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Physics Help >> Index to Physics Homework Help » LRC Circuits
2. Wearing a bracelet in a region of strong magnetic field could be hazardous. Discuss. 3. If a capacitor has opposite 5.2 x10-6 C charges on the plates, and an electric field of 2x103 V/m is desired between the plates, what must each plate's area be? 4. A parallel-plate capacitor is made from two aluminum-foil sheets, each 4.0 cm wide and 5.00 m long. Between the sheets is a Teflon strip of the same width and length that is 0.028 mm thick. What is the capacitance of this capacitor? (The dielectric constant of Teflon is 2.1.) 5. To operate a given flash lamp requires a charge of 25 µC. What capacitance is needed to store this much charge in a capacitor with a potential difference between its plates of 2.4 V? 6. When a given capacitor is filled with mica (mica=k=5.4) and connected to a 3.00V source, 9.00mJ of energy are stored in it. What potential would be needed to store the same energy in this capacitor if it is empty? 7. Initially, a 3.40F capacitor carries 5.50C and a 1.6F capacitor carries a 4.3C. If these two capacitors are now connected in parallel with unlike charges together, determine the final charge on the 3.4F capacitor. 8. What resistance is needed in series with a 10-uF capacitor at 1.0 kHz for a total impedance of 45 ohms? 9. An RL circuit has a resistor R and an inductor of L. The circuit is connected to a DC power supply of V. Find (a) the final current of the circuit. (b) How long does it take for the current in the circuit to reach nth its final value? 10. A 1.0 μF and a 2.0 μF capacitor are connected in series across a 3.0 V battery. What is the voltage across the 1.0 μF capacitor? 11. The electric potential energy stored in a capacitor is73 J, and the capacitance is 120 μF. What is the potential difference across the capacitor plates? 12. The plates of a capacitor are separated by 0.38mm of air and have a potential difference of 26 V between them. If the area of each plate is 100 cm squared, what is: (a) the capacitance, (b) the electric field strength between the plates, (c) the amount of charge stored on each plate? 13. A parallel-plate capacitor has 2.00-cm2 plates that are separated 5.00 mm with air between them. If a 12.0 V battery is connected to this capacitor, how much energy does it store? 14. The current in an RL circuit reaches 95% max in 3.00 seconds. The inductance is .310 mH. Find the inductive time constant and resistance in the circuit. 15. The timer circuit delaying the closing of an elevator door is to have a capacitance of 32.0 μF between points A and B. When the circuit is constructed, a 34.8 μF capacitor is used instead. To meet the specification, one additional capacitor can be placed between 2 points. What should it\'s capacitance be and should it be in series or parallel with the first capacitor? 16. A capacitor with air between its plates is charged to 100 V and then disconnected from the battery. When a piece of glass is placed between the plates, the voltage across the capacitor drops to 20 V. What is the dielectric constant of the glass? 17. A capacitor of capacitance 5.00 microfarad is charged to24.0 volt and another capacitor 6.0 microfarad is charged to 12.0 V. if the capacitors are connected positive-to-positive and negative-to-negative, find the new charges on the capacitors. 18. A capacitor in a single-loop RC circuit is charged to 63% of its final voltage in 1.5 sec. Find the time constant for the circuit and the percentage of the circuit's final voltage after 15 sec.
Answers
1. C1 and C2 are in parallel, so their combined capacitance is C1 + C2.
A resonant circuit has maximum current when 2πfL = 1/(2πfC), or
C = 1/(4π2f2L)
Since C = C1 + C2
C2 = 1/(4π2f2L) - C1
This will have to be solved twice: once for each frequency extreme.
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