Exercises: Electrical Charges, Conservation of Charge, and Transfer of Charge
Work through each section in order. Show your work on calculation problems.
Warm-Up: Prerequisite Review
These questions review prior knowledge needed for this section.
An atom has 6 protons and 6 electrons. What is its net electric charge?
+6
−6
0 — it is electrically neutral
+12
A proton has charge C and an electron has charge C. What is the total charge of a system containing one proton and one electron? Express your answer in coulombs.
Two charged objects are brought near each other and repel. What can you conclude about their charges?
One is positive and one is negative.
Both are neutral.
Both carry the same sign of charge (both positive or both negative).
One is larger than the other.
Fluency Practice
Apply core concepts from this section. Show your work on calculation problems.
A positively charged rod is brought near a neutral conducting sphere. Which statement correctly describes the resulting interaction?
The sphere is repelled because both objects have charge.
Nothing happens because the sphere is neutral.
The sphere is attracted because the rod's charge induces charge separation in the sphere.
The sphere becomes positively charged immediately.
A glass rod is rubbed with silk and becomes positively charged. Which particle transferred and in which direction?
Protons transferred from the silk to the glass rod.
Electrons transferred from the glass rod to the silk.
Positive charges transferred from the glass rod to the silk.
Neutrons transferred from the silk to the glass rod.
Two identical conducting spheres touch. Sphere A initially has a charge of nC and Sphere B has a charge of nC. After they touch and are separated, what is the charge on each sphere? Express your answer in nC.
A charged sphere with nC touches a neutral sphere of identical size. After separation, what is the charge on each sphere? Express your answer in nC.
Which of the following best explains why metals are good conductors of electricity?
Metal atoms have more protons than electrons, so they are positively charged.
Metal atoms are larger than non-metal atoms.
Metals have free electrons that can move throughout the material in response to electric forces.
Metal atoms share electrons with neighboring atoms, locking them in place.
A negatively charged rod is brought near a grounded neutral conductor (but does not touch it). The ground wire is then removed while the rod is still nearby. The rod is then moved away. What is the sign of the charge remaining on the conductor?
Negative — same sign as the rod
Positive — opposite sign to the rod
Zero — the charge drained into the ground
Unknown — it depends on the material of the conductor
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