Units — NEET Physics PYQ MCQs with Solutions
Free NEET Physics PYQ Units MCQs with step-by-step solutions (5 questions). Part of Units and Measurements. Practise online on Prepizo — no login needed.
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Questions with solutions
Q1 — Units · medium
The angle of $1'$ (minute of arc) in radian is nearly equal to
A. $2.91\times10^{-4}$ rad ✓ Correct
B. $4.85\times10^{-4}$ rad
C. $4.80\times10^{-6}$ rad
D. $1.75\times10^{-2}$ rad
Solution: $1$ minute $=\dfrac{1}{60}$ degree $=\dfrac{1}{60}\times\dfrac{\pi}{180}$ rad $=2.91\times10^{-4}$ rad.
Q2 — Units · medium
The unit of thermal conductivity is :
A. J m$^{-1}$ K$^{-1}$
B. W m K$^{-1}$
C. W m$^{-1}$ K$^{-1}$ ✓ Correct
D. J m K$^{-1}$
Solution: The rate of heat flow through a conductor of length $L$ and area of cross-section $A$ is given by $\dfrac{dQ}{dt}=KA\dfrac{\Delta T}{L}$ J/s or watt, where $K$ = coefficient of thermal conductivity and $\Delta T$ = change in temperature. $\Rightarrow K=\dfrac{L}{A\Delta T}\dfrac{dQ}{dt}$. $\therefore$ Unit of $K=\dfrac{\text{metre}}{(\text{metre})^2\times\text{kelvin}}\times\text{watt}=\text{Wm}^{-1}\text{K}^{-1}$.
Q3 — Units · medium
The unit of permittivity of free space, $\varepsilon_0$ is
A. coulomb/newton-metre
B. newton-metre$^2$ / coulomb$^2$
C. coulomb$^2$ /newton-metre$^2$ ✓ Correct
D. coulomb$^2$ /(newton - metre)$^2$
Solution: According to Coulomb's law, the electrostatic force $F=\dfrac{1}{4\pi\varepsilon_0}\times\dfrac{q_1q_2}{r^2}$, where $q_1$ and $q_2$ = charges, $r$ = distance between charges and $\varepsilon_0$ = permittivity of free space. $\Rightarrow \varepsilon_0=\dfrac{1}{4\pi}\times\dfrac{q_1q_2}{r^2F}$. Substituting the units for $q$, $r$ and $F$, we obtain unit of $\varepsilon_0=\dfrac{\text{coulomb}\times\text{coulomb}}{\text{newton-(metre)}^2}=\dfrac{(\text{coulomb})^2}{\text{newton-(metre)}^2}$.
Q4 — Units · medium
The value of Planck's constant in SI unit is
A. $6.63\times10^{-31}$ J-s
B. $6.63\times10^{-30}$ kg - m / s
C. $6.63\times10^{-32}$ kg - m$^2$
D. $6.63\times10^{-34}$ J - s ✓ Correct
Solution: The value of Planck's constant is $6.63\times10^{-34}$ and J-s is the unit of the Planck's constant.
Q5 — Units · medium
In a particular system, the unit of length, mass and time are chosen to be 10 cm, 10 g and 0.1 s respectively. The unit of force in this system will be equivalent to
A. 0.1 N ✓ Correct
B. 1 N
C. 10 N
D. 100 N
Solution: Force $F=[MLT^{-2}]=(10\text{ g})(10\text{ cm})(0.1\text{ s})^{-2}$. Changing these units into the MKS system, $F=(10^{-2}\text{ kg})(10^{-1}\text{ m})(10^{-1}\text{ s})^{-2}=10^{-1}$ N $=0.1$ N.