the option C is also incorrect.
Let us again consider the experiment stated above. Let us assume that the actual value of the time period is equal to $1.15s$. Let us pick up two values from the set of observations; $1.13s$ and $1.14s$. As we can clearly observe that the value $1.14s$ is more close to the actual value $1.15s$ than the value $1.13s$. So the value $1.14s$ is more accurate.

Hence, the correct answer is option B.

Note: In the measurement of an experimental quantity, we have another important term called as precision. It is often confused with accuracy. But we should always remember that the accuracy is the closeness of a particular value to the actual value, while the precision is the closeness of all the experimental values with each other.