A series combination of resistor 'R' and capacitor 'C' is connected to an a.c. source of angular frequency '$\omega$'. Keeping the voltage same, if the frequency is changed to $\left(\dfrac{\omega}{3}\right)$ the current becomes half of the original current. Then the ratio of capacitive reactance and resistance is

In the series LCR circuit shown in figure the impedance is

In an LCR series circuit, the potential difference across the terminals of the inductor, capacitor and resistor is 60 V, 30 V and 40 V respectively. Then supply voltage will be equal to

Refractive index of a glass convex lens is $1.5$. The radius of curvature of each of the two surfaces of the lens is 40 cm. The ratio of the power of the lens when immersed in a liquid of refractive index $1.25$ to that when placed in air is