Unit & Dimensions - NEET Previous Year Questions with Solutions

Here you will get Complete Unit & Dimensions NEET Previous Year Questions with complete and detailed solutions. Get complete NEET previous year questions for Physics, Chemistry, and Biology. You will find all the solutions at the end of this page:

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Key takeaways

• Chapter: Units and Measurements, the first topic of Class 11 Physics (often called Units and Dimensions).
• Typical weight: one or two questions per paper.
• Most tested: dimensional formulas, quantities with the same dimensions, dimensionless quantities and percentage error.
• Target time: under 60 seconds per question.

Units and Dimensions NEET Previous Year Questions: What to Expect

SI Base Units and Their Dimensions

The SI has seven base quantities, and every other unit and dimension is built from them.

Important Dimensional Formulas for NEET (Table)

Quantities with the Same Dimensions

• Work, energy, torque and heat: [ML²T⁻²]
• Planck's constant and angular momentum: [ML²T⁻¹]
• Impulse and momentum: [MLT⁻¹]
• Pressure, stress, Young's modulus and energy density: [ML⁻¹T⁻²]
• Frequency, angular velocity and decay constant: [T⁻¹]
• L/R, RC and √(LC): [T]
• Latent heat, gravitational potential and velocity squared: [L²T⁻²]
• Surface tension and spring constant: [MT⁻²]

Dimensionless Quantities in NEET

Strain, Poisson's ratio, refractive index, relative density, coefficient of friction, relative permittivity, Reynolds number, Mach number, angle (radian) and solid angle (steradian) are dimensionless. A quantity is dimensionless when it is a ratio of two like quantities. The argument of a sine, cosine, logarithm or exponential is also dimensionless.

Error in Measurement: Rules for NEET

• Sum or difference: absolute errors add, so Δx = Δa + Δb.
• Product or quotient: relative errors add, so Δx/x = Δa/a + Δb/b.
• Power: for x = aⁿbᵐ, Δx/x = n(Δa/a) + m(Δb/b).
• Maximum percentage error is the sum of the weighted percentage errors.

Worked example: for x = a²b³/c with errors of 1%, 2% and 3% in a, b and c, the maximum error in x is 2(1) + 3(2) + 3 = 11%.

How to Solve Dimensions Questions in Under 60 Seconds

1. Write each quantity in terms of M, L and T (add A and K only when needed).
2. For same-dimension questions, reduce every option to a known formula such as E = hν or F = ma.
3. To check an equation, make sure every term has identical dimensions.
4. For error questions, multiply each percentage error by its power and add.
5. Eliminate options by checking one base dimension, such as the power of T.

Dimensional analysis cannot give dimensionless constants (such as the ½ in kinetic energy) and cannot handle sums of different quantities.