In series LCR resonant circuit, R=800 $\Omega$, C = 2 $\mu$F and voltage across resistance is 200 V. The angular frequency is 250 rad/s. At resonance the voltage across the capacitance is

An alternating e.m.f. is given by $e = e_0 \sin \omega t$. In what time the e.m.f. will have half its maximum value, if 'e' starts from zero? ($\sin 30^\circ = 0.5$)

A resistor of 100 $\Omega$, inductor of self inductance $\left(\dfrac{4}{\pi^2}\right)$ H and a capacitor of unknown capacity are connected in series to an a.c. source of 200 V and 50 Hz. When the current and voltage are in phase, the value of capacity is

If a parallel beam of light is incident on spherical mirrors then after reflection they pass through focal point. If F is the focal length and R is the radius of curvature of mirror then