If you charge a pockeei ,tsnvj1 - 04yicc3gt comb by rubbing it with a silk scarf, how can you determine if the comb is positively or negativ10 ntc3sg4-vi cijy e,ely charged?

Why does a shirt or blouse taken from a clo p9k7sxi, 0hjlthes dryer sometimes cling to your body?j, k9xshi 0l7p

Explain why fog or rai( )t)3cbqoqq ,5.atu yiy2yojn droplets tend to form around ions or electrons in the aioa y2 u(),t.5)qt iyjqbc y3oqr.

A positively charged rodg pe.ijan5o4 ows2.,s is brought close to a neutral piece of paper, which it attracts. Draw a diagram showing the separation of charge and explain why attraction i2g,s jpoo5a .s.e4wn occurs.

Why does a plastic rulhdu.; kkj;8trer that has been rubbed with a cloth have the ability to pick up small pi;hd.8jkru; kteces of paper? Why is this difficult to do on a humid day?

Contrast the net charge on a conductor to the ojr51fauiv1y r6,kfq: q,g*m“free charges” in the conductor.

Figures 16–7 and 16–8 show how a charged rod placed near an unchargqf 5wqv*r 6sth30y ne;44mgni ed metal object can attract (or repel) ei4fn ws3rh65ygq ;vte0m 4*qnlectrons. 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 hmlwrq .4.h*ppbfr9p - ww.v*repel each other and remain at an angle. What balances the electric force of repulsion so that the leaves do.prmwpwr 4v. *hplq.wb9h-f *n’t separate further?

The form of Coulomb’s law is very similar to that for Newton’2q6ll 6myy)g9jgy,dh s law of universal gravitation. What are the differences between these two laws? Compare also gravitational mass gl hg66y y)9,ld2mqyj and electric charge.

We are not normally aware of the gravitational or electric 6u )cqtj52id qsm8 6khforce between two ordinary objects. What is the reason in each case? Give aktj65sch qqd 8im2)6 un example where we are aware of each one and why.

Is the electric force a conservative force? Why or why not? (See Chapter 6.4f/30jl qwv b g2q8zork rz:m.)

When a charged ruler attracts small pieces of paper, 8tpwk3 rr-8yvsometimes a piece jumps quickly away after 8kry 8pw r3v-ttouching the ruler. Explain.

Explain why the test charges we use when measuring electr2rnq /yiymq. pgvg/-, ic fields must be smallpqgrngi2/,q vm - y./y.

When determining an electric field, must we use a positive test cz4z-i hq50 -p4d7mi s xfk0vijzz.g/xharge, or would a negatzpixg/0-z 5hi 47-f . xz4svq0jzk midive one do as well? Explain.

Draw the electric field lines surrou9 v7h+tq*saqedk z0c+kev7g ,x 1v eu40yvwp;nding two negative electric charges a distan7 k0v+vhkp1uad4es*qg tx0ze,;+w 7 c yq 9evvce l apart.

Assume that the two opposite charges in Fig. 16–31a are 12.za clb oc6q zt;1e9,(/h*- uvyolfss50 cm apart. Consider the magnitude of the electric field 2.5 cm from the positive charge. On which side of this charge — top, bottom, left, or right — is the electric field the strongest? The weakest? Exp tbh9z5oyoq1-/cs;asvz l c*f ul,e6 (lain.

Consider the electric field at points A, i ,kigk33 vyyo0oo)o2B, and C in Fig. 16–48. First draw an arrow at each point indicating the direction of the net force that a positive test charg o03iv y3o)2yigkkoo, e would experience if placed at that point, then list the points in order of decreasing field strength (strongest first).

Why can electric field lines never crosriru oe9 ,zipr a mim-6-+c3(xs?

Show, using the three rules for field lines given in Section 16–8, thal9x *xkm0/an k6pad 7at the electric field lines starting or ending on a single point charge 9xp7xd am6*aalkk n0 /must be symmetrically spaced around the charge.

Given two point charges Q and 2Q, a distance l vk2vmu i+p7 a) bz(.ohapart, is there a point along the straight line that avzip )kmb .h(o2v+u 7passes 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 cha 6qh-(lv8 cnosrge located on an electric field line at some point, such as point P in Fig. 16–31a. Is the direction of the velon8ov (hc6q s-lcity and/or acceleration of the test charge along this line? Discuss.

Sketch the electric fieth+v 4w zg*0b4n:cqbb ld lines for a uniform line of charge which is infinitely long. (Hint: Use symmetry.) Is the:tbn b +hcv*4zgb0 qw4 electric field uniform in strength?

If the electric flux through a closed surq,;xzwb)t)1h8rrw g- kh .wk kface is zero, is the electric field necessarily zero at all points on the surface? Explain. What abw b.kr)w8k,-zhw;hx kq1gr )tout 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 ru z)qf sh x2)s.ost-c2adius r. If the sphere is replaced by a cube of side r,hctofz-s.)sq u 2 x)s2 will $\Phi_E$ be larger, smaller, or the same? Explain.

  

  How many electrons make up a charge oq xciu76 c2r)scy u6/jf $-30.0\mu C\,?$   $ \times10^{ 14}\, electrons $

  What is the magnitude of the electric force of attr*l6h. h8zyn5c-bq w,hg0u ypsaction between an iron nucleus c hqb-0,z6np .*s5ylwhhguy8 $(q\,=\,+26e)$ and its innermost electron if the distance between them is $ 1.5\times10^{-12 }\,m\,?$    $ \times10^{-3 }N$

  What is the repulsive electricm83( nmc jl(rcal force between two protons $ 5.0 \times10^{ -15}\,m$ apart from each other in an atomic nucleus?    N

  What is the magnitude of the forc wt,0n7e+fqx*v na+ku b2l(yp e a $+25\,\mu C\,C$ charge exerts on a $+\,3.0\,mC$ charge 35 cm away?    N

  Two charged dust partqw gh03dlyu6:icles 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 are 8.45 cm apart. They are moved, ani*xv(9ij 7ib8 9jq zow cn)x(od the force on each of them is found to have been tripled. Hijv bi(wi 989xx z*7 o)ojnq(cow far apart are they now?    cm

  A person scuffing her feet on a wool rug on a dry datqls6ank0ul9 . (wn.e;im gj6y accumulates a net charge o. sw i0 96majenq6.;lg(ukln tf $-42\,\mu C\,.$ 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 t9jn*lmh5c z k,he electrons in 1.0 kg of $H_2O\,?$    $ \times10^{ 7}\,C$

  Compare the electric forceobksz 8*v8; jt holding 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 fixed distance apart. The sum of their charah3uee5nm+7 smhrf: 6.deug-s56s nk ges is What charge must eaceg 6 u +dkhs:e.ansrhe6fu7s55m 3 m-nh have in order to
(a) maximize the electric force between them,
(b) minimize it?

  Particles of charge p0rq falmbqs:4 +noxi 56qkkw)2f 1:g$+75$,$+48$ 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 particle) q,e e67j.tqvqy d)vwhf:2sps of equal 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 corner of a square 0.100 m on a side. Det8vfhv 2cci/l/yk vwg gr1- ,p*ermine the magnitude and direction of thep/1 /vgck*-cv,fi 2yglw8 hrv force on each charge.
$F_4$ =   $ \times10^{ 7}\,N$
$\theta$ =    $^{\circ}$

  Repeat Problem 14 for the case when two of the positive charges, on opposite cohmt,nt1qw+t 69z(bl trners, are replaced by negatt+ mt(,6n1 z qhtb9lwtive 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 fy 5dm2g n/q.ncharges of magnitude Q, 2Q, 3Q, and 4Q (Fig. 16–52). Determine the force on (a) the charge 2Q, and (b) the charge 3Q, due to the other three cha q/.fn m52gyndrges.
$F_{2Q}$ =    $\frac{kQ^2}{l^2}$
$\theta_{2Q}$ =    $^{\circ}$
$F_{3Q}$ =    $\frac{kQ^2}{l^2}$
$\theta_{3Q}$ =    $^{\circ}$

  Three charged particles are pl +t,p2eh 48xmiyf 3tyxaced at the corners of an equilateral triangle of side 1.20 m (Fig. 16–53). Theexmpf+ x i4t,y2 y3t8h 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 ha4j ,/ozbh rhh6ve 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 nonconductin6oeb)gfq) 3c pqet/- cg 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 frl;/wzhu2 jw; obv w1y1om an initially uncharged plastic ball to an identical ball 12 cw wjbz1o;1h2/wvyu l;m 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 force on a;rnbs 1/2j, mx p+fk2(/qqyj3d1qp o tpaga(dn electron in a uniform electric nksm2pdjjr1( x 3g y/at fq;qpp(/q b+12d,aofield 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, a byn1pjqtv q m1 j-,1blr6m9c3nd it experiences an electric force of mrnmy- jbct 1b6 1l,j3q v19qp$ 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 i xkus0xc .wd d0woqn5vo d36+2s exerted on a $-8.8\,\mu C\,$ 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 direue kikku/,5eqf 0h0e /ctly above a05 ihe/k kuk /fuqe0,en isolated $33.0 \times10^{ -6}\,C$ charge?    $ \times10^{6 }\,N/C$ ----待选择----updown 

  What is the magnitude of the acceleratioc0xroujt x*hhmb2c0-cc3lj* 86 vud,n experienced by an electron in an electj,o* xv- 3c2*l800xchjcu6cud rt hbmric 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 magnitudeu p41/qnu*g hz and direction of the electric field at a point midway betwgu1z/ 4u pnh*qeen 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 field lines about wz) omo;il:-3/w r1p3z as jthtwo point charges, $+Q$ and $-3Q$ which are a distance l apart.

  What is the electric field strength at avegmk.3gcc8lo0cj/ ;y: w rp. point in 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 electric field and pfqtud,u ipjy1j,msv:b0vvs--d*8 2accelerates to them, j:dbfs -su0v2p,8qjp* uiv y1d t-v 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 poinmow0qtj *g++h/wgo m ,5mt0ubt charges 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 cent6+q e-4 -kixcthmk,m z23jm mter of a square 52.5 cm on a side if one corner is occupied byttkm6e j -ki mqxzcmh+,423-m 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 1.00 m on a side if b fyv 7*wq5*lpae2otv+uc)e1the other three corners are occupi**)e5w t7u2byoaclep fvvq1 + ed by $ 2.25\times10^{-6 }\,C$ charges.    $ \times10^{4 }\,N/C$   $^{\circ}\,$ from the x-direction.

Determine the direction and magnitude of the elect8jzm3, go9ju3m0+ki 1mey brx ric field at the point P in Fig. 16–54. The jj umm xe398, g3 k+m10ryobizcharges 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 eleco;(3dhx pj +iptric field $\vec{E}$ 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 ane5f q;bk r)xet:vbe7 nen,i9 )cb+4y qd direction of the electric field at points A and B in Fig. 16–57 due to the twvx bb);tb4q,ie+:rnek9n7 e cf)e q5y o 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 cha+gn8n-y0oyh n) y6r pxss0aj5rges, $Q_1$ 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 field at th/uhh ;: gh-: 8etjy,mpixy4 lhe 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 line joining the charges, a distance x from the mul:m8-e hi:x /4,h jtygyh ;hpidpoint 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 enters a uniform ele x n1u )q(aeydkcnp:6;ctric field parallel to its direction of motion. If the ele ca1;(d6 pqenxn)u:y kctron 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 oo6; qbt;txk9z1,vw(uj9 3 s m6f bputjn 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 2y, t(vy6 /x ym8n07d jq)6sthdguaof is placed in a uniform electric field of magnitude/7dynj a0 u2 x 6)sfy(vdh8,yttom gq6 $ 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 objei3k8;k nmq .hhguc)j/ o6e gh65izt e9cts, $O_1$ 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 unb* *l5pgz m-yuiform 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 The plates are 1.0 m onin* 2aoeaov 3t43a0yi a side and are separated by 3.0a4oy ae ii23*3anv0ot cm. What is the charge on each plate (assume equal and opposite)? Neglect edge effects.    $ \times10^{-9 }\,C$

  The field just outside a 3.50-cm,kdf3i .t*;; t/kb1vkjiuqy n-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 a total charge of 3geppg(:x4 cb $-3.5\mu C$ 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 )dzg38k i 8xoc+rwh4*wih d:6aq f7yxil 9ig4 of an 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 the shell, (b) inside the shell, and (c) beyond the shell? (d) Does the shell affect the field due to Q alone? Does the charxk8i7goihr3qx: 9 h glw+yc4ddf)6i w*i84 azge Q affect the shell?

  The two strands of the helix-shaped DNA molecule are held together by jxyj7:-xeqb3 :tl 3bk44cog5 dp7ax celectrostatic forces as shown in Fig. 16–44. Assume that the net average charge (due to electron sharing):pl-xkbtq45x3xbje4 a 3ocjd: 7cgy7 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 foz 7wbnfz )tr12qtqt4)h3)urgpqk./b dm i. p8rce between them is equal to the weight of2h)z7 gftu3)qirqmbt w4nkqz/ ..8)tp1r bdp either at the Earth’s surface?    m

  A 3.0-g copper penny has a positive chargep;0b*,brm ;mmi q bwm0x8ka 2l 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 surr qa cx(eay:+9xounding the Earth. Its magnitude is 9:exqay cx a+(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 electrk3zroi.7e v9fb9c x0df9-k(6butysa ic field of what is the acceleration experienced by an el(7x-cts9 eo96uk9b 3 r 0f y.viabzfkdectron near the surface 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. hzvox;uyn6atr4 im z*)zmu):l)wgp m*/lu1 )018 mm remains stationary in the air. If the downward-dgl:z*oh )lup*ru)/ w6txm4zzmun);v) a ym1 iirected 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+kid1q0ylql) tvd 7d;g,du 0z between the CO group and the HN group shown in Fig. 16–62. ld ,dqk;qddy+tg liz0u1) 0 v7The C and O 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 atub 9c 7uskit(gqf+( k tff-9/dom, the electron revolves in a circular orbit around the proton with a speed of tu-t kqfgfuf9 isck(+(db79/$ 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 responsible fopi *zuzrmv11fs5e;d 4r holding the Moon in orbit aroun zm;4pe* ufrzdv51si1 d 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 speedj.9 n6 mj ac lgx25-qyfjxs )oetp93k) $v_0\,=\, 21.5\times10^{6}\,m/s$ 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 cha-d vs41g qa. + gmhxkdr5nd1g7rge $Q_1\,=\, 2.5\times10^{-5}\,C$. 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 ud0xn t2lr4h3wjwl)jp vs08l1i3 -x rand suspended vertically from an ideal sprinl)nxt1r8 vx 2-3slhruij40dp l3wj0wg $(k\,=\,126N/m)$ 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-cm-long w evc aaa/2tvn2p( z16gires with tiny 24-g spheres at the ends. When charged, nearly all the cha2tv n2g pez 6a/a1c(varge 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 electric field exceeds ab9 g)fsx)fi p:0gpp+yk *; cxopout c;:pxpy))xf*g siogk+09ppf $ 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, and net charge iu6 dnrb+2 t4g$+0.340\,\mu C$, 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 alqoz0q: npxn0qn /xm-5 l the 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 conducting spheres A and B are a distance R apart; each s:l5cn6kk-h8x )wszm 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 A? (8hx snklw :6s5c mz)k-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. 16–686 eoz3(; t,pt quxf/,0a nuajd, at what position(s) x is the electric field zero? Is the field zero at an0a q;zp(,3 u,a onfe6j/tdxuty 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 char 04dpfk-7 zki)m-xzuuge $8.0\,\mu C$ 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?