At an airport,a person is made to walk through the doorway of a metal detector,for security reasons. If she/he is carrying anything made of metal,the metal detector emits a sound. On what principle does this detector work?

$A$ series $LCR$ circuit is connected to a $45 \sin (\omega t) \text{ V}$ source. The resonant angular frequency of the circuit is $10^5 \text{ rad s}^{-1}$ and current amplitude at resonance is $I_0$. When the angular frequency of the source is $\omega = 8 \times 10^4 \text{ rad s}^{-1}$, the current amplitude in the circuit is $0.05 I_0$. If $L = 50 \text{ mH}$, match each entry in List-$I$ with an appropriate value from List-$II$ and choose the correct option.

List-$I$	List-$II$
$(P)$ $I_0$ in $\text{mA}$	$(1)$ $44.4$
$(Q)$ The quality factor of the circuit	$(2)$ $18$
$(R)$ The bandwidth of the circuit in $\text{rad s}^{-1}$	$(3)$ $400$
$(S)$ The peak power dissipated at resonance in $\text{Watt}$	$(4)$ $2250$
	$(5)$ $500$

An $AC$ circuit has $R = 100 \, \Omega$,$C = 2 \, \mu F$,and $L = 80 \, mH$ connected in series. The quality factor of the circuit is $.......$

In an $L-C-R$ circuit,the power factor at resonance is

An inductance of $1\, mH$,a capacitor of $10\, \mu F$,and a resistance of $50\, \Omega$ are connected in series. The reactances of the inductor and the capacitor are the same. The reactance of either of them will be........$\Omega$.

$A$ resistor of resistance $R$, an inductor of inductive reactance $2R$, and a capacitor of capacitive reactance $X_C$ are connected in series to an $A.C.$ source. If the series $LCR$ circuit is in resonance, then the power factor of the circuit and the value $X_C$ are respectively: