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For the determination of refractive index of glass slab, a travelling microscope is used whose main scale contains 300 equal divisions equals to 15 cm. The vernier scale attached to the microscope has 25 divisions equals to 24 divisions of main scale. The least count (LC) of the travelling microscope is (in cm):

Solution & Explanation

### Related Formula 1text MSD = fractextTotal LengthtextTotal Divisions textLeast Count (LC) = 1text MSD - 1text VSD = 1text MSD cdot left(1 - frac2425right) ### Core Logic Calculate the value of one main scale division: 1text MSD = frac15text cm300 = 0.05text cm Given that 25text VSD = 24text MSD, we find: 1text VSD = frac2425text MSD ### Step 1: Compute Least Count textLC = 1text MSD cdot left(frac125right) = frac0.05text cm25 = 0.002text cm ### Pattern Recognition Least count calculation is conventionally textLC = frac1text MSDN where N represents the total count of divisions on the vernier scale whenever (N-1)text MSD = Ntext VSD. ### Evaluation Rubric / Model Answer null ### Chapter Mix Class 11 Physics: Units and Measurements

Reference Study Guides

More Units and Measurements Previous-Year Questions — Page 2

Q10 2025 Error Analysis
A quantity Q is formulated as X^-2Y^frac32Z^-frac25. X, Y and Z are independent parameters which have fractional errors of 0.1, 0.2 and 0.5, respectively in measurement. The maximum fractional error of Q is:
  • A. 0.1
  • B. 0.8
  • C. 0.7
  • D. 0.6

Solution

### Related Formula For a quantity Q = X^a Y^b Z^c, the maximum fractional error is: fracDelta QQ = |a| fracDelta XX + |b| fracDelta YY + |c| fracDelta ZZ where, fracDelta XX, fracDelta YY, fracDelta ZZ are fractional errors of individual variables ### Core Logic Given formula: Q = X^-2 Y^3/2 Z^-2/5. Identify the absolute exponents: - |a| = |-2| = 2 - |b| = left|frac32right| = frac32 - |c| = left|-frac25right| = frac25 Now write the error expression: fracDelta QQ = 2 fracDelta XX + frac32 fracDelta YY + frac25 fracDelta ZZ Substitute the given values: - fracDelta XX = 0.1 - fracDelta YY = 0.2 - fracDelta ZZ = 0.5 ### Step 1: Compute Maximum Fractional Error Calculate term by term: fracDelta QQ = 2 (0.1) + frac32 (0.2) + frac25 (0.5) fracDelta QQ = 0.2 + 0.3 + 0.2 = 0.7 ### Pattern Recognition Sees: Exponential algebraic relation for errors. Trap: Exponents are negative, but maximum error is cumulative. Always take the *absolute* value of exponents when summing errors! ✓ ### Evaluation Rubric / Model Answer null ### Chapter Mix Class 11 Physics: Units and Measurements
Q16 2025 Dimensional Analysis
Match List-I with List-II. beginarray|l|l|l|l| hline textbfList-I & & textbfList-II & \\ hline text(A) & textYoung's Modulus & text(I) & mathrmML^-1T^-1 \\ text(B) & textTorque & text(II) & mathrmML^-1T^-2 \\ text(C) & textCoefficient of Viscosity & text(III) & mathrmM^-1L^3T^-2 \\ text(D) & textGravitational Constant & text(IV) & mathrmML^2T^-2 \\ hline endarray Choose the correct answer from the options given below:
  • A. text(A)-(I), (B)-(III), (C)-(II), (D)-(IV)
  • B. text(A)-(II), (B)-(I), (C)-(IV), (D)-(III)
  • C. text(A)-(IV), (B)-(II), (C)-(III), (D)-(I)
  • D. text(A)-(II), (B)-(IV), (C)-(I), (D)-(III)

Solution

### Related Formula textYoung's Modulus: Y = fracF/ADelta ell / ell textTorque: tau = F cdot r textViscosity Force: F = eta A fracdvdx textGravitational Force: F = fracG m_1 m_2r^2 ### Core Logic Evaluating dimensions component-by-component: - **(A) Young's Modulus**: [Y] = frac[F][A] = fracmathrmMLT^-2mathrmL^2 = mathrmML^-1T^-2 quad rightarrow text(II) - **(B) Torque**: [tau] = [F][r] = (mathrmMLT^-2)(mathrmL) = mathrmML^2T^-2 quad rightarrow text(IV) - **(C) Coefficient of Viscosity**: [eta] = frac[F][A][dv/dx] = fracmathrmMLT^-2(mathrmL^2)(mathrmT^-1) = mathrmML^-1T^-1 quad rightarrow text(I) - **(D) Gravitational Constant**: [G] = frac[F][r^2][m_1][m_2] = frac(mathrmMLT^-2)(mathrmL^2)mathrmM^2 = mathrmM^-1L^3T^-2 quad rightarrow text(III) Matching path yields: (A)-(II), (B)-(IV), (C)-(I), (D)-(III). ### Pattern Recognition Torque and energy share the identical dimensional formula mathrmML^2T^-2. Modulus and pressure share mathrmML^-1T^-2. Spotting these matching associations cuts solving time significantly. ### Evaluation Rubric / Model Answer null ### Chapter Mix Class 11 Physics: Units and Measurements
Q23 2025 Combination of Errors
A physical quantity Q is related to four observables a, b, c, d as follows: Q = fracab^4cd where, a = (60 pm 3)mathrm~Pa ; b = (20 pm 0.1)mathrm~m ; c = (40 pm 0.2)mathrm~Nsm^-2 and d = (50 pm 0.1)mathrm~m , then the percentage error in Q is fracx1000 , where x = ______.
Numerical Answer. Answer: 7700 to 7700

Solution

### Related Formula fracDelta QQ = fracDelta aa + 4fracDelta bb + fracDelta cc + fracDelta dd ### Core Logic Write down fractional errors from the raw text configurations: - fracDelta aa = frac360 = 0.05 - fracDelta bb = frac0.120 = 0.005 - fracDelta cc = frac0.240 = 0.005 - fracDelta dd = frac0.150 = 0.002 Compute the total fractional error expression: fracDelta QQ = [0.05 + 4(0.005) + 0.005 + 0.002] fracDelta QQ = 0.05 + 0.02 + 0.005 + 0.002 = 0.077 Percentage error expression configuration: \% text Error = fracDelta QQ times 100 = 7.7 \% Given that percentage error equals fracx1000: fracx1000 = 7.7 implies x = 7700 ### Pattern Recognition Powers scale up error contributions via direct multiplication multipliers. The term b^4 contributes exactly 4 times its basic fraction error component to the compilation step. ### Evaluation Rubric / Model Answer null ### Chapter Mix Class 11 Physics: Units and Measurements
Q21 2025 Errors in Measurement
A tiny metallic rectangular sheet has length and breadth of 5 mathrm~mm and 2.5 mathrm~mm , respectively. Using a specially designed screw gauge which has pitch of 0.75 mathrm~mm and 15 divisions in the circular scale, you are asked to find the area of the sheet. In this measurement, the maximum fractional error will be fracmathrmx100 where mathrmx is ________.
Numerical Answer. Answer: 3 to 3

Solution

### Core Logic First, find the least count of the measurement tool: textLeast Count = fractextPitchtextNumber of circular scale divisions = frac0.75 mathrm~mm15 = 0.05 mathrm~mm
Least count calculation tracking diagram for Q21
Least count calculation tracking diagram for Q21
The area of the rectangular metallic sheet is calculated as: mathrmA = mathrmL cdot mathrmW Expressing the absolute error via fractional configuration parts: fracmathrmdAmathrmA = fracmathrmdLmathrmL + fracmathrmdWmathrmW Substituting the instrument limits (mathrmdL = mathrmdW = 0.05 mathrm~mm): fracmathrmdAmathrmA = frac0.055 + frac0.052.5 = frac1100 + frac2100 = frac3100 ### Step 1: Final Value Match Comparing this to the target format fracmathrmx100 gives: mathrmx = 3 ### Pattern Recognition The absolute measurement uncertainty matches the instrument's least count value directly. Sum up individual fractional errors to compute the total area uncertainty parameter. ### Evaluation Rubric / Model Answer null ### Chapter Mix Class 11 Physics: Units and Measurements
Q23 2025 Dimensional Analysis
In a measurement, it is asked to find modulus of elasticity per unit torque applied on the system. The measured quantity has dimension of left[mathrmM^mathrmamathrmL^mathrmbmathrmT^mathrmcright] . If b = 3 , the value of c is
Numerical Answer. Answer: 0 to 0

Solution

### Core Logic Let's find the dimensional formula for the ratio of Modulus of Elasticity to Torque: textTarget Dimensions = frac[textModulus of Elasticity][textTorque] textTarget Dimensions = frac[mathrmM L^-1 mathrmT^-2][mathrmM L^2 mathrmT^-2] = [mathrmM^0 mathrmL^-3 mathrmT^0] ### Step 1: Exponent Matching Comparing this output to the target layout formula [mathrmM^mathrma mathrmL^mathrmb mathrmT^mathrmc]: mathrmc = 0 ### Pattern Recognition Both dimensions share identical time dependence factors (mathrmT^-2), meaning they cancel out completely. This leaves the time exponent value as exactly zero. ### Evaluation Rubric / Model Answer null ### Chapter Mix Class 11 Physics: Units and Measurements

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