Physics 180B - Ch. 16-21 - Concepts (HW + Modules)

A: It is strongly attracted Correct: This charge is said to be "induced" by the presence of the electric field of the charged ball: It is not transferred by the ball.

There is negative charge spread evenly on both ends.

A: It is strongly repelled.

A: It is strongly repelled

A:The marble has lost the same number of electrons acquired by the piece of silk. A:The marble acquires a positive charge and attracts the piece of silk. Correct: This was a simple example of electrostatic interactions. When you rub a piece of glass against a piece of silk, the glass acquires a positive charge and the silk acquires a negative charge because some electrons were transferred from the glass to the silk in the rubbing process. The silk acquires the same net charge as the glass, but with the opposite sign. This charge distribution causes the silk and the glass marble to be attracted to one another.

A: Marbles 1 and 2 repel each other, but no interaction occurs with marble 3. Correct: As you have seen here, electrostatic interactions occur between charged objects. Objects with like charges repel each other, whereas objects with opposite charges attract each other.

Learning Goal: When a test charge is brought near a charged object, we know from Coulomb's law that it will experience a net force (either attractive or repulsive, depending on the nature of the object's charge). A test charge may also experience an electric force when brought near a neutral object. Any attraction of a neutral insulator or neutral conductor to a test charge must occur through induced polarization. In an insulator, the electrons are bound to their molecules. Though they cannot move freely throughout the insulator, they can shift slightly, creating a rather weak net attraction to a test charge that is brought close to the insulator's surface. In a conductor, free electrons will accumulate on the surface of the conductor nearest the positive test charge. This will create a strong attractive force if the test charge is placed very close to the conductor's surface.

A: Strongly attractive

A: Weakly attractive Correct: Recall that ball C is composed of insulating material, which can be polarized in the presence of an external charged object such as ball A. Once polarized, there will be a weak attraction between balls A and C, because the positive and negative charges in ball C are at slightly different average distances from ball A. If ball C had a very small negative charge the test charge would have the same response (weakly attractive) but it would have a weak repulsive interaction with ball A. However, a smaller negative charge is not one of the options.

A: Attractive

A: Neither attractive nor repulsive Correct: Because the test charge T is neither strongly attracted to nor repelled from ball C, ball C must have zero net charge. Since ball D also has zero net charge, there will not be any force between the two balls.

A: F = 14 N

A: F = 7.93×10^6 N

A: Along the line between the charge and the center of the square outward of the center

Learning Goal: Coulomb's law gives the electrostatic force F⃗ acting between two charges. The magnitude F of the force between two charges q1 and q2 depends on the product of the charges and the square of the distance r between the charges: F=k*(|q1*q2|)/(r^2) where k=1/(4*π*ϵ0) = 8.99×109N⋅m2/C2. The direction of the force is along the line connecting the two charges. If the charges have the same sign, the force will be repulsive. If the charges have opposite signs, the force will be attractive. In other words, opposite charges attract and like charges repel. Because the charges are not in contact with each other, there must be an intermediate mechanism to cause the force. This mechanism is the electric field. The electric field at any location is equal to the force per unit charge experienced by a charge placed at that location. In other words, if a charge q experiences a force F⃗ , the electric field E⃗ at that point is: E⃗ = F⃗ q. The electric field vector has the same direction as the force vector on a positive charge and the opposite direction to that of the force vector on a negative charge.