If you charge a pocket comb by rubbing it +bigoag c +w -64nlv9fwith a silk scarf, how can you determine if the comb is positively or negatively char6+ga4ci gfwn- 9l+o vbged?

Why does a shirt or blouse taken from a clothes dryer sometimes cling to your qocdp b axf9wbw(: *qcq1( ,5mbo5dp(9,qa1 w(b*wqxomcbf : qcdy?

Explain why fog or rain droplets tend topvxvh gau8 d0 5;kbb,( form around ions or electrons in the aixbg0vhv 8;p5 (, duabkr.

A positively charged rod is brought close to bsv yilkfm/e98ssm m02)e(b6 a neutral piece of paper, which it attracts. Draw a diagram showing the separation s)e2svk(6m9i/s 8 mbfm l0be yof charge and explain why attraction occurs.

Why does a plastic ruler that has been rubbed with a cloth have thei 9 t ,ro(68fw+cx 5ukp-sxnw7 bl4zwv ability to pick up small pieces of paper? Why is sz9ntplf7x6 or w4- wkbc w5xv8(,ui+this difficult to do on a humid day?

Contrast the net charge on a conductor to the “free charges” in the condtdfd -ga7n6j10k x)f ructor.

Figures 16–7 and 16–8 show how a charged rod placed near an uncharged metal ob*h u1 )uwza .k6ijcy5k5e 318zd nn qlgaa6z7bject can attract (or repel) electrons. There are a kz zdwu13 clj)n7bnai5hq.eya6 1 g*u8zak 56great many electrons in the metal, yet only some of them move as shown. Why not all of them?

When an electroscope is-z:qgf ank1e-w6i 9b l charged, its two leaves repel each other and remain at an angle. What balances the electric force of repulsion so that the leaves don’t separate furthe9if :1-qwn6zkgal b-er?

The form of Coulomb’s law is very similar 8x ioq9liju68z +. ts29iezf dto that for Newton’s law of universal gravitation. What are the diff8q.ziot 2u9x6 fzi ilj9ed8s+ erences between these two laws? Compare also gravitational mass and electric charge.

We are not normally aware of the gravitational or p ce y6 evdqw+nyd5++5electric force between two ordinary objcyn++ 6dpqedv ye5w+5ects. What is the reason in each case? Give an example where we are aware of each one and why.

Is the electric force a conservative force? Why or whyumm):8* pjlaw2 n*zjk not? (See Chapter 6.)

When a charged ruler attracts small pi6)ad sq)-e s0 eoac)-oif3 ivueces of paper, sometimes a piece jumps quickly away after touching thee6af3)doi0 ui)eas- )-s ocqv ruler. Explain.

Explain why the test charges we use when meas:a;r s7) i m.uopn/dqvuring electric fields must be smalla dspom.;vnuiqr :/)7.

When determining an electric field, must we use a posvo4rpun5nyhn- ,-s .w tdy.2pitive test charge, or would a negative one do as well? Expldn.t-p ry .us5 wnpvh ,4y2n-oain.

Draw the electric field lines surrol,i )sj-6by2 xhj. yslunding two negative electric charges a distance l l,b-6sy.ji2hs j yx) lapart.

Assume that the two opposite charges in Fig. 16–31a are 12.0 cm apart. Consmapw .t2tv e9)ider the magnitude of the electric field 2.5 cm from the poswt m epvt92).aitive charge. On which side of this charge — top, bottom, left, or right — is the electric field the strongest? The weakest? Explain.

Consider the electric f,fi ::*bylwto ield at points A, B, and C in Fig. 16–48. First draw an arrow at each point indicating the directionio b*:w ftly,: of the net force that a positive test charge would experience if placed at that point, then list the points in order of decreasing field strength (strongest first).

Why can electric field lxi.j0+e scy u3ines never cross?

Show, using the three rules for field lines given in Sectizk k w)eo8sg3 g7hsiqud(h9kbe 9(s2;on 16–8, that the electk 8eqkwgu oi2 hs 79(k;sg(zs39e)bdhric field lines starting or ending on a single point charge must be symmetrically spaced around the charge.

Given two point charges Q a6 r3go4xqg3 cand 2Q, a distance l apart, is there a point along the straight line that passes through them where E=0 when their signs are (a) opposite, g63cx3 4q gaor(b) the same? If yes, state roughly where this point will be.

Consider a small positim12mi 2g9qnqn ve test charge located on an electric field line at some point, such as point P in Fig. 16–31a. Is the direction2qnm2 1 iqmg9n of the velocity and/or acceleration of the test charge along this line? Discuss.

Sketch the electric field lines for a uniform lih 1gdzy sc*(f5ne of charge which is infinitely long. (Hint: Use symmetry.) Is the electric field uniform in 1d5hc*gf(s y zstrength?

If the electric flux through a closed surface is zero, is thx*3f e+ut f /o7-yulpue electric field necessarily 3-f*+t/u 7uufpxol ye zero at all points on the surface? Explain. What about the converse: If $\vec{E}\,=\,0$ at all points on the surface is the flux through the surface zero?

A point charge is surrounded by a spherical gaussian surface of radiusmd d: o*c(ke( u0vx*bp r. If the sphere is replaced by a cube o vdmkxb p d0e(uc*(o:*f side r, will $\Phi_E$ be larger, smaller, or the same? Explain.

  

  How many electrons make uifcpf)kl,4v;wvhf5./jr w 5np a charge of $-30.0\mu C\,?$   $ \times10^{ 14}\, electrons $

  What is the magnitude of the electric force ofkh)* b0m.t f*pd7yeb p attraction between an iron nucleusb)d h0*7b.efkm p*typ $(q\,=\,+26e)$ and its innermost electron if the distance between them is $ 1.5\times10^{-12 }\,m\,?$    $ \times10^{-3 }N$

  What is the repulsive electrical bx(du q5,gy m h1xt4j(force between two protons $ 5.0 \times10^{ -15}\,m$ apart from each other in an atomic nucleus?    N

  What is the magnitudoj- knw72wi *2(*tk; (wzwrd zuq.a hre of the force a $+25\,\mu C\,C$ charge exerts on a $+\,3.0\,mC$ charge 35 cm away?    N

  Two charged dust particles exert a force of 0 /i f4 hfa/eeyresl,r66:cxf $ 3.2\times10^{ -2}\,N$ on each other. What will be the force if they are moved so they are only one-eighth as far apart?    N

  Two charged spheres are 8.45 cm apart. Theyxa ,6v m mnofjp;i311m are moved, and the force on each of them is found to have beej 6v1; 3xn mmi1f,mopan tripled. How far apart are they now?    cm

  A person scuffing her feet on a wool rug on a dry daybh2gq/ 3ycf l* accumulates a net charge of3/*g hfl2cybq $-42\,\mu C\,.$ How many excess electrons does she get,    $ \times10^{14 }\,electrons$
by how much does her mass increase?    $ \times10^{-16 }kg$

  What is the total charcyqe;gr 8xap3 /) + rvhixo.5yge of all the electrons in 1.0 kg of $H_2O\,?$    $ \times10^{ 7}\,C$

  Compare the electric force holding theypn8vnv adk7z w,u2a+t5 ,6ye electron in orbit $(r\,=\,0.53 \times10^{-10 }\,m)$ around the proton nucleus of the hydrogen atom, with the gravitational force between the same electron and proton. What is the ratio of these two forces?    $ \times10^{39 }\,C$

Two positive point charges are a fixed distance apart. The sum of their t 6q t(nn-eye2 hk4c 6ht3so,mcharges is What charge hstc34eqe 6t(y2nk- ,nh6 om tmust each have in order to
(a) maximize the electric force between them,
(b) minimize it?

  Particles of charge -m3+ h/cnbn wc$+75$,$+48$ and $-85\,\mu C\,$ are placed in a line (Fig. 16–49). The center one is 0.35 m from each of the others. Calculate the net force on each charge due to the other two.

$F_{+75}$=   $NN$
$F_{+48}$=   $NN$
$F_{-85}$=   $NN$

  Three positive particles of equal me v3, elkg +qp(b.8jqcharge, $+11.0\,\mu C\,$ are located at the corners of an equilateral triangle of side 15.0 cm (Fig. 16–50). Calculate the magnitude and direction of the net force on each particle.


the force on the lower left charge is of magnitude    N, and
will point    $^{\circ}$below the-x axis. The force on the lower right charge is of magnitude    N, and will point    $^{\circ}$below the +x axis.

  A charge of 6.00 mC is placed at each corner 2zyu r4btn7g3of a square 0.100 m on a side. Determine the magnitude and direction of the forz2u4n brgy3t7ce on each charge.
$F_4$ =   $ \times10^{ 7}\,N$
$\theta$ =    $^{\circ}$

  Repeat Problem 14 for the case when two of the positive charges, 9 2du gm50m l+vnw92zq fc:xgoon opposite corners, are repln d v2xu0 gzf+c5oqm2w9 :9gmlaced by negative charges of the same magnitude (Fig. 16–51).
$F_4$ =   $ \times10^{ 7}\,N$
$\theta$ =    $^{\circ}$

  At each corner of a square of side l there are point charges of magnitude Q, 2Q,t fs9x. /c;lzr 3Q, and 4Q (Fig. 16–52). Determine the force on (a) the charge 2Q, and (b) the charge 3Q, due to the other three charget /9z x;frl.css.
$F_{2Q}$ =    $\frac{kQ^2}{l^2}$
$\theta_{2Q}$ =    $^{\circ}$
$F_{3Q}$ =    $\frac{kQ^2}{l^2}$
$\theta_{3Q}$ =    $^{\circ}$

  Three charged particles are placed at the corners of an equilateral triangh,vy,f d;i9y)/znyz hle of side 1.20 y, hfy z)hidn;9/y,vzm (Fig. 16–53). The charges are $+4.0\,\mu C\,,$$-8.0\,\mu C\,,$ and $-6.0\,\mu C\,.$ Calculate the magnitude and direction of the net force on each due to the other two.
$F_1$ =    N
$\theta_1$ =    $^{\circ}$
$F_2$ =    N
$\theta_2$ =    $^{\circ}$
$F_3$ =    N
$\theta_3$ =    $^{\circ}$

  Two point charges havevg7d7nh15sq a a total charge of $560\,\mu C\,.$ When placed 1.10 m apart, the force each exerts on the other is 22.8 N and is repulsive. What is the charge on each?
q = $ 5.54\times10^{a }\,C$ a =  ,
$ 5.54\times10^{b }\,C $ b =   
Q-q = $ 5.54\times10^{a }\,C$ a =  ,
$ 5.54\times10^{b }\,C$ b =   

Two charges, $-Q_0$ and $-3Q_0$ are a distance l apart. These two charges are free to move but do not because there is a third charge nearby. What must be the charge and placement of the third charge for the first two to be in equilibrium?

  A $+4.75\,\mu C\,$ and a $-3.55\,\mu C\,$ charge are placed 18.5 cm apart. Where can a third charge be placed so that it experiences no net force?    cm

  Two small nonconducting spheres have pu9pp f /n97qldfbhb*g-6ob) a total charge of $90.0\,\mu C\,.$
(a) When placed 1.06 m apart, the force each exerts on the other is 12.0 N and is repulsive. What is the charge on each?    $ \times10^{ -6}\,C$$\;\;\;\;$    $ \times10^{ -6}\,C$
(b) What if the force were attractive?    $ \times10^{ -6}\,C$$\;\;\;\;$    $ \times10^{ -6}\,C$

  A charge Q is transferred from an initially unchldya :l v..d(qgfn / kyx/wwo0 go7v1/3t7fn varged plastic ball to an identical ball 12 cm away. The force n0ga1 odwo37:.n k /q yl.7twv ffxv/ydg/vl( of attraction is then 17 mN. How many electrons were transferred from one ball to the other?    $ \times10^{ 12}$ electrons

  What are the magnitude and directio(gtdr95 bx ad n)gx8/un of the electric force on an electron in a uniform electric field of strengthrx9g/un )a( xd8tg5db $2360\,N/C$ that points due east?
   $ \times10^{ -16}\,N$
 ----待选择----westeast 

  A proton is released in a uniform electric field, and bsv )gtcxskwb 7h/q m g+s22mlfg,/ q y23s-x-it experiences an electric force ofg7 sf-/ts 2)2 wmb -yxg,v+glbcsmxq/h2 3qsk $ 3.75\times10^{ -14}\,N$ toward the south. What are the magnitude and direction of the electric field?
   $ \times10^{5 }\,N/C$
 ----待选择----southnorth 

  A downward force of 8.4 N is exerted on o,:wwhg8jui ujvoo a(j;7) / ma $-8.8\,\mu C\,$ charge. What are the magnitude and direction of the electric field at this point?    $ \times10^{5 }\,N/C$ ----待选择----updown 

  What are the magnitude and direction of the electric field 20.0 cm directly abo/x7reo0sg svq)vfeo 6r)h4h i9 p v0s5ve an o))vgxv7s/rr0vqe50e 946 o hfsisph isolated $33.0 \times10^{ -6}\,C$ charge?    $ \times10^{6 }\,N/C$ ----待选择----updown 

  What is the magnitude of the accelerationj lg37r(whj9i experienced by an electron in an electri 3(j jghlw97ric field of $750\,N/C\,?$ How does the direction of the acceleration depend on the direction of the field at that point?    $ \times10^{ 14}\,m/s^2$  ----待选择----opposite to the field in line with the direction of the field 

  What are the magnitude anbx (0utfr(j +gamn,5 nd direction of the electric field at a point midway betweb(xg ujtm+,rf0a5 (nnen a $-8.0\,\mu C\,$ and a $+7.0\,\mu C\,$ charge 8.0 cm apart? Assume no other charges are nearby.    $ \times10^{7 }\,N/C$ ----待选择---- towards the negative charde opposite to the negative charge 

Draw, approximately, the electric fit/6:62 hgtqo :uq k n9jsgg6wceld lines about two point charges, $+Q$ and $-3Q$ which are a distance l apart.

  What is the electric field strength at a point in space where a proton afofniw*024gr8 21qeqb txq 3$(m= 1.67\times10^{ -27}\,kg) $experiences an acceleration of 1 million “g’s”? $\approx$    N/C（Round it to one decimal place.）

  An electron is released from rest in a uniform electric fi f((+ cps9vxjneld and accelerates to th9cfj (p+ (vnxse north at a rate of $115\,m/s^2\,.$ What are the magnitude and direction of the electric field?    $ \times10^{-10 }\,N/C$ ----待选择----northsouth 

  The electric field midway between two equal but opposite point c8dr.le 9kam :4 maehp2harges is $745\,N/C\,,$ and the distance between the charges is 16.0 cm. What is the magnitude of the charge on each?    $ \times10^{-10 }\,C$

  Calculate the electric field at the center of a square 52.5 cm on a side ifv +j v;nhhn8d- one corner is occupied byvj;-8h nnh v+d a $+45.0\,\mu C\,$ charge and the other three are occupied by $-27\,\mu C\,$ charges.    $ \times10^{6 }\,N/C$ at    $^{\circ}\,$

  Calculate the electric field at one corner of a square 1.00s;)b6 vg+py*8gea kz f m on a side if the other three corners are occu8sf veb+)6zpy*akg g;pied by $ 2.25\times10^{-6 }\,C$ charges.    $ \times10^{4 }\,N/C$   $^{\circ}\,$ from the x-direction.

Determine the direction +;wqsfrr,x3z7w w y-q j-trw1and magnitude of the electric field at the point P in Fig. 16–54. The charges are separated by a distance 2a, and point P is a distance x from the midpoint between the two charges. Express your answer in;rw- r+ z71ftqx rqwys,wjw -3 terms of Q, x, a, and k.

  Two point charges, $Q_1\,\equiv\,25\,\mu C\,$ and $Q_2\,=\,+50\mu C\,,$ are separated by a distance of 12 cm. The electric field at the point P (see Fig. 16–55) is zero. How far from $Q_1$ is P?    cm

(a) Determine the electric fnsx 5 j25st,c *4ubqxzield $\vec{E}$ at the origin 0 in Fig. 16–56 due to the two charges at A and B. (b) Repeat, but let the charge at B be reversed in sign.

  Use Coulomb’s law to determine the magnitude and direction ob9 o oun)hav5;f the electric field at points A and B in Fvnu oo; 95ah)big. 16–57 due to the two positive charges $(Q\,=\,7.0\mu C\,)$ shown. Are your results consistent with Fig. 16–31b?
$E_A$ =    $ \times10^{6 }\,N/C$
$\theta_A$ =    $^{\circ}\,$
$E_B$ =    $ \times10^{7 }\,N/C$
$\theta_B$ =    $^{\circ}\,$
(16-51)
(16-31b)

  You are given two unknown point charges,v;bkn/) e cnk3 $Q_1$ and $Q_2$ At a point on the line joining them, one-third of the way from $Q_1$ to $Q_2$, the electric field is zero (Fig. 16–58). What is the ratio $Q_1/Q_2\,?$   

Determine the direction and magnitude of the electric fieo 84m7gnyckf1 ld at the point P shown in Fig. 16–59. The two charges are separated by a distance of 2a. Pn41cgfoyk8 7m oint P is on the perpendicular bisector of the line joining the charges, a distance x from the midpoint between them. Express your answers in terms of Q, x, a, and k.

  An electron (mass $m\,=\,9.11 \times10^{ -31}\,kg$) is accelerated in the uniform field $\overrightarrow{\mathbf{E}}\left(E=1.45 \times 10^{4} \mathrm{~N} / \mathrm{C}\right)$ between two parallel charged plates. The separation of the plates is 1.10 cm. The electron is accelerated from rest near the negative plate and passes through a tiny hole in the positive plate, Fig. 16–60.
(a) With what speed does it leave the hole?    $ \times10^{ 6}\,m/s$
(b) Show that the gravitational force can be ignored.

  An electron moving to the t,l5kkd5. :l wp pqk1bright at 1.0% the speed of light enters a uniform electric field parallel to its direction of motion. If the electron i5pt pqkdl kbk .,w51:ls to be brought to rest in the space of 4.0 cm,
(a) what direction is required for the electric field,  ----待选择----rightleft 
(b) what is the strength of the field?    N/C

  The total electric fl duc*yb:fc n1f; +a)t9qcujj -ux from a cubical box 28.0 cm on a side is $1.45 \times10^{3 }\,N\cdot m^2/C$. What charge is enclosed by the box?    $ \times10^{ -8}\,C$

  A flat circle of radius 18 cm is placed in a uniform electric field of mag j (p;in0ya16uepolw8 nitude oan;iju 10ye68wplp ( $ 5.8\times10^{2 }\,N/C$ What is the electric flux through the circle when its face is
(a) perpendicular to the field lines,    $N\cdot m^2/C$
(b) at 45° to the field lines,    $N\cdot m^2/C$
(c) parallel to the field lines?   

  In Fig. 16–61, two objects,aw vjlk 2.xolqvy/ 4nh 1r.7z5 $O_1$ and $O_2$ have charges $+1.0\mu C$ and $-2.0\mu C$ respectively, and a third object, $O_3$ is electrically neutral.
(a) What is the electric flux through the surface $A_1$ that encloses all three objects?    $ \times10^{5}\,$$N\cdot m^2/C$
(b) What is the electric flux through the surface $A_2$ that encloses the third object only?   

A cube of side l is placed inr(u c1yti9m0u a uniform field $ E\,=\,6.50\times10^{3 }\,N/C$ with edges parallel to the field lines.
(a) What is the net flux through the cube?
(b) What is the flux through each of its six faces?

  The electric field between two square metal plat/(/j yu,dhb r 2zwhvt9)pyl -ues is The plates are 1.0 m on a side and are separated by 3.0 cm. What is the charge on each plat/u/uvh2btz (l hj, -ry)d9pywe (assume equal and opposite)? Neglect edge effects.    $ \times10^{-9 }\,C$

  The field just outside a +a8b0lb) 8uqvyfhj2 d3.50-cm-radius metal ball is $ 2.75\times10^{2}\,N/C$ and points toward the ball. What charge resides on the ball?    $ \times10^{-11 }\,C$

  A solid metal sphere of radius 3.00 m carries 7w. wbh3isn1u:g* i7u cj 8guja total charge of $-3.5\mu C$ What is the magnitude of the electric field at a distance from the sphere’s center of
(a) 0.15 m,   
(b) 2.90 m,   
(c) 3.10 m,    N/C
(d) 6.00 m?    N/C
(e) How would the answers differ if the sphere were a thin shell?

A point charge Q rests at the center of anm f,j35x dusq:e qb2r- uncharged thin spherical conducting shell. (See Fig. 16–33.) What is the electric field E as a function of r (a) for r less than the inner radius of r 5-: fqms2e x3dq,bujthe shell, (b) inside the shell, and (c) beyond the shell? (d) Does the shell affect the field due to Q alone? Does the charge Q affect the shell?

  The two strands of the helix-shaped DNA molecf. iu.ljc hzy244w z5dule are held together by electrostatic forces as shown in Fig. 16–44. Assume that the net average charge (due to electron sharing) indicated on H and N atoms is 0.2e and on the indicated C and O atoms is 0.4e.luzd.z4 j4hywi.f c2 5 Assume also that atoms on each molecule are separated by $ 1.0\times10^{ -10}\,m$. Estimate the net force between
(a) a thymine and an adenine;    $ \times10^{-10 }\,N$
(b) a cytosine and a guanine. For each bond (red dots) consider only the three atoms in a line (two atoms on one molecule, one atom on the other).    $ \times10^{-10 }\,N$
(c) Estimate the total force for a DNA molecule containing $10^5$ pairs of such molecules.    $ \times10^{-5 }\,N$

  How close must two ele--zg: tt0skj o-;csij ctrons be if the electric force between them is equal to the weight of either at the Earth’s si- :ojsgct- ztjs-k 0;urface?    m

  A 3.0-g copper penny has a positive chargezdal+q )lnkjyc+g7, 2 of $38\mu C$. What fraction of its electrons has it lost?    $ \times10^{-10 }\,$

  A proton $(m\,=\,1.67 \times10^{-27}\,kg)$ is suspended at rest in a uniform electric field $\vec{E}$. Take into account gravity at the Earth’s surface, and determine $\vec{E}$.    $ \times10^{-7 }\,N/C$  ----待选择----updown 

  Measurements indicate that there is an electric field sur:i ,aqshwla ;8rounding the Earth. Its magnitude is about 8iwsqha; la, :$150\,N/C$ at the Earth’s surface and points inward toward the Earth’s center. What is the magnitude of the electric charge on the Earth? Is it positive or negative? [Hint: the electric field outside a uniformly charged sphere is the same as if all the charge were concentrated at its center.]    $ \times10^{5 }\,C$  ----待选择----positivenegative 

  (a) Given the local electric field of what is the acceleration mg4:g ,ncg2;i4avk u(re.l;ri ye5nj m3 ,hczexperienced by an electron near the surface ,c;,34 i g.;z2kn uigmegrnjev:aym45 l( rhc of the Earth?    $ \times10^{13 }\,m/s^2$, ----待选择----updown 
(b) What about a proton?    $ \times10^{10 }\,m/s^2$, ----待选择----updown 
(c) Calculate the ratio of each acceleration to $g\,=\,9.8\,m/s^2$ For the electron: $\approx$    $ \times10^{12 }$ For the proton: $\approx$    $ \times10^{9 }$

  A water droplet of radius 0.018 mm remains 4gg:3an /kk g7lv yqj1stationary in the air. If the downward-directed electric fieldnj1 kg:/kg 43qaygvl7 of the Earth is $150\,N/C$ how many excess electron charges must the water droplet have?    $ \times10^{ 6}$ electrons

  Estimate the net force between the CO group and the HN group shown in Fido 9e.vun69 qwg. 16–62. The C and O have w9o69vu e .qdncharges $\pm0.40e$, and the H and N have charges $\pm0.20e$, where $e\,=\, 1.6\times10^{-19}\,C$. [Hint: Do not include the “internal” forces between C and O, or between H and N.]    $ \times10^{ -10}\,NN$

  In a simple model of the h0f 8yknxil3 h.ydrogen atom, the electron revolves in a circular orbit around the proton with a speed of.ify knl0h 83x $ 1.1\times10^{6 }\，m/s,$. Determine the radius of the electron’s orbit. [Hint: See Chapter 5 on circular motion.]    $ \times10^{-10 }\, m$

  Suppose that electrical attraction, rather than gravity, ,vo+j6nl eb52x:8h/yw9 n cr iltc0oswere responsible for holding the Moon in orbit around the Earthnox: l826n9+c05 e /stybir c hojlv,w. If equal and opposite charges Q were placed on the Earth and the Moon, what should be the value of Q to maintain the present orbit? Use these data: mass of $Earth\,=\, 5.98\times10^{24}\,kg$, mass of $Moon\,=\, 7.35\times10^{22}\,kg$, radius of $orbit\,=\, 3.84\times10^{8}\,m$. Treat the Earth and Moon as point particles.    $ \times10^{13 }\,C$

  An electron with speed bc+2 j a1fpe(iy2 tzn4bj(,ku$v_0\,=\, 21.5\times10^{6}\,m/s$ is traveling parallel to an electric field of magnitude $E\,=\, 11.4\times10^{3}\,N/C$.
(a) How far will the electron travel before it stops?    m
(b) How much time will elapse before it returns to its starting point?    $ \times10^{-8 }\,s$

  A positive point cha0,jcv ve 5heqaso:guu6.6 c pp ami95h qvz+4,rge $Q_1\,=\, 2.5\times10^{-5}\,C$. is fixed at the origin of coordinates, and a negative charge $Q_2\,=\, -5.0\times10^{-6}\,C$. is fixed to the x axis at $x\,=\,+2.0m$ Find the location of the place(s) along the x axis where the electric field due to these two charges is zero.    m from $Q_1$,   m from $Q_2$

A small lead sphere is encased in insulating plasxy(r90worcwnn/mdu+ r qg- /3tic and suspended vertically from an ideal spring ncm 9/xd oqr(w/rgn r -yuw+03$(k\,=\,126N/m)$ above a lab table, Fig. 16–63. The total mass of the coated sphere is 0.800 kg, and its center lies 15.0 cm above the tabletop when in equilibrium. The sphere is pulled down 5.00 cm below equilibrium, an electric charge $Q\,=\, -3.00\times10^{-6}\,C$ is deposited on it and then it is released. Using what you know about harmonic oscillation, write an expression for the electric field strength as a function of time that would be measured at the point on the tabletop (P) directly below the sphere.

  A large electroscope is made with “leaves” that are 78-c d-ceog+5mr/wmb( s o xd9:)w7df)r tom-long wires with tiny 24-g spheres at the ends. When charged, nearly all the charge resides on the bds 7dmw /r9og (t)fmr ow-oc)e 5:dx+spheres. If the wires each make a $30^{\circ}$ angle with the vertical (Fig. 16–64), what total charge Q must have been applied to the electroscope? Ignore the mass of the wires.    $ \times10^{-6 }\,CC$

  Dry air will break dowctyir mcbi.. ;v3g:r 6n and generate a spark if the electric field exceeds aboutimr. :ctb .6v;yi3cr g $ 3\times10^{6 }\,N/C$. How much charge could be packed onto a green pea (diameter 0.75 cm) before the pea spontaneously discharges? [Hint: Eqs. 16–4 work outside a sphere if r is measured from its center.]    $ \times10^{-9 }\,C$

  Two point charges, $Q_1\,=\,-6.7\mu C$ and $Q_2\,=\,1.8\mu C$ are located between two oppositely charged parallel plates, as shown in Fig. 16–65. The two charges are separated by a distance of $x\,=\,0.34\,m$ Assume that the electric field produced by the charged plates is uniform and equal to $E\,=\,73,000\,N/C$ Calculate the net electrostatic force on $Q_1$ and give its direction.    N  ----待选择----right left 

  A point charge $(m\,=\,1.0\,g)$ at the end of an insulating string of length 55 cm is observed to be in equilibrium in a uniform horizontal electric field of $12,000\,N/C$ when the pendulum’s position is as shown in Fig. 16–66, with the charge 12 cm above the lowest (vertical) position. If the field points to the right in Fig. 16–66, determine the magnitude and sign of the point charge.
   $ \times10^{-7 }\,C$
 ----待选择----positivenegative 

  A point charge of mass lcbja -sw-wv13l: ;lk0.210 kg, and net charge $+0.340\,\mu C$, hangs at rest at the end of an insulating string above a large sheet of charge. The horizontal sheet of uniform charge creates a uniform vertical electric field in the vicinity of the point charge. The tension in the string is measured to be 5.67 N. Calculate the magnitude and direction of the electric field due to the sheet of charge (Fig. 16–67).    $ \times10^{7 }\,N/C$  ----待选择----updown 

  What is the total charge of all the electrons in a 15-kg bar ofsr wnii+mf hr8 / .mby+;)+(hkkfug7 c aluminum?    $ \times10^{8 }\,C$What is the net charge of the bar?    C (Aluminum has 13 electrons per atom and an atomic mass of 27 u.)

Two small, identical conducting spheres A and B- yz d64lcktn- are a distance R apart; each carries the same charge Q. (a) What is the force sphere B exerts on sphere A? (b) An identical sphere with zero charge, sphere C, makes contact with sphere B and is then moved very far away. What is the net force now acting on sphere -yz4n-ltdc 6 kA? (c) Sphere C next makes contact with sphere A and is then moved far away. What is the force on sphere A in this third case?

Given the two charges shown in Fig. 16–65p9h8cwdwuq . 8, at what position(s) x is the electric field zero? Is tp wwhu.59c 8qdhe field zero at any other points, not on the x axis?

Two point charges, $+Q$ and $-Q$ of mass m, are placed on the ends of a massless rod of length L, which is fixed to a table by a pin through its center. If the apparatus is then subjected to a uniform electric field E parallel to the table and perpendicular to the rod, find the net torque on the system of rod plus charges.

Four equal positive point chaq1hgakt lhyx js6r049v:j;5 erges, each of charge $8.0\,\mu C$ are at the corners of a square of side 9.2 cm. What charge should be placed at the center of the square so that all charges are at equilibrium? Is this a stable or unstable equilibrium (Section 9–4) in the plane?