Think you’ve got your head wrapped around Electricity and Magnetism? Put your knowledge to
the test. Good luck — the Stickman is counting on you!
Q. What is the magnitude and direction of the force felt by a +1 mC charge that sits at the middle of a square whose vertices are all charged according to the diagram below? The sides of the square are 1 m long, and all charges are in mC.
0 N
18,000 N up and to the right
18,000 N down and to the left
25,456 N to the left
25,456 N to the right
Q. Agent Shmoop is placed on a Teflon slab by the evil Dr. Nyet and rubbed violently with a piece of rabbit's fur until an excess charge of 5 mC builds up on him. If Dr. Nyet then releases a 30 kg bomb charged to -10 mC from 30 m across the room, how fast will the bomb initially accelerate towards Agent Shmoop? The floor is frictionless, of course—dastardly megalomaniacs like Dr. Nyet hate friction in their lairs.
0.05 m/s2
1.67 m/s2
16.7 m/s2
33.4 m/s2
500 m/s2
Q. What is the net electric field 2 m away from a tight cluster of three +1 nC charges and two -2 nC charges?
-2.25 N/C
+2.25 N/C
-4.50 N/C
+4.50 N/C
+27.0 N/C
Q. What is the electric field at a point r inside a sphere of radius R which has a uniform charge density (charge per volume) of ρ?
Q. What is the electric field at a point r outside a sphere of radius R which has a uniform charge density of ρ?
Q. Which point on the graph below has the highest electric potential? The distance between each notch is equal.
A
B
C
D
E
Q. A very, very, very large metal sheet—even bigger than the one you're picturing, but very thin—has a surface charge density (charge per area) of σ. What is the electric field a distance r above the sheet?
Q. A +5 μC charge is attached to a spring that is anchored to a fixed charge. If the spring's natural length is 10 cm and its coefficient of stiffness is 1000 N/m, how big must the anchored charge be to stretch the spring 5 cm?
1.25 μC
2.77 μC
5.00 μC
11.1 μC
25.0 μC
Q. The earth is approximately 6.0 × 1024 kg. The moon is around 7.3 × 1022 kg. If the earth and moon both were magically charged with +q, how big would q have to be to cancel out their gravitational attraction?
5.7 × 1013 C
5.7 × 1024 C
3.2 × 1027 C
7.7 × 1033 C
We can't answer without knowing the distance between the earth and the moon (but it's really, really big)
Q. A +1 μC charge is hung from a pendulum, and a +3 μC charge is placed at the lowest point of the pendulum's swing. If the pendulum's rope is 0.3 m long and swings out 30º from vertical when released, how heavy is the smaller charge?
7.91 g
8.83 g
15.3 g
29.5 g
59.0 g