Physics 1112 Exam 3
Two large parallel metal plates are uniformly and oppositely charged and the electric field between them is 7.6 c 10^6 N/C. (a) What is the charge density on each plate? (b) If the very large charged plates are moved 2 times farther apart, what is the electric field between the plates now?
(a) - +/-67 µC/m^2 (b) 7.6 x 10^6 N/C, unchanged
An electron in placed in a constant electric field of 4.5 x 10^4 N/C (a) What is the force on the electron? (b) If the electron is released from rest, what is its speed after 3.0 ps?
(a) 7.2 x 10^-15 N opposite the field (b) 24 km/s
Thirty microcoulombs of NEGATIVE charge experiences an electrostatic force of 27. mN. What is the magnitude and direction of the electric field?
0.90 kN/C (or kV/m) in the direction opposite the force
A particle with a charge of 4.0 µC has a mass of 5.0 x 10 ^-3 kg. What electric field directed upward will exactly balance the weight of the particle? A) 4.1 x 10^2 N/C B) 8.2 x 10^2 N/C C) 4.4 x 10^4 N/C D) 1.2 x 10^4 N/C E) 5.1 x 10^6 N/C
1.2 x 10^4 N/C
Consider an equilaterial triangle of side 20. cm. A charge of +2.0 µC is placed at one vertex and charges of -4.0 µC are placed at the other two vertices. Determine the magnitude and direction of the electric field at the center of the triangle.
2.7 x 10^6 V/m
Three 3.0 µC charges are at the three corners of an square of side 0.50 m. The last corner is occupied by a -3.0 µC charge. Find the electric field at the center of the square.
4.3 x 10^5 N/C
A 5.0-C chage is 10m from a small test charge. What is the magnitude and direction of the electric field at the location of the test charge?
4.5 x 10^8 B/C, directed away from the 5.0 C
A 5.0-µC charge is placed at the 0 cm mark of a meter stick and a -4.0 µC charge is placed at the 50 cm mark. At what point on a line joining the two charges is the electric field zero?
4.7 m from the 0 cm mark
A metal sphere of radius 2.0 cm carries a charge of 3.0 µC. What is the electric field 6.0 cm from the center of the sphere?
7.5 x 10^6 V/m
A point charge Q = 7.00 x 10^-9 C is placed at the origin of an xy-coordinate system. What is the electric field intensity E at a distance of x = 30 cm from this charge? (k = 9 x 10^9 Nm^2/C^2.) A) 100 N/C B) 400 N/C C) 500 N/C D) 600 N/C E) 700 N/C
700 N/C
Two point charges of +20.0 µC and - 8.00 µC are separated by a distance of 20.0 cm. What is the intensity of electric field E midway between these two charges? A) 25.2 x 10^6 N/C directed towards the negative charge B) 25.2 x 10^6 N/C directed towards the positive charge C) 25.2 x 10^5 N/C directed towards the negative charge D) 25.2 x 10^5 N/C directed towards the positive charge E) 25.2 x 10^4 N/C directed towards the negative charge
A - 25.2 x 10^6 N/C directed towards the negative charge
Three equal point charges are placed at the corners of a square of side d as shown in Figure 19-7. Which of the arrows shown represents the direction of the net electric field at the center of the square? A) A B) B C) C D) D E) none of the above
A - A
Three equal point charges of varying signs are placed on the corners of a square of side d as shown in Figure 19-8. Which of the arrows shown represents the direction of the net electric field at the center of the square? A) A B) B C) C D) D E) none of the above
A - A
Which of the arrows shown in Figure 19-12 represents the correct direction of the electric field between the two metal plates? A) A B) B C) C D) D E) none of the above
A - A
A charged particle traveling along the +x axis enters an electric field directed vertically upward along the +y-axis. If the charged particle experiences a force downward because of this field, what is the sign of the charge on this particle? A) It is negative. B) It is positive. C) It is neutral. D) None of the other choices is correct
A - It is negative
A charged rod carrying a negative charge is brought near two spheres that are in contact with each other but insulated from the ground. If the two spheres are then separated, what kind of charge will be on the spheres? A) The sphere near the charged rod becomes positive and the other becomes negative B) The sphere near the charged rod becomes negative and the other becomes positive C) The sphere do not get any charge D) None of the other choices is correct
A) The sphere near the charged rod becomes positive and the other becomes negative
A force of 6.0 N acts on a charge of 3.0 µC when it is placed in a uniform electric field. What is the magnitude of this electric field? A) 18 MN/C B) 2.0 MN/C C) 1.0 MN/C D) 0.50 MN/C E) 130 MN/C
B - 2.0 MN/C
A uniform electric field with a magnitude of 6 x 10^6 N/C is applied to a cube of edge length 0.1 m as shown in Figure 19-15. If the direction of the E-field is along the +x-axis, what is the electric flux passing through the shaded face of the cube? A) 0.6 x 10^4 Nm^2/C B) 6 x 10^4 Nm^2/C C) 60 x 10^4 Nm^2/C D) 600 x 10^4 Nm^2/C E) 6000 x 10^4 Nm^2/C
B - 6 x 10^4 Nm^2/C
A metal sphere of radius 10 cm carries a charge of +2.0 µC. What is the magnitude of the electric field 5.0 cm from the sphere's surface? A) 4.0 c 10^5 N/C B) 8.0 x 10^5 N/C C) 4.0 x 10^7 N/C D) 8.0 x 10^7 N/C E) 4.0 x 10^9 N/C
B - 8.0 x 10^5 N/C
Three equal point charges of varying signs are placed on three of the corners of a square of side d as shown in Figure 19-11. Which of the arrows shown represents the direction of the net electric field at the vacant corner of the square? A) A B) B C) C D) D E) none of the above
B - B
An electron traveling along the +x-axis enters an electric field that is directed vertically down, i.e., along the negative y-axis. What will be the direction of the electric force acting on the electron after entering the electric field? A) downward B) upward C) to the left D) to the right E) into the page
B - Upward
Three equal point charges are placed at three of the corners of a square of side d as shown in Figure 19-10. Which of the arrows shown represents the direction of the net electric field at the vacant corner of the square? A) A B) B C) C D) D E) none of the above
B -B
A negative charge, if free, tries to move
B) From low potential to high potential
Figure 19-13 shows four Gaussian surfaces surrounding a distribution of charges. Which Gaussian surfaces have an electric flux of +1/e0 through them? A) a B) b C) c D) b and d E) b and c
B) b
Two point charges of +5.00 µC and +8.00 µC are placed inside a cube of edge length 0.100 m. The net electric flux due to these charges is given by A) 0.340 x 10^6 Nm^2/C B) 0.450 x 10^6 Nm^2/C C) 1.47 x 10^6 Nm^2/C D) 3.80 x 10^6 Nm^2/C E) 4.20 x 10^6 Nm^2/C
C - 1.47 x 10^6 Nm^2/C
A proton is placed in an electric field of intensity 700 N/C. What is the magnitude and direction of the acceleration of this proton due to this field? A) 6.71 x 10^9 m/s^2 opposite to the electric field B) 6.71 x 10^10 m/s^2 opposite to the electric field C) 6.71 x 10^10 m/s^2 in the direction of the electric field A) 67.1 x 10^10 m/s^2 opposite to the electric field A) 67.1 x 10^10 m/s^2 in the direction of the electric field
C - 6.71 x 10^10 m/s^2 in the direction of the electric field
Three equal point charges are placed at three of the corners of a square of side d as shown in Figure 19-9. Which of the arrows shown represents the direction of the net electric field at the center of the square? A) A B) B C) C D) D E) none of the above
C - C
By what method will a positively charged rod produce a negative charge on a conducting sphere that is placed on an insulating surface? A) by means of conduction B) by means of convection C) by means of induction D) None of the other choices is correct
C) by means of induction
Figure 19-13 shows four Gaussian surface surrounding a distribution of charges. Which Gaussian surfaces have no electric flux through them? A) a B) b C) c D) b and d E) b and c
C) c
Gaussian surfaces A and B enclose the same positive charge +Q. The area of Gaussian surface A is three times larger than that of Gaussian surface B. The flux of electric field through Gaussian surface A is A) nine times larger than the flux electric field through Gaussian surface B B) three times larger than the flux of electric field through Gaussian surface B C) equal to the flux of electric field through Gaussian surface B. D) three times smaller than the flux of electric field through Gaussian surface B E) unrelated to the flux of electric field through Gaussian surface B
C) equal to the flux of electric field through Gaussian surface B.
What are the magnitude and direction of the electric field at a distance of 1.50 m from a 50.0-nC charge? A) 20 N/C away from the charge B) 20 N/C toward from the charge C) 10 N/C away from the charge D) 200 N/C away from the charge E) 200 N/C toward from the charge
D - 200 N/C away from the charge
A conductor is placed in an electric field under electrostatic conditions. Which of the following statements is correct for this situation? A) The electric field is zero inside the conductor B) All the valence electrons go to the surface of the conductor C) The electric field on the surface of the conductor is perpendicular to the surface D) All of the other answers apply
D) All of the other answers apply
The work done in moving a positive charge against an electric field does not depend on the path chosen in moving the charge in that field. Based on the statement, what kind of force field is the electrostatic field ?
D) Conservative
A metal sphere of radius 2.0 cm carries a charge of 3.0 µC. What is the electric field 6.0 cm from the center of the sphere? A) 4.2 x 10^6 N/C B) 5.7 x 10^6 N/C C) 6.4 x 10^6 N/C D) 7.5 x 10^6 N/C E) 9.3 x 10^6 N/C
D- 7.5 x 10^6 N/C
State three reasons for adding a dielectric material between the plates of a capacitor
Dielectrics do not break down as readily as air, so a higher voltage can be applied without charge passing across the gap A dielectric allows the plates to be placed closer together without touching thus allowing an increased capacitance because the plates separation is less If a dielectric fills the space between the two conductors, it increases the capacitance
A styrofoam ball of mass 0.120 g is placed in an electric field of 6000 N/C pointing downward. What charge must be placed on the ball for it to be suspended? A) -16.0 nC B) -18.0 nC C) -57.2 nC D) -125 nC E) -196 nC
E - -196 nC
Two point charges of +40.0 µC and - 10.0 µC are separated by a distance of 20.0 cm. A +7.00 µC charge is placed midway between these two charges. What is the electric force acting on this charge because of the other two charges? A) 0.453 N directed towards the negative charge B) 3.15 N directed towards the negative charge C) 3.15 N directed towards the positive charge D) 315 N directed towards the positive charge E) 315 N directed towards the negative charge
E - 315 N directed towards the negative charge
An electron is held up against the force of gravity by the attraction of a fixed proton some distance above it. How far above the electron is the proton? A) 1.5 m B) 2.3 m C) 3.7 m D) 4.6 m E) 5.1 m
E - 5.1 m
A 5.0 µC charge is placed at the 0 cm mark of a meter stick and a -4.0 µC charge is placed at the 50 cm mark. At what point on a line joining the two charges is the electric field zero? A) 1.4 m from the 0 cm mark B) 2.5 m from the 0 cm mark C) 2.9 m from the 0 cm mark D) 3.3 m from the 0 cm mark E) 4.7 m from the 0 cm mark
E) 4.7 m from the 0 cm mark
The electron-volt is a unit of
E) energy
In the expression for the definition of capacitance C = Q/V, Q is the total charge on the plates of a capacitor
False
The capacitance of a parallel plate capacitor is directly proportional to its plate separation
False
The electric field is continuous
False
The electric potential at a point P due to a positive charge is along the direction of that charge
False
Unlike electric potential, the electric potential energy is a vector quantity
False
If you were a parallel plate capacitor manufacturer, state three ways you might make larger valued capacitors
Increase plate area, decrease separation, increase dielectric constant
After being charged from a a battery, the plates of a parallel plate capacitor are moved closer together. When they are half as far apart as originally, by how much does the stored energy change?
The capacitance doubles but charge remains the same so energy, Q^2/(2C), reduces to half of what it was
A capacitor, in addition to storing charge, also stores electrical energy
True
A positive charge placed in an electric field experiences a force in the direction of the field
True
A potential changes at the greatest rate in the direction of the gradient of the potential
True
Electric field lines and equipotential lines meet perpendicular to one another
True
Electric potential is a scalar quantity
True
Equipotential lines and electric field lines meet perpendicular to one another
True
Every point on an equipotential surface is the same potential
True
If a conductor is placed in an electric field under electrostatic conditions, the electric field is excluded from the inside of the conductor
True
The direction of an electric field is from higher to lower potential
True
The electric field between the plates of a parallel plate capacitor is inversely proportional to the plate separation
True
When a proton moves in a direction of the electric field, its potential increases, but its potential energy decreases
True
When an electron moves in a direction opposite to the electric field, its potential increases but the potential energy decreases
True
