Ch. 15 Number Questions

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

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

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

Four charges are at the corners of a square, with B and C on opposite corners. Charges A and D, on the other two corners, have equal charge, while both B and C have a charge of +1.0 C. What is the charge on A so that the force on B is zero?

-0.35 C

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

Two point charges are placed along a horizontal axis with the following values and positions: +3.0 µC at x = 0 cm and -7.0 µC at x = 20 cm. At what point along the x axis is the electric field zero?

-38 cm

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?

-8 C

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 * 10^7 m/s^2

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 * 10^17 m/s^2

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

1.2 * 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 * 10^-5 C

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

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 * 10^6 N/C

Two identical spheres each carry a charge of -40.0 µC. The spheres are separated by a distance of 1.00 m. What is the electric force between the spheres? (ke = 8.99 ´ 109 N·m2/C2)

14.4 N (repulsive)

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 ´ 10-19C)

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 * 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

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

20 radiate in

In a thundercloud there may be an electric charge of +40 C near the top of the cloud and -40 C near the bottom of the cloud. These charges are separated by about 2.0 km. What is the electric force between these two sets of charges? (ke = 8.99 ´ 109 N·m2/C2)

3.6 * 10^6 N

Two point charges, separated by 1.5 cm, have charge values of +2.0 and -4.0 µC, respectively. What is the value of the mutual force between them? (ke = 8.99 ´ 109 N×m2/C2)

320 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

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

4

Two identical iron spheres have equal positive charges and the force between them when they are 1 m apart is 1 N. What percentage of the electrons has been removed from each sphere if each sphere has 1 mole (6 ´1023) of iron atoms? (ke = 8.99 ´ 109 N×m2/C2, the atomic number of iron is 26, and the electron charge is-1.6 ´ 10-19 C)

4 * 10^-10 %

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:

4 C/Eo

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?

4.0 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 * 10^42

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)

4.8 * 10^6 N/C

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

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)

5.1 * 10^7 N/C

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 * 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 * 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 * 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 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 * 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

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 * 10^6 N/C

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 uC

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

r^2