Q: A red blood cell carries a net negative charge of $$2.5 \times 10$$^{-16}$$\ \mathrm{C}. If $$two such cells are $$2.0 \times 10$$^{-6}$$\ \mathrm{m}$$ apart, what is the magnitude of the electric force between them? (Use $$k = 8.99 \times 10^9$\ \mathrm{N\cdot m^2$/C^2$$}$)

$$1.4 \times 10$$^{-14}$$\ \mathrm{N}$$

Q: A parallel-plate capacitor is connected to a battery and produces a uniform electric field of $$1.0 \times 10^4$\ \mathrm{N/C}$$ between the plates separated by $$1.0\ \mathrm{cm}. An $$electron is released from rest at the upper plate. What is its kinetic energy when it reaches the lower plate? (Charge of electron $$e = 1.6 \times 10$$^{-19}$$\ \mathrm{C})$$

$$1.6 \times 10$$^{-21}$$\ \mathrm{J}$$

Question 1

Which of the following statements best describes why metals are good electrical conductors?

Accepted Answer

Metals have a 'sea of electrons' where valence electrons are only weakly bound and can move throughout the metal.

Question 2

A neutral lithium atom contains 3 protons, 4 neutrons, and 3 electrons. What is the net charge of this atom?

Accepted Answer

$$0$$

Question 3

Which equation correctly expresses Coulomb's law for the magnitude of the force between two point charges $$q_1$$ and $$q_2$$ separated by a distance $$r$$?

Accepted Answer

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

Question 4

A red blood cell carries a net negative charge of $$2.5 	imes 10$$^{-16}$$\ \mathrm{C}. If $$two such cells are $$2.0 	imes 10$$^{-6}$$\ \mathrm{m}$$ apart, what is the magnitude of the electric force between them? (Use $$k = 8.99 	imes 10^9$\ \mathrm{N\cdot m^2$/C^2$$}$)

Accepted Answer

$$1.4 	imes 10$$^{-14}$$\ \mathrm{N}$$

Question 5

Which of the following best explains why red blood cells do not clump together under normal conditions?

Accepted Answer

They carry a net negative charge, causing mutual electrostatic repulsion.

Question 6

A small glass bead of mass $$15\ \mathrm{mg}$$ and charge $$+10\ \mathrm{nC} is $$placed $$1.0\ \mathrm{cm}$$ below a fixed plastic sphere charged to $$-10\ \mathrm{nC}. $$What is the direction of the electric force on the bead?

Accepted Answer

Upwards, toward the plastic sphere

Question 7

Which of the following correctly describes the electric field produced by a uniformly charged infinite plane?

Accepted Answer

The electric field is uniform and perpendicular to the plane.

Question 8

A point charge $$q = -8.0\ \mathrm{nC} is $$located at the origin. What is the electric field at the point $$(1.2\ \mathrm{m}, -1.6\ \mathrm{m})$$? (Use $$k = 8.99 	imes 10^9$\ \mathrm{N\cdot m^2$/C^2$$}$)

Accepted Answer

$$\vec{E} = (-11\ \mathrm{N/C})\hat{i} + (14\ \mathrm{N/C})\hat{j}$$

Question 9

Which of the following statements about electric field lines is correct?

Accepted Answer

Electric field lines never cross and are tangent to the electric field vector at every point.

Question 10

A parallel-plate capacitor is connected to a battery and produces a uniform electric field of $$1.0 	imes 10^4$\ \mathrm{N/C}$$ between the plates separated by $$1.0\ \mathrm{cm}. An $$electron is released from rest at the upper plate. What is its kinetic energy when it reaches the lower plate? (Charge of electron $$e = 1.6 	imes 10$$^{-19}$$\ \mathrm{C})$$

Accepted Answer

$$1.6 	imes 10$$^{-21}$$\ \mathrm{J}$$

Question 11

Which of the following best describes the direction of the electric dipole moment for a water molecule?

Accepted Answer

From the negative oxygen atom to the positive hydrogen atoms

Question 12

A DNA fragment is placed in an electric field during gel electrophoresis. Which of the following statements is true regarding its motion?

Accepted Answer

The DNA fragment quickly reaches a constant terminal velocity due to viscous drag.

Question 13

What is the electric field inside a conductor in electrostatic equilibrium?

Accepted Answer

It is zero.

Question 14

A point charge $$Q is $$placed at the center of a uniformly charged sphere of radius $$R$$ and total charge $$Q. $$What is the electric field at a distance $$r \u003e R$$ from the center?

Accepted Answer

$$E = \frac{1}{4\pi\$$epsilon_0$$} \frac{Q}{r^2$}$$

Question 15

A dipole with moment $$\vec{p} is $$placed in a uniform electric field $$\vec{E}. $$What is the torque $$\vec{	au}$$ acting on the dipole?

Accepted Answer

$$\vec{	au} = \vec{p} 	imes \vec{E}$$

Question 16

If a charge $$q is $$placed in an electric field $$\vec{E}$$, what is the force $$\vec{F}$$ experienced by the charge?

Accepted Answer

$$\vec{F} = q \vec{E}$$

Question 17

Which of the following is true about the surface charge on a conductor in electrostatic equilibrium?

Accepted Answer

The charge resides entirely on the surface.

Question 18

A particle of mass $$6.64 	imes 10$$^{-27}$$\ \mathrm{kg}$$ travels $$2.00\ \mathrm{cm}$$ between two parallel plates in $$1.77 	imes 10$$^{-6}$$\ \mathrm{s}$$ under a uniform electric field of $$1.0 	imes 10^4$\ \mathrm{N/C}. $$What is the magnitude of the charge of the particle?

Accepted Answer

$$3.29 	imes 10$$^{-19}$$\ \mathrm{C}$$

Electric Charge and Electric Field: Study Notes for Bioscience and Bioengineering

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