CT1. A positively charged object is placed close to a conducting object attached to an insulating glass pedestal (a). After the opposite side of the conductor is grounded for a short time interval (b), the conductor becomes negatively charged (c).
Based on this information, we can conclude that within the conductor
CT2. A pair of equal and opposite charges are placed as illustrated.
CT3. A negatively charged object is placed in an electric field as shown below
the four field patterns shown. Assuming there are no charges in the
regions shown, which of the patterns represent(s) a possible
CT1: The answer
is 4. All we know is that there is a net surplus
positive charge in one position and a net surplus of negative charge in
another. This could be caused by negative charge carriers moving
toward the rod or positive charge carriers moving away. There is
no way of discerning the microscopic behavior by examining the net
Our knowledge of ordinary matter tells us that electrons and protons carry charge and that electrons are usually more able to move about. However, if someone clever manufactured some material in which positive charges could move about more easily, exactly the same result would be achieved.
CT3: The answer is 2. At the object's position, the electric field is to the right. Therefore, the force on the negatively charged object is in the opposite direction, to the left. It doesn't matter what charges created the field, the field itself gives sufficient information to answer the question.
CT4: The answer is 2. Pattern (a) can be eliminated because field lines cannot simultaneously emanate from and converge at a single point; (c) can be eliminated because there are no charges in the region, and so there are no sources of field lines; (d) can be eliminated because electrostatic field lines do not close on themselves.
is 5. An electric dipole in a uniform electric field
experiences a zero net force because the forces exerted on each end are of equal
magnitude but opposite direction. In (a) and (b) the speading of
the field lines indicates a diminishing field strength to the
left. There is a torque on (d), but no net force.
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