If velocity of light $c$, Planck’s constant $h$ and gravitational constant $G$ are taken as fundamental quantities, then express mass, length and time in terms of dimensions of these quantities.
We know that, dimensions of $(h)=\left[\mathrm{M}^{1} \mathrm{~L}^{2} \mathrm{~T}^{-1}\right]$ (From $\left.\mathrm{E}=h f\right]$ Dimensions of $(c)=\left[\mathrm{L}^{1} \mathrm{~T}^{-1}\right] \quad(c$ is velocity $)$
Dimensions of gravitational constant
$(\mathrm{G})=\left[\mathrm{M}^{-1} \mathrm{~L}^{3} \mathrm{~T}^{-2}\right] \quad\left(\text { From } \mathrm{F}=\frac{\mathrm{G} m_{1} m_{2}}{r^{2}}\right)$
$(i)$ Let $\mathrm{m} \propto c^{a} h^{b} \mathrm{G}^{c}$
$\Rightarrow \mathrm{m}=k c^{a} h^{b} \mathrm{G}^{c}$
where, $k$ is a dimensionless constant of proportionality. Substituting dimensions of each term in Eq.$ (i)$, we get
$\left[\mathrm{ML}^{0} \mathrm{~T}^{0}\right] =\left[\mathrm{LT}^{-1}\right]^{x} \times\left[\mathrm{ML}^{2} \mathrm{~T}^{-1}\right]^{y}\left[\mathrm{M}^{-1} \mathrm{~L}^{3} \mathrm{~T}^{-2}\right]^{z}$
$=\left[\mathrm{M}^{b-c} \mathrm{~L}^{a+2 b+3 c} \mathrm{~T}^{-a-b-2 c}\right]$
Comparing powers of same terms on both sides, we get
$b-c=1\ldots \text { (ii) }$
$a+2 b+3 c=0\ldots\text { (iii) }$
$-a-b-2 c=0\ldots\text { (iv) }$
$\ldots \text { (ii) }$
$\ldots \text { (iii) }$
Adding Eqs. $(ii)$, $(iii)$ and $(iv)$, we get
$2 b=1 \Rightarrow b=\frac{1}{2}$
Substituting value of $\mathrm{b}$ in eq. $(ii)$, we get
$c=-\frac{1}{2}$
From eq. $(iv)$,
$a=-b-2 c$
Substituting values of $b$ and $c$, we get
$a=-\frac{1}{2}-2\left(-\frac{1}{2}\right)=\frac{1}{2}$
A massive black hole of mass $m$ and radius $R$ is spinning with angular velocity $\omega$. The power $P$ radiated by it as gravitational waves is given by $P=G c^{-5} m^{x} R^{y} \omega^{z}$, where $c$ and $G$ are speed of light in free space and the universal gravitational constant, respectively. Then,
Match List$-I$ with List$-II$.
List$-I$ | List$-II$ |
$(A)$ Angular momentum | $(I)$ $\left[ ML ^2 T ^{-2}\right]$ |
$(B)$ Torque | $(II)$ $\left[ ML ^{-2} T ^{-2}\right]$ |
$(C)$ Stress | $(III)$ $\left[ ML ^2 T ^{-1}\right]$ |
$(D)$ Pressure gradient | $(IV)$ $\left[ ML ^{-1} T ^{-2}\right]$ |
Choose the correct answer from the options given below:
A neutron star with magnetic moment of magnitude $m$ is spinning with angular velocity $\omega$ about its magnetic axis. The electromagnetic power $P$ radiated by it is given by $\mu_{0}^{x} m^{y} \omega^{z} c^{u}$, where $\mu_{0}$ and $c$ are the permeability and speed of light in free space, respectively. Then,
The velocity $v$ (in $cm/\sec $) of a particle is given in terms of time $t$ (in sec) by the relation $v = at + \frac{b}{{t + c}}$ ; the dimensions of $a,\,b$ and $c$ are