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JEE • PHYSICS • UNITS & MEASUREMENTS

Units & measurements practice · Medium

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391 Medium
391 of 502
Application +4 | -1
In a Vernier Calipers, 10 divisions of Vernier scale is equal to the 9 divisions of main scale. When both jaws of Vernier calipers touch each other, the zero of the Vernier scale is shifted to the left of zero of the main scale and 4th 4^{\text {th }} Vernier scale division exactly coincides with the main scale reading. One main scale division is equal to 1 mm1 \mathrm{~mm}. While measuring diameter of a spherical body, the body is held between two jaws. It is now observed that zero of the Vernier scale lies between 30 and 31 divisions of main scale reading and 6th 6^{\text {th }} Vernier scale division exactly coincides with the main scale reading. The diameter of the spherical body will be
View answer and explanation
Correct option: C
3.10 cm3.10 \mathrm{~cm}
Option C (3.10 cm3.10 \mathrm{~cm}) is the closest to the calculated diameter of the spherical body after accounting for zero error and Vernier scale reading.
392 Medium
392 of 502
Analyzing +4 | -1
S=A(1−e−Bxt)S = A(1 - {e^{ - Bxt}}) where S is speed and x is displacement. Then unit of B is
View answer and explanation
Correct option: A
m−1s−1{m^{ - 1}}{s^{ - 1}}
The correct answer is A (m−1s−1{m^{ - 1}}{s^{ - 1}}) because the exponent of 'e' must be dimensionless, so the units of Bxt must be 1. Therefore, the unit of B is inverse of x and t.
393 Medium
393 of 502
Understanding +4 | -1
[ML2T−3]\left[ {M{L^2}{T^{ - 3}}} \right] is the dimension of
View answer and explanation
Correct option: B
Power
Option B (Power) is correct because the dimension of power is given by [ML2T−3]\left[ {M{L^2}{T^{ - 3}}} \right].
394 Medium
394 of 502
Understanding +4 | -1
Assertion: ‘Light year’ and ‘Wavelength’ both measure
distance.
Reason : Both have dimension of time.
View answer and explanation
Correct option: C
Assertion is correct, reason is incorrect
Option C is correct because a light year and wavelength both measure distance, but they have dimensions of length, not time.
395 Medium
395 of 502
Application +4 | -1
A screw gauge has 50 divisions on its circular scale. The circular scale is 4 units ahead of the pitch scale marking, prior to use. Upon one complete rotation of the circular scale, a displacement of 0.5 mm is noticed on the pitch scale. The nature of zero error involved and the least count of the screw gauge, are respectively.
View answer and explanation
Correct option: B
positive,10μm\mathrm{positive, 10 \mu m}
Option B (positive, 10 μ m) is correct because the circular scale is ahead of the pitch scale, indicating a positive zero error, and the least count is calculated to be 10 μ m.
396 Medium
396 of 502
Analyzing +4 | -1
In a typical combustion engine, the work done by a gas molecule is given W=α2βe−βx2kT,W = {\alpha ^2}\beta {e^{\frac{{ - \beta {x^2}}}{{kT}}}}, where xx is the displacement, kk is the Boltzmann constant and TT is the temperature. If α \alpha \, and β\beta are constants, dimensions of α\alpha will be
View answer and explanation
Correct option: B
[M0LT0][{M^0}L{T^0}]
Option B ([{M0}L{T0}]) is correct because after dimensional analysis, the dimension of alpha is found to be [L].
397 Medium
397 of 502
Understanding +4 | -1
Which physical quantities have same dimensions?
View answer and explanation
Correct option: B
Torque & Energy
Option B (Torque & Energy) is correct because both torque and energy have the same dimensional formula: ML2T−2ML^2T^{-2}.
398 Medium
398 of 502
Application +4 | -1
The dimensions of length are expressed as GxCyhzG^x C^y h^z. G\mathrm{G} is the universal gravitational constant, c\mathrm{c} is the speed of light and h\mathrm{h} is the Planck's constant. The value of (x−yz)1x\left(\frac{x-y}{z}\right)^{\frac{1}{x}} is
View answer and explanation
Correct option: A
16
Option A (16) is correct because after finding the values of x, y, and z by comparing the dimensions, the expression (x−yz)1x(\frac{{x-y}}{{z}})^{\frac{{1}}{{x}}} evaluates to 16.
399 Medium
399 of 502
Understanding +4 | -1
The unit "henry" is equivalent to:
View answer and explanation
Correct option: A
volt-second/ampere
Option A is correct because the inductance (L) is defined as the ratio of voltage (V) to the rate of change of current (di/dt), hence Henry = Volt-second/Ampere.
400 Medium
400 of 502
Understanding +4 | -1
Dimensions of charge are
View answer and explanation
Correct option: D
TATA
Option D (TATA) is correct because charge is the product of current and time, and current has dimensions of A (Amperes) and time has dimensions of T (Time).
401 Medium
401 of 502
Application +4 | -1
The screw gauge has least count equal to 0.02 mm0.02 \mathrm{~mm} and there are 50 divisions in its circular scales. The pitch of the screw gauge is
View answer and explanation
Correct option: B
1 mm1 \mathrm{~mm}
Option B (1 mm1 \mathrm{~mm}) is correct because the pitch is calculated by multiplying the least count by the number of divisions on the circular scale.
402 Medium
402 of 502
Understanding +4 | -1
Assertion: Avogadro number is the number of atoms in one gram mole.
Reason: Avogadro number is a dimensionless constant.
View answer and explanation
Correct option: C
If assertion is true but reason is false
Option C (If assertion is true but reason is false) is correct because Avogadro's number is the number of atoms in one gram mole, but it is not a dimensionless constant.
403 Medium
403 of 502
Application +4 | -1
The dimensions of (μ0ε0)−12\left(\mu_0 \varepsilon_0\right)^{-\frac{1}{2}} are
View answer and explanation
Correct option: C
[LT−1][L T^{-1}]
Option C ([LT−1][L T^{-1}]) is correct because (μ0ε0)−12(\mu_0 \varepsilon_0)^{-\frac{1}{2}} represents the speed of light, which has dimensions of length per time.
404 Medium
404 of 502
Understanding +4 | -1
The current flowing through a resistor 10.932 ohm10.932\, \mathrm{ohm} is 4.25 amp4.25\, \mathrm{amp}. The potential difference is 46.461 volt. The potential in significant figures is
View answer and explanation
Correct option: D
46.0 V46.0 \mathrm{~V}
Option D (46.0 V46.0 \mathrm{~V}) is correct because the potential difference should be rounded to the least number of significant figures in the given values, which is 3 (from 4.25 amp).
405 Medium
405 of 502
Application +4 | -1
The velocity v\mathrm{v} of a particle at time t\mathrm{t} is given by v=at+bt+c\mathrm{v}=\mathrm{at}+\frac{\mathrm{b}}{\mathrm{t}+\mathrm{c}}, where a,b\mathrm{a}, \mathrm{b} and c\mathrm{c} are constants. The dimensions of a\mathrm{a}, b\mathrm{b} and c\mathrm{c} are respectively:
View answer and explanation
Correct option: A
LT−2,L and T\mathrm{LT^{-2}, L \,and\, T}
Option A (LT−2,L and T\mathrm{LT^{-2}, L \,and\, T}) is correct because it correctly identifies the dimensions of a, b, and c based on the principle of dimensional homogeneity.
406 Medium
406 of 502
Understanding +4 | -1
How many wavelengths of Kr86  K{r^{86}}\mathrm{\;} are there in one metre
View answer and explanation
Correct option: B
1650764
Option B (1650763.73) is correct because this is the defined number of wavelengths of Kr86K{r^{86}} in one meter according to the historical definition of the meter.
407 Medium
407 of 502
Application +4 | -1
The dimensional formula of coefficient of permittivity for free space (ε0)\left( {{\varepsilon _0}} \right) in the equation F=14πε0q1q2r2,F = \frac{1}{{4\mathrm{\pi }{\varepsilon _0}}}\frac{{{q_1}{q_2}}}{{{r^2}}}, where symbols have their usual meanings, is
View answer and explanation
Correct option: B
[M−1L−3T4A2]\left[ {{\mathrm{M}^{ - 1}}{\mathrm{L}^{ - 3}}{\mathrm{T}^4}{\mathrm{A}^2}} \right]
Option B ([M−1L−3T4A2][{\mathrm{M}^{ - 1}}{\mathrm{L}^{ - 3}}{\mathrm{T}^4}{\mathrm{A}^2}]) is correct because it is the correct dimensional formula for the permittivity of free space, derived from Coulomb's law.
408 Medium
408 of 502
Understanding +4 | -1
The physical quantity that has the same dimensional formula as pressure is:
View answer and explanation
Correct option: D
Young's modulus of elasticity
Option D is correct because Young's modulus and pressure both have the same dimensional formula of ML−1T−2ML^{-1}T^{-2}.
409 Medium
409 of 502
Application +4 | -1
The relative error in calculating the value of gg from the relation T=2πlgT=2 \pi \sqrt{\frac{l}{g}} is (given the relative errors in calculating T\mathrm{T} and ll are ±x\pm x and ±y\pm y respectively)
View answer and explanation
Correct option: C
2x+y2 x+y
Option A (x+yx+y) is incorrect. The correct answer is 2x+y2x+y because the relative error in g is the sum of the relative error in l and twice the relative error in T.
410 Medium
410 of 502
Remembering +4 | -1
The dimensional formula for impulse is
View answer and explanation
Correct option: A
[MLT−1]\left[ {\mathrm{ML}{\mathrm{T}^{ - 1}}} \right]
Option A [MLT−1]\left[ {\mathrm{ML}{\mathrm{T}^{ - 1}}} \right] is correct because impulse is the product of force and time, resulting in these dimensions.
411 Medium
411 of 502
Analyzing +4 | -1
Surface tension has the same dimensions as that of
View answer and explanation
Correct option: D
Spring constant
Option D (Spring constant) is correct because both surface tension and spring constant have the same dimensional formula: [ML⁰T⁻²].
412 Medium
412 of 502
Application +4 | -1
Dimensional formula of magnetic flux is
View answer and explanation
Correct option: A
ML2T−2A−1M{L^2}{T^{ - 2}}{A^{ - 1}}
Option A (ML2T−2A−1M{L^2}{T^{ - 2}}{A^{ - 1}}) is correct because it is derived from the formula for magnetic flux, which is the product of magnetic field and area.
413 Medium
413 of 502
Understanding +4 | -1
Statement-I: The length of an object is measured with two instruments as l=4.01 cml=4.01 \mathrm{~cm} and l=4.009 cml=4.009 \mathrm{~cm}. The second instrument has a better resolution.
Statement-II: More value is the least count of an instrument, better is the resolution.
View answer and explanation
Correct option: B
Statement-I is true and statement-II is false
Option B is correct because the instrument with more decimal places (4.009 cm) has better resolution, and a smaller least count implies better resolution, not more.
414 Medium
414 of 502
Analyzing +4 | -1
Which physical quantities have the same dimension
View answer and explanation
Correct option: A
Couple of force and work
Option A is correct. Couple of force and work both have the same dimensions of [ML²T⁻²], representing energy or torque.
415 Medium
415 of 502
Analyzing +4 | -1
Which of the following quantities can have SI unit kg m2 A−2 s−3\mathrm{kg} \mathrm{~m}^2 \mathrm{~A}^{-2} \mathrm{~s}^{-3}.
View answer and explanation
Correct option: C
Resistance
Option C (Resistance) is correct because its SI unit, when expressed in base units, matches the given unit: kg m² A⁻² s⁻³.
416 Medium
416 of 502
Application +4 | -1
The wavelength associated with a moving particle depends upon power p of its mass m, qth power of its velocity v and rth power of planck’s constant h. Then the correct set of values of p,q and r is
View answer and explanation
Correct option: D
p=−1,q=−1,r=1p = - 1,q = - 1,r = 1
Option D (p=−1,q=−1,r=1p = - 1,q = - 1,r = 1) is correct because it satisfies the dimensional analysis for de Broglie wavelength.
417 Medium
417 of 502
Application +4 | -1
The value of 0.99-0.989 is
View answer and explanation
Correct option: C
0.01×10−10.01 \times {10^{ - 1}}
Option C (0.01×10−10.01 \times {10^{ - 1}}) is correct because the subtraction 0.99 - 0.989 = 0.001, which can be written as 0.01×10−10.01 \times 10^{-1}. The result should have the same number of decimal places as the least precise number (0.99).
418 Medium
418 of 502
Analyzing +4 | -1
For a real gas the equation of gas is given by (P+an2V2)(V−bn)=nRT\left(P+\frac{a n^2}{V^2}\right)(V-b n)=n R T. If symbols have their usual meaning, then the dimensions of v2an2\frac{v^2}{a n^2} is same as that of
View answer and explanation
Correct option: A
Compressibility
Option A (Compressibility) is correct because V2an2\frac{V^2}{a n^2} has the dimensions of inverse pressure, which is the dimension of compressibility.
419 Medium
419 of 502
Remembering +4 | -1
Unit of moment of inertia in MKS system
View answer and explanation
Correct option: C
kg×m2kg \times {m^2}
Option C (kg×m2kg \times {m^2}) is correct because the moment of inertia is mass times the square of the distance, hence kg×m2kg \times {m^2}.
420 Medium
420 of 502
Analyzing +4 | -1
What will be dimensions of aa in the formula p=(p0+a)(b+t)p=\left(p_0+a\right)(b+t) here p=p= pressure, t=t= time, and x=x= distance:
View answer and explanation
Correct option: A
[ML−1T−3]\left[\mathrm{ML}^{-1} \mathrm{T}^{-3}\right]
Option A ([ML-1 T-3]) is correct because, based on dimensional analysis, the dimensions of 'a' in the given formula are [ML-1 T-3].
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