When you walk through a metal detector carrying a metal object in your pocket,it raises an alarm. This phenomenon works on

In a series $LCR$ resonant circuit,the quality factor is measured as $100$. If the inductance is increased by two fold and resistance is decreased by two fold,then the quality factor after this change will be .........

The resonance point in the $X_L - f$ and $X_C - f$ curves is

An a.c. e.m.f. of peak value $V_0 = 230 \ V$ and frequency $f = 50 \ Hz$ is connected to a circuit with $R = 11.5 \ \Omega$,$L = 2.5 \ H$ and a capacitor $C$ all in series. For the current in the circuit to be maximum,the circuit must be in resonance. Find the value of $C$ and the maximum current $I_{max}$ (take $\pi^2 = 10$).

In a series $LCR$ circuit, the voltage across $R$ is $100 \text{ V}$, $R = 1 \text{ k}\Omega$ and $C = 2 \mu\text{F}$. The angular frequency $\omega$ is $200 \text{ rad s}^{-1}$. At resonance, the voltage across '$L$' is (in $V$)

An inductor of inductance $2 \mu H$ is connected in series with a resistance,a variable capacitor and an a.c. source of frequency $5 \text{ kHz}$. The value of capacitance for which maximum current is drawn into the circuit is $\frac{1}{x} \text{ F}$,where the value of '$x$' is (Take $\pi^2 = 10$).