Physical World & Measurement
Units, dimensions, significant figures and error analysis
Key Concepts
- SI base units: metre, kilogram, second, ampere, kelvin, mole, candela
- Dimensional analysis: used to check equations and derive relations
- Significant figures: reflect precision of a measurement
- Types of error: systematic, random, gross; absolute, relative, percentage
- Least count of an instrument limits measurement precision
Important Formulae
| Percentage error | ΔA/A × 100% |
| Error in product/quotient (A·B or A/B) | ΔZ/Z = ΔA/A + ΔB/B |
| Error in power (Aⁿ) | ΔZ/Z = n · ΔA/A |
| Dimensional formula of force | [MLT⁻²] |
| Dimensional formula of energy | [ML²T⁻²] |
Quick Tips
- Dimensionally incorrect equations are always wrong, but dimensionally correct ones may still be wrong (missing dimensionless constants).
- Errors add for sums and differences; fractional errors add for products and quotients.
- Round off: if the digit after the last significant figure is 5 and the preceding digit is odd, round up; if even, round down.
Sample Practice Questions
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The instrument used to measure very small distances of the order of 10⁻⁵ m is:
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Answer: Screw gauge
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Which physical quantity has the same dimension as that of Planck's constant?
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Answer: Angular momentum
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Dimensions of magnetic flux are:
Show answer
Answer: ML²T⁻²A⁻¹
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The number of significant figures in 3.0800 is:
Show answer
Answer: 5
Practice Questions
Practice 20 randomly selected NEET questions on Physical World & Measurement. Answers are revealed after each question.
Start Practice →Frequently Asked Questions
What are the key concepts in Physical World & Measurement for NEET?
SI base units: metre, kilogram, second, ampere, kelvin, mole, candela; Dimensional analysis: used to check equations and derive relations; Significant figures: reflect precision of a measurement; Types of error: systematic, random, gross; absolute, relative, percentage; Least count of an instrument limits measurement precision.
Which formulae are important for Physical World & Measurement in NEET?
Percentage error: ΔA/A × 100%; Error in product/quotient (A·B or A/B): ΔZ/Z = ΔA/A + ΔB/B; Error in power (Aⁿ): ΔZ/Z = n · ΔA/A; Dimensional formula of force: [MLT⁻²]; Dimensional formula of energy: [ML²T⁻²].
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