A transformer is used to light a 100 W and 110 V lamp using a 220 V main supply. If the supply current is 0.5 A, then the efficiency of the transformer is
100 %
99 %
90.1 %
87.7 %
If E = 100 sin (100 t) volt and are the instantaneous values of voltage and current, then the rms values of voltage and current are respectively
70.7 V, 70.7 mA
70.7 V, 70.7 A
141.4 V, 141.4 mA
141.4 V, 141.4 A
The core of a transformer is laminated to reduce
flux leakage
output power
eddy current
copper loss
C.
eddy current
After lamination of the core of a transformer eddy current reduces. Because transformers are basically two coils of wire wrapped around a core of iron. They work by induction. Induction works when current flows in one conductor and the magnetic filed forms around that conductor sweeps the other conductor and induces the voltage. If we didn't laminate core, the core would provide a place for the magnetic lines to produce current, and that current in the core would heat and the core really fast and waste energy. So by laminating the cores, we break up the current paths within core and limited eddy current.
If E0 is the peak emf, IO is the peak current and is the phase diference between them, then the average power dissipation in the circuit is
An L-C-R series AC circuit is at resonance with 10 V each across L, C and R. If the resistance is halved, the respective voltages across L, C and R are
10 V, 10 V and 5 V
10 V, 10 V and 10 V
20 V, 20 V and 5 V
20 V,20 V and 1O V
A transformer is used to light a 100 W and 110 V lamp from a 220 V main supply. If the main current is 0.5 A, then the efficiency of the transformer is nearly
89 %
100 %
91 %
85 %
An L-C-R series circuit is at resonance. Then
the phase difference between current and voltage is 90°
the phase difference between current and voltage is 45°
its impedance is purely resistive
its impedance is zero
The impedance of a R-C circuit is Z1 for frequency f and Z2 for frequency 2f. Then Z1/Z2 is
between 1 and 2
2
2 between and 1
In an L-C-R series AC circuit the voltage across L, C and R is 10 V each. If the inductor is short circuited, the voltage across the capacitor would become
10 V