EXAMPLE 21-10 Cell phone charger. The charger for a cell phone contains a transformer that reduces 120-V (or 240-V) ac to 5.0-V ac to charge the 3.7-V battery (Section 19-4). (It also contains diodes to change the 5.0-V ac to 5.0-V dc.) Suppose the secondary coil contains 30 turns and the charger supplies 700 mA. Calculate (a) the number of turns in the primary coil, (b) the current in the primary, and (c) the power transformed.

EXAMPLE 21-10 Cell phone charger. The charger for a cell phone contains a transformer that reduces 120-V (or 240-V) ac to 5.0-V ac to charge the 3.7-V battery (Section 19-4). (It also contains diodes to change the 5.0-V ac to 5.0-V dc.) Suppose the secondary coil contains 30 turns and the charger supplies 700 mA. Calculate (a) the number of turns in the primary coil, (b) the current in the primary, and (c) the power transformed.

College Physics

11th Edition

ISBN:9781305952300

Author:Raymond A. Serway, Chris Vuille

Publisher:Raymond A. Serway, Chris Vuille

Chapter1: Units, Trigonometry. And Vectors

Section: Chapter Questions

Problem 1CQ: Estimate the order of magnitude of the length, in meters, of each of the following; (a) a mouse, (b)...

See similar textbooks

Similar questions

Suppose a large power plant generates electricity at 12.0 kV. Its old transformer once converted this voltage to 325 kV. The secondary coil of this transformer is being replaced so that its output can be 755 kV for more efficient cross-country transmission on upgraded transmission lines. V1= 325 kV V,= 755 kV (a) If the overall power output is 1000.0 MW and line resistance is 2.00 N, what was the power loss, in watts, in the old power lines which left the plant? Ploss,1 = b) If the overall power output is 1000.0 MW and line resistance is 2.00 Q, what is the power loss, in watts, in the new power lines which leave the plant? Ploss,2=
The secondary coil of a step-up transformer provides the voltage that operates an electrostatic air filter. The turns ratio of the transformer is 45:1. The primary coil is plugged into a standard 120-V outlet. The current in the secondary coil is 1.9 x 10-3 A. Find the power consumed by the air filter.
A typical wall outlet voltage in the United States is 120 volts. Personal MP3 players require much smaller voltages, typically 302.1 mV. If the number of turns in the primary coil is 35753575, calculate the number of turns NS on the secondary coil of the adapter transformer.
(5%) Problem 19: A multipurpose transformer has a secondary coil with several points at which a voltage can be extracted, giving outputs of 6.75, 14.5, and 485 V. The transformer's input voltage is 240 V, its maximum input current is 5.00 A, and its primary coil consists of 280 turns. 17% Part (a) How many turns N 1 are in the part of the secondary used to produce the output voltage 6.75 V? A 17% Part (b) How many turns N 2, are in the part of the secondary used to produce the output voltage 14.5 V? a 17% Part (c) How many turns Ng 3, are in the part of the secondary used to produce the output voltage 485 V? a 17% Part (d) What is the maximum output current I, 1. for 6.75 V, in amps? A 17% Part (e) What is the maximum output current I,2, for 14.5 V, in amps? A 17% Part (f) What is the maximum output current I, 3, for 485 V, in amps?
To ignite a mixture of gasoline and air inside an internal combustion engine--like in your car--a spark is generated by a high voltage across the spark plug, usually in the 10's of thousands of volts, but the battery is only 12 V. This massive increase in voltage is achieved through a transformer called the 'ignition coil'. A typical ignition coil has a primary with 300 turns wrapped around a radius of 2 cm over a linear distance of 15 cm. The secondary has 60,000 turns of wire over the same cylinder. The spark is generated when the current is suddenly shut off to the coil. Assuming that the magnetic field is uniform inside the primary and secondary coils, and that all of the magnetic field lines that go through the primary go through the secondary, what voltage is generated in the secondary coil if the current in the primary coil drops from 10 A to 0 A at a steady rate over the course of 50 mirco-seconds? Give your answer to 2 significant digits. Hint: Remember the definition of flux…
The transformer on a utility pole steps the voltage down from 10000 V to 220 V for use in a college science building. During the day, the transformer delivers electric energy at the rate of 10.0 kW. a) Assuming the transformer to be ideal, during that time, what are the primary and secondary currents in the transformer? b) If the transformer is only 90 % efficient (but still delivers electric power at 10.0 kW), how does its input current compare to the ideal case? c) At what rate is heat lost in the nonideal transformer? d) If you wanted to keep the transformer cool and to do this needed to dissipate half of the joule heating of part c) using water cooling lines (the other half is taken care of by air cooling), what should be the rate of flow (in liters per minute) of water in the lines? Assume the input cool water is at 68∘∘F and the maximum allowable output water temperature is 98∘∘F} .
Help A V = 86-V source is connected in series with an R = 1.8-kΩ resistor and an L = 28-H inductor and the current is allowed to reach maximum. At time t = 0 a switch is thrown that disconnects the voltage source, but leaves the resistor and the inductor connected in their own circuit. After the current decreases to 53 % of its maximum value, the battery is reconnected into the circuit by reversing the switch. 1) At what value of the time t, in milliseconds, does the current reach 77 % of its maximum? 2) How much energy, in millijoules, is supplied in total by the battery, both in initially bringing the current to maximum and in bringing the current back to the 77 % level from 53 %? Ignore energy dissipated in the resistor during those processes.
The primary coil in an ideal transformer has 1000 turns of wire and an emf of 100 V. The secondary coil has an emf of 10 V. How many turns of wire does the secondary coil have? 100 1000 10,000 100,000
When the current in an inductor decreases from Ito 0.5 I then the energy stored in the inductor will O a. doubled o b. not change O c. decrease to the half . O d. decrease to the quarter
A 6.00-V battery is connected across the primary coil of a transformer having 50 turns. If the secondary coil of the transformer has 100 turns, what voltage appears across the secondary?