If you charge a pocket comb by rubbing it with a silk scaf*ivd.a nkt+4cw )(ou rf, how can you determine if the comb is positively or negative *nkut4 ic() dwfoa+v.ly charged?

Why does a shirt or blouse taken from a clothedowsmf+vxxu o:)k g2.0xtfvy(0al (9s dryer sometimes cling to your boxtf0)xus0g o 2.( :vyvoalwf +x m(d9kdy?

Explain why fog or rain droplets tend ty,sex kphu 7;fc8h(5ho form around ions or electrons in the aie8hckh;7huxp(, 5s f yr.

A positively charged rod is brought close to a yf-67u;xz yadcez /s0bkv7r; lzw ))qneutral piece of paper, which it attracts. Draw a diagram showing the sep7- syulw fx0vc6 /z) z 7yb;)eadqrkz;aration of charge and explain why attraction occurs.

Why does a plastic ruler that has been rubbed with a cloth have the ability to xk7.b,9 ffnt-na xr1 *(quyvy pick up small pieces of paper? Wv17,naf*y yfx.nxb q utkr 9(-hy is this difficult to do on a humid day?

Contrast the net charge on a conductor to8hh ctpk2xufgy3bcl ssb-;q:(3* jyfe .py03 the “free charges” in the conductor.

Figures 16–7 and 16–8 show how a charged rod placed nexxfy/ge .nwqw6:)so .ar 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 not all of the /ywnexf.x:wqs.g6o )m?

When an electroscope is chamnc0 j) fg8o*arged, its two leaves repel each other and remain at an nf*)8 0gmcao jangle. What balances the electric force of repulsion so that the leaves don’t separate further?

The form of Coulomb’s law is very similar to that for Newton’s law of unb 4wuq0ltop5r 6 8s ie4wtyhjo(0dw52iversal gravitation. What are the differences between these two laws? Compare also gravitational mass aney50hw l56(o qr04p8to w4b2ut jidwsd electric charge.

We are not normally aware of the gravitational or electric for8tt. ahthib2+ce between two ordinary objects. What is the reason in eachtt2a tb i+h.8h case? Give an example where we are aware of each one and why.

Is the electric force a conservative force? Why or why not? (Saf0q:6d iw*e 1hopo- jee Chapter 6.)

When a charged ruler attrac: *illqrmk:5 ats small pieces of paper, sometimes a piece jumps quickly away after *5lq :kam:r iltouching the ruler. Explain.

Explain why the test charges we use when measuring electric ficf37fup4) t6w e2:qc o- qfhinefx7-qelds must be smallnq -ef7 :fu7)ocqxpf24 -wqht6ie3fc .

When determining an electric field, must we use a positive test charge, or woulalum+ye7z8ld)-o.aj;ar-v. ej i1;o ff w zv: d a negative one do as f) e-am;e1wd7iul z:v+a fyoj v.j- oz.8ra l;well? Explain.

Draw the electric field lines surrounding two negatqd 9ucjoh r/0jr,h-8tive electric charges a distance- j8hj0t9,/hudro rq c l apart.

Assume that the two opposite charges in Fig. 164rgikv95dxfz6: yqr(a . lf :c–31a are 12.0 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, d9ffv5 ir y6:a4gqlx.c(rz: k or right — is the electric field the strongest? The weakest? Explain.

Consider the electric field at points A, B, and C in Fig. 16–48)p.bn5 smfcx.. First draw an arrow at each point indicating the direction of the net force t f.b.mn)sx5pchat 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 lines neverkgl 9l(;g1g awu2g;n i)3sk pp-x-e jt cross?

Show, using the three rules for field lines given in Sectie/ r55x excyg6on 16–8, that the electric field lines starting ory6 erecg55/ xx ending on a single point charge must be symmetrically spaced around the charge.

Given two point charges Q and 2Qv7 9gfgji:wue 3sdrf-k-v0 .o, 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, (b) the same? If yes, statr 0v9ejf3w -:- io7vug.f gdkse roughly where this point will be.

Consider a small positive test charge located on an electriwgdft4;ti nxv0p0g4 h fv ,.u5c field line at some point, such as point P in Fig. 16–31a. Is the direction of the velocity and/or acceleration of the test charge w fdn4,xft5g;v.0ip g4h vut0along this line? Discuss.

Sketch the electric field lines - za wfd-yxabww010smaq*- bgh1gb 15v2 (l rmfor a uniform line of charge which is infinitely long. (Hint: Use symmetry.) Is the e yabmm z1w10* fr-w0b1 2qlaw( gbgd5avhs-- xlectric field uniform in strength?

If the electric flux through a closed surface is zero, is thgzf1j 2fl4 7y d (7zm1bsan(tve electric field necessarily zero at all points on the surface? Explain.1gta(bfsz 1 zd2(4n7lmy vfj7 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-maq * j6 ; abg:ofrus/1tc2g8jj lrt4 spherical gaussian surface of radius r. If the sphere is uj /;t j:l fq*81 sa2m6bj-rc4atgrogreplaced by a cube of side r, will $\Phi_E$ be larger, smaller, or the same? Explain.

  

  How many electrons make h,oj9 hz; j34chl,hod up a charge of $-30.0\mu C\,?$   $ \times10^{ 14}\, electrons $

  What is the magnitude of t47q0ybi o. 78bzhqf pdhe electric force of attraction between an iron nucleus 7iy hof z7p8bq. q0b4d$(q\,=\,+26e)$ and its innermost electron if the distance between them is $ 1.5\times10^{-12 }\,m\,?$    $ \times10^{-3 }N$

  What is the repulsive electrical3 .1ppo e(* ;r/zslhfr*sade:u:ph iu force between two protons $ 5.0 \times10^{ -15}\,m$ apart from each other in an atomic nucleus?    N

  What is the magnitude of t(-p6y-c.h roxzeu z)phe force a $+25\,\mu C\,C$ charge exerts on a $+\,3.0\,mC$ charge 35 cm away?    N

  Two charged dust particgbtx/qsgd u,b ohr51d,6u + t+les 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, and the force)y5m; (c-qhe p1cyo bn on each of them is found to have been tripled1hqmybeoynp c5c-)( ; . How far apart are they now?    cm

  A person scuffing her fe u r:fwb0/r9cd2hth-eet on a wool rug on a dry day accumulates a net charge ofrerhft c:w2/-b0ud h9 $-42\,\mu C\,.$ How many excess electrons does she get,    $ \times10^{14 }\,electrons$
by how much does her mass increase?    $ \times10^{-16 }kg$

  What is the total charge17rieog) qo)qmmp s 58 of all the electrons in 1.0 kg of $H_2O\,?$    $ \times10^{ 7}\,C$

  Compare the electric force holdingyqodg 6ej;-4 u) hg9yq 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 theis:n1i qjpd k1xm5js- qcx, v:8r charges is What charge mxs8d5 i :j-pm,1q x1ckn:jsqvust each have in order to
(a) maximize the electric force between them,
(b) minimize it?

  Particles of charge db1iabz):2m 9n0:o4h mj lg)cyx s u0k$+75$,$+48$ 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 d:y yq(2bdqa75d,5xlq(f p qrox s.n;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 yvh ,g(sd+ d+ jpzmcguo0,p. (of a square 0.100 m on a side. Determine the magnitude and direction of the force on eys,.j hpdopu +vg0g(, +cdzm( ach charge.
$F_4$ =   $ \times10^{ 7}\,N$
$\theta$ =    $^{\circ}$

  Repeat Problem 14 for tn*forxm*.l34z b7wm 5a 9zlctdlh8l4he case when two of the positive charges, on opposite corners, are replaced by negative charges of the same magnitude (F*moblln.44z d7x389wfl tl*ahrm c z 5ig. 16–51).
$F_4$ =   $ \times10^{ 7}\,N$
$\theta$ =    $^{\circ}$

  At each corner of a square of sidew+l3a 2ubgreqr:dv qyo4 y17- l there are point charges of magnitude Q, 2Q, 3Q, and 4Q (Fig. 16–52). Determine the forcg:3oybv4e ql+arqd 7w12y r-u e 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 ply,co3uclx yu-9s4 g5swt-x/ y aced at the corners of an equilateral triangle of side 1.20 m (Fisgu/9x 5c- x w 3tclu4,o-yyysg. 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 1(mz 6+aznzl1 fsa(fxbq+v;5 ca v8p za 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 a 4nd rx(hfv+2(:vbq)l1 mz ubutotal 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 to11 ghtb 5qd2c1vm6 vzz an identical ball 12 cm away. The force of attraction is then 17 mN. How many electrons were transferred from one ball to the othev 1zz1t21vmb dc5g6 hqr?    $ \times10^{ 12}$ electrons

  What are the magnitude and direction o, j /ork(+hxquf the electric force on an electron in a uniform electric field/rqkjh(+ ,xou of strength $2360\,N/C$ that points due east?
   $ \times10^{ -16}\,N$
 ----待选择----westeast 

  A proton is released in a u 4)0og*tqrp4h h3dlukniform electric field, and it experiences an electric force of 3ud 0qkt4lhg rop4h*) $ 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 kat9r:-o.l.by9m t y iN is 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 a/)(q2exim rp-h1l -bd7kqikj nd direction of the electric field 20.0 cm directly above an isolaplq-x qberd/ -jimki2 (hk1) 7ted $33.0 \times10^{ -6}\,C$ charge?    $ \times10^{6 }\,N/C$ ----待选择----updown 

  What is the magnitude of the accelera /6;:uoj*ff fjrvn. xztion experienced by an electron in an electric fieloffuz/nrf6*j. ;j v x:d 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 fvow( qgx5iuu1.y f-ogr8vpn - ,p+4yand direction of the electric field at a point midway betwee5x(1f.,u-qnwpgf4 -ygvy +uo8or i p vn 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 two point eqpon2 6 7(y:5wqsu4fm/ -fhsm,am iz charges, $+Q$ and $-3Q$ which are a distance l apart.

  What is the electric field stre( n0is(ds:tal;*lkc j ngth at a 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 . x+*/swsqr)vm/s btz field and accelerates to thsvm+w/q.s / b) rzstx*e 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 midh241i 6bbmrzv way between two equal but opposite point 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 electrycqi ojf kn18 rh0s9zrhg1e).-bc +,mic field at the center of a square 52.5 cm on a side if one corner is occupied by a-c1y81jz0h9+s n r i.m, o rbkfhegc)q $+45.0\,\mu C\,$ charge and the other three are occupied by $-27\,\mu C\,$ charges.    $ \times10^{6 }\,N/C$ at    $^{\circ}\,$

  Calculate the electric field at onef76ka xp wv8ukdpif7j/ml,83 corner of a square 1.00 m on a side if the other three corners are occupied vwp 7x d7388 6lkfpaufi,jk/mby $ 2.25\times10^{-6 }\,C$ charges.    $ \times10^{4 }\,N/C$   $^{\circ}\,$ from the x-direction.

Determine the direction and magnitude os0i8 ,th b4eyef the electric field at the point P in Fig. 16–54. The charges are separated by a i h,s8 y4eb0tedistance 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 electrcoy7tzy*6 uxpz6 x1n8ic 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 magnitudek5 myf+xm)muk w.+7si and direction of the electric field at points A and B in )sk mf5 imkm+xy.u7w+Fig. 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 unknc on5ltg..(6c eksoi: slk;qsa 8*s)vown point charges, $Q_1$ 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;us(cdymrrf3(d.a1 g magnitude of the electric field at the point P shown in Fig. 16–59. The two charges are segacrm; y(.u rs f(1dd3parated by a distance of 2a. Point 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 right at 1.ncsg7 ryb 7d.,0% the speed of light enters a uniform electric field parallel to its direction of motion. If the electron is to be brought to rest ib yg 7,sd7cnr.n 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 fluja 3 )pdyjcq,rm1 :g-mx 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 sx58mokt 3-szp va /4yplaced in a uniform electric field of magnitude t kvso8- mszp y5ax34/$ 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 d,9p;cfp dxh6ects, $O_1$ 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 pl6 u8btu q363n9jl3fptscq - fh1r1d claced 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 pzjt(ix)h c1c+n 3i9a) wlc,yc lates is The plates are 1.0 m on a side and are separated by 3.0 cm. What is the charge on each plate (as)ncjy9)ch 1zw x,+ilac i3t c(sume equal and opposite)? Neglect edge effects.    $ \times10^{-9 }\,C$

  The field just outside a 3.50-cm-radius metal b ium lq(*9s8,jz:0x nph oyl5zall 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 3.0k)ik49v* t.4cwl,h kxjd80i pme j5k3 nslh *i0 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 spheri+l/o ,cznrul :bzwd6*ca vc+i-pb,(r cal 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 affec u,nw a/c-z:ll+c(dirz,bc+op6r v *bt the field due to Q alone? Does the charge Q affect the shell?

  The two strands of the helix-shaped DNA molecule are held together by electg3xrb1i ; w8jotc4fvr* m1uc2rostatic forces as shown in Fig. 16–44. Assume that the net average charge (due to electron sharing) indicated otrxu1 1rcf ;gw*vib4o 2j 83mcn 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 between them is equal th(kb 9fqny 22uqb yp(u)za.m 6o the weight un 96b2p(m a .2yubq)(fkhqzy of either at the Earth’s surface?    m

  A 3.0-g copper penny has a positivek2z2zay2 )goov3m b-f charge 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 t,sp90pat(v5mtg1f k9 dg1rzahat there is an electric field surrounding the Earth. Its magnitua1pz 9m f(,tvg sgkt1r5p90dade 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 what is the acceleration experienco dxa6,(lg 4 onx8jxc;dcjp6:ed by an electron near g4xl xo6d j 6:o(c,dcxaj 8;pnthe 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 ra/6kjeor6 n5u 9 hc,lb- n4gzwadius 0.018 mm remains stationary in the air. If the downward-directegjon5 ecnrhl4w-bku,a69z 6/ d 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 shown i ar+0 x mbjf3yl(k52rpn Fig. 16–62. 3(l + bfamr25yjxkpr0 The 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 j rpcw+7 zb pfko2, p45ubkz4+hydrogen atom, the electron revolves in a circular orbit around the proton with a speuw k2 pfbr,b p4ok 5p+zzj47+ced 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 2jvi--nfahk f+ mq- / de ;lo7ze8n.rhgravity, were responsible for holding the Moon in orbit around the Earth. If equal and opposite charges Q were placed on the Eartone l aej-fm;k+zh-i/ 8h2q.n7v-d r fh 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 6d(e0q xr3tva$v_0\,=\, 21.5\times10^{6}\,m/s$ 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 charge j rm:b7upn j :i+u,xj5kj+ dihh-,q5k$Q_1\,=\, 2.5\times10^{-5}\,C$. 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 vertic*dj 0, 8vgdvqhally from an idv d8dvj q0,h*geal spring $(k\,=\,126N/m)$ 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” ts(5)+qzddk z twk5k7 nhat are 78-cm-long wires with tiny 24-g sphenz)5( z k+5d7tkswq kdres at the ends. When charged, nearly all 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 spark if the electric ksot nn6s/xptrln/k l)n9 +-1field exceeds aboutrtp-k snls9oln nt /k/n1x)6+ $ 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 kod,xyx) s1c: ng, 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 5c3zr-b-x rx11b jbvmall 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 conduc-3k9xlguoh 88b 1*norix0io zting 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 -zk0rx on13h*o u8iglxiob 9 8zero 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? (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 position(s) x io.ov6*wv)9mkdev1:t giy 6 eways)b 6e- tx)is the electric field zero? Is the .kse1 ):wygb9we otv v) 6tmiv6aoi* yed)x6- 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 charges, each of chargeb,ubx -5ylku5o/ tw,g3m5o :qy vped6 $8.0\,\mu C$ 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?