thin A stream of water bends toward a negatively charged rod. When a positively charged rod is placed near the stream, it will bend in the 1. opposite direction. 2. same direction. 3. ... but it won't bend at all.
Water is a neutral conductor. If you bring and charged object near it, it will polarize the water so that the water will always end up attracting the charged object (whether it is positively or negatively charged)
1
Rank in order, from most positive to most negative, the charges qa to qe of these five systems.
1) qa > qe > qd > qc > qb 2) qa = qb > qe > qc > qd 3) qd > qc > qe > qa = qb 4) qd > qc > qe > qa > qb 5) qe > qa > qd > qb > qc
Look at the net charge of each case and rank the most positive to the most negative. D is neutral and anything missing electrons is positively charged.
2
Charges A and B exert repulsive forces on each other. qA = 4qB. Which statement is true?
1) FA on B > FB on A 2) FA on B < FB on A 3) FA on B = FB on A
Newton's third law applies here. They exert an equal but opposite force on each other.
3
What can we conclude from the attractive nature of the force between a positively charged rod and an object?
+ + + + + +
?
1. The object is a conductor. 2. The object is an insulator. 3. Cannot be determined.
If two objects attract, then either, both objects are charged (either insulator or conductor), or the other object is a neutral conductor that will be polarized and attract any charged object brought near it.
4
A charged rod is brought near a suspended object, which is repelled by the rod. The suspended object must be charged. 1. True 2. False
See previous slides.
5
A charged rod is brought near a suspended object, which is attracted to the rod. The suspended object must be charged. 1. True 2. False
See previous slides.
6
A charge q is to be placed at either point A or point B in the accompanying figure. Assume points A and B lie on a line that is midway between the two positive charges. Is the net force experienced at point A 1. greater than the net force experienced at point B. 2. to equal the net force experienced at point B. 3. less than the net force experienced at point B.
At point A, the force due to both charges cancels out to zero. That is not true at point B where the x-components cancel out but the y-components add up.
7
Three equal charges are at three of the corners of a square of side d. A fourth charge of equal magnitude is at the center of the square as shown in the Figure. Which of the arrows shown represents the net force acting on the charge at the center of the square?
1) A 2) B 3) C 4) D
All the charges are positive so they all want to repel each other. The two charges in the corners cancel out leaving the one on the bottom.
8
An electron is placed at the position marked by the dot. The force on the electron is
1) to the left. 2) to the right. 3) zero. 4) There's not enough information to tell.
Electric field lines point towards negative charges. So a negative charge will go in the opposite direction to that of the field lines.
9
Rank in order, from largest to smallest, the electric field strengths E1 to E4 at points 1 to 4.
1) E2 > E4 > E1 > E3 2) E2 > E1 = E4 > E3 3) E2 > E1 > E4 > E3 4) E1 = E2 > E3 = E4 5) E1 > E2 > E3 > E4
Calculate E using:
E=
kq r2
10
At the position of the dot, the electric field points
1) Left. 2) Down. 3) Right. 4) Up. 5) The electric field is zero.
The two fields from the positive charges cancel out and the field due to the negative charge points up toward the negative charge
11
Rank in order, from largest to smallest, the electric field strengths Ea to Ee at these five points near a plane of charge.
1) Ea = Eb = Ec = Ed = Ee 2) Ea > Ec > Eb > Ee > Ed 3) Eb = Ec = Ed = Ee > Ea 4) Ea > Eb = Ec > Ed = Ee 5) Ee > Ed > Ec > Eb > Ea
The electric field is uniform (same size arrows) so all points have equal field.
12
The picture shows the electric field lines in a certain region of space. Object A is 1. a conductor 2. an insulator
The field lines are perpendicular to the surface of the object and there are no field lines inside the object.
13