Electricity and Magnetism Quiz True or False

1. 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
2. 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. -> 16.7 m/s2
3. What is the net electric field 2 m away from a tight cluster of three +1 nC charges and two -2 nC charges? -> +4.50 N/C
4. 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? ->
5. What is the electric field at a point r outside a sphere of radius R which has a uniform charge density of ρ? ->
6. Which point on the graph below has the highest electric potential? The distance between each notch is equal.

-> A
7. 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? ->
8. 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? -> 25.0 μC
9. 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
10. 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? -> 29.5 g

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