Exercise (Previous Year Questions)

A transformer is used to light a $100 \mathrm{w}$ and $110 \mathrm{V}$ lamp from a $220 \mathrm{V}$ mains. If the main current is $0.5$ amp, the efficiency of the transformer is approximately -

In an a.c. circuit the e.m.f. $\left(e\right)$ and the current $\left(i\right)$ at any instant are given respectively by:
$e=E_0\sin \omega t$
$i=I_0\sin \left(\omega t-\varphi \right)$
The average power in the circuit over one cycle of a.c. is :

A condenser of capacity C is charged to a potential difference of V₁. The plates of the condenser are then connected to an ideal inductor of inductance L. The current through the inductors when the potential difference across the condenser reduces to V₂ is ?

In a given series LCR circuit $\mathrm{R}=4\Omega ,{\mathrm{X}}_{\mathrm{L}}=5\Omega$ and $X_C=8\Omega ,$the current

An electrical device operate at $12 \mathrm{A}$ current and$120 V DC$ . If it is connected with $250 V$and  $30 \mathrm{Hz} AC$ . Then power consumption :- 

A series R-C circuit is connected to an alternating voltage source. Consider two situations :-
(a) When capacitor is air filled.
(b) When capacitor is mica filled.
Current through resistor is i and voltage across capacitor is V then :- 

In the given circuit the potential difference across resistance is $54 \mathrm{V}$ and power consumed by it is $16 \mathrm{W}$. If $AC$ frequency is $60 \mathrm{Hz}$find the value of $L$: 
                     

A series L-C-R circuit R = 10 k$\Omega$, L = 20mH, C = 5µF is connected to AC source V = 10sin$\omega$t. Find out band width of signal :