Download HW: Complete Electric Fields

IB PHYSICS FIELDS PRACTICE
1.
Two charges of –e and +4e are fixed at the positions shown below. At which position along the line XY is
the electric field due to these charges equal to zero?
–e
X
B.
A.
+4e
D.
C.
Y
(1)
2.
Electric field strength is defined as
A.
the force exerted on a test charge.
B.
the force per unit positive charge.
C.
the force per unit charge.
D.
the force per unit charge exerted on a positive test charge.
(1)
3.
Two positive point charges P and Q are held a certain distance apart.
X
P
Q
Y
+
Z
+
At which point(s) could the electric field strength, due to the charges, be zero?
A.
X only
B.
Y only
C.
Z only
D.
X and Z only
(1)
4.
The diagram below shows two positive point charges of equal magnitude. A negative point charge is placed
at P.
P

Positive charge
Positive charge


+
+
Which one of the following diagrams best shows the direction of the resultant force on the negative charge
at P?
A.
B.
P
+
C.
+
+
D.
P
+
P
+
+
P
+
+
(1)
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5.
The electric field strength at a point may be defined as
A.
the force exerted on unit positive charge placed at that point.
B.
the force per unit positive charge on a small test charge placed at that point.
C.
the work done on unit positive charge to move the charge to that point from infinity.
D.
the work done per unit positive charge to move a small test charge to that point from infinity.
(1)
6.
The diagram below shows a positively charged rod brought near an isolated uncharged metal plate.
+ + ++
+ + ++
rod
plate
As a result of bringing the rod near to the plate,
A.
the metal plate will gain a charge dependent on the separation of the rod and the plate.
B.
the metal plate will remain uncharged.
C.
the metal plate will gain a negative charge.
D.
the metal plate will gain a positive charge.
(1)
7.
Three equal point charges X, Y and Z are fixed in the positions shown.
Z
q3
1.0 m
90
X
1.0 m
q1
Y
q2
The distance between q1 and q2 and the distance between q2 and q3 is 1.0 m. The electric force between the
charges at X and Y is F. The electric force between the charges at X and Z is
A.
B.
C.
D.
F
.
2
F
2
.
F.
2F.
(1)
8.
Two point charges of magnitude +2Q and −Q are fixed at the positions shown below. At which point is the
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electric field due to the two charges most likely to be zero?
–Q
+2Q
A.
B.
C.
D.
(1)
9.
X and Y are two identical conducting spheres separated by a distance d. X has a charge +6 μC and Y has a
charge –2 μC. The electric force between them is + F (ie attractive). The spheres are touched together and
are then returned to their original separation d. The force between them now is
A.
+F.
B.
–F.
C.
D.
F
.
3
F
 .
3

(1)
1.
This question is about forces on charged particles in electric and magnetic fields.
The diagram shows two parallel plates situated in a vacuum. One plate is at a positive potential with respect
to the other.
+
Path of positively charged particle
–
A positively charged particle passes into the region between the plates. Initially, the particle is travelling
parallel to the plates.
(a)
On the diagram,
(i)
draw lines to represent the electric field between the plates.
(3)
(ii)
show the path of the charged particle as it passes between, and beyond, the plates.
(2)
(b)
An electron is accelerated from rest in a vacuum through a potential difference of 750 V.
(i)
Determine the change in electric potential energy of the electron.
7
–1
(ii)
Deduce that the final speed of the electron is 1.6 × 10 m s .
...........................................................................................................................
...........................................................................................................................
...........................................................................................................................
(2)
2.
A positively charged sphere falls vertically in a vacuum between two long parallel plates carrying opposite
charges. Which one of the following diagrams best shows the path followed by the sphere?
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A.
B.
–
+
–
+
–
+
–
+
–
+
–
+
C.
D.
–
+
–
+
–
+
–
+
–
+
–
+
(1)
3.
This question is about forces on charged particles.
(a)
A charged particle is situated in a field of force. Deduce the nature of the force-field (magnetic,
electric or gravitational) when the force on the particle
(i)
is along the direction of the field regardless of its charge and velocity;
(ii)
is independent of the velocity of the particle but depends on its charge;
(iii)
depends on the velocity of the particle and its charge.
(5)
(b)
An electron is accelerated from rest in a vacuum through a potential difference of 2.1 kV. Deduce
7
–1
that the final speed of the electron is 2.7 × 10 m s .
(3)
The electron in (b) then enters a region of uniform electric field between two conducting horizontal
metal plates as shown below.
+95 V
Path of
electron
P
2.2 cm
7
2.7 × 10 m s
–1
0V
12 cm
The electric field outside the region of the plates may be assumed to be zero. The potential difference
between the plates is 95 V and their separation is 2.2 cm.
As the electron enters the region of the electric field, it is travelling parallel to the plates.
(c)
(i)
On the diagram above, draw an arrow at P to show the direction of the force due to the
electric field acting on the electron.
(1)
Calculate the force on the electron due to the electric field.
(3)
(d)
The plates in the diagram above are of length 12 cm. Determine
(i)
the time of flight between the plates.
(1)
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(ii)
the vertical distance moved by the electron during its passage between the plates.
(3)
(e)
Suggest why gravitational effects were not considered when calculating the deflection of the
electron.
(2)
4.
The diagram below shows lines of electric equipotential. The change in potential on moving from one line
to the next is always the same. At which point does the electric field strength have its greatest magnitude?
A
B
C
D
(1)
5.
The diagram below shows two lines of equipotential in a region of a uniform electric field. Line X has a
potential of +50 V and line Y has a potential of +100V. The distance between X and Y is 2.0 cm.
X
Y
+50 V
+100 V
2.0 cm
Which one of the following correctly gives the direction of the electric field and its strength?
Direction
A.
B.
C.
D.
XY
XY
YX
YX
–1
Strength / V cm
25
100
25
100
(1)
6.
Two isolated spheres X and Y of unknown materials are touching one another as shown below.
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sphere X,
earthed
sphere Y,
negatively charged
Sphere Y is negatively charged and sphere X is earthed. The earth connection is removed from sphere X
and then the spheres are separated as shown below.
sphere Y,
negatively charged
sphere X,
positively charged
Sphere X is found to be positively charged and sphere Y remains negatively charged.
Which of the following describes the nature of the materials from which the spheres are made?
Sphere X
Sphere Y
A.
Insulator
Insulator
B.
Insulator
Conductor
C.
Conductor
Insulator
D.
Conductor
Conductor
(1)
7.
The diagram below shows two parallel conducting plates that are oppositely charged.
+
+
–
–
+
X
+
+
–
–
Y
–
The line XY is perpendicular to the plates.
Which of the following diagrams shows the variation along the line XY of the magnitude E of the electric field
strength between the plates?
A.
B.
E
X
E
Y
distance
C.
X
Y
distance
Y
distance
D.
E
X
E
Y
distance
X
(1)
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