Significant Figures and its Rules

Most simplified notes to understand the concept of  Significant Figures in Physics Class 11

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The significant figures express the accuracy of a measured value. More significant figures we use to express a value, the more accurate a value is.

The significant Figures of a measured  value can be expressed as the number of digits used to express a value in which we have confidence.

Example: 

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Consider, we measure the length of a road. We are 3 people there to measure the length one by one. The 1st person measures the length as 2 m. 2nd person measures as 2.1 m and the 3rd one measures it as 2.11 m.

All three persons measured the approximate value of about 2 m. But the 3rd person tried to find the value in more significant figures as he used 3 digits to express the value. Hence the 3rd value is more accurate. The number of significant figures in the  3rd value is 3, in 2nd value is 2, while in the 1st value the significant figure is 1.

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Rules to find significant figures of a value:

1. All non - zero digits are significant. Ex.- 2314, 22.13 ; in both examples the significant Figures are 4.

2. Trailing zeros on the right end are insignificant (for non decimal value). Ex.- in 42000 and 3200 the significant figures are 3 and 2 respectively. Trailing zeros on the right end will not be counted.

3. In decimal values, the zeros on the right end after decimal are significant. Ex.- In 23.200, the rightmost zeros are countable. The significant Figures are 5.

4. For less than one or decimal values, the zero on the left is insignificant. Ex.- in 0.2 or 0.03, the significant figure is 1. Zeros on the left are not countable.

5. All zeros between two non zero numbers are significant. Ex.- 1004 ( significant figures are 4).

6. Change of units doesn't change numbers of significant figures. Ex.- in 25 m, the significant figures are 2. If we change the unit in cm then we write it as 2500 cm or 25 ×102, i.e. the significant figures are still 2.

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Physics Class 11 ( based on new revised syllabus )

1. Physical world

• Physical world, part -1
• Scope and excitement of Physics, part -2
• Nature of physical laws, part - 3

2. Units and Measurements

• Units and Measurements, part-1
• Length, mass and time Measurements
• Estimation or Calculation of errors