University of California, San Diego
Physics 1b - Thermal Physics & Electromagnetism

H. E. Smith   Spring 2000

Physics 1B - Tutorial #5


  1. Half Dome in Yosemite National Park has a vertical north face which rises about 1450 m from the floor of Yosemite Valley.
    • What is the gravitational potential difference (gravitational potential energy difference per unit mass) between Yosemite Valley and the top of Half Dome.
    • What is the gravitational field near half dome.
    • What is the potential gradient down the north face.
    • During the summer there are hand railings which allow hikers to climb the south face of half dome. Using the picture above and a ruler or piece of graph paper, estimate the effective potential gradient and gravitational field down the south face.
    • What do the lines of equipotential correspond to on a map of Yosemite Valley?

  2. Does a bird sitting on an uninsulated high voltage line get a shock? Explain.

  3. Figure (a) below shows measurements of the electrical potential on a grid. Figure (b) shows equipotential contours.
    • Draw 50V, 70V & 100V contours in Fig. (a).
    • If the gridlines in (a) are 1cm apart, estimate the electric field (magnitude and direction) at points A, B, C, & D.
    • In Fig. (b) where is the electric field strongest?
    • Where is it weakest?
    • Suppose you were "pushing" a proton from the lowest contour to the highest contour. Which route would you take.
    • Do you save energy by selecting one route over another.
    • What happens to an electron which starts out at the 0V contour?

  4. A very large conducting plate is charged with 1 C/m.
    • What is the electric field above and below the plate?
    • Draw a graph of the electric potential from below the plate to above the plate.
    • What is the force on an electron 1 m above the plate?
    A second plate, charged with -1 C/m is placed 1cm below the positively charged plate, parallel to it.
    • What is the electric field below the lower plate? Between the plates? Above the upper plate.
    • Draw a graph of the electric potential from below the lower plate to above the upper plate.
    • Now what is the force on the electron?



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Gene Smith

Last modified: Tues., 2 May 2000