14. Two parallel conducting plates are connected to a constant voltage source. T

Question

14. Two parallel conducting plates are connected to a constant voltage source. The magnitude of the elec¬tric field between the plates is 2,000 N/C. If the voltage is doubled and the distance between the plates is reduced to 1/5 the original distance, the magnitude of the new electric field is
(A) 800 N/C (B) 1,600 N/C (C) 2,400 N/C (D) 5,000 N/C (E) 20,000 N/C

18. What is the potential energy of a particle of charge +q that is held at point P ?


20. A certain coffeepot draws 4.0 A of current when it is operated on 120 V household lines. If electrical energy costs 10 cents per kilowatt hour, how much does it cost to operate the coffeepot for 2 hours?
(A) 2.4 cents (B) 4.8 cents (C) 8.0 cents (D) 9.6 cents (E) 16 cents

21. An electron is in a uniform magnetic field B that is directed out of the plane of the page, as shown above. When the electron is moving in the plane of the page in the direction indicated by the arrow, the force on the electron is directed
(A) toward the right (B) out of the page (C) into the page (D) toward the top of the page
(E) toward the bottom of the page

Explanation / Answer

E=-V/m So if we double the V, we double E, if we take 1/5 of the distance we multiply it by 5. So 10x original = E 20,000. It depends on the V at P, but q*V=potential energy. watt/voltage=amps w=480 per hour. 9.6 cents. 21 needs a picture

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