Physics 114, Summer 2007
To be turned in
at the end each discussion session, stapled on top of #2 & #1
-TA (HW grading, tutoring, solution manual,…) information: Praveen Nittala (Praveen.nittala@umb.edu),
S-3-013
-Tutoring
schedule (in room S-3-013):
Student’s Name:____________________ Team #________
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1.- (a)
The electric potential is constant throughout an entire volume, what must be
true of the electric field in that region? What happens if instead the
potential increases linearly with distance?:
(b) Is the potential at the
center of a hollow, uniformly charged spherical shell higher, lower, or the
same as that at the surface?. Explain:
2.- Electric potential. Find the on-axis
potential for a charged ring (Q) and calculate the electric field from the
potential. Compare with the field obtained using vector superposition. (Hint:
use scalar superposition for potential from infinitesimal elements of charge)
3.- (a) A solid conducting slab with
thickness a little bit smaller than the separation between the two plates of a
capacitor is introduced between them. Does the capacitance increase, decrease,
or stay the same? Explain.
(b) A capacitor is said to carry
a charge Q, what is the net charge on the entire capacitor?
4.- Capacitors. A solid conducting slab is inserted
between the plates of a charged capacitor, separated at a distance d. The slab
thickness is 50% of the plates spacing, with area that of the plates. (a) what happens to the capacitance (Hint: the thickness of
the field region is reduced with the introduced slab)
(b)
What happens to the stored energy is the capacitor is isolated?
5.- (a) A 50W and a 100W light bulb are both
designed to operate at 120V. Which has a lower resistance?
(b) How would you connect a pair
of equal resistors across an ideal battery in order to get the most power
dissipation in the resistors?
6.- Electric circuits. A battery’s voltage is
measured with a voltmeter whose resistance is 1000 Ohm, the result is 4.5V.
When the measurement is repeated with a 1500 Ohm meter, the result is
4.2V. (a) What is the battery voltage? (Hint:
the internal resistance of the battery and the resistance of the voltmeter are
in series with the battery’s emf)
(b)
What is the battery’s internal resistance?
7.- An electron moves through a region in a straight line at
constant speed. Can you conclude that there is no magnetic field in the
region? Yes No. What if there were no electric or
gravitational forces on the electron? Explain.
8.- The magnetic field. In 2 μs, an
electron moves 15 cm in the direction of a 0.1 T magnetic field. If the electron’s
velocity components perpendicular and parallel to the field are equal (a) what
is the length of its actual spiral trajectory?
(b) How many orbits about the field direction does
it complete? (Hint: the cyclotron period is T=2πm/(eB)).
9.- Sources of Magnetic Field. A conducting
slab extends infinitely in the x and y directions and has thickness h in the z
direction. It carries a uniform current density J= J i. Find
the magnetic field strength (a) inside the slab (Hint: use Ampere’s Law)
(b)
outside the slab as a function of the distance z from
the center plane of the slab.