Question 1

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

Accepted Answer

Electric field lines are continuous curves that are tangent to the electric field vector at every point.

Question 2

A proton is released from rest in a uniform electric field of magnitude $$E. $$What is the acceleration of the proton?

Accepted Answer

$$a = \frac{qE}{m_p}$$

Question 3

A charged particle of mass $$m$$ and charge $$q$$ moves in a uniform electric field $$\vec{E}. If $$the only force acting is the electric force, what is the equation for its acceleration?

Accepted Answer

$$\vec{a} = \frac{q}{m}\vec{E}$$

Question 4

Which of the following best describes the electric field inside an ideal parallel-plate capacitor (ignoring edge effects)?

Accepted Answer

The electric field is uniform and given by $$E = \frac{\sigma}{\$$epsilon_0$$}$$, where $$\sigma is $$the surface charge density.

Question 5

A long, straight wire has a uniform linear charge density $$\lambda. $$What is the magnitude of the electric field a distance $$r$$ from the wire (assuming $$r is $$much less than the length of the wire)?

Accepted Answer

$$E = \frac{\lambda}{2\pi \$$epsilon_0$$ r}$$

Question 6

Which of the following is true about the electric field produced by an infinite uniformly charged plane with surface charge density $$\eta$$?

Accepted Answer

The electric field is constant and given by $$E = \frac{\eta}{2\$$epsilon_0$$}.$$

Question 7

A dipole with dipole moment $$\vec{p} is $$placed in a uniform electric field $$\vec{E}. $$What is the magnitude of the torque experienced by the dipole?

Accepted Answer

$$	au = pE\sin	heta$$

Question 8

A ring of radius $$R$$ carries a total charge $$Q$$ uniformly distributed along its circumference. What is the electric field at a point on the axis of the ring, a distance $$x$$ from its center?

Accepted Answer

$$E = \frac{1}{4\pi\$$epsilon_0$$} \frac{Qx}{(R^2$ + x^2$)^{3/2}$$}$

Question 9

Which of the following is a correct statement about the direction of electric field lines?

Accepted Answer

They start on positive charges and end on negative charges.

Question 10

A small test charge $$q is $$placed at a point where the electric field is $$\vec{E}. $$What is the force experienced by the test charge?

Accepted Answer

$$F = qE$$

Question 11

A charged rod of length $$L$$ has a total charge $$Q$$ uniformly distributed along its length. What is the linear charge density $$\lambda$$?

Accepted Answer

$$\lambda = Q/L$$

Question 12

Which of the following best describes the net force on an electric dipole placed in a uniform electric field?

Accepted Answer

The net force is always zero, but there may be a torque.

Question 13

A parallel-plate capacitor has plate area $$A$$ and plate separation $$d. If $$the plates carry charges $$+Q$$ and $$-Q$$, what is the magnitude of the electric field between the plates (ignoring edge effects)?

Accepted Answer

$$E = \frac{Q}{\$$epsilon_0$$ A}$$

Question 14

Which of the following is a property of electric field lines for two like charges placed near each other?

Accepted Answer

The field lines repel each other and do not cross, showing a region of zero field between the charges.

Question 15

A charged particle moves with velocity $$v$$ perpendicular to a uniform electric field $$E. $$What is the shape of its trajectory?

Accepted Answer

Parabolic

Question 16

For a continuous charge distribution, the electric field at a point $$\vec{r} is $$given by which of the following integrals?

Accepted Answer

$$\vec{E}(\vec{r}) = \int \frac{dq}{4\pi\$$epsilon_0$$ r^2$} \hat{r}$$

Question 17

A molecule of water is a good example of a dipole. What is the direction of its dipole moment vector?

Accepted Answer

From the positive hydrogen atoms to the negative oxygen atom

Question 18

If a dipole is placed in a uniform electric field, what is the potential energy of the dipole in terms of the dipole moment $$\vec{p}$$ and the electric field $$\vec{E}$$?

Accepted Answer

$$U = -\vec{p} \cdot \vec{E}$$

Electric Fields and Field Lines: Chapter 23 Study Notes

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