If you charge a pocket comb by rubbing it with a silk scarf, how ca hd;s* bj+ ws:+xtk-nhn you determine if the com+xt;k *s-dbj: w+snhhb is positively or negatively charged?

Why does a shirt or blouset k7/va3,gwv0;b xm kq taken from a clothes dryer sometimes cling to your bodw k3kgm;v,7v b0x/a tqy?

Explain why fog or raiqa((5,ac 2ie q0 ckejpn droplets tend to form around ions or electrons in the aiae(25cj 0 (qiqkecpa, r.

A positively charged rod is broughupd(6z-i -zvr-qest/ t close to a neutral piece of paper, which it attracts. Draw a q/zi--vzt6rde ups-( diagram showing the separation of charge and explain why attraction occurs.

Why does a plastic ruler that has been rubbed with 3x it,) d/b k,xz)rdyf.7q pzla cloth have the ability to pick up small pieces of paper? Why is this diykbr,dq) z 7lxd,iz/3 x.tf)p fficult to do on a humid day?

Contrast the net charge on a conductor to the “free charges” pxb qo(lppx d r:f0 /w2kp((w*p8qb:qin the conductor.

Figures 16–7 and 16–8 show how a charged rod placed near9wmt s 53kix* 7hgyvh) an uncharged metal object can attract (mkvg57)sx3h w hti y*9or repel) electrons. 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, o/fchxp.c ni8:b ;5jhits two leaves repel each other and remain at an angle. What balances the electric force of repulsion so that the leaves don’.; n c op85jcxhh:bif/t separate further?

The form of Coulomb’s law is very similar to that for Newton’s law of universa cjlp,z+d7 zahzi7 e /7*fz,sdl gras 7zcalzz+,7p, * fze7h/di jdvitation. What are the differences between these two laws? Compare also gravitational mass and electric charge.

We are not normally aware of the gravitational or 7d*o4 qjj;hdozd7gy) electric force between two ordinary objects. What is the ;yqo)d7 *4jgdj o zd7hreason in each case? Give an example where we are aware of each one and why.

Is the electric force a conservative force? Why or why not? (See Chapti6 wsr7 eqe d/0z1+cz4 muj0iker 6.)

When a charged ruler attracts small pieces of paper, sometimeu xz -6o p7xus5g3,hlis a piece jumps quickly away auhgp o-3s xl7u6x, iz5fter touching the ruler. Explain.

Explain why the test c o: imngn/2 rzlvs-qo e,3f2g ;/6cuyvharges we use when measuring electric fields must be small,s 6gflynrcn;32o ze qv: moiu2-g//v.

When determining an electric field, must we use a positive test chargbfagc,5:p3 ye e, or would a negative one do as well? Explain.gy, c5efab:3 p

Draw the electric field lines surrounding two negativt 9c9b.s (pc.s ud:qr zi:cu)re electric charges a distanc.spiz 9:cu9 rbqut(c.c:d r)se l apart.

Assume that the two opposite charges in Fig.j.b3t8q j n2zi 16–31a are 12.0 cm apart. Consider the magnitude of the electric field 2.5 cm from the positive charge. On wh3nt2i8qj zb.j ich side of this charge — top, bottom, left, or right — is the electric field the strongest? The weakest? Explain.

Consider the electric field a6gba5cu r8 (wmu, kgjr;i*g5 yt 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 placedcg5r,i g6um(yk;g*bjw 8a5r u at that point, then list the points in order of decreasing field strength (strongest first).

Why can electric field lines nevx 0, * taubwo.rk03ctxer cross?

Show, using the three rules for field lines given in Section 16–8, thmcvrq(- k c(-tkurx 6tjs724cat the electric field line6cxcvr t km(r j(us7 c4q-kt-2s starting or ending on a single point charge must be symmetrically spaced around the charge.

Given two point charges Q b(43omi w -n 1klfp0ct2,zlhz and 2Q, a distance l apart, is there a point along the straight line thatc kto1 z0n izp23 4mwlh-(lb,f 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 charge loca0sb b6gol.0hd ted on an electric field line at some po0 0blsboh.g6d int, such as point P in Fig. 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 oq )x t.edt5r942hkcdz f charge which is infinitely long. (Hint: Use symmetry.) Is the electric field uniform inxdq.e) 2tczkd9r54th strength?

If the electric flux through a closed surface is zero, is the elqug 6-kwq bg::ectric field necessarily zero at all points on the surface? Explain. What abuk :q: -wg6qgbout 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 radius ut( q( (h8goxer. If the sphere is replaced by a cube ofo (8u((eqxthg side r, will $\Phi_E$ be larger, smaller, or the same? Explain.

  

  How many electrons make up a ch) nkmc.tmyn+o.+c6, ekm:q wrarge of $-30.0\mu C\,?$   $ \times10^{ 14}\, electrons $

  What is the magnitude of the electric force of attraction between an iron nuo. w,jqu:m 1kfix 1edy2dp* zh299hhkcleusy*2, xmd1fe jzui2hkq: 9kpoh hw9.1 d $(q\,=\,+26e)$ and its innermost electron if the distance between them is $ 1.5\times10^{-12 }\,m\,?$    $ \times10^{-3 }N$

  What is the repulsive* j3n3fcr7xk j electrical force between two protons $ 5.0 \times10^{ -15}\,m$ apart from each other in an atomic nucleus?    N

  What is the magnitude of the fov7 ght/cdqn2:y7 fc 7mrce a $+25\,\mu C\,C$ charge exerts on a $+\,3.0\,mC$ charge 35 cm away?    N

  Two charged dust particles688uzb:q0 fm zjgu)l m 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 3*w fjx drkx, y + ijx5m0+8h;tf.qegoforce on each of them is found to have been tripled. How far apart are ty,30;ie5 j+*r jfm.g8+xxf kdhxq owthey now?    cm

  A person scuffing her feet on a wool rug on a dry day accum,dd-detiwli,i(s xsa / rv3+1 ulates a net charge of i tils(1/x+i d v -3,,readsdw$-42\,\mu C\,.$ 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 oaa4/4lrx 9t/hz :ar1 hehs o)xf all the electrons in 1.0 kg of $H_2O\,?$    $ \times10^{ 7}\,C$

  Compare the electric force holding the electron n5b:xs y*6usrj0o c 4pin 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 char)g6 s4vwlwz p .v.)tgwges are a fixed distance apart. The sum of their charges is What charge must each have in w4gz.v)t 6lwswgp v ).order to
(a) maximize the electric force between them,
(b) minimize it?

  Particles of charge * ubydo6ocy02; 9)paakiy1qg+nz)e c $+75$,$+48$ 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 equaljqs) blwh:q/t 3i(7x0 r e1kpl 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 si67zp mlf +swd;de. Determine the magnitude +dms 7 l;pwzf6and direction of the force on each charge.
$F_4$ =   $ \times10^{ 7}\,N$
$\theta$ =    $^{\circ}$

  Repeat Problem 14 for the case when two of the positive char)zuuiry+ ulv*+g k 0m.lm9p3x29h*xvkn )ffeges, on opposite corners, are replaced by negative charges of the same magnitude (vmh+ g )9)3f.ix l p2 k 0*z*euumfyn9xvuklr+Fig. 16–51).
$F_4$ =   $ \times10^{ 7}\,N$
$\theta$ =    $^{\circ}$

  At each corner of a square of side l there are point charges of magnitude Q, 6y2o7qb0:m vp hvgg4*s vvi -xk*oz*n2Q, 3Q, and 4Q (Fig. 16–52). Determine the fobxk s g*g*v-h y4 mv:o*z6vnqi20po7v rce 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 corni:vo sg5/+rs/5tifiners of an equilateral triangle of side 1.205soi ti/:gn/vf 5 +isr 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 char ixbcat)ef k)b76vl65 ge 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 total charge*ibyo332h:kbq m ozp sg)n* ,e 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 be( l h.s1 j0w ojk;h(hqlt-tx8)6iqepall to an identical ball 12 cm away. The force of attraction jloxw;t)p.h68h(jhqt0 qs-kl (1iee is then 17 mN. How many electrons were transferred from one ball to the other?    $ \times10^{ 12}$ electrons

  What are the magnitude andaqg) rw7*)pp(f.tjb+j 2xi6 x7fgru y direction of the electric force on an electron in a uniform electric fie()rf2f7.+ xruqjga6j) wb7* xp pytgild 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, and it experiences an ele-r9x;yitx yfb h;w0 /vctric fox/ivwxbh;-; t9yrf0y 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 is6;st .v fegm mm6dx:2e 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 theygo0zr//mnhmb )rg 5 1 electric field 20.0 cm directly above an isolatedom/gzy/h)rr1b0 n 5gm $33.0 \times10^{ -6}\,C$ charge?    $ \times10^{6 }\,N/C$ ----待选择----updown 

  What is the magnitude of the acceleration experienced by an eleciw *db;i,av. jtron in an electric f v;iia,w*j d.bield 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 direction of the elecs37vk rvxoa( qp33k6f6q s+q6,r tyxstric field at a point midway between , 6ofqyr3r( vk3q6kvx3a7x ts+q6pssa $-8.0\,\mu C\,$ 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 ch) u m-ztawc,u9m,wm0uarges, $+Q$ and $-3Q$ which are a distance l apart.

  What is the electric field strength at a point in space where m;ytmsp-u :q 3a 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 fitpn3w0ns gk1 of7r ;b7eld and accelerates to tw;g77b3nnksp0o ft1r he 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 opiuaonngb 620y t0p280 0wiujw posite 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 electric field at the center of a sq96 ptea ;x3z,kmd+q pwuare 52.5 cm on a side if one corner is occupieddk;we+,3xtqp9 p6zam 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+c8l+:he-q l,j zpeo s6zee qp.6ae/g.00 m on a side if the other three corners are occupiedh6aj 8e+eq pe-qgs :e+/z6, lzp loe.c by $ 2.25\times10^{-6 }\,C$ charges.    $ \times10^{4 }\,N/C$   $^{\circ}\,$ from the x-direction.

Determine the direction and magnitude of the electric fto:vl2p-w4.dv3e+ qe an nn2cield at the point P in Fig. 16–54. The charges are separated by a distance 2a, and point P is a distance x from tl nqne-v2:cndw34vao2p .e t+he 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 electric0(w4 vk(r-pjj mn5ma a 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 and direction of the en 6c4)yepb:u-ckm h-t lectric field at points Ab4h :nc)-6 ckep mytu- and B in 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 unknown point charges, l sa4 cte*,j.hlm75nq $Q_1$ 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 anda 0o7ixsqw73u magnitude 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 line joining osui0w7x7a 3q 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 oty fw.)9h mdhh n 3vj:ih+ufg 73.zj(kf light enters a uniform electric field par+w j.t fhhuygh3hj.fn 9(z:dik m v)73allel to its direction 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 );i4d.oc; tdlldqj 9m.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 magnitudafiw4dl ez8 -4-k tkl2e -4ktze liw -842f dkla$ 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 objeoz +a 6ehwk1)scts, $O_1$ 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 uniforxx cz+8e4nz 6u8u 3aaa r+f:okm 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 p g8x6p /4daiislates are 1.0 m on a side and are separated by 3/xsa ii68gd4p .0 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-radiusw)u8 9dbqbmj ydawb 5-*ppq2+ 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 charg.a46y,rcj;g0/ bjpf /d1fjy w wt/aage 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 conductiz5.8dgq ) 6hts*qm o*u+qnmcs ng 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 charge Q aff) tqs*qu qm.sg8m z65ndch +*oect the shell?

  The two strands of the helix-shaped DNA molecule +dz *wljqbqt0f8;kky3-kx:w are held together by electrostatic forces as shown in Fig. 16–44. Assume that the net average charge (due to electron sharing-ywx twdq3k0*:z;+fljq k k8 b) 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 th8nzsnb w6wqpdb8pt)gu7k 0s r*n, 1:ve electric force between them is equal to t:086 ndbpvunz7 pg btr1* swqns,k8w)he weight of either at the Earth’s surface?    m

  A 3.0-g copper penny has a positi0 xi6:x5tjuh -crhco b )ggg91j1z. ch.:lnh ive 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 th.7; j.c(jdu 2zbgxqppat there is an electric field surrounding the Earth. Its z(.cp q 2xjgp b;.7dujmagnitude 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 acce4cb( k4rpf5aou3,hs. qmdgh(*i r 9nyleration experienced by an electron near the surface of thu gp4ys.,ci dh*o r3a r m4qh5(f(kn9be 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 i 7h7k1k emikt g/axi 7k65s8ubn the air. If the downward-directed electric field ofke/thx7 kbg7k6 57iuiksm18a 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 al1ow:9(vg uxm w4pou:zl zn7 0nd the HN group shown in Fig. 16–62. The C and O have chv:10l(oumwz9n7xu l ozg p4:warges $\pm0.40e$, 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 revolves in ae;u87t w pu/zf/*hyhg circular orbit around theuuhz *pyf;h/7g/we 8t 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.uoc.1t lh0k f, rather than gravity, were responsible for holding the Moon in orbit around the Earth. If equal and opposite charges Q were placed on the Earth and the Moon, what should be thc..tou0l 1kh fe 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 spee5i;nxqfrxb7i,4 c- 2,o c00n yghecord $v_0\,=\, 21.5\times10^{6}\,m/s$ 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 charz/17)toev d+q sktc8 age $Q_1\,=\, 2.5\times10^{-5}\,C$. 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 yvmjf0cob hp: ea.:k;lo+eur 6:s /z+and suspended vertically from an ideal spri0z.6bjmyrl;uv +ao:+ ce:o :kfsp/heng $(k\,=\,126N/m)$ 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 wires wixl.)cyk/* ojy th tiny 24-g spherek /cy*.ojlxy )s 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 dxc qs)ua/ xm. 7-cv1wgvew h5+8)kea3l qi9moown and generate a spark if the electric field exceeds about 5l qv) aumkeo3 wxiw -q xvgm8a9c1 c+)/.eh7s$ 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 kgpl 5ku 8v6 ;v:tq7exuzpz7v e(, and net charge $+0.340\,\mu C$, hangs at rest at the end of an insulating string above a large sheet of charge. The horizontal sheet of uniform charge creates a uniform vertical electric field in the vicinity of the point charge. The tension in the string is measured to be 5.67 N. Calculate the magnitude and direction of the electric field due to the sheet of charge (Fig. 16–67).    $ \times10^{7 }\,N/C$  ----待选择----updown 

  What is the total charge of all the electrons in ajhdtzx6i4y,.:sr*qamo , 9qb 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 ard+uxpk)gv6 cguu* i+ss r7 2l*e a distance R apart; each carries the same charge Q. (a) What is the force sphere B exerts on sphere A? (b) An k+xp*g i*slvgucs2d7)+u 6ur 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? (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 is dwp.usjzrct:r+) 8gn:m1 cyp(pts- + the electric +:mtj1spzc+. -yg c )nw8:turr(psdpfield zero? Is the 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 kc su7,dy+gt 0point charges, 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?