Ncert Exercises & Solutions

The mean length of an object is 5 cm. Which of the following measurements is most accurate?
1. 4.9 cm
2. 4.805 cm
3. 5.25 cm
4. 5.4 cm

Hint: The accuracy of a measurement depends on the closeness of the measurement to the true value.

Step 1: Find the difference between the measured values and the true value.
Given length l = 5 cm
Now, checking the errors with each option one by one, we get:

$\begin{array}{l} {Δl}_{1} = 5 - 4 .9 = 0 .1 cm \\ {Δl}_{2} = 5 - 4 .805 = 0 .195 cm \\ {Δl}_{3} = 5 .25 - 5 = 0 .25 cm \\ {Δl}_{4} = 5 .4 - 5 = 0 .4 cm \end{array}$

Step 2: Find the most accurate value.

Error $∆ l_{1}$ is the least.
Therefore, 4.9 cm is the most precise.
Hence, option (1) is the correct answer.

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