De-Broglie wavelength of an electron orbiting in the $n=2$ state of hydrogen atom is close to

(Given Bohr radius $=0.052 \mathrm{~nm}$ )

To an ac power supply of 220 V at 50 Hz , a resistor of $20 \Omega$, a capacitor of reactance $25 \Omega$ and an inductor of reactance $45 \Omega$ are connected in series. The corresponding current in the circuit and the phase angle between the current and the voltage is, respectively

Which of the following options represent the variation of photoelectric current with property of light shown on the x-axis?

A pipe open at both ends has a fundamental frequency $f$ in air. The pipe is now dipped vertically in a water drum to half of its length. The fundamental frequency of the air column is now equal to: