Which of the following statements is TRUE for n-type semiconductor?

When a current in the conducting coil is changed from 5 A in one direction to 5 A in opposite direction in 0.5 second, an average induced e.m.f in the coil is 2 V . The selfinductance of the coil is

The electric field intensity near a conducting surface having uniform surface charge density ' $\sigma$ ' is given by ( $\varepsilon_0=$ permittivity of free space)

The excess pressure inside first soap bubble is three times that of a second soap bubble. The ratio of volumes of the first to second bubble