Units & Measurements · Physics · JEE Advanced
Numerical
In a particular system of units, a physical quantity can be expressed in terms of the electric charge $e$, electron mass $m_{e}$, Planck's constant $h$, and Coulomb's constant $k=\frac{1}{4 \pi \epsilon_{0}}$, where $\epsilon_{0}$ is the permittivity of vacuum. In terms of these physical constants, the dimension of the magnetic field is $[B]=[e]^{\alpha}\left[m_{e}\right]^{\beta}[h]^{\gamma}[k]^{\delta}$. The value of $\alpha+\beta+\gamma+\delta$ is _______.
MCQ (Single Correct Answer)
A dimensionless quantity is constructed in terms of electronic charge $e$, permittivity of free space $\varepsilon_0$, Planck's constant $h$, and speed of light $c$. If the dimensionless quantity is written as $e^\alpha \varepsilon_0{ }^\beta h^\gamma c^\delta$ and $n$ is a non-zero integer, then $(\alpha, \beta, \gamma, \delta)$ is given by :
Area of the cross-section of a wire is measured using a screw gauge. The pitch of the main scale is $0.5 \mathrm{~mm}$. The circular scale has 100 divisions and for one full rotation of the circular scale, the main scale shifts by two divisions. The measured readings are listed below.
Measurement condition | Main scale reading | Circular scale reading |
---|---|---|
Two arms of gauge touching each other without wire |
0 division | 4 divisions |
Attempt-1: With wire | 4 divisions | 20 divisions |
Attempt-2: With wire | 4 divisions | 16 divisions |
What are the diameter and cross-sectional area of the wire measured using the screw gauge?
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$$$z \pm \Delta z = {{x \pm \Delta x} \over {y \pm \Delta y}} = {x \over y}\left( {1 \pm {{\Delta x} \over x}} \right){\left( {1 \pm {{\Delta y} \over y}} \right)^{ - 1}}.$$$
The series expansion for $${\left( {1 \pm {{\Delta y} \over y}} \right)^{ - 1}},$$ to first power in $$\Delta y/y.$$ is $$1 \pm \left( {\Delta y/y} \right).$$ The relative errors in independent variables are always added. So the error in $$z$$ will be
$$$\Delta z = z\left( {{{\Delta x} \over x} + {{\Delta y} \over y}} \right).$$$
The above derivation makes the assumption that $$\Delta x/x < < 1,$$ $$\Delta y/y < < 1.$$ Therefore, the higher powers of these quantities are neglected.
Consider the ratio $$r = {{\left( {1 - a} \right)} \over {1 + a}}$$ to be determined by measuring a dimensionless quantity $$a.$$ If the error in the measurement of $$a$$ is $$\Delta a\left( {\Delta a/a < < 1.} \right.$$ then what is the error $$\Delta r$$ in determining $$r$$?
$$$z \pm \Delta z = {{x \pm \Delta x} \over {y \pm \Delta y}} = {x \over y}\left( {1 \pm {{\Delta x} \over x}} \right){\left( {1 \pm {{\Delta y} \over y}} \right)^{ - 1}}.$$$
The series expansion for $${\left( {1 \pm {{\Delta y} \over y}} \right)^{ - 1}},$$ to first power in $$\Delta y/y.$$ is $$1 \pm \left( {\Delta y/y} \right).$$ The relative errors in independent variables are always added. So the error in $$z$$ will be
$$$\Delta z = z\left( {{{\Delta x} \over x} + {{\Delta y} \over y}} \right).$$$
The above derivation makes the assumption that $$\Delta x/x < < 1,$$ $$\Delta y/y < < 1.$$ Therefore, the higher powers of these quantities are neglected.
In an experiment the initial number of radioactive nuclei is $$3000.$$ It is found that $$1000 \pm 40$$ nuclei decayed in the first $$1.0s.$$ For $$\left| x \right| < < 1.$$ $$\ln \left( {1 + x} \right) = x$$ up to first power in $$x.$$ The error $$\Delta \lambda ,$$ in the determination of the decay constant $$\lambda ,$$ in $${s^{ - 1}},$$ is
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List I
P. Boltzmann ConstantQ. Coefficient of viscosity
R. Plank Constant
S. Thermal conductivity
List II
1. [ML2T-1]2. [ML-1T-1]
3. [MLT-3K-1]
4. [ML2T-2K-1]
Taking the electronic charge as 'e' and the permittivity as $$'{\varepsilon _0}'$$. Use dimensional analysis to determine the correct expression for $${\omega _p}$$.
Student I, II and III perform an experiment for measuring the acceleration due to gravity (g) using a simple pendulum. They use different length of the pendulum and/or record time for different number of oscillations. The observations area shown in the table.
Least count for length = 0.1 cm
Least count for time = 0.1 s
Student | Length of the pendulum (cm) |
No. of oscillations (n) |
Total time for(n) oscillations (s) |
Time periods (s) |
---|---|---|---|---|
I | 64.0 | 8 | 128.0 | 16.0 |
II | 64.0 | 4 | 64.0 | 16.0 |
III | 20.0 | 4 | 36.0 | 9.0 |
If EI, EII and EIII are the percentage errors in g, i.e., $$\left(\frac{\triangle g}g\times100\right)$$ for students I, II and III, respectively,then
Column I
(A) GMeMs ,
G $$ \to $$ universal gravitational constant, Me $$ \to $$ mass of the earth,
Ms $$ \to $$ mass of the Sun
(B) $${{3RT} \over M}$$,
R $$ \to $$ universal gas constant, T $$ \to $$ absolute temperature,
M $$ \to $$ molar mass
(C) $${{{F^2}} \over {{q^2}{B^2}}}$$ ,
F $$ \to $$ force, q $$ \to $$ charge, B $$ \to $$ magnetic field
(D) $${{G{M_e}} \over {{R_e}}}$$,
G $$ \to $$ universal gravitational constant,
Me $$ \to $$ mass of the earth, Re $$ \to $$ radius of the earth
Column II
(p) (volt) (coulomb) (metre)
(q) (kilogram) (metre)3 (second)−2
(r) (meter)2(second)−2
(s) (farad) (volt)2 (kg)−1
A student performs an experiment to determine the Young's modulus of a wire, exactly 2 m long, by Searle's method. In a particular reading, the student measures the extension in the length of the wire to be 0.8 mm with an uncertainty of $$\pm0.05\;\mathrm{mm}$$ at a load of exactly 1.0 kg. The student also measures the diameter of the wire to be 0.4 mm with an uncertainty of $$\pm0.01\;\mathrm{mm}$$. Take g = 9.8 m/s2 (exact). The Young's modulus obtained from the reading is
In a screw gauge, the zero of main scale coincides with the fifth division of circular scale in figure (i).The circular division of screw gauge is 50. It moves 0.5 mm on main scale in one rotation.The diameter of the ball in figure (ii) is
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A cube has a side of length 1.2 ✕ 10-2 m. Calculate its volume.
( $${\varepsilon _0}$$ : permittivity of free space, E electric field )
MCQ (More than One Correct Answer)
Subjective
Column - I gives the three physical quantities. Select the appropriate units for the choices given in Column - II. Some of the physical quantities may have more than one choice correct:
Column I | Column II |
---|---|
Capacitance | (i) ohm-second |
Inductance | (ii) coulomb2 - joule-1 |
Magnetic Induction | (iii) coulomb (volt)-1 |
(iv) newton (amp-meter)-1 | |
(v) volt-second (ampere)-1 | |
Column I | Column II |
---|---|
Angular Momentum | ML2T-2 |
Latent heat | ML2Q-2 |
Torque | ML2T-1 |
Capacitance | ML3T-1Q-2 |
Inductance | M-1L-2T2Q2 |
Resistivity | L2T-2 |
(i) magnetic flux
(ii) rigidity modulus
(i) Young's modulus
(ii) Magnetic Induction
(iii) Power of a lens