A uniform solid sphere of mass ' $m$ ' and radius ' r ' is surrounded by a uniform thin spherical shell of radius ' $2 r$ ' and mass ' $m$ ' then the gravitational field

A current of 5 A is flowing at 220 V in a primary coil of a transformer. If the voltage produced in the secondary coil is 2200 V and $50 \%$ of power is lost, then the current in the secondary coil will be

The magnetic field at the centre of a current carrying circular coil of area ' $A$ ' is ' $B$ '. The magnetic moment ( M ) of the coil is ( $\mu_0=$ permeability of free space)

A pipe open at both ends produces a fundamental frequency $n_1$. When the pipe is kept with $\frac{3^{\text {th }}}{4}$ of its length in water, it produces a note of fundamental frequency $\mathrm{n}_2$. The ratio of $\frac{\mathrm{n}_1}{\mathrm{n}_2}$ is