09:03Transformers - working & applications (step up and step down) | A.C. | Physics | Khan AcademyKhan Academy India - English579views
Multiple ChoiceAn outlet in North America outputs electricity at 120 V, but a typical laptop needs to operate at around 20 V. In order to do so, a transformer is placed in a laptop's power supply. If the coil in the circuit connected to the laptop has 20 turns, how many turns must the coil in the circuit with the outlet have?462views12rank2comments
Multiple ChoiceA transformer has 200 turns in the primary and 25 turns in the secondary. If the primary is hooked up to a 120V household outlet, what is the potential across the secondary coil?343views
Textbook QuestionThe primary windings of a transformer which has an 85% efficiency are connected to 110-V ac. The secondary windings are connected across a 2.4-Ω, 75-W lightbulb. (a) Calculate the current through the primary windings of the transformer. (b) Calculate the ratio of the number of primary windings of the transformer to the number of secondary windings of the transformer.81views
Textbook Question(I) Neon signs require 12 kV for their operation. To operate from a 240-V line, what must be the ratio of secondary to primary turns of the transformer? What would the voltage output be if the transformer were connected in reverse?64views
Textbook QuestionA Step-Down Transformer. A transformer connected to a 120-V (rms) ac line is to supply 12.0 V (rms) to a portable electronic device. The load resistance in the secondary is 5.00 Ω. (a) What should the ratio of primary to secondary turns of the transformer be?195views
Textbook QuestionA transformer has 680 turns in the primary coil and 85 in the secondary coil. What kind of transformer is this, and by what factor does it change the voltage? By what factor does it change the current?22views
Textbook QuestionA model-train transformer plugs into 120-V ac and draws 0.35 A while supplying 6.5 A to the train. (a) What voltage is present across the tracks? (b) Is the transformer step-up or step-down?23views
Textbook QuestionPower is generated at 24 kV at a generating plant located 75 km from a town that requires 65 MW of power at 12 kV. Two transmission lines from the plant to the town each have a resistance of 0.10 Ω/km. What should the output voltage of the transformer at the generating plant be for an overall transmission efficiency of 98.5%, assuming a perfect transformer?21views
Textbook QuestionA high-intensity desk lamp is rated at 35 W but requires only 12 V. It contains a transformer that converts 120-V household voltage. (a) Is the transformer step-up or step-down? (b) What is the current in the secondary coil when the lamp is on?20views
Textbook QuestionA high-intensity desk lamp is rated at 35 W but requires only 12 V. It contains a transformer that converts 120-V household voltage. (c) What is the current in the primary coil? (d) What is the resistance of the bulb when on?37views
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