Physics Chapter 15 HW
Electric charges of the opposite sign
attract each other
A positively charged metal sphere A is brought into contact with an uncharged metal sphere B. As a result:
both spheres are positively charged
The charge on a glass rod that has been rubbed with silk is called positive:
by arbitrary convention
Experimental evidence indicates that
charge is quantized and conserved
An electron is moving horizontally east in an electric field that points vertically upward. The electric force on the electron is
downward
After running a plastic comb through you hair several times you hold it above a small scrap of paper. The paper jumps off the table and sticks to the comb because the paper becomes
electrically polarized
You have just pulled your clothes from the dryer and find that a sock is clinging to your jeans with static electricity. You hold the jeans in one hand and the sock in the other and pull the two apart. As jeans and sock move apart, the forces between them become weaker because the
forces between electric charges become weaker with increasing distance
Three charges +q, +Q, and -Q are placed at the corners of an equilateral triangle as shown. The net force on charge +q due to the other two charges is
horizontal to the right
An object becomes positively charged when it _______.
loses electrons
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
A negatively charged rod is brought near one end of an uncharged metal bar. The end of the metal bar farthest from the rod will be charged
negative
When a hard rubber rod is given a negative charge by rubbing it with wool:
negative charges are transferred from wool to rod
A positively charged insulating rod is brought close to an object that is suspended by a string. If the object is attacted toward the rod we can conclude:
none of the other choices
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
Two charged objects attract each other with a certain force. If the charges on both objects are both doubled with no change in separation, the force between them
quadruples
Electric field lines near positive point charges
radiate outward
To make an uncharged object have a positive charge:
remove some electrons
Electric charges of the same sign
repel each other
To be safer from lightning it is best to be inside a building framed with
steel
Five particles are shot from the left into a region that contains a uniform electric field. All the particles have the same mass. The numbered lines show the paths taken by the five particles. A negatively charged particle with a charge -3Q follows path 2 while it moves through this field. Do not consider any effects due to gravity. In which direction does the electric field point?
toward the bottom of the page
A proton is moving horizontally north in an electric field that points vertically upward. The electric force on the proton is
upward
A ping-pong ball covered with a conducting graphite coating has a mass of 5.0x10-3kg and a charge of 4.0 µC. What electric field directed upward will exactly balance the weight of the ball?
1.2x104 N/C
A 5.0 mC charge is placed at the 0 cm mark of a meter stick and a -4.0 mC charge is placed at the 50 cm mark. What is the magnitude of the electric field at the 30 cm mark?
1.4 MN/C
Three charges are located at 100-m intervals along a horizontal line: a charge of -3.0 C on the left, 2.0 C in the middle, and 1.0 C on the right. What is the electric field on the horizontal line halfway between the -3.0 C and 2.0 C charges?
1.8x107 N/C to the left
If the distance between two electric charges doubles, then the force they exert on each other changes by how much?
1/4 as big
Four point charges are placed at the corners of a square as shown in the figure. Each side of the square has length 2.0 m. Determine the magnitude of the electric field at the point P, the center of the square.
18 kN/C
Two charges Q1 and Q2 are 8.0 cm apart. Charge Q1 = 5.0 nC and Q2 = -5.0 nC. The magnitude of the electric field at point P, 3.0 cm from the midpoint of the line joining Q1 and Q2, is
29 kN/C
A positive charge of 94.0 nC is 12.0 cm from a negative charge of 53.0 nC. The force on one of the charges due to the other is approximately
3.11 mN
How many electrons must be transferred to a body to produce a charge of 125 nC?
7.81x10^11
Distinguish between a conductor and an insulator.
A conductor allows electrons to move easily through it; an insulator does not
Most commercial airliners have static dissipaters on their wingtips. These sharp metal spikes extend from the end of each metal wing and point toward the rear of the plane. Suppose a plane had just flown through a negatively charged cloud and acquired a large negative charge. It is now flying through neutral air. Which of the following should you expect to happen near the static dissipaters?
A corona discharge at the dissipater tips will spray negative charge into the air.
In the figure, the direction of the electric field at a point equidistant from two equally charged bodies A and B is indicated by a vector. The direction of the vector indicates that
A is positive and B is negative
If a charge of +2Q were placed at the origin (the crossing point of the vertical and horizontal lines) of the above figure, into which quadrant would it feel a net force?
C
Five particles are shot from the left into a region that contains a uniform electric field. All the particles have the same mass. The numbered lines how the paths are taken by the five particles. A negatively charged particle with a charge -3Q follows path 2 while it moves through this field. Do not consider any effects due to gravity. Which path would be followed by a helium atom (an electrically neutral particle)?
Path 3
Five particles are shot from the left into a region that contains a uniform electric field. All the particles have the same mass. The numbered lines show the paths taken by the five particles. A negatively charged particle with a charge -3Q follows path 2 while it moves through this field. Do not consider any effects due to gravity. Which path would be followed by a charge of +6Q?
Path 5 (in picture above)
Which one of the following statements is true concerning the electrostatic charge on a conductor?
The charge is entirely on the surface and it is distributed according to the shape of the object.
Who is credited with the discovery that electric charge resides on the surface of conductors?
Michael Faraday
Charge Q1 has 50 electric field lines radiating outward and charge Q2 has 100 field lines converging inward. What is the ratio Q1/Q2?
-0.5
Two positive charges (+8.0 mC and +2.0 mC) are separated by 300 m. A third charge is placed at distance r from the +8.0 mC charge in such a way that the resultant electric force on the third charge due to the other two charges is zero. The distance r is
0.20 km
A positive charge of 63.0 nC is 15.0 cm from a negative charge of 45.0 nC. The force on one of the charges due to the other is approximately
1.13x10-3 N
In x-ray machines, electrons are subjected to electric fields as great as 6.0x105 N/C. Find an electron's acceleration in this field. (me = 9.11x10-31 kg)
1.1x1017 m/s2
A particle with a charge of 4.0 mC has a mass of 5.0 g. What is electric field directed upward will exactly balance the weight of the particle?
12000 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?
14.4 N (repulsive)
An electric force of 10 N acts on a charge of 5.0 μC when it is place in a uniform electric field. What is the magnitude of the this electric field?
2.0 MN/C
An electric field with a magnitude of 6.0x104 N/C is directed parallel to the positive y axis. A particle with a charge q = 4.8x10-19 C is moving along the x axis with a speed v = 3.0x106 m/s. The force on the charge is approximately
2.9x10-14 N in the y direction
Two small spheres, each with mass m = 5.0 g and charge q, are suspended from a point by threads of length L = 0.30 m. What is the charge on each sphere if the threads make an angle of 20º with the vertical?
2.9x10-7 C
In Frame 1, two identical conducting spheres, A and B, carry equal amounts of excess charge that have the same sign. The spheres are separated by a distance d; and sphere A exerts an electrostatic force on sphere B that has a magnitude F. A third sphere, C, which is handled only by an insulating rod, is introduced in Frame 2. Sphere C is identical to A and B except that it is initially uncharged. Sphere C is touched first to sphere A, in Frame 2, and then to sphere B, in Frame 3, and is finally removed in Frame 4. Determine the magnitude of the electrostatic force that sphere A exerts on sphere B in Frame 4.
3F/8
A square has equal positive charges at three of its corners, as shown. The direction of the electric field at point P is
4
An electron is released from rest in a uniform electric field. If the electric field is 1.25 kN/C, at the end of 20 ns the electron's velocity will be approximately
4.4x10^6 m/s
Four point charges, each of the same magnitude, with varying signs are arranged at the corners of a square as shown. Which of the arrows labeled A, B, C, and D gives the correct direction of the net force that acts on the charge at the upper right corner?
B
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
Who originally named electric charges as positive and negative?
Benjamin Franklin
Which of the following statements about electric field lines is not true?
Electric field lines cross midway between charges that have equal magnitude and sign.
An electroscope has a positive charge which is evidenced by the foil leaves that stand apart due to mutual repulsion. If a negative charge is brought nearby and touches the electroscope, the leaves
Fall closer together
Which one of the following statements is true concerning the spacing of the electric field lines in the vicinity of two point charges of equal magnitude and opposite sign?
It indicates the relative magnitude of the electric field
A conductor is distinguished from an insulator with the same number of atoms by the number of:
Nearly free electrons
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.
Two metal spheres are sitting on an insulating table. Sphere A carries a net positive charge, and sphere B is neutral. They are placed near each other on the insulating table. Sphere B is briefly touched on the side the furthest away from Sphere A with a wire that is grounded. Which statement is correct?
Sphere B is now negatively charged.
At what point is the charge per unit area greatest on the surface of an irregularly shaped conducting solid?
Where curvature is greatest
If you bring a negatively charged insulator near two uncharged metallic spheres that are in contact and then separate the spheres, the sphere on the right will have
a negative charge
If nonelectric forces are negligible, a positively charged particle released from rest in a nonuniform electric field
accelerates in the direction of the field.
To make an uncharged object have a negative charge we must:
add some electrons
In a uniform electric field a proton has
an approximately constant acceleration the direction of the field.
The direction of the electric field at a point is the same as
the force on a proton placed at that point.
A positively charged insulating rod is brought close to an object that is suspended by a string. If the object is repelled away from the rod we can conclude:
the object is positively charged
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
An isolated large particle has twice the electric charge as an isolated neighboring smaller particle. The charge of each particle is positive, so they mutually repel each other. Compared to the force on the large particle, the magnitude of the force on the small particle is
the same
The electric field associated with a uniformly charged hollow metallic sphere is the greatest at:
the sphere's outer suface
A neutral metal ball is suspended by a string. A positively charged insulating rod is placed near the ball, which is observed to be attracted to the rod. This is because:
there is a rearrangement of the electrons in the ball
An electrical insulator is a material:
through which electrons do not flow easily
You are standing on a plastic bench that insulates you from your surroundings. Both you and the helium filled balloon that you are holding are electrically neutral. You now rub the balloon against your sweater, so that the balloon becomes negatively charged. You then let the balloon float away. You are left
with a positive electric charge
A point charge of +Q is placed at the center of a square. When a second point charge of -Q is placed at one of the square's corners, it is observed that an electrostatic force of 2.0 N acts on the positive charge at the square's center. Now, identical charges of -Q are placed at the other three corners of the square. What is the magnitude of the net electrostatic force acting on the positive charge at the center of the square?
zero
