Q: Two spheres, one glass and one plastic, each with a mass of 1 kg, are placed 1 m apart. What is the gravitational force between them? Use $$G = 6.67 \times 10$$^{-11}$$ \ \mathrm{N} \cdot \mathrm{m}^2/\mathrm{kg}^2.$$

$$6.67 \times 10$$^{-11}$$ \ \mathrm{N}$$

Q: What is the magnitude of the electrostatic force between two $$1 \ \mathrm{C}$$ charges placed $$1 \ \mathrm{m}$$ apart? Use $$K = 9 \times 10^9$ \ \mathrm{N} \cdot \mathrm{m}^2/\mathrm{C}^2.$$

$$9 \times 10^9$ \ \mathrm{N}$$

Q: A singly charged calcium ion ($$q = +e) is in a $$cell membrane electric field of $$1.0 \times 10^7$ \ \mathrm{N/C}. $$What is the magnitude of the force on the ion? ($$e = 1.6 \times 10$$^{-19}$$ \ \mathrm{C})$$

$$1.6 \times 10$$^{-12}$$ \ \mathrm{N}$$

Question 1

Two spheres, one glass and one plastic, each with a mass of 1 kg, are placed 1 m apart. What is the gravitational force between them? Use $$G = 6.67 	imes 10$$^{-11}$$ \ \mathrm{N} \cdot \mathrm{m}^2/\mathrm{kg}^2.$$

Accepted Answer

$$6.67 	imes 10$$^{-11}$$ \ \mathrm{N}$$

Question 2

After rubbing a glass sphere with silk and a plastic sphere with wool, the force between them at 1 m is measured to be $$0.009 \ \mathrm{N}. $$What does this result most likely indicate?

Accepted Answer

The spheres have acquired electric charges, and the force is now primarily electrostatic.

Question 3

Which of the following statements about electric charge is FALSE?

Accepted Answer

Charge can be created or destroyed in ordinary processes.

Question 4

A rod attracts a positively charged hanging ball. The rod must be:

Accepted Answer

Negatively charged or neutral.

Question 5

Which material is a good conductor of electricity?

Accepted Answer

Copper metal

Question 6

What is the net charge $$q of an $$object with $$N_p$$ protons and $$N_e$$ electrons?

Accepted Answer

$$q = (N_p - N_e)e$$

Question 7

What is the process called when a charged object causes a shift in the electron cloud of a nearby atom, creating a separation of charge?

Accepted Answer

Polarization

Question 8

Which of the following best describes a dipole?

Accepted Answer

A separation of equal positive and negative charges.

Question 9

A charged rod is brought near two touching metal spheres, which are then separated while the rod is still present. What is the resulting charge on the spheres?

Accepted Answer

One sphere is positive, the other is negative.

Question 10

What is the magnitude of the electrostatic force between two $$1 \ \mathrm{C}$$ charges placed $$1 \ \mathrm{m}$$ apart? Use $$K = 9 	imes 10^9$ \ \mathrm{N} \cdot \mathrm{m}^2/\mathrm{C}^2.$$

Accepted Answer

$$9 	imes 10^9$ \ \mathrm{N}$$

Question 11

Which equation correctly expresses Coulomb’s Law for the force between two point charges $$q_1$$ and $$q_2$$ separated by distance $$r$$?

Accepted Answer

$$F = K \frac{|q_1$||q_2$|}{r^2$}$$

Question 12

What is the SI unit of electric charge?

Accepted Answer

Coulomb

Question 13

Which of the following is true about the electric field $$\vec{E}$$ created by a point charge $$q at a $$distance $$r$$?

Accepted Answer

$$\vec{E} = K \frac{q}{r^2$} \hat{r}$$

Question 14

A singly charged calcium ion ($$q = +e) is in a $$cell membrane electric field of $$1.0 	imes 10^7$ \ \mathrm{N/C}. $$What is the magnitude of the force on the ion? ($$e = 1.6 	imes 10$$^{-19}$$ \ \mathrm{C})$$

Accepted Answer

$$1.6 	imes 10$$^{-12}$$ \ \mathrm{N}$$

Question 15

Which of the following best describes the direction of the electric field created by a positive point charge?

Accepted Answer

Radially outward from the charge

Question 16

If three forces act on a charge, how is the net force calculated?

Accepted Answer

By vector addition of all three forces

Question 17

Which of the following is a property of water that results from its molecular dipole moment?

Accepted Answer

High surface tension

Question 18

Which of the following is the correct vector form of Coulomb’s Law for the force on $$q_2$$ due to $$q_1$$?

Accepted Answer

$$\vec{F}_{1 	ext{ on } 2} = K \frac{q_1$ q_2$}{r^2$} \hat{r}$$

Question 19

What is the unit of a unit vector such as $$\hat{r}$$?

Accepted Answer

It has no units.

Electric Charges and Forces: Structured Study Notes

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