When a.c. source is connected across a pure capacitor, the correct phase relation between current and emf is shown in figure.

In series LCR circuit $R = 10\,\Omega$ and impedance is $30\,\Omega$. An r.m.s. voltage $210$ V, is applied across the circuit. The true power consumed in AC circuit is

Light travels a distance 'x' in time '$t_0$' in air and '$4x$' in time '$t_1$' in another denser medium. The critical angle for this medium is

In a biprism experiment, a steady interference pattern is observed on the screen kept at a distance of 100 cm using a light of wavelength $5000$ Å. Without changing the distance between the virtual images of the slit, the source of light is replaced by a source of wavelength $6400$ Å. Now, to reduce the fringe width by $20\%$ of its initial value, the screen should be moved