CollegePhysics17 - Chapter 17 ELECTRIC POTENTIAL Conceptual...

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665 Chapter 17 ELECTRIC POTENTIAL Conceptual Questions 1. (a) The electric field does positive work on – q as it moves closer to + Q . (b) The potential increases as – q moves closer to + Q . (c) The potential energy of – q decreases. (d) If the fixed charge instead has a value – Q , the electric field does negative work, the potential decreases, and the potential energy increases. 2. Such a capacitor can be built by replacing the air between the capacitor plates with a dielectric material. This change not only increases the maximum possible voltage across the capacitor but also increases the amount of charge on the capacitor plates for a given potential difference. 3. While standing on a high voltage wire, the magnitude of a bird’s electric potential varies between –100 kV and +100 kV. Important for the bird is the fact that although its body is at a non-zero potential, the potential difference across its body is small. If a large potential difference existed across its body, the bird would be electrocuted. 4. A positive charge in an electric field moves toward a position of lower potential. A negative charge in this situation moves toward a position of higher potential. 5. Zero work is required to move a charge between two points at the same potential. An external force may need to be applied to move the charge but the work done to start the charge in motion will be negated by the work done to stop it. 6. If the charge of a point particle is negative, its electric potential energy decreases as it is moved towards a region of higher electric potential. 7. If all parts of a conductor in electrostatic equilibrium were not at the same potential, electric fields would exist within the conductor and charges would not remain stationary. The assumption of electrostatic equilibrium would therefore be invalid. 8. There is no physical significance to zero potential—only potential differences have physical consequences. The potential of the earth is often taken to be zero and therefore an object that is grounded has zero potential. This is only a reference value however and the potential of the earth could be taken to be any other quantity as long as other values were appropriately offset by the same potential. 9. If the electric field is zero throughout a region of space, the electric potential must be constant throughout that region. 10. At point P , the electric field must be in the –x direction. 11. If the potential is constant throughout a region of space, the electric field must be zero throughout that region. 12. If a uniform electric field exists throughout a region of space, the potential must be linearly increasing in the direction parallel to the field and unchanging in the other two directions.
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Chapter 17: Electric Potential College Physics 666 13. It doesn’t matter which points we choose because the potential on each plate is constant over the whole plate.
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