Physics Midterm chapter 15

A charge Q accumulates on the hollow metallic dome, of radius R, of a Van de Graaff generator. A probe measures the electric field strength at various points outside the sphere surface. If the probe is initially at a distance 3R from the sphere's center and then is moved to 4R, by what factor will the electric field reading change?

(3/4)^2

We have a hollow metallic sphere with charge -5.0 µC and radius 5.0 cm. We insert a +10-µC charge at the center of the sphere through a hole in the surface. What charge now rests on the outer surface of the sphere?

+5 µC

Q1 has 50 electric field lines radiating outward and Q2 has 100 field lines converging inward. What is the ratio Q1/Q2?

-1/2

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?

-10 µC

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

-8C

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

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 proton initially moves left to right long the x axis at a speed of 2.00 ´ 103 m/s. It moves into an electric field, which points in the negative x direction, and travels a distance of 0.200 m before coming to rest. If the proton's mass and charge are 1.67 ´ 10-27 kg and 1.60 ´ 10-19 C respectively, what is the magnitude of the electric field?

0.104 N/C

A proton initially moves left to right long the x axis at a speed of 2.00 ´ 103 m/s. It moves into an electric field, which points in the negative x direction, and travels a distance of 0.200 m before coming to rest. What acceleration magnitude does the proton experience?

1.00 x 10^7 m/s2

In x-ray machines, electrons are subjected to electric fields as great as 6.0 ´ 105 N/C. Find an electron's acceleration in this field. (me = 9.11 ´ 10-31 kg, e = 1.6 ´ 10-19 C)

1.1 x 10^17 m/s2

A ping-pong ball covered with a conducting graphite coating has a mass of 5.0 ´ 10-3 kg and a charge of 4.0 µC. What electric field directed upward will exactly balance the weight of the ball? (g = 9.8 m/s2)

1.2 x 10^4 N/C

A Van de Graaff generator has a spherical dome of radius 20 cm. Operating in dry air, where "atmospheric breakdown" is at Emax = 3.0 ´ 106 N/C, what is the maximum charge that can be held on the dome? (ke = 8.99 ´ 109 N×m2/C2)

1.3 x 10^-5

Charge A and charge B are 3.00 m apart, and charge A is +2.00 C and charge B is +3.00 C. Charge C is located between them at a certain point and the force on charge C is zero. How far from charge A is charge C?

1.35 m

Charges of 4.0 µC and -6.0 µC are placed at two corners of an equilateral triangle with sides of 0.10 m. At the third corner, what is the electric field magnitude created by these two charges? (ke = 8.99 ´ 109 N·m2/C2)

1.6 x 10^6 N/C

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

1/9

About how many electrons are in 30 grams of water (H2O)?

10^25

Two point charges are separated by 10.0 cm and have charges of +2.00 µC and -2.00 µC, respectively. What is the electric field at a point midway between the two charges? (ke = 8.99 ´ 109 N·m2/C2)

14.4 x 10^6 N/C

Electrons in a particle beam each have a kinetic energy of 3.2 ´ 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 ´ 10-19 C)

2,000 N/C

An electron with a speed of 2.0 ´ 106 m/s moves into a uniform electric field of 500 N/C that is parallel to the electron's motion. How long does it take to bring the electron to rest? (me = 9.11 ´ 10-31 kg, e = 1.6 ´ 10-19 C)

2.3 ´ 10^-8 s

A metallic object holds a charge of -3.8 ´ 10-6 C. What total number of electrons does this represent? (e = 1.6 ´ 10-19 C is the magnitude of the electronic charge.)

2.4 x 10^13

An electron is sent at high speed toward a gold nucleus (charge +79e). What is the electrical force acting on the electron when it is 3.0 ´ 10-14 m away from the gold nucleus? (e = 1.6 ´ 10-19 C, ke = 8.99 ´ 109 N·m2/C2)

20 N

The electric field in a cathode ray tube is supposed to accelerate electrons from 0 to 1.60 ´ 107 m/s in a distance of 2.00 cm. What electric field is required? (me = 9.11 ´ 10-31 kg and e = 1.60 ´ 10-19 C

36 400 N/C

A spherical volume of space has an electric field of intensity 100 N/C directed radially outward from its surface of radius 0.600 m. What is the net charge enclosed within this surface?

4 nC

Two electrons are separated by one cm. What is the ratio of the electric force to the gravitational force between them? (me = 9.11 ´ 10-31 kg, ke = 8.99 ´ 109 N×m2/C2, G = 6.67 ´ 10-11 N×m2/kg2, and e = 1.6 ´ 10-19 C)

4.2 x 10^42

A charge Q accumulates on the hollow metallic dome, of radius R, of a Van de Graaff generator. A probe measures the electric field strength at various points outside the sphere surface. By what factor will the electric field value at the 2R distance be changed if the charge value were increased to (4/3)Q?

4/3

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

4C/eo

The average distance of the electron from the proton in the hydrogen atom is 0.51 ´ 10-10 m. What is the electric field from the proton's charge at the location of the electron? (ke = 8.99 ´ 109 N×m2/C2, e = 1.6 ´ 10-19 C)

5.5 x 10^11 N/C

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

6.4 x 10^-17 N

A proton moving at 3.0 ´ 104 m/s is projected at an angle of 30° above a horizontal plane. If an electric field of 400 N/C is acting down, how long does it take the proton to return to the horizontal plane? (Hint: Ignore gravity. mproton = 1.67 ´ 10-27 kg, qproton = 1.6 ´ 10-19 C)

7.8 x 10^-7 s

An airplane is flying through a thundercloud at a height of 2 000 m. (This is a very dangerous thing to do because of updrafts, turbulence, and the possibility of electric discharge.) If there is a charge concentration of +40 C at height 3 000 m within the cloud and -40 C at height 1 000 m, what is the magnitude of the electric field E at the aircraft? (ke = 8.99 ´ 109 N·m2/C2)

720 000 N/C

In Millikan's oil drop experiment, if the electric field between the plates was of just the right magnitude, it would exactly balance the weight of the drop. Suppose a tiny spherical oil droplet of radius 1.6 ´ 104 cm carries a charge equivalent to one electron. What electric field is required to balance the weight? (The density of oil is 0.85 g/cm3, e = 1.6 ´ 10-19 C.)

8.9 x 10^5 N/C

If the size of the charge value is tripled for both of two point charges maintained at a constant separation, the mutual force between them will be changed by what factor?

9.0

A 6.0 mC 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 mC

We have an initially uncharged hollow metallic sphere with radius of 5.0 cm. I place a small object with a charge of +10 µC at the center of the sphere through a hole in the surface. Find the electric field present at a point 10 cm from the sphere's center. (ke = 8.99 ´ 109 N×m2/C2)

9.0 x 10^6 N/C

Charge A has 10 electric field lines coming out, Charge B has 20 lines coming out, and Charge C has 30 lines coming in. Which pair of these charges will have the largest force between them if placed one cm apart?

B and C

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

Charges are of like signs

Doug rubs a piece of fur on a hard rubber rod, giving the rod a negative charge. What happens?

Electrons are added to the rod.

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

Field Strength

Of the following substances, which one contains the highest density of free electrons?

Iron

Who was the first to determine the electron's charge?

Millikan

Electric field is dimensionally equivalent to which of the following?

N/C

Two identical balls have the same amount of charge, but the charge on 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 is correct.

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

N×m2/C2

I wish to use a positively charged rod to charge a ball by induction. Which statement is correct?

The ball must be a conductor.

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

The charges in the uncharged object can become polarized

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?

Zero

Which of the following best characterizes electrical insulators?

charges on the surface don't move

In the Millikan oil-drop experiment it was found that oil droplets:

could have positive, negative, or zero net charge.

The combination of two separated point charges of opposite sign but equal magnitude is called an electric:

dipole

Which of the following best characterizes electrical conductors?

electric charges move freely

The beam of electrons that hits the screen of an oscilloscope is moved up and down by:

electrical charges on deflecting plates.

When a glass rod is rubbed with silk, which of the following statements best describes what happens?

electrons are removed from the rod

If body M, with a positive charge, is used to charge body N by induction, what will be the nature of the charge left on the latter?

must be negative

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 positive

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

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

r^2

If a conductor is in electrostatic equilibrium near an electrical charge

the electric field inside the conductor must be zero.

The Millikan oil-drop experiment demonstrated that:

the electronic charge is quantized

If a charge +Q is placed inside a hollow isolated conductor that is originally neutral and the charge does not touch that conductor at any time:

the outside surface of the conductor will become positively charged.

Relative distribution of charge density on the surface of a conducting solid depends on:

the shape of the conductor

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

the sphere's outer surface

When charging two objects by rubbing them together:

they must be made of different material.

At what point is the charge per unit area greatest on the surface of an irregularly shaped conducting solid?

where curvature is greatest

Two point charges each have a value of 30.0 mC and are separated by a distance of 4.00 cm. What is the electric field midway between the two charges? (ke = 8.99 ´ 109 N·m2/C2)

zero