Q: Two objects, A and B, are connected by a wire. Object A has $$1.5 \times 10$$^{-8}$$ \ \mathrm{C}$$ and object B has $$-1.2 \times 10$$^{-8}$$ \ \mathrm{C}. $$After connecting and then removing the wire, what is the final charge on each object?

$$0.15 \times 10$$^{-8}$$ \ \mathrm{C} on $$both

Question 1

When an object is said to have a net charge, what does this mean in terms of its atomic structure?

Accepted Answer

It has an unequal number of protons and electrons.

Question 2

What does it mean to say an object is neutral?

Accepted Answer

It has an equal number of protons and electrons.

Question 3

Does a neutral object have no electric charges at all? Explain.

Accepted Answer

No, it contains equal numbers of positive and negative charges.

Question 4

Why is it generally easier to transfer electrons rather than protons between objects?

Accepted Answer

Electrons are located outside the nucleus and are less tightly bound.

Question 5

When rubbing a plastic pipe with a piece of fur, the fur becomes positively charged. Which particle was transferred, and to which object?

Accepted Answer

Electrons were transferred from the fur to the pipe.

Question 6

If a plastic pipe gains mass after being rubbed with fur, what can you infer about the particles transferred?

Accepted Answer

Electrons were transferred to the pipe, increasing its mass.

Question 7

How many electrons must be added to a neutral object to give it a charge of $$-1 \ \mu \mathrm{C}$$? (Elementary charge $$e = 1.6 	imes 10$$^{-19}$$ \ \mathrm{C})$$

Accepted Answer

$$6.25 	imes 10$$^{12}$$

Question 8

Two objects, A and B, are connected by a wire. Object A has $$1.5 	imes 10$$^{-8}$$ \ \mathrm{C}$$ and object B has $$-1.2 	imes 10$$^{-8}$$ \ \mathrm{C}. $$After connecting and then removing the wire, what is the final charge on each object?

Accepted Answer

$$0.15 	imes 10$$^{-8}$$ \ \mathrm{C} on $$both

Question 9

If two objects with charges $$q_1$$ and $$q_2$$ are connected and then separated, and $$q_1$$ 
eq $$q_2$$, what is conserved during the process?

Accepted Answer

The total charge.

Question 10

Suppose two objects with charges $$+2 \ \mu \mathrm{C}$$ and $$-1 \ \mu \mathrm{C}$$ are connected and then separated. What is the final charge on each object?

Accepted Answer

$$+0.5 \ \mu \mathrm{C}$$

Question 11

Three charged objects are arranged at the corners of a right triangle. If $$q_1 = 2.0$$ 	imes $$10^{-6}$$ \ \mathrm{C}$$ at (0$$,0)$$, q_2$ = -1.0 	imes 10$$^{-6}$$ \ \mathrm{C} at$$ $$(0,4)$$, and $$q_3 = 3.0$$ 	imes $$10^{-6}$$ \ \mathrm{C}$$ at (3$$,0)$$ (all distances in meters), what is the magnitude of the net force on q_1$? (Use k = 8.99$$ 	imes $$10^9$$ \ \mathrm{N} \cdot \mathrm{m}^2/\mathrm{C}^2$$)

Accepted Answer

$$0.027 \ \mathrm{N}$$

Question 12

If three charges are arranged as in the previous question, what is the direction of the net force on $$q_1$$?

Accepted Answer

At an angle between the x- and y-axes, toward the third quadrant

Question 13

A neutral object is brought near a negatively charged rod. What happens to the charges in the neutral object?

Accepted Answer

Electrons in the object are repelled, causing a separation of charge.

Question 14

Which of the following best explains why static electricity is more noticeable on dry days?

Accepted Answer

Dry air is a poor conductor, so charges are less likely to dissipate.

Question 15

If a glass rod is rubbed with silk and becomes positively charged, what happens at the atomic level?

Accepted Answer

Electrons are transferred from the rod to the silk.

Question 16

A student claims that a neutral object cannot exert an electric force on a charged object. Is this correct?

Accepted Answer

No, because a neutral object can become polarized and exert a force.

Question 17

If an object has a net charge of $$+3.2 	imes 10$$^{-19}$$ \ \mathrm{C}$$, how many excess protons does it have?

Accepted Answer

2

Question 18

Which of the following statements about conservation of charge is correct?

Accepted Answer

The total charge in an isolated system remains constant.

Question 19

A metal sphere is given a negative charge by contact with a negatively charged rod. What happens to the electrons?

Accepted Answer

Electrons move from the rod to the sphere.

Question 20

If a charged object is grounded, what happens to its excess charge?

Accepted Answer

It is transferred to the ground.

Electrostatics: Charge, Transfer, and Forces Study Notes

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