Toggerson-Units3-4-Additional Units 3 and 4 problems randomized (2).pdf

Toggerson P132 - University of Massachusetts, Amherst
Exam II: all Unit III - Physical Optics AND Unit IV - Electrostatics Problems
Randomized so you can practice choosing the principle
1)
When the electric field is zero at a point, the potential must also be zero there.
A)
True
B)
False
2) As shown in the figure, three charges are at corners of a rectangle. The charge in the bottom right corner is Q
= -
90 nC, and all the other quantities are accurate to two significant figures. What is the magnitude of the net
electrical force on Q due to the other two charges? ( k
=
1/4 ΔΉ
0
=
9.0
×
10
9
N
·
m
2
/C
2
)
2
N
3)
A point charge Q = -500 nC and two unknown point charges, q
1
and q
2
, are placed as shown in
the figure. The electric field at the origin O , due to charges Q , q
1
and q
2
, is equal to zero. The
charge q
1
is closest to
1

4)
The figure shows three electric charges labeled Q
1
, Q
2
, Q
3
, and some electric field lines in the
region surrounding the charges. What are the signs of the three charges?
5) Electrons with a speed of 2.1 × 10
6
m/s are directed towards a 1.0 - μm wide slit. An electron detector is placed
1.0 m behind the slit. How wide is the central maximum of the electron diffraction pattern (from the first dark
on one side to the first dark on the other side) at the detector? ( h = 6.626 × 10
-
34
J · s, m
electron
= 9.11 × 10
kg)
-
31
A) 690 μm B) 1000 μm C) 350 μm D) 1400 μm
2

6) Four tiny charged particles (two having a charge + Q and two having a charge - Q ) are distributed on the x -
y - axes as shown in the figure. Each charge is equidistant from the origin. In which direction is the net electric
field at the point P on the y - axis?
and
7) In a two - slit experiment, monochromatic coherent light of wavelength 600 nm passes through a pair of slits
separated by 2.20 × 10
- 5
m. At what angle away from the centerline does the second dark fringe occur?
8) Two protons are released from rest, with only the electrostatic force acting. Which of the following statements
must be true about them as they move apart? (There could be more than one correct choice.)
9) A proton and an electron are released from rest, with only the electrostatic force acting. Which of the following
statements must be true about them as they move toward each other? (There could be more than one correct
choice.)
A) Their electric potential energy keeps decreasing.