A step down transformer drops the main supply voltage of 220 V to 10 V. The primary draws a current of 5 A and the current induced in the secondary in 100 A. Calculate the efficiency of the transformer.


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An L C R circuit has L = 10 mH connected in series to a source of  volt. Calculate the current-amplitude and the average power dissipated per cycle at a frequency 10% lower than the resonant frequency. 


A 750-Hz, 20-V source is connected to a resistance of , an inductance of 0.1803 H and a capacitance of , all in series. Calculate the time in which the resistance (thermal capacity = 2 JoC–1) will get heated by 10oC. 


Obtain the resonant frequency and Q-factor of a series LCR circuit with L= 3.0 H. How will you improve the sharpness of resonance of the circuit by reducing its full width at half maximum by a factor of 2?  


A virtual current of 4 A flows in a coil when it is connected in a circuit having a.c. of frequency 50 Hz. The power consumed in the coil is 240 W. Calculate the inductance of the coil if the virtual p.d. across it is 100 V. 


An a.c. circuit having an inductor and a resistor in series draws a power of 560 W from an a.c. source marked 210 V-60 Hz. The power factor of the circuit is 0.8. Calculate the impedance of the circuit and the inductance of the inductor. 


A town situated 20 km away from a power plant generating power at 440 V, requires 600 kW of electric power at 200 V. The resistance of the two-wire line carrying power is  /km. The town gets power from the line through a 3000-220 V step-down transformer at a sub-station in the town. Estimate the line power loss as heat.  


The ratio of the number of turn in the primary and the secondary coil of a step-up transformer is 1 : 200. It is connected to A-C mains of 200 V. Calculate the voltage developed in the secondary. Determine the current in the secondary, when a current of 2.0 A flows through the primary.   


Calculate the current drawn by the primary of a transformer which steps down 200 V to 20 V to operate a device of resistance . Assume the efficiency of transformer to be 80%.  


A transformer of 100% efficiency has 200 turns in the primary and 40000 turns in the secondary. It is connected to a 220-V main supply and the secondary feeds to a  resistance. Calculate the output potential difference per turn and the power delivered to the load. 


An alternating emf of 120 V is applied to the primary of a step-up transformer. The current in the primary is 1.85 A while that induced in the secondary is 150 mA. Find the voltage across the secondary, assuming 95% efficiency.