If you charge a pocket comb by rubbing it with a silk scarf, how can 0pte h8a k4q3m;m(snsmvg1w9 you determine i gm;9(30vs14atw nkmqme h8psf the comb is positively or negatively charged?

Why does a shirt or blouse taken from a clothes dryer somet:+1h f1a s8t gzogfg9simes cling to your body9 sgg +g:f1z8hato 1sf?

Explain why fog or rain dropletir - jls63fep(s tend to form around ions or electrons in the ai6-( 3i sljprfer.

A positively charged rod is brought close to a neutral piece of paper, whic l g5(0yyrv.kvqpz (c,h it attracts. Draw a diagram showing the separation of chr.v5yp 0k cg(lqv ,z(yarge and explain why attraction occurs.

Why does a plastic ruler that -q;cqtcul*0hgve 5z l.7fa,zhas been rubbed with a cloth have the ability to pick up small pieces of paper? Why is this difficulfga7t5;zc0*v . qeq zuhl -lc,t to do on a humid day?

Contrast the net charge on a 4+w-y*tekev0rju qr syh2b )c:k+*hyconductor to the “free charges” in the conductor.

Figures 16–7 and 16–8 show how a charged rod placed near an uncharged metwyg*5. c6w8zf +uz odxy5d0 otal object can attract (or repel) 5xtgyz.ofyc w+d6 o*zuwd805electrons. There are a great many electrons in the metal, yet only some of them move as shown. Why not all of them?

When an electroscope is charged, its two leaves repel each other 5ddh46vwhku1z:o;a5g)bmey: (shytn *tir* and remain at an angle. What balances the electric force of repulsion so that tbnh(toyh541 ; imzsdt*h:gdvre 6ka )wy 5u*:he leaves don’t separate further?

The form of Coulomb’s vh 8xcrf3,yqao/s b7q,3 2nz 2ot5kf elaw is very similar to that for Newton’s law of universal gravitation. What are the differe2 oafcs3q2t 7evo/y5 fn8z3bqhk r,x, nces between these two laws? Compare also gravitational mass and electric charge.

We are not normally aware of the gravitational or electric force betwe-ymyu9n-wel zd*5g7 : gpkglwz)r ; )cen two ordinary objects. What is the reason in each case? Give an examplww e9gr-5gl ;dylgzy: u cmz)7-) n*pke where we are aware of each one and why.

Is the electric force a conservatic 8qxp t(h5m uoh-n+r+2w56 njsrrc5t ve force? Why or why not? (See Chapter 6.)

When a charged ruler attracts small pieces of paper, sometimes a piei kfyg),lg s94cuqdrk4q 8w9hfy5y 8+ce jumps quickly away after touching the ruler. Exp)i5wq 94g, lqkud9hyy4+yc g8kr f8 sflain.

Explain why the test charges we use when measuringdt6hne; 8 nh-yvx8 b7e electric fields must be small.eht8nyb eh8;76 xnvd-

When determining an electric field, must we use a positive test charge, or would7gcf )e :jge) w;wvnt1 a negative onjgv)c )g feww 1e7:n;te do as well? Explain.

Draw the electric fiel vugefmodu7-)c.y+v1 d lines surrounding two negative electric charges a distance l apart..oug d u1-vefvcy)m7+

Assume that the two opposite charges in Fig. 16–31a are 12.0 cm agd7w7( u k1 z smrbq)/wtz(8zapart. Consider the magnitude of the electric field 2.5 cm from the positive charge. On which side of this charge — top, bottom,87ur)tgzz akb( sw1m/7w d(q z left, or right — is the electric field the strongest? The weakest? Explain.

Consider the electric field at points A, B, and C inrr) (muua c 60i.fju0w 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 orde uucj0r.r uw0a) i6mf(r of decreasing field strength (strongest first).

Why can electric field lina:)e nb z*7dpmes never cross?

Show, using the three rules for field lines given in pqni(xhng-m8m5p* 4 nuiz)jhei1y 9 sr ,(u. pSection 16–8, that the electric field lines starting or ending on a single point charge mu.qn*(m 9x ri 8i,m pp1g)iu4jz(e yhs-unhnp 5st be symmetrically spaced around the charge.

Given two point charges Q and 2Q, a distance l apart, is there a pointp,yj5v:3 f r)k xc5nef along the straight line that passes through them where E=0 when their signs ary3kv 5e xnfpf):5jc,re (a) opposite, (b) the same? If yes, state roughly where this point will be.

Consider a small positive test charge located on an ele .nkztksark e,+ma x igh0);vs1*8-zml1s: z tctric field line at some point, such as point P in Fig. 16–31a. Is the dir .etkz1801 *kmasn-a; itkx sszg+rzv:) l mh,ection of the velocity and/or acceleration of the test charge along this line? Discuss.

Sketch the electric field lines for a uniform line of vt(gh kgu,q:2charge which is infinitely long. (Hint: Use symmetry.) Is the electric field uniform ikgt :qvg(u,h 2n strength?

If the electric flux through a closed surfac7 mzoq i/lx0wdt3g3m 1e is zero, is the electric field necessarily zero at all po733 o0q z wdgli1mmt/xints 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 spherq( z a-,u2uyxhw 2vat-ical gaussian surface of radius r. If the sphere is replaced by a cube of si(qhz w-2-vyu2,a ta xude r, will $\Phi_E$ be larger, smaller, or the same? Explain.

  

  How many electrons make u5t/ tauddl.a 9m2g.g wp a charge of $-30.0\mu C\,?$   $ \times10^{ 14}\, electrons $

  What is the magnitude of the elec5e;x ;ybg m,ua5* otyh ;wu2mxtric force of attraction between an iron nucleus y;5;xheg;u 5yaxt bow2um m,* $(q\,=\,+26e)$ and its innermost electron if the distance between them is $ 1.5\times10^{-12 }\,m\,?$    $ \times10^{-3 }N$

  What is the repulsive electrn v8fqgm */posrjrl9.cn -c6* ical force between two protons $ 5.0 \times10^{ -15}\,m$ apart from each other in an atomic nucleus?    N

  What is the magnitude of the ffbqt cqi9;2 z:orce a $+25\,\mu C\,C$ charge exerts on a $+\,3.0\,mC$ charge 35 cm away?    N

  Two charged dust particl q.)xscy;g14wrtid -n es exert 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 arhnsr*lg it441q, tpz23jh, hp e 8.45 cm apart. They are moved, and the force on each of th,igtpn4 p l2 1jr4,th*3qszhhem is found to have been tripled. How far apart are they now?    cm

  A person scuffing her feet on a wool r(gqc ,gwj9z p 55xb-jbug on a dry day accumulates a net charge of- 5(cgpbbg, j w9zx5jq $-42\,\mu C\,.$ 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 electrons in 1niqsc of a2 roc -*mg*vo)4o+7.0 kg of $H_2O\,?$    $ \times10^{ 7}\,C$

  Compare the electric force holdiba -bhz1g-sl pn + 05r6tr*kqpng the 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 s3cxo0a*rhq6 fixed distance apart. The sum of their charges is What charge must each have in oo h03rq6*xascrder to
(a) maximize the electric force between them,
(b) minimize it?

  Particles of charge hqjqv +(rr,6a$+75$,$+48$ 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 eq/ma 72j(zmc ykual charge, $+11.0\,\mu C\,$ 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 co c c.hsi8-8rgxrner of a square 0.100 m on a side. Determigxi-8 r sc8ch.ne the magnitude and direction of the force on each charge.
$F_4$ =   $ \times10^{ 7}\,N$
$\theta$ =    $^{\circ}$

  Repeat Problem 14 for t4f z2ex s*90 exk.fpao*xhf(rhe case when two of the positive charges, on opposite corners, are replafa2ex he fzo9(0xk*4 *pfrxs.ced 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 poihtzim;y40b4u7 jbr n1,1tl l1ymt ixf2u5 w6knt charges of magnitude Q, 2Q, 3Q, and 4Q (,5tl7lt1; wmkfiub44bu1 zmx n 2yity1h j6r0Fig. 16–52). Determine 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 particles are placed at the corners of an equilateral triangle of qza 2ns+b-pf .sis+baz-f p qn.2de 1.20 m (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 have a total:+2 n vgwl:8xxv,8 moycs 5lpco(pm v9 k*7hvk 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 f( j31pjcrk*m spheres 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 bal 7g3dlup8 qj: s,vly8ctrqx(p( (z bi,l to an identical ball 12 cm away. The for p(p(biy:,t,lc gz qj3 dus7lx8rqv (8ce 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 force on an electron/edp idwunx,+qrk o a6/;8-j/ e7fqgf in a uniform electric field of strengthkq87/w+eanj f/ odd;f -p6gqx /,ieur $2360\,N/C$ that points due east?
   $ \times10^{ -16}\,N$
 ----待选择----westeast 

  A proton is released in a uniform electric field, kq8+r5 e 13ax:kanti rand it experiences an electric force o5k1 i:t+ reaqa n3r8kxf $ 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 a nob, v d0gu; zxh8y,p6$-8.8\,\mu C\,$ 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 magnitu z eyh63w,y8mode and direction of the electric field 20.0 cm directly above an isw 36em8, hyyozolated $33.0 \times10^{ -6}\,C$ charge?    $ \times10^{6 }\,N/C$ ----待选择----updown 

  What is the magnitude of the acceleration experienced t+6pz,he99 q ocfajm (by an electron in an electricetfmoq,(99j6z+ ph ac 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 and direr shq-kl8lo-9-o 2o h.lhfs0ection of the electric field at a point midway between aqhoo0-8 sr.h-9ol2- fhs lkel $-8.0\,\mu C\,$ 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 field lines about two point chargest8s88jhv3u0it c tb6-h sjzv1 , $+Q$ and $-3Q$ which are a distance l apart.

  What is the electric field strength at a point in cy0iyz2/m v7yyqb3-o8 ryzo8 space where a proton $(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 electri0c*39co nanw24qbsyi(3etcto 1; nq oc field and accelerates to the north at a rate of 3 *boyw qiqo;0ctn ce n4( 9nstc1o23a$115\,m/s^2\,.$ 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 charges ilpv uv0v j3ogo6 ani68/j,ox9s $745\,N/C\,,$ 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 uq(sx 2d0j(f4 ic6s2gwrld4 m.5 cm on a side if one corir s(m s 0j(w4xudg2dqfl426c ner is occupied 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 onbz:y0 ns, s ,od:h)unse corner of a square 1.00 m on a side if the other three corners are occupied by nz:)ss,bn0 ous :,dhy$ 2.25\times10^{-6 }\,C$ charges.    $ \times10^{4 }\,N/C$   $^{\circ}\,$ from the x-direction.

Determine the direction and magnitude of the electric field w:ual 1( jy/otat the point P in Fig. 16–54. The charges are separated by a /ow1y(jual t: 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 fhns6,n96kckm uuh 0 b8l g)dx)ield $\vec{E}$ 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 zftjn,z,0: /pa ludj, and direction of the electric field at points A and B in Fig. 16–57 due to the two positivej,zfjan ,,ul/: pt0d z 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, itd(46t -bhc sy -jis1$Q_1$ 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 magnit.cz,.v4f tsq 3*tmxg fude of the electric 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 bisector of the liv. f 4m xtfc*qg.,zs3tne 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 ay bl4;w,zj-qj t 1.0% the speed of light enters a uniform electric field parallel to its direct,-j; 4wbyjzlq ion of motion. If the electron 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 cubical box 28.0 cm on a sidetf) 728ycsk fx 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 eloc*cu oq-a0d9ectric field of magnitudeo*cd-a q90ouc $ 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 obj aqp+ ;o3b2ccuects, $O_1$ 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 place* gug78ihxp:uj-n: c pd in 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 plates is T/ndbw2lar04/vzlo5 yo uwa 2*he plates are 1.0 m on a side and are separated by 3.0 cm. What is the charge on each pla0 nwza/oy vu l4wld2ba*ro 52/te (assume equal and opposite)? Neglect edge effects.    $ \times10^{-9 }\,C$

  The field just outside a 3.50-cm-radius metal b.)hvs47adz l4s:h qdu 8 sb.ncall 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 ca2y i5 jw *fw)o kh.i*6gxhcrc:rries 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 g6gsorpf 5 1ur5nqm1 *thin spherical conducting shell. (See Fig. 16–33.) What is the electric field E as a functif1n 5p5*gsqro 16mrg uon of r (a) for r less than the 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 helix-shaped DN 89vtr o0qjlt+cd(p 0l 4fcu5ttfy 4*sA molecule are held together by electrostatic forces as shown in Fig. 16–44. Assume that the net average ch8f fldr tul o yqtcp0s4v(9c 0j4+t5*targe (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 the electric force bedu - .tmn;.auhtween them is equal to the weight of eitherut h;a.du.-m n at the Earth’s surface?    m

  A 3.0-g copper penny has a positive char/t d ev n3xq(67g2betgge 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 elec /l59io ce 3fwguh1pz;gn,(idtric field surrounding the Earth. Itshnzw13plf g cd /;o5iug9e ,(i magnitude is 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 lbe-t: r*kx q5g*a;zq tkp2z oa (x7vom: p*,z what is the acceleration experienced by an electron near the surface of thez*b5 7*p l,o*(-;a: kzetrmxvao2p k zq:txgq 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 tbxj z6k;88e8h 7erb4 rh wmcj9he air. If the downward-directed electric field of thek h j6zrhbe;rxwm48 8e87bj9c Earth is $150\,N/C$ how many excess electron charges must the water droplet have?    $ \times10^{ 6}$ electrons

  Estimate the net force between thus zxt 4r.93rk1tjv)te CO group and the HN group shown in Fig. 16–62. The C and O have charges r. vstz tr14utx3 )k9j$\pm0.40e$, 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 e(*3o ctbts x6dlectron revolves in a circular orbits( xdb*co6 tt3 around 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, were 6qg-a3hej b8; bl) zp8g-zibs responsible for holding the Moon zibg6l -8b;zgj aep-)q8b3 hsin orbit around the Earth. 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 ha/*hb)(qft95i fucv ekj*-c $v_0\,=\, 21.5\times10^{6}\,m/s$ 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 chat/ o)z 6*z,,weavxwox) m j4v c)n btltr;.+corge $Q_1\,=\, 2.5\times10^{-5}\,C$. 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 suspended verticalaef5k*lo 4ma ,ly from an ideal sa,fk4 e5ola *mpring $(k\,=\,126N/m)$ 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 mad x*)myg*n b; .vmg9czne with “leaves” that are 78-cm-long wires with tiny 24-g spheres at the ends. When charged, nearly all thxbmg)n cmnvy *g;.z*9e 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 spark if the electriic 1wxjwjs9*yyjl) 72c field exceeds about 9yycxlj*jj 72wi ws)1$ 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 0.210 kg, nv *zrh/j3: leand 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 of aluminuy+,tx-i (:h:(pdo wkzom2 fd km?    $ \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 are a zf ;sma -i0xig*rod4omkqr08 u0* n/ jdistance 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 actinknmf**0o z00i;4o xri s u-drmqja8/ gg 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, a+qxxi ;iccmzbm ne5) a(2-pt: t what position(s) x is the electric field zero? Is the field zero q ;ezi-tix:m(+ncmx a2c bp)5 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 charges, each of chargew2 xo6 pxtvh8r0wpf.ld7,j /y $8.0\,\mu C$ 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?