Units and MeasurementsNEET MCQs with solutions

Not quite — the answer is D.

Percentage error = (ΔA/A) × 100 = (0.2/25.0) × 100 = 0.8%. Option A (0.20%) is the trap for using the raw error value 0.2 directly as percentage without dividing by the measured value. Option B (0.40%) arises from halving the measured value incorrectly.

Not quite — the answer is A.

Accuracy means closeness to the true value. Precision means repeatability of readings. Least count is the smallest measurable value; sensitivity is the smallest detectable change. These are four distinct instrument properties.

Not quite — the answer is B.

Pressure = [ML⁻¹T⁻²]; Energy density = Energy/Volume = [ML⁻¹T⁻²]. Both match. Force [MLT⁻²] differs from Impulse [MLT⁻¹]. Power [ML²T⁻³] differs from Torque [ML²T⁻²].

Not quite — the answer is C.

The primary purpose of dimensional analysis is to verify dimensional homogeneity — every term in a physical equation must have identical dimensions. Unit conversion (D) is secondary; without homogeneity no equation can be physically valid.

Not quite — the answer is B.

Measurement is comparing an unknown quantity with a predefined standard unit. Speed of calculation and equation derivation depend on measurement but are not its primary purpose.

Not quite — the answer is C.

The CGPM (Conférence Générale des Poids et Mesures) is the international body that establishes and updates the SI system. UNESCO, WHO, and IAEA serve entirely different mandates and have no role in defining units.

Not quite — the answer is D.

A screw gauge has the smallest least count (~0.01 mm) among common instruments and is preferred for thin wire diameter. A vernier caliper (LC ~0.1 mm) suits larger dimensions such as cylinder outer diameters. Metre scale (1 mm) is far too coarse.

Not quite — the answer is B.

Significant figures include all certain digits plus the first uncertain digit. Leading zeros only locate the decimal point and are excluded. Captive zeros, trailing zeros after the decimal, and all non-zero digits are included.

Not quite — the answer is B.

Dimensions express how a physical quantity depends on the fundamental base quantities — e.g. velocity = [LT⁻¹]. Numerical value and unit are concepts separate from dimensions.

Not quite — the answer is D.

A physical balance compares unknown mass against standard masses and is the standard school laboratory instrument. A spring balance measures weight (force), a measuring cylinder measures volume, and an analytical balance is a specialised instrument used in advanced labs, not typical school settings.

Not quite — the answer is D.

The second (s) is the SI base unit of time. Minute (60 s), hour (3600 s), and day (86400 s) are accepted for practical use but are not SI base units.

Not quite — the answer is C.

Metre (m) is one of the seven SI base units. Newton (kg·m·s⁻²), joule (kg·m²·s⁻²), and watt (kg·m²·s⁻³) are all derived units formed from combinations of base units.

Not quite — the answer is A.

If the discarded digit is less than 5, the retained digit stays unchanged. The dropped portion is less than half a unit in the last retained place, so no correction is needed.

Not quite — the answer is C.

Experimental verification requires numerical data from measurements. Mathematical proof or dimensional consistency alone cannot substitute for measured values in confirming a law.

Not quite — the answer is C.

Speed = distance/time, derived from two base quantities. Mass, length, and time are all SI base quantities and cannot be derived from simpler physical quantities.

Not quite — the answer is D.

Statements I, II, III are correct. Statement IV is false — most physical quantities have dimensions; only ratios like refractive index or strain are dimensionless exceptions.

Not quite — the answer is A.

A unit is a defined, fixed magnitude of a quantity that serves as a reference for comparison. The numerical value and instrument are separate components of the measurement process.

Not quite — the answer is B.

A physical quantity requires both a number and a unit. Without a unit, the standard of comparison is absent, making the measurement physically meaningless.

Not quite — the answer is C.

A physical quantity is fully specified only when both numerical value and unit are present together. Neither the number nor the unit alone is sufficient.

Not quite — the answer is D.

Using 1 m = 100 cm: 125 cm = 125/100 = 1.25 m. Dividing by 1000 gives 0.125 m — this is the trap of confusing the cm-to-m conversion with the mm-to-m conversion.

Not quite — the answer is A.

No measurement can be perfectly exact — every measurement retains some irreducible uncertainty from instrument limitations and technique. Reducing error is possible; eliminating it is not.

Not quite — the answer is B.

SI base units are defined independently, not derived from other units — that is precisely what makes them "base" units. Derived units (like newton or pascal) are formed from base units, not the reverse.

Not quite — the answer is D.

Velocity needs length, force needs acceleration (requiring length), and density needs volume. With only mass and time, none of the listed quantities can be determined.

Not quite — the answer is D.

International standardisation allows scientists globally to compare, reproduce, and communicate results consistently. Standard units do not eliminate errors but provide the universal reference needed for valid comparison.