Download In a television set, electrons are first accelerated from rest through a

Practice: Uniform Electric Fields Solutions
Level 1
An electron is accelerated from rest for a time of 10-9 second by a uniform electric field that exerts a force of 8.0 x 10–
15 newton on the electron.
1. What is the magnitude of the electric field?
(A) 8.0 × 10–24 N/C (B) 9.1 × 10–22 N/C (C) 8.0 × 10–6 N/C (D) 2.0 × 10–5 N/C (E) 5.0 × 104 N/C
2. The speed of the electron after it has accelerated for the 10–9 second is most nearly
(A) 101 m/s (B) 103 m/s (C) 105 m/s (D) 107 m/s (E) 109 m/s
Level 2
3.
Which of the following is true about the net force on an uncharged conducting sphere in a uniform electric
field?
(A) It is zero. (B) It is in the direction of the field. (C) It is in the direction opposite to the field.
(D) It produces a torque on the sphere about the direction of the field.
(E) It causes the sphere to oscillate about an equilibrium position.
4. Consider the two oppositely charged plates as shown in the diagram. At which of the marked points shown in
the diagram would a positively charged particle have the greatest electrical potential energy?
(A) A (B) B (C) C (D) D (E) E
Two large, flat, parallel, conducting plates are 0.04 m apart, as shown above. The lower plate is at a potential of 2 V with
respect to ground. The upper plate is at a potential of 10 V with respect to ground. Point P is located 0.01 m above the
lower plate.
5. The electric potential at point P is
(A) 10 V (B) 8 V (C) 6 V (D) 4 V (E) 2 V
6. The magnitude of the electric field at point P is
(A) 800 V/m (B) 600 V/m (C) 400 V/m (D) 200 V/m (E) 100 V/m
7. A proton is released between the two parallel plates of the fully charged capacitor shown above. What would be
the resulting acceleration of the proton?
(A) 1.0 × 10–7 m/s2 (B) 7.3 × 1013 m/s2 (C) 9.6 × 108 m/s2 (D) 6.3 × 1019 m/s2 (E) 3.8 × 1011 m/s2
Jedi
In a television set, electrons are first accelerated from rest through a potential difference in an
electron gun. They then pass through deflecting plates before striking the screen.
a. Determine the potential difference through which the electrons must be accelerated in the electron gun
in order to have a speed of 6.0 x 107 m/s when they enter the deflecting plates.
The pair of horizontal plates shown below is used to deflect electrons up or down in the television set
by placing a potential difference across them. The plates have length 0.04 m and separation 0.012 m,
and the right edge of the plates is 0.50 m from the screen. A potential difference of 200 V is applied
across the plates, and the electrons are deflected toward the top of the screen. Assume that the
electrons enter horizontally midway between the plates with a speed of 6.0 x 10 7 m/s and that fringing
effects at the edges of the plates and gravity are negligible
b. Which plate in the pair must be at the higher potential for the electrons to be deflected upward? Check
the appropriate box below.
c. Considering only an electron's motion as it moves through the space between the plates, compute the
following.
i. The time required for the electron to move through the plates
ii. The vertical displacement of the electron while it is between the plates
d. Show why it is a reasonable assumption to neglect gravity in part c.
e. Still neglecting gravity, describe the path of the electrons from the time they leave the plates until they
strike the screen. State a reason for your answer.
Practice: Equipotential
8.
A positive electric charge is moved at a constant speed between two locations in an electric field, with no work
done by or against the field at any time during the motion. This situation can occur only if the
(A) charge is moved in the direction of the field
(B) charge is moved opposite to the direction of the field
(C) charge is moved perpendicular to an equipotential line
(D) charge is moved along an equipotential line
(E) electric field is uniform
A fixed charge distribution produces the equipotential lines shown in the figure above.
9. Which of the following expressions best represents the magnitude of the electric field at point P ?
(A) 10 V/0.14 m (B) 10 V/0.04 m (C) 25 V/0.14 m (D) 25 V/0.04 m (E) 40 V/0.25 m
10. The direction of the electric field at point P is most nearly
(A) toward the left
(B) toward the right
(C) toward the bottom of the page
(D) toward the top of the page
(E) perpendicular to the plane of the page