A satellite moves in a stable circular orbit round the earth if (where $$\mathrm{V}_{\mathrm{H}}, \mathrm{V}_{\mathrm{c}}$$ and $$\mathrm{V}_{\mathrm{e}}$$ are the horizontal velocity, critical velocity and escape velocity respectively)

The mean electrical energy density between plates of a charged air capacitor is (where $$\mathrm{q}=$$ charge on capacitor, $$\mathrm{A}=$$ Area of capacitor plate)

A person is observing a bacteria through a compound microscope. For better observation and to improve its resolving power he should

The inductive reactance of a coil is '$$\mathrm{X}_{\mathrm{L}}$$'. If the inductance of a coil is tripled and frequency of a.c. supply is doubled, then the new inductive reactance will be