Physics 1302 Chapter 19 Electric Charges, Forces and Fields Exam 1

Which of the following best characterizes electrical conductors? - low mass destiny - high tensile strength - electric charges move freely - poor heat conductors

Electric charges move freely

If body P, with a positive charge, is placed in contact with body Q (initially uncharged), what will be the nature of the charge left on Q?

Must be negative

Two identical balls have the same amount of charge, but the charge on the ball A is positive and the charge on ball B is negative. The balls are placed on a smooth, level, frictionless table whose top is an insulator. Which of the following is true?

None of the above

An ion is released from rest and moves due to the force from an electric field from a position in the field having a potential of 14 V to a position having a potential of 8 V. The ion:

0.18 J

A proton (+1.6 ´ 10-19 C) moves 10 cm along the direction of an electric field of strength 3.0 N/C. The electrical potential difference between the proton's initial and ending points is:

0.30 V

A 9.0-V battery is connected between two parallel metal plates 4.0 mm apart. What is the magnitude of the electric field between the plates?

2.3 x 10^3 N/C

Two point charges, separated by 1.5 cm, have charge values of +2.0 and -4.0 microC, respectively. Suppose we determine that 10 field lines radiate out from the +2.0 microC charge. If so, what might be inferred about the -4.0 microC charge with respect to field lines?

20 radiate in

Electrons in a particle beam each have a kinetic energy of 3.2 x 10^-17 J. What is the magnitude of the electric field that will stop these electrons in a distance of 0.1 m? (e = 1.6 x 10^-19 C)

2000 N/C

A uniform electric field, with a magnitude of 600 N/C, is directed parallel to the positive x-axis. If the potential at x = 3.0 m is 1000V, what is the potential at x = 1.0 m?

2200 V

A proton (+1.6 x 10^-19 C) moves 10 cm on a path in the direction of a uniform electric field of strength 3.0 N/C. How much work is done on the proton by the electrical field?

4.8 x 10^-20 J

The electric field at the surface of a positively charged conductor has a direction characterized by which of the following?

Perpendicular outward and away from the charge

An uncharged conductor is supported by an insulating stand. I pass a positively charged rod near the left end of the conductor, but do not touch it. The right end of the conductor will be:

Positive

If the distance between two isolated parallel plates that are oppositely charged is doubled, the electric field between the plate is essentially unchanged. However the:

Potential difference between the plates will double

The quantity of electric potential, the volt, is dimensionally equivalent to:

electric field x distance

The electric field of a point charge has an inverse ___________ behavior.

r^2

Two point charges each have a value of 30.0 mC and are separated by a distance of 4.00cm. What is the electric field midway between the two charges? (ke = 8.99 x 10^9 N*m^2/C^2)

zero

How can a charged object attract an uncharged object made of non-conducting material?

The charges in the uncharged object can become polarized

There is a hollow, conducting, uncharged sphere with a negative charge inside the sphere. Consider the electrical potential at the inner and outer surfaces of the sphere. Which of the following is true?

The potentials on both surfaces are equal but not zero

Which of the following best characterizes electrical insulators? - charges on the surface don't move - high tensile strength - electric charges move freely - good heat conductors

Charges on the surface don't move

A free electron is in an electric field. With respect to the field, it experiences a force acting:

anti-parallel (opposite in direction)

Then number of electric field lines passing through a unit cross sectional area is indicative of:

field strength

Which of the following characteristics are held in common by both gravitational and electrostatic forces when dealing with either point masses or charges?

inverse square distance law applies, forces are conservative, & potential energy is a function of distance of separation

A point charge of +3.0 mC is located at the origin of a coordinate system and a second point charge of -6.0 mC is at x = 1.0 m. At what point on the x axis is the electrical potential zero?

+0.33 m

Two point charges of values +3.4 and +6.6 µC, respectively, are separated by 0.20 m. What is the potential energy of this 2-charge system?

+1.0 J

Two point charges of values +3.4 and +6.6 µC, respectively, are separated by 0.20 m. What is the electrical potential at the point midway between the two point charges? (ke = 8.99 x 10^9 N*m^2/C^2)

+1.8 x 10^6 V

An initially uncharged hollow metallic sphere with radius of 5 cm has a small object with a charge of +10 µC carefully placed at the center of the sphere through a hole in the latter's surface. With the charge in place, what charge is now present on the outside surface of the sphere?

+10 µC

A charge of +2 is at the origin. When charge Q is placed 2m along the positive x axis, the electric field at 2m along the negative x axis becomes zero. What is the value of Q?

-8 C

A thin uncharged conducting spherical shell has a charge q carefully placed at its center through a small hole in the shell. The charge q does not touch the shell. What is the charge on the shell?

0

A 0.25- µF capacitor is connected to a 400-V battery. What potential energy is stored in the capacitor?

0.020 J

Very Large capacitors have been considered as a means for storing electrical energy. If we constructed a very large parallel-plate capacitor of plate area 1.0 m^2 using paper (K=3.7) of thickness 1.0 mm as a dielectric, how much electrical energy would it store at a plate voltage of 5000 V? (e0 = 8.85 x 10^-12 C^2/N*m^2)

0.41 J

Two equal charges, each Q, are separated by some distance. What third charge would need to be placed half way between the two charges so that the net force on each charge would be zero?

-Q/4

Two protons, each of charge 1.60 x 10^-19 C, are 2.00 x 10^-5 m apart. What is the change in the potential energy if they are brought 1.00 x 10^-5 m closer together? (ke = 8.99 x 10^9 N*m^2/C^2)

1.15 x 10^-23 J

Two point charges are 4cm apart. They are moved to a new separation of 2cm. By what factor foes the resulting mutual force between them change?

4

A closed surface contains the following point charges: 6C, 4C, -2C, and -4C. The electric flux coming out of the surface is:

4 C/e0

An initially uncharged hollow metallic sphere with radius of 5 cm has a small object with a charge of +10 µC carefully placed at the center of the sphere through a hole in the latter's surface. What charge resides inner surface of the sphere?

Zero

An electron is released from rest at the negative plate of a parallel-plate capacitor. If the distance across the plate is 5.0 mm and the potential difference across the plate is 5.0 V, with what velocity does the electron hit the positive plate? (me = 9.1 x 10^-31 kg, e = 1.6 x 10^-19)

1.3 x 10^6 m/s

A uniform electric field, with a magnitude of 600 N/C, is directed parallel to the positive x-axis. If the potential at x = 3.0 m is 1000V, what is the change in potential energy of a proton as it moves from x = 3.0 m to x = 1.0m? (qp = 1.6 x 10^-19)

1.9 x 10^-16 J

If the distance between two negative point charges is increased by a factor of three, the resultant potential energy is what factor times the inital potential energy?

1/3

If the distance between two point charges is tripled, the mutual force between them will be changed by what factor?

1/9

A "sandwich" is constructed of two flat pieces of metal (2.00 cm on a side) with a 2.00 - mm - thick piece of dielectric called Rutile (K=100) in between them. What is the capacitance? (e0 = 8.85 x 10^-12 C^2/N*m^2)

177 pF

Two parallel-plate capacitors have the same plate area, and the gap between the plates is filled with a dielectric with a dielectric constant equal to 4. The gap in capacitor A is one half that in capacitor B. What is the ratio of the capacitance of A to B?

2

A 10.0- µF capacitor is attached to a 20-V power supply. How much energy is stored in the capacitor?

2.0 x 10^-3 J

If an electron is accelerated from rest through a potential difference of 1200 V, find its approximate velocity at the end of this process (e = 1.6 x 10 ^-19 C, me = 9.1 x 10^-31 kg)

2.1 x 10^7 m/s

A metallic object holds a charge of -3.8x10^-6 C. What total number of electrons does this represent? (e = 1.6x10^-19 C is the magnitude of the electronic charge)

2.375x10^13

An electron is sent at a high speed toward a gold nucleus (charge +79e). What is the electrical force acting on the electron when it is 3.0 x 10^-14 m away from the gold nucleus? (e = 1.6 x 10^-19, ke = 8.99 x 10^9 N*m^2/C^2)

20 N

Find the electrical potential at 0.15 m from a point charge of 6.0 mC. (ke = 8.99 ´ 109 N×m2/C2)

3.6 x 10^5 V

Two point charges, separated by 1.5 cm, have charge values of +2.0 and -4.0 microC, respectively. What is the value of the mutual force between them? (ke = 8.99 x 10^9 N*m^2/C^2)

320 N

If a doubly-ionized oxygen atom (O-2) is accelerated from rest by going through a potential difference of 20 V, what will be the change in its kinetic energy?

40 eV

An electron with a charge of 1.6 x 10^-19 is moving in the presence of an electric field of 400 N/C. What force foes the electron experience?

6.4 x 10^-17 N

A 6.0 microC charge is placed at the origin and a second charge is placed on the x-axis at x = 0.30 m. If the resulting force on the second charge is 5.4 N in the positive x-direction, what is the value of its charge?

9.0 microC

A repelling force must occur between two charged object under which conditions?

A charge of like signs

In which case does an electric field do positive work on a charged particle?

A negative charge moves opposite to the direction of the electric field

The unit of capacitance, the farad, is dimensionally equivalent to which of the following?

C/V

Increasing the separation of the two charged parallel plates of a capacitor, which are disconnected from a battery, will produce what effect on the capacitor?

Decrease Capacitance

Inserting a dielectric material between two charged parallel conducting plates, originally separated by air and disconnected from a battery, will produce what effect on the capacitor?

Increase capacitance

Increasing the voltage across the two plates of a capacitor will produce what effect on the capacitor?

Increase charge

The unit of electric potential, the volt, is dimensionally equivalent to:

J/C

The constant ke, which appears in Coulomb's law formula, is equivalent dimensionally to which of the following?

N*m^2/C^2

An electric field is dimensionally equivalent to what unit?

N/C

A charge, +Q, is placed inside a balloon and the balloon is inflated. As the radius of the balloon r increases the number of field lines going through the surface of the balloon:

Stays the same

I wish to use a positively charged rod to charge a ball by induction. Which statement is correct? - The charge on the ball will be positive - The ball must be a conductor - The charges must be an insulator that is connected temporarily to the ground - The ball is charged as the area of contact between the two increases

The ball must be a conductor

The electric field associated with a uniformly charged hollow metallic sphere is the greatest at:

The sphere's outer surface

A 0.25- µF capacitor is attached across a 1000-V power supply. What is the net charge on the capacitor?

none of the above

An electron (charge -1.6 x 10^-19) moves on a path perpendicular to the direction of a uniform electric field of strength 3.0 N/C. How much work is done on the electron as it moves 15cm?

zero