Physics 222: Chapter 21 Homework

If the earth's electric field is 100 N/C downward, what must be the charge on a 1-kg object so that it would be "weightless"?

-9.8 × 10-2 C

Two charged objects are separated by a distance "d". The first charge is larger in magnitude than the second charge.

The charges exert forces on each other equal in magnitude and opposite in direction.

Two point charges each have a value of 3.0 C and are separated by a distance of 4.0 m. What is the electric field at a point midway between the two charges?

zero

Can electric field lines intersect in free space?

No

In a region where the electric field is uniform, the electric field lines

are parallel to one another and equally spaced.

Two large, flat plates are parallel to each other. Plate A , located at y = 1 cm, is along the xz-plane and carries a uniform charge density σA = -1.00 μC/m2. Plate B is located at y = -1 cm and carries a uniform charge density σB = +2.00 μC/m2. What is the electric field at the point of coordinates (x, y, z) = (-0.5 cm, 0 cm, 0 cm)?

+1.69x105 N/C)

A piece of plastic has a net charge of +2.00 μC. How many more protons than electrons does this piece of plastic have?

1.25 × 1013

Two point charges, initially 2.0 cm apart, experience a 1.0-N force. If they are moved to a new separation of 8.0 cm, what is the electric force between them?

1/16 N

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?

25.2 × 106 N/C directed towards the negative charge

A thin, circular disk of radius R = 30 cm is oriented in the yz-plane with its center as the origin. The disk carries a total charge Q = +3 μC distributed uniformly over its surface. Calculate the magnitude of the electric field due to the disk at the point x = 15 cm along the x-axis.

3.32 × 105 N/C

Two point charges of magnitudes +5.00 μC, and +7.00 μC are placed along the x-axis at x = 0 cm and x = 100 cm, respectively. Where must a third charge be placed along the x-axis so that it does not experience any net force because of the other two charges?

45.8 cm

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 × 106 N/C

Four point charges of varying magnitude and sign are arranged on the corners of the square of side d as shown in Fig. 21-6. Which of the arrows shown represents the net force acting on the point charge with a charge +Q?

A

Is it possible to have a zero electric field value between a negative and positive charge along the line joining the two charges?

No, a zero electric field cannot exist between the two charges.

Fig. 21-11 shows 3 electric charges labeled Q1, Q2, Q3 and some electric field lines in the region surrounding the charges. What are the signs of the 3 charges?

Q1 is positive, Q2 is negative, Q3 is positive.

A positive object touches a neutral electroscope, and the leaves separate. Then a negative object is brought near the electroscope, does not touch. What happens to the leaves?

They move closer together

When static equilibrium is established for a charged conductor, the electric field just inside the surface of the conductor is

Zero

If an electroscope is charged by induction

its leaves will separate because of the interaction of the charges.

A ring of negative, uniform charge density is placed on the xz-plane with the center of the ring at the origin. A positive charge moves along the y axis toward the center of the ring. At the moment the charge passes through the center of the ring

its velocity is maximum and its acceleration is zero.

A long line of charge with uniform linear charge density λ1λ1 is located on the xx-axis and another long line of charge with uniform linear charge density λ2λ2 is located on the yy-axis with their centers crossing at the origin. In what direction is the electric field at point zz = aa on the positive zz-axis if λ1λ1 and λ2λ2 are positive?

the positive zz-direction