The density of a solid ball is to be determined in an experiment. The diameter of the ball is measured with a screw gauge,whose pitch is $0.5 \ mm$ and there are $50$ divisions on the circular scale. The reading on the main scale is $2.5 \ mm$ and that on the circular scale is $20$ divisions. If the measured mass of the ball has a relative error of $2 \%$,the relative percentage error in the density is (in $\%$)

Fill in the blanks:
$(a)$ To measure the direct distance of a mountain,....... is used.
$(b)$ For the measurement of time,the ........... clock is the most accurate.
$(c)$ Rounding off $15.753$ to three significant figures gives ....... .

If we use permittivity $\varepsilon$,resistance $R$,gravitational constant $G$,and voltage $V$ as fundamental physical quantities,then:

Which of the following pairs does not have similar dimensions?

Names of units of some physical quantities are given in List-$I$ and their dimensional formulae are given in List-$II$. Match the correct pairs in the lists:

$A$. $Pa \cdot s$	$(i)$. $[L^2 T^{-2} K^{-1}]$
$B$. $N \cdot m \cdot K^{-1}$	$(ii)$. $[MLT^{-3} K^{-1}]$
$C$. $J \cdot kg^{-1} \cdot K^{-1}$	$(iii)$. $[ML^{-1} T^{-1}]$
$D$. $W \cdot m^{-1} \cdot K^{-1}$	$(iv)$. $[ML^2 T^{-2} K^{-1}]$

The diameter of a wire measured by a screw gauge of least count $0.001 \text{ cm}$ is $0.08 \text{ cm}$. The length measured by a scale of least count $0.1 \text{ cm}$ is $150 \text{ cm}$. When a weight of $100 \text{ N}$ is applied to the wire,the extension in length is $0.5 \text{ cm}$,measured by a micrometer of least count $0.001 \text{ cm}$. The error in the measured Young's modulus is $\alpha \times 10^9 \text{ N/m}^2$. The value of $\alpha$ is . . . . . . . (Ignore the contribution of the load to Young's modulus error calculation)