If you charge a pocket comb by rubbing it with a silk scarf, how can od(i; w:bvt3hfs6e5 xx nvs5x9fh 9e2you determine if the comb is positively or negatively chsen x:h ed6b;xx 3(si5t5wvh9 92fofv arged?

Why does a shirt or blouse taken from a clothes dryer sometimestagv:c p ft)e w2izwo1/1s4 whs (*d/k cling to your body?atfktsvhd)gs:w*zw p2 o e(1 14/wi/c

Explain why fog or rain droplets tend to 39 6rnlcrwi+am .n*bo form around ions or electrons in the airi *.crnw o96+r3nlmab.

A positively charged rod is brought close to a neutral piece of *bive7yno v:.paper, which it attracts. Draw a diagram showing the separation of charge a*vivnob.y7 e:nd explain why attraction occurs.

Why does a plastic ruler that has lq1(0 vhgtb2 (e eecz7been rubbed with a cloth have the ability to pick up sm eqg 2hve1ec0 (blz(7tall pieces of paper? Why is this difficult to do on a humid day?

Contrast the net charge on a conductor to the “free charges” ik5(zge;7 nhy w9t+0,cbd ux,dq n7slmn the conductor.

Figures 16–7 and 16–8 show how a charged sq9 z06,kwhe1m1gdc yrod placed near an uncharged metal object can attract (or repel) electrons. There are a great many electrons in the metal, yet only some of them move as shown. Why qc90skwem11,dy6h zg not all of them?

When an electroscope is charged, its two leaves repel each other and remain )7mb ii88w3c doi1ws naw,jr ,at an angle. What balances the electric force of repulsion so that8n,7 r8jmi wd w)ciw1 s3io,ab the leaves don’t separate further?

The form of Coulomb’s law is very similad)9g v;h-p7. g3eq7mlg3ylyp h(eln zr to that for Newton’s law of universal gravitation. 3. neqd9m3l) vygy-lggzpe l7(h;7hp What are the differences between these two laws? Compare also gravitational mass and electric charge.

We are not normally aware of the gravitationaltu;m*2s 9 *ptnmnlc i qkz/-c) or electric force between two ordinary objects. What is the reason in each case? Give an example where we are awtq-n/tsucp) m29czikn*m;*l are of each one and why.

Is the electric force a conservative force? Whyxy-1w4dij s;2l-: h5ko emod a or why not? (See Chapter 6.)

When a charged ruler attracts small pieces of paper, sometimi8w*b z enc ndxi3c.e7c.a) qqk 5vq+2es a piece jumps quickly away after touca 7x)d2iq. e+cn.85cebiqvq*n c3w kzhing the ruler. Explain.

Explain why the test charges we us2yv (t3 o sg8t9qt5kruo lhg0:e when measuring electric fields must be small.t (r 3sytkh0 o9u5tlgq:o2 gv8

When determining an electric field, must we use a positive te6.)vp olekr 1-hra;.f trcj+ast charge, or would a negative one do as wtc;l1v+o arfph ..j)ker6-ar ell? Explain.

Draw the electric field lines surrounxzoc9f c4wk-. ding two negative electric charges a distanceo.xw4k-c9 zcf l apart.

Assume that the two opposite charges in Fig. 16–31a are 12.0 cm apart. Co58c am( 8zgji3jcz .agf*0dcunsider the magnitude of the electric field 2.5 cm from the poz.c3gi*cac z 8d5( ajum0fj 8gsitive charge. On which side of this charge — top, bottom, left, or right — is the electric field the strongest? The weakest? Explain.

Consider the electric ft9mh 7asx) ax5vhu e() fp0c.yield at points A, B, and C in Fig. 16–48. First draw an arrow at each point indicating the direction of the net force that a positive test charge would experience if placed at that point, then list the points in order of decreasip x.5y va9auhe s 0fm))(hxtc7ng field strength (strongest first).

Why can electric field line /h:ksq3a )1fw7iz/rh2iwic xs never cross?

Show, using the three rules3bfn (dxxy6qy :.-k 6v od6lru for field lines given in Section 16–8, that the electric field lines starting or ending on a single point charge mustv-6:.uyox 6fxl3n(d 6 krdbyq be symmetrically spaced around the charge.

Given two point charges Q and 2Q, a distance l apart, b) ygrh2k .h6)dc f qaagoeqcz. zx/;.1 k:ue)is there a point along the straieya 1 gk/k c a );g6er..hhcbx.qoqu)2fz d):zght line that passes through them where E=0 when their signs are (a) opposite, (b) the same? If yes, state roughly where this point will be.

Consider a small positive test ch y 0su0c+i nkrk2,fh5garge located on an electric field line at some point, such as point P in k+n02ry uic05ks g ,hfFig. 16–31a. Is the direction of the velocity and/or acceleration of the test charge along this line? Discuss.

Sketch the electric field lines for a uniform line of zx vmighz ,(vt7lp2iosz jh4 y2+1+o, charge which is infinitely long. (Hint: U, y2l vit izjhg4pzm+,12xs ov (z+7ohse symmetry.) Is the electric field uniform in strength?

If the electric flux through a closed surface is zerofmwzs6.q o-7vsioo+- xmza(7l;yft5, is the electric field necessarily zero at all points on the surface? Explai 6q.woiof7f-zl a yst5 o ;zmm(xsv-7+n. 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 surroujgu iu)f,z( *lf 7k;qzb0aqi/vg ;gu+nded by a spherical gaussian surface of radius r. If the sphere is replacedk*z gu ,fb i;q)7fg0;+zjl auivqgu (/ by a cube of side r, will $\Phi_E$ be larger, smaller, or the same? Explain.

  

  How many electrons make up a charge o6kvq.sc9if-:2 0 w tgly4dfrof $-30.0\mu C\,?$   $ \times10^{ 14}\, electrons $

  What is the magnitude of the electric force of attraction betm,.8u*x q/opp4o zxeg-djx6 2l bzu6 aween an iron nucleuo8uu4zgd p pq zm 6b-j.a,xxl*e6x/o2s $(q\,=\,+26e)$ and its innermost electron if the distance between them is $ 1.5\times10^{-12 }\,m\,?$    $ \times10^{-3 }N$

  What is the repulsive electrical force between t 4o,c 3ov2cv(ldy5larb7 myj) wo protons $ 5.0 \times10^{ -15}\,m$ apart from each other in an atomic nucleus?    N

  What is the magnitude of the qz7i,omtkiwsax2o -, 9s9y 3iforce a $+25\,\mu C\,C$ charge exerts on a $+\,3.0\,mC$ charge 35 cm away?    N

  Two charged dust particles eijy,4+yc;t 43ei b h+jd z,dts;w j7lbxert a force of $ 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. 2de4ckeeu: /s They are moved, and the force on each of them is found to have been tripled. How kceu:2es d/4 efar apart are they now?    cm

  A person scuffing her feet on a wool rug on a dr+8+odju6qo7.t uq 6pgmhlw1m y day accumulates a net charge of uw.ml 687tjh uo1goq+ +qpmd6 $-42\,\mu C\,.$ How many excess electrons does she get,    $ \times10^{14 }\,electrons$
by how much does her mass increase?    $ \times10^{-16 }kg$

  What is the total charge of all the electron a-r+u)(, gui5r;vqag78wn syxns6 ats in 1.0 kg of $H_2O\,?$    $ \times10^{ 7}\,C$

  Compare the electric force holding the electron in oi eyaz24 zaqf-3g(i78;gjmffrbit $(r\,=\,0.53 \times10^{-10 }\,m)$ 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 chd83vm0xd2 r,ax joe+6rs-ilcarges are a fixed distance apart. The sum of their charges is What charge must each have d e3 ,vs8o6d0-majlixx r +rc2in order to
(a) maximize the electric force between them,
(b) minimize it?

  Particles of charge /g: v3vboj( wr$+75$,$+48$ 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 cha q6;s.tqhlxp8rge, $+11.0\,\mu C\,$ 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 cor+ojq8sra f* (tner of a square 0.100 m on a side. Determine the magnitude and directiona o r8(+fjs*qt of the force on each charge.
$F_4$ =   $ \times10^{ 7}\,N$
$\theta$ =    $^{\circ}$

  Repeat Problem 14 for the case when two of the positive charges, on oppositehu*-k i+ozlf8 p, *n8n.x1(hxs nufea corners, are replaced by negative chf*8.xu*+fsn u hip l,( xzone1a8 hk-narges of the same magnitude (Fig. 16–51).
$F_4$ =   $ \times10^{ 7}\,N$
$\theta$ =    $^{\circ}$

  At each corner of a square of side l tbi-jzx)/h yg 7i)*d +tx5ej* szde(gthere are point charges of magnitude Q, 2Q, 3Q, and 4Q (Fig. 16–52). )j/bdtd(i g* -+jtes5* )hxz gixye7zDetermine the force on (a) the charge 2Q, and (b) the charge 3Q, due to the other three charges.
$F_{2Q}$ =    $\frac{kQ^2}{l^2}$
$\theta_{2Q}$ =    $^{\circ}$
$F_{3Q}$ =    $\frac{kQ^2}{l^2}$
$\theta_{3Q}$ =    $^{\circ}$

  Three charged partickt.8ftky; x 4nles are placed at the corners of an equilateral triangle of side 1.20 m (Fig. 16–;nk8x yt4 .ktf53). 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 have a h lb d5o*:nt/a)lggw /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 sp:paeu 3jd (1khheres have 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 uncharged plastic ball to *7i brvl) +7gj pdfn iu3;cyq+omn :f7an identical ball 1n :lo++q*;cjigpbd3fr v u)77ynmi f72 cm away. The force 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 direction of the electric forcy5t9 bj tnbvz di4o7-1e on an electron in a uniform electric fiel id9btj- ot7bn415z yvd of strength $2360\,N/C$ that points due east?
   $ \times10^{ -16}\,N$
 ----待选择----westeast 

  A proton is released in a uniform electric field, andh(9ss lv r*7ld it experiences an electric fov rs 7h9(llsd*rce of $ 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 ah)g18 hzgct(m $-8.8\,\mu C\,$ 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 direcddl,cpw 6e7 d+tly above an l e7w ,dpdd+c6isolated $33.0 \times10^{ -6}\,C$ charge?    $ \times10^{6 }\,N/C$ ----待选择----updown 

  What is the magnitude g* zy+v(4unjxah (x kgfill :d o790*rof the acceleration experienced by an electron in an electrn * u9f+dra4zyxl*hkvg0: iojx(7gl (ic 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 3d9b9s2gi gcpc*wm 7gand direction of the electric field at a point midway between bc 23p *9gdg igm7w9sca $-8.0\,\mu C\,$ 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 fields cj* fovwz635,e5xnu 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 p59;b:oep lmyloix2uxj 5h d) 2roton $(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 releas5mjd qhh; kk 9b-6kht 6;fbx2aed from rest in a uniform electric field and accelerates to the north at a rhakb;bkd52xm ; 9tkqhj-6 6fh ate 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 cha 7;u2ukef v seg: ,fgycq2v:+lrges 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 + ae2i;wa;tyz g6 4xtre8y*api l/.jksquare 52.5 cm on a side if one corner is occupieyx2zk 4eagl;yi+ a wi rj*te8p6/ta.;d by 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. 215ga s::cqxbtxj+k+w 9lpwuq5 j,b s00 m on a side if the other three corners are o:1qtbq25a+:wjx+jbgxls upwc5 9 s ,kccupied by $ 2.25\times10^{-6 }\,C$ charges.    $ \times10^{4 }\,N/C$   $^{\circ}\,$ from the x-direction.

Determine the direction and magn cy/utf*26p.tmbxzj j g/-9xnitude of the electric field at the point P in Fig. 1 2j/tmyz 9njucx . -6t/pxb*gf6–54. 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 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 fieldx)iolq b65:0pg xpv)h $\vec{E}$ 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 mas9nmb egrc 2 wt/yyo4at8)l (+gnitude and direction of the electric field at points A and B in Fig. 16–57 due to the two positiv n+2wogcrasm84(b 9te /ltyy)e 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 chargeswtmd5xdwxl w-) (61qw, $Q_1$ 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 electrix8swag2auea/ 2k8z3 f c field at the point P shown in Fig. 16–59. The two charges are separated by a distance of 2a. Point P is on the perpendicular axzu wefsk838/22 gaabisector 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 right at 1.0% the speed of light ent1; pstfse/fy /c 2bi:x.. hpsaers a uniform electric field parallel to its direction of motion. If the electr fx./1pe /a 2;ci.htfssb:ypson is 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 flux from a cxfc97ios; a pr0q; z-aubical 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 magjh wjh dl i+j27c* i7b(*yng2knitude +whyl2d b2h7k7*ni( *ijg jc j$ 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, wrgna3h- z 0xz5 gw2a,$O_1$ 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 in a uniform field m ij4c,sd mzp7 bo/wpszurp h-4h32( 5$ 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 plates is The plates are 1.0 mu( oo d1qy5s8o on a side and are separated by 3.0 cm. What is the charge on each plate (assume 1o d 5usqo(y8oequal and opposite)? Neglect edge effects.    $ \times10^{-9 }\,C$

  The field just outside a 3.50-cm-radius metal ball m7aaj-9j :gykis $ 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 radi-1i u*43exoiq9zfyzq f; 4muosc1q*aus 3.00 m carries a 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 an uncharged thin spherical conducting sv. .st:luknc i 5e,ir:hell. (See Fig. 16–33.) What is the electric field E as a function of r (a) for r less than thetrc s.5:eik:,un vil. inner radius of the 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 heliuaco vjt j501.x-shaped DNA molecule are held together by electrostatic forces as shown in Fig. aj 5.tcuvj1o016–44. 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. 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 electrons be if the3o6g3x ns, ojm electric force between them is equal to the wen,6jox33ms o gight of either at the Earth’s surface?    m

  A 3.0-g copper penny has a positive charc)ts ty5:qx r+bzw) 6qge 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 thuc ytjcb0jho85aci.-3 u / nm/ere is an electric field surrounding the Earth. Its magnitude ioaj .380t ic/j-mucbcu hy5/ns about $150\,N/C$ 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 accel5l+ oa3)dm:p4ymyymj- ; pd tlf9 1 zck(xgpi6eration experienced by an electron near the surface of the(g)xf+5jz-19ip kd pl3:; ylct6po mdy4 m yma 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 stationary in the aiav2/ bp afy9v4r. If the downwarpv a2f v9aby/4d-directed electric field 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 shownv, a zr:b95l h0zzv.bu in Fig. 16–62. The C and 9urvbhl0z.,ba z : 5zvO have charges $\pm0.40e$, 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 hydrogen atom, the electron r7 szlgnu )u/xdtjb3 :8evolves in a circular orbit aroundn jgt:uxs/)87z dl3ub the proton with a speed of $ 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, wertwkfd7*c 8r3p fbcm1z/bf j)02 9b qiie responsible for holding the Moon in orbit around the Etp 0 */c8i 7 w9f31qcb)fimj2bbdk frzarth. 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 spem zija9 lcrlw32di60/ed $v_0\,=\, 21.5\times10^{6}\,m/s$ 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 charwu;:uzldp;* xi u3jf +ge $Q_1\,=\, 2.5\times10^{-5}\,C$. 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 plastic and susp4+mo5qtdk. aw ended vertically from an ideal spring wa5dto .kmq4+ $(k\,=\,126N/m)$ 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 w)k2igqj;w,twnuc -9 sith “leaves” that are 78-cm-long wires with tiny 24-g spheres at the ends. When charged, nearly alltj;cw2sin,u- g qwk9) the charge resides on the 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 down and generate a spah44wlef4h1 mk t og*hy1w+h7fd/j .yrvf +w g-rk if the electric field exceeds about l*wg+rydw.ewfhmf+4- / hyhtk74g f4o jhv11$ 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 mass4xh9k z f bifyw me.c7w+s*8m q7d0ua0 0.210 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 thev5oef ymvpf-xq9)i*q.3 ;huo electrons in a 15-kg bar of 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 c sx. rl gg0lfq8z3hlg:ks1b 24 fi96jdonducting spheres A and B 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 n3s lfq s 2bl: 168gk9rj.0hxifggzl4dow acting on sphere A? (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. 16–68, at what posqjj;5bxpdn gt2-8n83h+ if faition(s) x is the electric field zero? Is the fi;nbtpfj3h58x- 2nij+d8 q a fgeld 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 v:vk 3qpbdfq tl-5d 2wi4nx kr7842drcharges, 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?