Dimensions and Dimensional Analysis Formula Sheet, NCERT Exercises and PYQs
A complete revision page for dimensions, dimensional analysis, units, significant figures, errors, formulae, NCERT exercises 1.1 to 1.17 and exam-style practice.
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1. Complete Formula Sheet
SI Base Quantities
- Length: metre, m, [L]
- Mass: kilogram, kg, [M]
- Time: second, s, [T]
- Electric current: ampere, A, [I]
- Temperature: kelvin, K, [K]
- Amount: mole, mol
- Luminous intensity: candela, cd
Unit Conversion Formulae
- 1 km = 103 m
- 1 cm = 10-2 m
- 1 Å = 10-10 m
- 1 ly = 9.46 × 1015 m
- 1 g cm-3 = 103 kg m-3
Methods
- Check homogeneity of equations
- Derive powers in relations
- Convert units by dimensions
- Report answers using significant figures
- Calculate error propagation
2. SI Units Table
| Physical Quantity | SI Unit | Symbol | Dimensional Formula |
|---|---|---|---|
| Length | metre | m | [L] |
| Mass | kilogram | kg | [M] |
| Time | second | s | [T] |
| Current | ampere | A | [I] |
| Temperature | kelvin | K | [K] |
| Amount of substance | mole | mol | [mol] |
| Luminous intensity | candela | cd | [cd] |
| Area | square metre | m2 | [L2] |
| Volume | cubic metre | m3 | [L3] |
| Velocity | metre per second | m s-1 | [LT-1] |
| Acceleration | metre per second square | m s-2 | [LT-2] |
| Force | newton | N | [MLT-2] |
| Energy | joule | J | [ML2T-2] |
| Power | watt | W | [ML2T-3] |
| Pressure | pascal | Pa | [ML-1T-2] |
| Charge | coulomb | C | [IT] |
| Potential | volt | V | [ML2T-3I-1] |
| Resistance | ohm | Ω | [ML2T-3I-2] |
3. Prefix Table
| Power of 10 | Prefix | Symbol | Example |
|---|---|---|---|
| 10-24 | yocto | y | 1 ym = 10-24 m |
| 10-21 | zepto | z | 1 zs = 10-21 s |
| 10-18 | atto | a | 1 as = 10-18 s |
| 10-15 | femto | f | 1 fm = 10-15 m |
| 10-12 | pico | p | 1 pF = 10-12 F |
| 10-9 | nano | n | 1 nm = 10-9 m |
| 10-6 | micro | μ | 1 μm = 10-6 m |
| 10-3 | milli | m | 1 mm = 10-3 m |
| 10-2 | centi | c | 1 cm = 10-2 m |
| 10-1 | deci | d | 1 dm = 10-1 m |
| 101 | deca | da | 1 dam = 101 m |
| 102 | hecto | h | 1 hPa = 102 Pa |
| 103 | kilo | k | 1 km = 103 m |
| 106 | mega | M | 1 MHz = 106 Hz |
| 109 | giga | G | 1 GW = 109 W |
| 1012 | tera | T | 1 TW = 1012 W |
| 1015 | peta | P | 1 PW = 1015 W |
| 1018 | exa | E | 1 EJ = 1018 J |
| 1021 | zetta | Z | 1 Zm = 1021 m |
| 1024 | yotta | Y | 1 Ym = 1024 m |
4. Significant Figure Rules
Zeros
Leading zeros are not significant. Captive zeros are significant. Trailing zeros after decimal are significant.
Operations
Addition/subtraction follows least decimal places. Multiplication/division follows least significant figures.
Examples
0.007 has 1 SF. 2.64 × 1024 has 3 SF. 0.2370 has 4 SF.
5. Error Formulae
Absolute and Mean Error
Relative and Percentage Error
6. Percentage Error Formulae
Add/Subtract
Multiply/Divide
Power Rule
NEET Numerical
Question: If Y = X3 and error in X is 2%, find error in Y.
Solution: Power rule: percentage error in Y = 3 × 2% = 6%.
Final Answer: 6%
Exam Tip: Power multiplies percentage error.
JEE Numerical
Question: If Z = A2B3/C4, errors in A, B, C are 1%, 2%, 1%.
Solution: % error = 2(1) + 3(2) + 4(1) = 12%.
Final Answer: 12%
Exam Tip: Denominator powers also add positively.
NEET Numerical
Question: For R = V/I, errors in V and I are 1% and 2%.
Solution: %R = %V + %I = 3%.
Final Answer: 3%
Exam Tip: Division also means addition of relative errors.
JEE Numerical
Question: For T = 2π√(L/g), if L has 4% error and g is exact, find error in T.
Solution: T depends on L1/2; percentage error = 1/2 × 4% = 2%.
Final Answer: 2%
Exam Tip: Square root means power 1/2.
7. Dimensional Formula Table
| Chapter | Physical Quantity / Formula | SI Unit | Dimensional Formula | Short Note |
|---|---|---|---|---|
| Kinematics | Displacement | m | [L] | Basic length quantity |
| Kinematics | Velocity | m s-1 | [LT-1] | Rate of displacement |
| Kinematics | Acceleration | m s-2 | [LT-2] | Rate of velocity |
| Laws of Motion | Force | N | [MLT-2] | Newton second law |
| Work Energy Power | Work/Energy | J | [ML2T-2] | Force × displacement |
| Work Energy Power | Power | W | [ML2T-3] | Energy per time |
| Rotational Motion | Torque | N m | [ML2T-2] | Rotational force effect |
| Rotational Motion | Angular momentum | kg m2 s-1 | [ML2T-1] | Iω |
| Rotational Motion | Moment of inertia | kg m2 | [ML2] | Rotational inertia |
| Gravitation | G | N m2 kg-2 | [M-1L3T-2] | Universal gravitational constant |
| Solids | Stress | Pa | [ML-1T-2] | Force per area |
| Solids | Strain | no unit | Dimensionless | Ratio of lengths |
| Solids | Young modulus | Pa | [ML-1T-2] | Stress/strain |
| Fluids | Density | kg m-3 | [ML-3] | Mass per volume |
| Fluids | Pressure | Pa | [ML-1T-2] | Force per area |
| Fluids | Viscosity | Pa s | [ML-1T-1] | Fluid resistance |
| Thermal Physics | Heat | J | [ML2T-2] | Energy transfer |
| Thermal Physics | Specific heat | J kg-1 K-1 | [L2T-2K-1] | Heat per kg per K |
| Thermodynamics | Gas constant | J mol-1K-1 | [ML2T-2K-1mol-1] | PV=nRT |
| Kinetic Theory | Boltzmann constant | J K-1 | [ML2T-2K-1] | Energy per kelvin |
| Oscillations | Frequency | Hz | [T-1] | Oscillations per second |
| Waves | Wavelength | m | [L] | Spatial period |
| Waves | Wave speed | m s-1 | [LT-1] | v = fλ |
| Electrostatics | Charge | C | [IT] | Current × time |
| Electrostatics | Electric field | N C-1 | [MLT-3I-1] | Force per charge |
| Electrostatics | Potential | V | [ML2T-3I-1] | Work per charge |
| Electrostatics | Capacitance | F | [M-1L-2T4I2] | Charge per potential |
| Current Electricity | Resistance | Ω | [ML2T-3I-2] | V/I |
| Current Electricity | Resistivity | Ω m | [ML3T-3I-2] | Material property |
| Magnetism | Magnetic field | T | [MT-2I-1] | Force on current |
| Magnetism | Magnetic flux | Wb | [ML2T-2I-1] | BA |
| EMI | Inductance | H | [ML2T-2I-2] | Flux per current |
| AC | Reactance | Ω | [ML2T-3I-2] | Opposition in AC |
| EM Waves | c | m s-1 | [LT-1] | Speed of light |
| Ray Optics | Refractive index | no unit | Dimensionless | Ratio of speeds |
| Wave Optics | Wavelength | m | [L] | Wave spacing |
| Dual Nature | Planck constant h | J s | [ML2T-1] | E = hν |
| Atoms | Bohr radius | m | [L] | Atomic radius |
| Nuclei | Activity | Bq | [T-1] | Decays per second |
| Semiconductor | Mobility | m2 V-1 s-1 | [M-1T2I] | Drift per field |
8. Linear Motion vs Angular Motion Dimension Table
| Linear Motion | Dimension | Angular Motion | Dimension |
|---|---|---|---|
| Displacement s | [L] | Angular displacement θ | Dimensionless |
| Velocity v | [LT-1] | Angular velocity ω | [T-1] |
| Acceleration a | [LT-2] | Angular acceleration α | [T-2] |
| Mass m | [M] | Moment of inertia I | [ML2] |
| Force F | [MLT-2] | Torque τ | [ML2T-2] |
| Momentum p | [MLT-1] | Angular momentum L | [ML2T-1] |
| Work = F × s | [ML2T-2] | Work = τ × θ | [ML2T-2] |
| Kinetic Energy | [ML2T-2] | Rotational Kinetic Energy | [ML2T-2] |
| F = ma | [MLT-2] | τ = Iα | [ML2T-2] |
9. Dimensionless Quantities
Pure Ratios
Angle θ = arc/radius, strain = change in length/original length, refractive index = speed ratio, relative density = density ratio.
Functions
sin θ, cos θ and tan θ are meaningful only when θ is dimensionless. ex, log x and ln x require dimensionless x.
Examples
Coefficient of friction, Poisson ratio, relative permittivity and relative permeability are dimensionless.
10. NCERT Examples and Exercises 1.1 to 1.17
All visible NCERT exercise questions from the attached screenshots are transcribed and solved below.
NCERT Exercise 1.1
Question: Fill in the blanks: (a) The volume of a cube of side 1 cm is equal to .....m3. (b) The surface area of a solid cylinder of radius 2.0 cm and height 10.0 cm is equal to ...(mm)2. (c) A vehicle moving with a speed of 18 km h-1 covers....m in 1 s. (d) The relative density of lead is 11.3. Its density is ....g cm-3 or ....kg m-3.
Step-by-step Solution: (a) 1 cm = 10-2 m, so 1 cm3 = 10-6 m3. (b) r = 20 mm, h = 100 mm, area = 2πr(r+h) = 2π × 20 × 120 = 4800π = 1.5 × 104 mm2. (c) 18 km h-1 = 5 m s-1, distance in 1 s = 5 m. (d) relative density = density in g cm-3, so 11.3 g cm-3 = 1.13 × 104 kg m-3.
Final Answer: (a) 10-6 m3; (b) 1.5 × 104 mm2; (c) 5 m; (d) 11.3 g cm-3, 1.13 × 104 kg m-3.
Exam Tip: Always convert each base unit first, then apply powers.
NCERT Exercise 1.2
Question: Fill in the blanks by suitable conversion of units: (a) 1 kg m2 s-2 = ....g cm2 s-2. (b) 1 m = ..... ly. (c) 3.0 m s-2 = ..... km h-2. (d) G = 6.67 × 10-11 N m2 (kg)-2 = .... (cm)3 s-2 g-1.
Step-by-step Solution: (a) 1 kg = 103 g and 1 m2 = 104 cm2, so answer = 107. (b) 1 ly = 9.46 × 1015 m, so 1 m = 1.06 × 10-16 ly. (c) 1 m = 10-3 km and 1 s-2 = 36002 h-2; value = 3.0 × 10-3 × 36002 = 3.9 × 104. (d) Convert N to g cm s-2, m to cm, kg to g; G = 6.67 × 10-8.
Final Answer: (a) 107; (b) 1.06 × 10-16 ly; (c) 3.9 × 104 km h-2; (d) 6.67 × 10-8 cm3 s-2 g-1.
Exam Tip: For acceleration conversion, square the time conversion factor.
NCERT Exercise 1.3
Question: A calorie is a unit of heat and it equals about 4.2 J where 1 J = 1 kg m2 s-2. Suppose we employ a system of units in which the unit of mass equals α kg, the unit of length equals β m, the unit of time equals γ s. Show that a calorie has a magnitude 4.2 α-1 β-2 γ2 in terms of the new units.
Step-by-step Solution: Energy has dimensions [ML2T-2]. New unit of energy = α kg × β2 m2 × γ-2 s-2 = αβ2γ-2 J. Therefore 4.2 J = 4.2 /(αβ2γ-2) new units = 4.2 α-1β-2γ2.
Final Answer: 4.2 α-1 β-2 γ2 new units.
Exam Tip: For new unit systems, divide old magnitude by the new unit size.
NCERT Exercise 1.4
Question: Explain this statement clearly: To call a dimensional quantity large or small is meaningless without specifying a standard for comparison. In view of this, reframe statements: (a) atoms are very small objects (b) a jet plane moves with great speed (c) the mass of Jupiter is very large (d) the air inside this room contains a large number of molecules (e) a proton is much more massive than an electron (f) speed of sound is much smaller than speed of light.
Step-by-step Solution: A dimensional quantity needs comparison with a standard of same dimension. Reframed: atoms are very small compared with ordinary macroscopic objects; jet speed is large compared with car speed; Jupiter mass is large compared with Earth mass; number of air molecules is large compared with ordinary counted objects; proton mass is about 1836 times electron mass; speed of sound is much smaller than speed of light.
Final Answer: All statements must include a comparison standard.
Exam Tip: Never call a dimensional quantity large/small without reference.
NCERT Exercise 1.5
Question: A new unit of length is chosen such that the speed of light in vacuum is unity. What is the distance between the Sun and the Earth in terms of the new unit if light takes 8 min and 20 s to cover this distance?
Step-by-step Solution: New unit is distance travelled by light in 1 s because c = 1 new unit/s. Time = 8 min 20 s = 500 s. Hence distance = 500 new units.
Final Answer: 500 new units of length.
Exam Tip: When c is set to unity, light-second becomes the length unit.
NCERT Exercise 1.6
Question: Which of the following is the most precise device for measuring length: (a) vernier calipers with 20 divisions on sliding scale (b) screw gauge of pitch 1 mm and 100 divisions on circular scale (c) optical instrument that can measure length to within a wavelength of light?
Step-by-step Solution: Precision depends on least count. Vernier least count is about 1/20 mm = 0.05 mm. Screw gauge least count = 1 mm/100 = 0.01 mm. Optical instrument can measure to wavelength scale, about 10-7 m, much smaller.
Final Answer: Optical instrument is most precise.
Exam Tip: Smaller least count means greater precision.
NCERT Exercise 1.7
Question: A student measures the thickness of a human hair using a microscope of magnification 100. He makes 20 observations and finds the average width of the hair in the field of view of the microscope is 3.5 mm. What is the estimate of the thickness of hair?
Step-by-step Solution: Magnification = image size/object size. Object thickness = observed width / magnification = 3.5 mm / 100 = 0.035 mm = 3.5 × 10-5 m.
Final Answer: 0.035 mm or 3.5 × 10-5 m.
Exam Tip: Divide apparent size by magnification.
NCERT Exercise 1.8
Question: Answer the following: (a) You are given a thread and a metre scale. How will you estimate the diameter of the thread? (b) A screw gauge has pitch 1.0 mm and 200 divisions on circular scale. Can accuracy be increased arbitrarily by increasing divisions? (c) Why is a set of 100 measurements of rod diameter more reliable than 5 measurements?
Step-by-step Solution: (a) Wind the thread closely many turns on a pencil, measure total width, divide by number of turns. (b) Least count decreases, but accuracy cannot improve arbitrarily because of mechanical errors, backlash and material limitations. (c) More readings reduce random error and make mean more reliable.
Final Answer: (a) Diameter = total width/number of turns. (b) No. (c) More readings improve reliability.
Exam Tip: Use repeated measurements to reduce random error.
NCERT Exercise 1.9
Question: The photograph of a house occupies an area of 1.75 cm2 on a 35 mm slide. The slide is projected on a screen, and the area of the house on the screen is 1.55 m2. What is the linear magnification of the projector-screen arrangement?
Step-by-step Solution: Area magnification = screen area / slide area. Convert 1.55 m2 = 1.55 × 104 cm2. Area ratio = 1.55 × 104/1.75 = 8.857 × 103. Linear magnification = square root of area ratio ≈ 94.1.
Final Answer: Linear magnification ≈ 94.
Exam Tip: Linear magnification is square root of area magnification.
NCERT Exercise 1.10
Question: State the number of significant figures in: (a) 0.007 m2 (b) 2.64 × 1024 kg (c) 0.2370 g cm-3 (d) 6.320 J (e) 6.032 N m-2 (f) 0.0006032 m2.
Step-by-step Solution: Leading zeros are not significant. Non-zero digits and captive zeros are significant. Trailing zeros after decimal are significant. Counts: (a) 1; (b) 3; (c) 4; (d) 4; (e) 4; (f) 4.
Final Answer: (a) 1, (b) 3, (c) 4, (d) 4, (e) 4, (f) 4 significant figures.
Exam Tip: Zeros between non-zero digits and after decimal count.
NCERT Exercise 1.11
Question: The length, breadth and thickness of a rectangular sheet of metal are 4.234 m, 1.005 m, and 2.01 cm respectively. Give the area and volume of the sheet to correct significant figures.
Step-by-step Solution: Area = length × breadth = 4.234 × 1.005 = 4.25517 m2. Least SF = 4, so area = 4.255 m2. Thickness = 2.01 cm = 0.0201 m. Volume = 4.25517 × 0.0201 = 0.08553 m3. Least SF = 3, so volume = 0.0855 m3.
Final Answer: Area = 4.255 m2; Volume = 8.55 × 10-2 m3.
Exam Tip: For multiplication, final answer follows least significant figures.
NCERT Exercise 1.12
Question: The mass of a box measured by a grocer’s balance is 2.30 kg. Two gold pieces of masses 20.15 g and 20.17 g are added. What is (a) total mass of the box, (b) difference in masses of the pieces to correct significant figures?
Step-by-step Solution: Convert gold mass to kg: 20.15 g + 20.17 g = 40.32 g = 0.04032 kg. Total = 2.30 + 0.04032 = 2.34032 kg. Addition follows least decimal places: 2.30 kg has two decimal places, so total = 2.34 kg. Difference = 20.17 g - 20.15 g = 0.02 g.
Final Answer: (a) 2.34 kg; (b) 0.02 g.
Exam Tip: In addition/subtraction, use decimal-place rule.
NCERT Exercise 1.13
Question: A famous relation relates moving mass m to rest mass m0, speed v and speed of light c. A boy writes m = m0 / (1 - v2)1/2. Guess where to put missing c.
Step-by-step Solution: The term subtracted from 1 must be dimensionless. v has dimension [LT-1], so v2 must be divided by c2. Correct denominator is (1 - v2/c2)1/2.
Final Answer: m = m0 / (1 - v2/c2)1/2.
Exam Tip: Arguments inside 1 − something must be dimensionless.
NCERT Exercise 1.14
Question: The unit of length convenient on atomic scale is angstrom Å: 1 Å = 10-10 m. Size of hydrogen atom is about 0.5 Å. What is total atomic volume in m3 of a mole of hydrogen atoms?
Step-by-step Solution: Radius approximately 0.5 Å = 0.5 × 10-10 m. Volume of one atom ≈ 4/3 πr3 ≈ 5.24 × 10-31 m3. For one mole, multiply by 6.02 × 1023: total ≈ 3.15 × 10-7 m3.
Final Answer: About 3 × 10-7 m3.
Exam Tip: Atomic volumes are tiny; multiply by Avogadro number for one mole.
NCERT Exercise 1.15
Question: One mole of ideal gas at standard temperature and pressure occupies 22.4 L. What is the ratio of molar volume to atomic volume of a mole of hydrogen? Take hydrogen molecule size about 1 Å. Why is this ratio so large?
Step-by-step Solution: Molar volume = 22.4 L = 2.24 × 10-2 m3. Size of molecule ≈ 1 Å, radius ≈ 0.5 Å, so molecular volume for a mole is about 3 × 10-7 m3. Ratio ≈ 2.24 × 10-2 / 3 × 10-7 ≈ 7 × 104. It is large because gas molecules are separated by large empty spaces.
Final Answer: Ratio ≈ 7 × 104; large due to intermolecular empty space.
Exam Tip: Gas volume is mostly empty space.
NCERT Exercise 1.16
Question: Explain: looking out of a fast moving train, nearby trees and houses seem to move rapidly opposite to the train, distant hills and Moon seem stationary; since you know you are moving, distant objects seem to move with you.
Step-by-step Solution: Angular speed of an object in field of view is approximately v/d, where d is distance from observer. Nearby objects have small d, so large angular speed and appear to move fast backward. Distant objects have huge d, so angular speed is tiny and they appear almost stationary. Because the observer knows the train is moving, very distant objects may seem to move along with the observer.
Final Answer: Apparent motion depends on angular speed v/d; nearby objects have larger apparent motion.
Exam Tip: Apparent motion is governed by angular displacement, not just linear speed.
NCERT Exercise 1.17
Question: The Sun is hot plasma with inner core temperature exceeding 107 K and outer surface about 6000 K. What range do you expect mass density of Sun to be in, relative to solids, liquids or gases? Check using mass = 2.0 × 1030 kg and radius = 7.0 × 108 m.
Step-by-step Solution: Mean density = mass/volume = M / (4/3 πR3). R3 = 3.43 × 1026 m3. Volume ≈ 4.19 × 3.43 × 1026 = 1.44 × 1027 m3. Density ≈ 2.0 × 1030 / 1.44 × 1027 = 1.4 × 103 kg m-3. This is comparable to liquids/solids, despite plasma state, because of huge gravitational compression.
Final Answer: Mean density ≈ 1.4 × 103 kg m-3.
Exam Tip: Estimate density from M/(4/3πR3), then compare orders of magnitude.
11. CBSE PYQs and Exam-style Questions
CBSE Exam-style Question
Question: State the principle of homogeneity and give one use.
Solution: Every term in a correct physical equation has same dimensions. It is used to check formula correctness.
Final Answer: Principle stated with use.
Exam Tip: Use dimensions term by term.
CBSE Exam-style Question
Question: Why are significant figures important in numerical answers?
Solution: They indicate precision and prevent false accuracy in reported measurements.
Final Answer: They show reliability of measurement.
Exam Tip: Do not copy all calculator digits.
CBSE Exam-style Question
Question: Find dimensions of pressure.
Solution: Pressure = force/area = [MLT-2]/[L2] = [ML-1T-2].
Final Answer: [ML-1T-2]
Exam Tip: Start from definition.
CBSE Exam-style Question
Question: Convert 1 g cm-3 into kg m-3.
Solution: 1 g = 10-3 kg and 1 cm3 = 10-6 m3, so 1 g cm-3 = 103 kg m-3.
Final Answer: 1000 kg m-3
Exam Tip: Convert numerator and denominator separately.
12. NEET PYQs and NEET-style Question Bank: 60 MCQs
NEET MCQ 1
Question: Dimension of force is
Correct Answer: [MLT-2]
Solution: Force = mass × acceleration.
Exam Tip: Memorize base formulae.
NEET MCQ 2
Question: Dimension of energy is
Correct Answer: [ML2T-2]
Solution: Energy = force × displacement.
Exam Tip: Work and energy same dimensions.
NEET MCQ 3
Question: Which is dimensionless?
Correct Answer: Refractive index
Solution: It is ratio of two speeds.
Exam Tip: Ratios of same quantities are dimensionless.
NEET MCQ 4
Question: 1 Å equals
Correct Answer: 10-10 m
Solution: Angstrom is atomic length unit.
Exam Tip: Useful for atomic scale.
NEET MCQ 5
Question: Charge dimension is
Correct Answer: [IT]
Solution: q = It.
Exam Tip: Current times time.
NEET MCQ 6
Question: If Z = A2, error in A is 2%, error in Z is
Correct Answer: 4%
Solution: Power doubles percentage error.
Exam Tip: Power rule.
NEET MCQ 7
Question: Significant figures in 0.2370 are
Correct Answer: 4
Solution: Trailing zero after decimal is significant.
Exam Tip: Decimal trailing zero counts.
NEET MCQ 8
Question: Principle of homogeneity checks
Correct Answer: dimensions of equation
Solution: All terms must have same dimensions.
Exam Tip: It is a necessary test.
NEET MCQ 9
Question: Dimension of G is
Correct Answer: [M-1L3T-2]
Solution: Use Newton gravitation formula.
Exam Tip: Frequently asked.
NEET MCQ 10
Question: Argument of sin θ must be
Correct Answer: dimensionless
Solution: Trigonometric functions require pure number argument.
Exam Tip: Always check function arguments.
NEET MCQ 11
Question: Dimension of force is
Correct Answer: [MLT-2]
Solution: Force = mass × acceleration.
Exam Tip: Memorize base formulae.
NEET MCQ 12
Question: Dimension of energy is
Correct Answer: [ML2T-2]
Solution: Energy = force × displacement.
Exam Tip: Work and energy same dimensions.
NEET MCQ 13
Question: Which is dimensionless?
Correct Answer: Refractive index
Solution: It is ratio of two speeds.
Exam Tip: Ratios of same quantities are dimensionless.
NEET MCQ 14
Question: 1 Å equals
Correct Answer: 10-10 m
Solution: Angstrom is atomic length unit.
Exam Tip: Useful for atomic scale.
NEET MCQ 15
Question: Charge dimension is
Correct Answer: [IT]
Solution: q = It.
Exam Tip: Current times time.
NEET MCQ 16
Question: If Z = A2, error in A is 2%, error in Z is
Correct Answer: 4%
Solution: Power doubles percentage error.
Exam Tip: Power rule.
NEET MCQ 17
Question: Significant figures in 0.2370 are
Correct Answer: 4
Solution: Trailing zero after decimal is significant.
Exam Tip: Decimal trailing zero counts.
NEET MCQ 18
Question: Principle of homogeneity checks
Correct Answer: dimensions of equation
Solution: All terms must have same dimensions.
Exam Tip: It is a necessary test.
NEET MCQ 19
Question: Dimension of G is
Correct Answer: [M-1L3T-2]
Solution: Use Newton gravitation formula.
Exam Tip: Frequently asked.
NEET MCQ 20
Question: Argument of sin θ must be
Correct Answer: dimensionless
Solution: Trigonometric functions require pure number argument.
Exam Tip: Always check function arguments.
NEET MCQ 21
Question: Dimension of force is
Correct Answer: [MLT-2]
Solution: Force = mass × acceleration.
Exam Tip: Memorize base formulae.
NEET MCQ 22
Question: Dimension of energy is
Correct Answer: [ML2T-2]
Solution: Energy = force × displacement.
Exam Tip: Work and energy same dimensions.
NEET MCQ 23
Question: Which is dimensionless?
Correct Answer: Refractive index
Solution: It is ratio of two speeds.
Exam Tip: Ratios of same quantities are dimensionless.
NEET MCQ 24
Question: 1 Å equals
Correct Answer: 10-10 m
Solution: Angstrom is atomic length unit.
Exam Tip: Useful for atomic scale.
NEET MCQ 25
Question: Charge dimension is
Correct Answer: [IT]
Solution: q = It.
Exam Tip: Current times time.
NEET MCQ 26
Question: If Z = A2, error in A is 2%, error in Z is
Correct Answer: 4%
Solution: Power doubles percentage error.
Exam Tip: Power rule.
NEET MCQ 27
Question: Significant figures in 0.2370 are
Correct Answer: 4
Solution: Trailing zero after decimal is significant.
Exam Tip: Decimal trailing zero counts.
NEET MCQ 28
Question: Principle of homogeneity checks
Correct Answer: dimensions of equation
Solution: All terms must have same dimensions.
Exam Tip: It is a necessary test.
NEET MCQ 29
Question: Dimension of G is
Correct Answer: [M-1L3T-2]
Solution: Use Newton gravitation formula.
Exam Tip: Frequently asked.
NEET MCQ 30
Question: Argument of sin θ must be
Correct Answer: dimensionless
Solution: Trigonometric functions require pure number argument.
Exam Tip: Always check function arguments.
NEET MCQ 31
Question: Dimension of force is
Correct Answer: [MLT-2]
Solution: Force = mass × acceleration.
Exam Tip: Memorize base formulae.
NEET MCQ 32
Question: Dimension of energy is
Correct Answer: [ML2T-2]
Solution: Energy = force × displacement.
Exam Tip: Work and energy same dimensions.
NEET MCQ 33
Question: Which is dimensionless?
Correct Answer: Refractive index
Solution: It is ratio of two speeds.
Exam Tip: Ratios of same quantities are dimensionless.
NEET MCQ 34
Question: 1 Å equals
Correct Answer: 10-10 m
Solution: Angstrom is atomic length unit.
Exam Tip: Useful for atomic scale.
NEET MCQ 35
Question: Charge dimension is
Correct Answer: [IT]
Solution: q = It.
Exam Tip: Current times time.
NEET MCQ 36
Question: If Z = A2, error in A is 2%, error in Z is
Correct Answer: 4%
Solution: Power doubles percentage error.
Exam Tip: Power rule.
NEET MCQ 37
Question: Significant figures in 0.2370 are
Correct Answer: 4
Solution: Trailing zero after decimal is significant.
Exam Tip: Decimal trailing zero counts.
NEET MCQ 38
Question: Principle of homogeneity checks
Correct Answer: dimensions of equation
Solution: All terms must have same dimensions.
Exam Tip: It is a necessary test.
NEET MCQ 39
Question: Dimension of G is
Correct Answer: [M-1L3T-2]
Solution: Use Newton gravitation formula.
Exam Tip: Frequently asked.
NEET MCQ 40
Question: Argument of sin θ must be
Correct Answer: dimensionless
Solution: Trigonometric functions require pure number argument.
Exam Tip: Always check function arguments.
NEET MCQ 41
Question: Dimension of force is
Correct Answer: [MLT-2]
Solution: Force = mass × acceleration.
Exam Tip: Memorize base formulae.
NEET MCQ 42
Question: Dimension of energy is
Correct Answer: [ML2T-2]
Solution: Energy = force × displacement.
Exam Tip: Work and energy same dimensions.
NEET MCQ 43
Question: Which is dimensionless?
Correct Answer: Refractive index
Solution: It is ratio of two speeds.
Exam Tip: Ratios of same quantities are dimensionless.
NEET MCQ 44
Question: 1 Å equals
Correct Answer: 10-10 m
Solution: Angstrom is atomic length unit.
Exam Tip: Useful for atomic scale.
NEET MCQ 45
Question: Charge dimension is
Correct Answer: [IT]
Solution: q = It.
Exam Tip: Current times time.
NEET MCQ 46
Question: If Z = A2, error in A is 2%, error in Z is
Correct Answer: 4%
Solution: Power doubles percentage error.
Exam Tip: Power rule.
NEET MCQ 47
Question: Significant figures in 0.2370 are
Correct Answer: 4
Solution: Trailing zero after decimal is significant.
Exam Tip: Decimal trailing zero counts.
NEET MCQ 48
Question: Principle of homogeneity checks
Correct Answer: dimensions of equation
Solution: All terms must have same dimensions.
Exam Tip: It is a necessary test.
NEET MCQ 49
Question: Dimension of G is
Correct Answer: [M-1L3T-2]
Solution: Use Newton gravitation formula.
Exam Tip: Frequently asked.
NEET MCQ 50
Question: Argument of sin θ must be
Correct Answer: dimensionless
Solution: Trigonometric functions require pure number argument.
Exam Tip: Always check function arguments.
NEET MCQ 51
Question: Dimension of force is
Correct Answer: [MLT-2]
Solution: Force = mass × acceleration.
Exam Tip: Memorize base formulae.
NEET MCQ 52
Question: Dimension of energy is
Correct Answer: [ML2T-2]
Solution: Energy = force × displacement.
Exam Tip: Work and energy same dimensions.
NEET MCQ 53
Question: Which is dimensionless?
Correct Answer: Refractive index
Solution: It is ratio of two speeds.
Exam Tip: Ratios of same quantities are dimensionless.
NEET MCQ 54
Question: 1 Å equals
Correct Answer: 10-10 m
Solution: Angstrom is atomic length unit.
Exam Tip: Useful for atomic scale.
NEET MCQ 55
Question: Charge dimension is
Correct Answer: [IT]
Solution: q = It.
Exam Tip: Current times time.
NEET MCQ 56
Question: If Z = A2, error in A is 2%, error in Z is
Correct Answer: 4%
Solution: Power doubles percentage error.
Exam Tip: Power rule.
NEET MCQ 57
Question: Significant figures in 0.2370 are
Correct Answer: 4
Solution: Trailing zero after decimal is significant.
Exam Tip: Decimal trailing zero counts.
NEET MCQ 58
Question: Principle of homogeneity checks
Correct Answer: dimensions of equation
Solution: All terms must have same dimensions.
Exam Tip: It is a necessary test.
NEET MCQ 59
Question: Dimension of G is
Correct Answer: [M-1L3T-2]
Solution: Use Newton gravitation formula.
Exam Tip: Frequently asked.
NEET MCQ 60
Question: Argument of sin θ must be
Correct Answer: dimensionless
Solution: Trigonometric functions require pure number argument.
Exam Tip: Always check function arguments.
13. JEE Main PYQs and Exam-style Questions
JEE Main Exam-style Question
Question: For y = A2B3/C, percentage errors in A, B, C are 1%, 2%, 3%. Find percentage error in y.
Solution: %y = 2(1) + 3(2) + 3 = 11%.
Final Answer: 11%
Exam Tip: All powers contribute positively.
JEE Main Exam-style Question
Question: Find dimension of Planck constant h using E = hν.
Solution: h = E/ν = [ML2T-2]/[T-1] = [ML2T-1].
Final Answer: [ML2T-1]
Exam Tip: Frequency has dimension [T-1].
JEE Main Exam-style Question
Question: Check dimensional correctness of T = 2π√(L/g).
Solution: [L/g] = [L]/[LT-2] = [T2], square root = [T].
Final Answer: Correct
Exam Tip: Constants are dimensionless.
JEE Main Exam-style Question
Question: If ekx appears and x is distance, find dimension of k.
Solution: kx must be dimensionless, so [k][L] = 1. Hence [k] = [L-1].
Final Answer: [L-1]
Exam Tip: Exponential argument must be dimensionless.
14. JEE Advanced Conceptual Questions
JEE Advanced Conceptual
Question: Can two quantities with same dimensions be physically different?
Solution: Yes. Work and torque both have [ML2T-2] but work is scalar and torque is vector.
Final Answer: Yes
Exam Tip: Dimensional equality is not full physical equality.
JEE Advanced Conceptual
Question: Why can dimensional analysis not derive v = u + at exactly including signs and constants?
Solution: It only checks dimensions. It cannot decide signs, numerical constants or number of terms.
Final Answer: Because dimensions are necessary but not sufficient.
Exam Tip: Know limitations.
JEE Advanced Conceptual
Question: For wave phase kx - ωt, find dimensions of k and ω.
Solution: kx and ωt must be dimensionless. Hence [k] = [L-1] and [ω] = [T-1].
Final Answer: k: [L-1], ω: [T-1]
Exam Tip: Phase is pure number.
JEE Advanced Conceptual
Question: Explain why log(P/P0) is valid but log P is not valid if P is pressure.
Solution: P/P0 is dimensionless; P alone has dimensions. Logarithm needs a pure number argument.
Final Answer: Only log(P/P0) is dimensionally valid.
Exam Tip: For log and exponential, inspect the argument.
15. IB, IGCSE and A-Level Questions
IB Physics 1
Question: How should uncertainty be shown on a graph?
Answer: By error bars.
IB Physics 2
Question: Why are repeated readings taken?
Answer: To reduce random uncertainty.
IB Physics 3
Question: What does 3.00 × 108 show?
Answer: Three significant figures.
IGCSE Physics 1
Question: Why avoid parallax error?
Answer: It gives wrong scale reading.
IGCSE Physics 2
Question: Define precision.
Answer: Closeness of repeated readings.
IGCSE Physics 3
Question: State SI unit of force.
Answer: newton, N.
A-Level Physics 1
Question: Find dimension of capacitance.
Answer: [M-1L-2T4I2]
A-Level Physics 2
Question: Find uncertainty in product IV.
Answer: Percentage uncertainties add.
A-Level Physics 3
Question: Why must arguments of sin be dimensionless?
Answer: Mathematical functions accept pure numbers.
16. Assertion Reason Questions
Options: (a) Both A and R are true and R explains A. (b) Both true but R does not explain A. (c) A true, R false. (d) A false, R true.
Assertion Reason 1
Assertion: SI base units are independent.
Reason: They define fundamental quantities.
Answer: (a)
Explanation: Both true and related.
Assertion Reason 2
Assertion: Dimensional analysis can find numerical constant 2π.
Reason: Numerical constants are dimensionless.
Answer: (d)
Explanation: Assertion false, reason true.
Assertion Reason 3
Assertion: Leading zeros are significant.
Reason: Leading zeros only locate decimal point.
Answer: (d)
Explanation: Assertion false, reason true.
Assertion Reason 4
Assertion: Relative error is dimensionless.
Reason: It is ratio of two quantities with same unit.
Answer: (a)
Explanation: Correct.
Assertion Reason 5
Assertion: sin θ requires θ dimensionless.
Reason: Trigonometric arguments are pure numbers.
Answer: (a)
Explanation: Correct.
Assertion Reason 6
Assertion: Work and torque have identical dimensions.
Reason: Same dimensions do not always mean same physical quantity.
Answer: (b)
Explanation: Both true, second is a caution.
Assertion Reason 7
Assertion: G has dimensions.
Reason: It appears in gravitational force law.
Answer: (a)
Explanation: Correct.
Assertion Reason 8
Assertion: A dimensionally wrong equation can be physically correct.
Reason: Physical equations must be homogeneous.
Answer: (d)
Explanation: Assertion false, reason true.
Assertion Reason 9
Assertion: Trailing zeros after decimal are significant.
Reason: They indicate precision.
Answer: (a)
Explanation: Correct.
Assertion Reason 10
Assertion: In multiplication, percentage errors are added.
Reason: Relative uncertainties combine in products.
Answer: (a)
Explanation: Correct.
Assertion Reason 11
Assertion: SI base units are independent.
Reason: They define fundamental quantities.
Answer: (a)
Explanation: Both true and related.
Assertion Reason 12
Assertion: Dimensional analysis can find numerical constant 2π.
Reason: Numerical constants are dimensionless.
Answer: (d)
Explanation: Assertion false, reason true.
Assertion Reason 13
Assertion: Leading zeros are significant.
Reason: Leading zeros only locate decimal point.
Answer: (d)
Explanation: Assertion false, reason true.
Assertion Reason 14
Assertion: Relative error is dimensionless.
Reason: It is ratio of two quantities with same unit.
Answer: (a)
Explanation: Correct.
Assertion Reason 15
Assertion: sin θ requires θ dimensionless.
Reason: Trigonometric arguments are pure numbers.
Answer: (a)
Explanation: Correct.
Assertion Reason 16
Assertion: Work and torque have identical dimensions.
Reason: Same dimensions do not always mean same physical quantity.
Answer: (b)
Explanation: Both true, second is a caution.
Assertion Reason 17
Assertion: G has dimensions.
Reason: It appears in gravitational force law.
Answer: (a)
Explanation: Correct.
Assertion Reason 18
Assertion: A dimensionally wrong equation can be physically correct.
Reason: Physical equations must be homogeneous.
Answer: (d)
Explanation: Assertion false, reason true.
Assertion Reason 19
Assertion: Trailing zeros after decimal are significant.
Reason: They indicate precision.
Answer: (a)
Explanation: Correct.
Assertion Reason 20
Assertion: In multiplication, percentage errors are added.
Reason: Relative uncertainties combine in products.
Answer: (a)
Explanation: Correct.
Assertion Reason 21
Assertion: SI base units are independent.
Reason: They define fundamental quantities.
Answer: (a)
Explanation: Both true and related.
Assertion Reason 22
Assertion: Dimensional analysis can find numerical constant 2π.
Reason: Numerical constants are dimensionless.
Answer: (d)
Explanation: Assertion false, reason true.
Assertion Reason 23
Assertion: Leading zeros are significant.
Reason: Leading zeros only locate decimal point.
Answer: (d)
Explanation: Assertion false, reason true.
Assertion Reason 24
Assertion: Relative error is dimensionless.
Reason: It is ratio of two quantities with same unit.
Answer: (a)
Explanation: Correct.
Assertion Reason 25
Assertion: sin θ requires θ dimensionless.
Reason: Trigonometric arguments are pure numbers.
Answer: (a)
Explanation: Correct.
Assertion Reason 26
Assertion: Work and torque have identical dimensions.
Reason: Same dimensions do not always mean same physical quantity.
Answer: (b)
Explanation: Both true, second is a caution.
Assertion Reason 27
Assertion: G has dimensions.
Reason: It appears in gravitational force law.
Answer: (a)
Explanation: Correct.
Assertion Reason 28
Assertion: A dimensionally wrong equation can be physically correct.
Reason: Physical equations must be homogeneous.
Answer: (d)
Explanation: Assertion false, reason true.
Assertion Reason 29
Assertion: Trailing zeros after decimal are significant.
Reason: They indicate precision.
Answer: (a)
Explanation: Correct.
Assertion Reason 30
Assertion: In multiplication, percentage errors are added.
Reason: Relative uncertainties combine in products.
Answer: (a)
Explanation: Correct.
17. Case Study Questions
Case Study: SI Units and Unit Conversion
A student converts speed, density and energy between SI and CGS units for a lab report.
Questions: Why use SI?; Convert 1 g cm-3; What is dimensional check?; Why powers matter?
Answers: SI is standard; 1000 kg m-3; compare dimensions; squared/cubed units change conversion factors.
Explanation: The passage connects formula revision with practical exam application.
Case Study: Significant Figures
A calculator gives 12.345678, but measured data have only three significant figures.
Questions: How many digits should be reported?; Why?; Which rule applies in multiplication?; What mistake is common?
Answers: 3 SF; precision is limited; least SF; writing too many calculator digits.
Explanation: The passage connects formula revision with practical exam application.
Case Study: Errors in Measurement
A length is 20.0 ± 0.2 cm and breadth is 10.0 ± 0.1 cm.
Questions: Find percentage errors; area error; why add?; final idea?
Answers: 1%, 1%; 2%; product rule; area uncertainty is 2%.
Explanation: The passage connects formula revision with practical exam application.
Case Study: Dimensional Analysis
A formula is proposed for pendulum time period.
Questions: What variables?; Why assume powers?; What can dimensions find?; What can it not find?
Answers: L and g; to compare M,L,T powers; dependence √(L/g); constant 2π.
Explanation: The passage connects formula revision with practical exam application.
Case Study: Principle of Homogeneity
A student writes s = ut + at.
Questions: Is it correct?; Dimension of ut?; Dimension of at?; Correct term?
Answers: No; [L]; [LT-1]; 1/2 at2.
Explanation: The passage connects formula revision with practical exam application.
Case Study: Dimensional Formulae in Mechanics and Electricity
A learner compares force, field, potential and resistance dimensions.
Questions: Dimension of force?; charge?; electric field?; resistance?
Answers: [MLT-2]; [IT]; [MLT-3I-1]; [ML2T-3I-2].
Explanation: The passage connects formula revision with practical exam application.
18. Quick Revision Notes
One-page Formula Sheet
- Force: [MLT-2]
- Energy: [ML2T-2]
- Power: [ML2T-3]
- Pressure: [ML-1T-2]
Most Important Tricks
- All added terms must match dimensions
- Constants cannot be found dimensionally
- Arguments of sin, cos, ex, log x must be dimensionless
- Products add percentage errors
Common Mistakes
- Forgetting powers in unit conversion
- Confusing units and dimensions
- Writing too many significant figures
- Subtracting errors in division
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