Transcript Electro-Statics

The sphere on the right has a charge of +2q. The
sphere to the left has a charge of – 3q.
Which of the following pictorial descriptions
of the electric field best matches the above
verbal description?
2
1
3
4
Jenny, a student in an introductory physics class sees the
following equation:
(1.6 x 10-5 C) (5.0 x 106 N/C) – 10 N = (0.015 kg) a
Which of the following verbal descriptions best
matches the above mathematical representation?
1 A proton is in electric field that experiences a 10
N force holding it back.
2 A 0.015 kg object experiences just one force due
to a 5.0 x 106 N/C electric field.
3 A charged particle is accelerating in an electric
field but also experiences a 10 N opposing force.
4 A particle with charge of 1.6 x 10-5 C is
accelerated by a 10 N force.
Two charged spheres are brought together. The electric field
measured at point A, points at a 45o angle North of West.
Which of the following pictures below
matches the above description?
1
3 A
A
2 A
x
x
+q
x
+√2 q
x
+q
x
+q
+q
+q
x
A proton starts at rest between metal sheets with a potential
difference of 100 Volts across them.
Vinit = 100 V
Vfinal = 0 V
Which motion diagram could match the
proton’s motion when released?
1
2
3
4
Sarah is looking over her physics textbook and sees a
situation described mathematically below.
(3 x 1012 ) (1.6 x 1019 )
I
(3060)
Ne
I
t
The same situation is described in words
below. Decide which description fits the
mathematical description best.
1 3 x 1012 protons travel through a wire each hour.
2 3 x 1012 electrons travel through a wire in each hour.
3 3 x 1012 electrons travel through a wire in just under an
hour.
4 3 x 1012 Coulombs of charge travel through a wire in just
under an hour.
A picture is drawn below showing equipotential surfaces for
two fixed charged pith balls.
Which of the following verbal descriptions best
match the above equipotential surfaces?
1. Both pith balls are positively charged.
2. Both pith balls are negatively charged.
3. One pith ball is positively charged, the other is
negatively charged.
4. Both 1 and 2 are possible solutions
A situation is described with an energy bar chart below.
Ko PEgo PEso PEqo W K PEg PEs PEq Eint
0
Which of the following verbal representations best matches
the above bar chart?
1 A charged object shoots straight up away from another charged
object and reaches its highest point.
2 A charged object is high above the ground in an electric field. The
field pulls the charged particle downward. We see the system’s
energy when it is halfway down to the ground.
3 A charged object initially at rest moves at an angle away from a
second like charged object. At the top of the projectile path the
object is moving horizontally.
4 A proton is held below a negatively charged sphere and released.
Three identical magnitude charged spheres are shown below.
+q1
-q3
+q2
Which electrical force diagram for objects corresponds to the
pictorial representation?
1
2

Fq2 on q3 y

x
Fq1 on q3

Fq2 on q3 y

x
Fq1 on q3
3
4

Fq2 on q3 y

x
Fq1 on q3

Fq2 on q3

Fq1 on q3
y
x
A student sees in a textbook the picture below of two charged
spheres and the corresponding electric field lines.
Which of the following verbal descriptions best
matches the above pictorial representation?
1 The two spheres have charges that are opposite but equal
in magnitude.
2 The left sphere has a positive charge that is twice the
magnitude of the negative charge on the right.
3 The left sphere has a negative charge that is twice the
magnitude of the positive charge on the right.
4 The right sphere must not have all of the lines drawn into it.
A positively charged sphere is held in a fixed
position relative to a negatively charged sphere on
the left with half the magnitude of electric charge.
Which pair of electric force diagrams below best
matches the above verbal description?
y
1
y

Fneg on pos
2

Fneg on pos

Fpos on neg
x
y
y
3
y

Fneg on pos
y

Fpos on neg
x
y

Fpos on neg
x
4

Fneg on pos
y

Fpos on neg
x
Four charged spheres, not necessarily the same
magnitude charge, are placed at the corners of a
square. The net electrical force on sphere C is zero.
A
C
B
D
What are the signs of the charged spheres to match
the above verbal description?
A
B
C
D
1
+
–
–
+
2
–
–
–
+
3
–
–
+
+
4
+
+
+
+
5
+
–
+
–
A process is shown in the picture below. The charged sphere
on the right is fixed. The left charged sphere is on a
moveable cart. It is initially held by a wedge, then let go.
Initial
+
+

v
Final
+
+
What energy bar chart best matches the pictorial representation?
Ko PEgo PEso PEqo W K PEg PEs PEq Eint
1
2
3
A real situation is described mathematically:
½ m vo2 + q Vo = ½ m v2 + q V
½ (0.001 kg) (0 m/s)2 + (1.0 x 10-6 C) (12 V) =
½ (0.001 kg) v2 + (1.0 x 10-6 C) (0 V)
The same situation is described verbally below. Which
description fits the above mathematical description best?
1 A 0.001-kg object is moving between the plates of a capacitor
at a constant speed.
2 A 1.0 x 10-6 C object initially moves at some speed v away
from a 12-V plate until it comes to rest at a 0-V plate.
3 A 0.001-kg charged object that is initially at rest at a 12-V
plate moves away from the plate to a place at zero potential.
4 The plate where the object arrives has no charge on it.