A 12.6-µF isolated capacitor is constructed with Teflon, having a dielectric constant of 2.1, between the plates. The capacitor is initially charged to 1.5 volts, and then the Teflon is removed
(a) How much excess charge was originally stored on the plates of the capacitor? (b) After removing the Teflon, what is the potential difference across the capacitor plates?
(a) 19 µC (b) 3.2 V
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Why does the plasma tail of a comet always point away from the Sun?
A) It is allergic to sunlight. B) Gases from the comet, heated by the Sun, push the tail away from the Sun. C) Radiation pressure from the Sun's light pushes the ions away. D) The conservation of the angular momentum of the tail keeps it always pointing away from the Sun. E) The solar wind blows the plasma ions directly away from the Sun.
What is the angular magnification of a magnifying glass of focal length 4.0 cm if the image is to be viewed by a relaxed eye having a near point of 25 cm?
A) 2.0 B) 3.0 C) 3.6 D) 4.0 E) 6.3
Suppose one's hand exerts a force of 12 N upward on a book weighing 10 N. The reaction to the force of the hand on the book is a force of
A. 2 N exerted by the book on the hand. B. 10 N exerted by the Earth on the book. C. 10 N exerted by the book on the hand. D. 10 N exerted by the book on the Earth. E. 12 N exerted by the book on the hand.
An inventor develops a stationary cycling device by which an individual, while pedaling, can convert all of the energy expended into heat for warming water. What minimum power must be generated if 300 g of water (enough for 1 cup of coffee) is to be heated in 10 min from 30°C to 90°C? (1 cal = 4.186 J, the specific heat of water is 4 186 J/kg • °C)
a. 9400 W c. 160 W b. 590 W d. 130 W