Q: A parallel-plate capacitor is connected to a 100 V battery, creating a uniform electric field of $$1 \times 10^4$\ \mathrm{N/C}$$ between the plates. If an electron is released from rest at the upper plate, what is its kinetic energy after traveling 1.0 cm to the lower plate?

$$K = 1.6 \times 10$$^{-17}$$\ \mathrm{J}$$

Question 1

A lightning bolt, as seen in the image, is a dramatic example of electric charge movement in the atmosphere. Which of the following best describes the physical principle behind the force that drives the lightning bolt from the cloud to the ground?

Accepted Answer

The force is due to the electric field created by charge separation between the cloud and the ground.

Question 2

Which of the following statements about the electric field $$\vec{E}$$ produced by a point charge $$Q is $$correct?

Accepted Answer

The electric field $$\vec{E} is $$zero at the location of the source charge $$Q.$$

Question 3

A positive test charge $$q_0 is $$placed in the electric field of a positive source charge $$Q. $$What is the direction of the force $$\vec{F} on$$ $$q_0$$?

Accepted Answer

The force $$\vec{F} is $$directed away from the source charge $$Q.$$

Question 4

Which equation correctly gives the magnitude of the electric field $$\vec{E} at a $$distance $$r$$ from a point charge $$Q$$?

Accepted Answer

$$E = \dfrac{kQ}{r^2$}$$

Question 5

Two point charges, $$q_1 = +12$$\ \mathrm{nC}$$ and q_2$ = -12\ \mathrm{nC}$$, are placed 10 cm apart. What is the direction of the electric field at a point exactly midway between them?

Accepted Answer

Toward $$q_2$$

Question 6

A charge $$q is $$placed in a uniform electric field $$\vec{E}. $$What is the magnitude of the force $$\vec{F}$$ acting on the charge?

Accepted Answer

$$F = qE$$

Question 7

An electron is projected horizontally into a uniform electric field directed upward. What is the shape of the electron's trajectory?

Accepted Answer

A parabola

Question 8

A particle of charge $$q$$ and mass $$m is $$released from rest in a uniform electric field $$E. $$What is its acceleration?

Accepted Answer

$$a = \dfrac{qE}{m}$$

Question 9

Two charges, $$+q$$ and $$-q$$, are placed at the vertices of an equilateral triangle, with point $$P at $$the third vertex. What is the direction of the net electric field at point $$P$$?

Accepted Answer

In the $$+y$$ direction

Question 10

A test charge $$q_0 is $$placed at a point where the electric field is $$\vec{E}. If$$ $$q_0 is $$replaced by $$-q_0$, what happens to the electric field at that point?

Accepted Answer

The electric field is unaffected.

Question 11

Which of the following best describes the superposition principle for electric fields?

Accepted Answer

The total electric field at a point is the vector sum of the fields due to all charges.

Question 12

An electron (charge $$-e) is $$released from rest in a uniform electric field $$E = 1 	imes 10^4$\ \mathrm{N/C}$$ directed upward. What is the direction of the electron's acceleration?

Accepted Answer

Downward

Question 13

A particle with charge $$+3Q$$ and a particle with charge $$-2Q$$ are both shot into a region with a uniform electric field pointing in the $$-y$$ direction. Both have the same initial velocity in the $$+x$$ direction. Which statement best describes their resulting paths?

Accepted Answer

The $$+3Q$$ particle curves in the $$-y$$ direction, and the $$-2Q$$ particle curves in the $$+y$$ direction.

Question 14

A parallel-plate capacitor is connected to a 100 V battery, creating a uniform electric field of $$1 	imes 10^4$\ \mathrm{N/C}$$ between the plates. If an electron is released from rest at the upper plate, what is its kinetic energy after traveling 1.0 cm to the lower plate?

Accepted Answer

$$K = 1.6 	imes 10$$^{-17}$$\ \mathrm{J}$$

Question 15

Which of the following is a real-world application of the motion of charged particles in electric fields?

Accepted Answer

Radiotherapy equipment for cancer treatment

Question 16

A positive point charge $$q of $$mass $$m is $$released from rest in a uniform electric field $$E$$ directed along the $$x-$$axis. What is the equation for its displacement $$x as a $$function of time $$t$$?

Accepted Answer

$$x = \dfrac{1}{2} \dfrac{qE}{m} t^2$

Question 17

Which of the following best explains why the electric field at the location of a point charge is undefined?

Accepted Answer

The electric field is infinite at the location of the point charge.

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