If you charge a pocket comb by rubbing it with a si:3j hpv0yhjhn.+v 4k ulk scarf, how can you determine if the c 3 pk0hu.hjvyv+:nhj4omb is positively or negatively charged?

Why does a shirt or blouse taken from a clothes drs)-x48w ir bjiyer sometimes cling to your bod4)rwx -8 ibisjy?

Explain why fog or rain droplets tend to form around ions orso4p+ mc xoi(ctnm*t(b,7r ,r electrons in the air ,poinr+c *7( ,rm xmot4btcs(.

A positively charged rod is brought close toe(nb*q5hcy6 r a neutral piece of paper, which it attracts. Draw a diagram showing the separation of charge and ec5(rhy6 nqe*bxplain why attraction occurs.

Why does a plastic ruler that has been(m7i7cpj4qj d rubbed with a cloth have the ability to pick ud7q4m7 p(jijc p small pieces of paper? Why is this difficult to do on a humid day?

Contrast the net charge on a conductor to the “free charges” ckde h9m l),dc k.r+8:kq e6stin the conductor.

Figures 16–7 and 16–8 show how a charged rod placed near an unch oore4b 4fd9:de.t9tzyih(9parged metal object can attract (or repel) electrons. There are a great many electrons in the metal, yet only some of them move as sh9r9d 4b4zi.eo d : ftophte9y(own. Why not all of them?

When an electroscope is cha(x,kvq2x r6whf xv, w3rged, its two leaves repel each other and remain at an angle. What balances the electric force of repulsion so that the leaves do23khv x(vwfx,r, w6qxn’t separate further?

The form of Coulomb’s d y-t/ap8jbd3law is very similar to that for Newton’s law of universal gravitation. Wht-p dj3dby a/8at are the differences between these two laws? Compare also gravitational mass and electric charge.

We are not normally aware of the gravitational or electric force betweebhumjf 48qlfx (0uz 69h;k)i jn two ordinary objects. What is the reason in each )juqu69b0lm;xz8 i k4hhff j( 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 Chapter oq :,jw* x4nac6.)

When a charged ruler attracts small piece pf75w ils6 q+d5uzxzec59(ujs of paper, sometimes a piece jumps quickly away after touchic+es5 xz(69jifl5 zw 7dpu5uqng the ruler. Explain.

Explain why the test charges we use when mea 2-+tvmz (eajssuring electric fields must be smallet+ mzjas-v(2 .

When determining an electric field, must we use a p7cye,l1+tf+vg)g:* uwyrv b mositive test charge, or would a n ytlrc7me1v+ *wg+uv,b g yf:)egative one do as well? Explain.

Draw the electric field lines surrounding two negative elejfx( ()ttf6:ymt qmm /ctric charges a distance l (jftt/tfm( :my)6q xm apart.

Assume that the two opposite charges in Fig. 16–31a are 12.0 cm apart. Considekn.lh. zpw5 6gr the magnitude of the electric field 2.5 cm from the positive chhwn65gzpl. k. arge. On which side of this charge — top, bottom, left, or right — is the electric field the strongest? The weakest? Explain.

Consider the electric fieldfblw8cnu,l6nw-o4 c d+3p)q8 b6j*h 5daz cas at points A, B, and C in Fig. 16–48. First draw an arrow at each point indicating the direction of the net force that a positive test charge would experience if plac hlf658-a+bq4p dz*3ucwsadn)6, nc l ocbw8j ed at that point, then list the points in order of decreasing field strength (strongest first).

Why can electric field lines never crossue webfrjq9p, co*7.b.m +c: l?

Show, using the three rules for fieldw b4 zif9efhsrml -r:ni7d:. ri(*2g zgag 5h+ lines given in Section 16–8, that the electric field lines startind9smrhiehl fg:4i gn.( r2w zg:7+5 bz*-fiarg or ending on a single point charge must be symmetrically spaced around the charge.

Given two point charges Q and 2Q, a distaby u+4 y dx ;fetwd54z3hqrmuf*+ 6f6xnce l apart, is there a point along the straight line that passes through them wherrt*ed y bhxyf4;qm+ 3+z46duf x6uw5 fe 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 chaw gl,j1u ody:(rge located on an electric field line at some point, such as point P in Fig. 16–31a. Is the direction of the velociu (oj1l:y,wg dty and/or acceleration of the test charge along this line? Discuss.

Sketch the electric field lines for a uniform line of charge which i4ov,vsnjfd b:ed: r4 7s infinitely long. (Hintv44vn ,r :j7 esdb:dof: Use symmetry.) Is the electric field uniform in strength?

If the electric flux thr8c:e tmi0a vx1ough a closed surface is zero, is the electric field necessarily zero at all points on the surface? Explain. What about th1x 0e8tc ima:ve 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 gauss tu8/ us7yc3xzcmzv(l7f +8zpian surface of radius r. If the sphere is replaced by a cu st7z 8(uymuz/78cc3p fvz+xlbe of side r, will $\Phi_E$ be larger, smaller, or the same? Explain.

  

  How many electrons make up a ch0ex3ryhj+)t k 4ta,voarge of $-30.0\mu C\,?$   $ \times10^{ 14}\, electrons $

  What is the magnitude of the electric force of attractiagh0rw 06 o)zmon between an iron nucleuswz rg amho600) $(q\,=\,+26e)$ and its innermost electron if the distance between them is $ 1.5\times10^{-12 }\,m\,?$    $ \times10^{-3 }N$

  What is the repulsive electrical force between two protonspq/ 7chz +fcxn77j8 dz $ 5.0 \times10^{ -15}\,m$ apart from each other in an atomic nucleus?    N

  What is the magnitude of the force a) ao*f 3bvr(su $+25\,\mu C\,C$ charge exerts on a $+\,3.0\,mC$ charge 35 cm away?    N

  Two charged dust particles exer8/z fv jv8ug9zt 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, an :2o:7+r a-a mxqmwlbsd the force on each of them is found to h+qalm 2w7sx ob ::arm-ave been tripled. How far apart are they now?    cm

  A person scuffing her feet on a wool rug on a dry day acmg0iz7s9 hc2;job2t w uj0 zo1cumulates a net charge of zobowg01h0jm 97izs ;c2j t 2u$-42\,\mu C\,.$ 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 electronsyqwfuz*xs/4 hd0 ,j/kum a9h) in 1.0 kg of $H_2O\,?$    $ \times10^{ 7}\,C$

  Compare the electric force hol8 rnv5nj98gp qqx ;fj:ding 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 fii9jdpkj 5 9i/ixed distance apart. The sum of their charges is What charge must each have in order to 9jid9i/ij5 kp
(a) maximize the electric force between them,
(b) minimize it?

  Particles of charge ups qh/ 5nkg)6$+75$,$+48$ and $-85\,\mu C\,$ are placed in a line (Fig. 16–49). The center one is 0.35 m from each of the others. Calculate the net force on each charge due to the other two.

$F_{+75}$=   $NN$
$F_{+48}$=   $NN$
$F_{-85}$=   $NN$

  Three positive particles of equal+ 8 eiv6(wbsds 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 n5,o ghxh514n zk15pm qgrv)aa side. Determine the magnitude and direction of the forc1hkgh 1 anop45z, qnrx55g)vme on each charge.
$F_4$ =   $ \times10^{ 7}\,N$
$\theta$ =    $^{\circ}$

  Repeat Problem 14 for the case wh3qj f,qh7qwq)o:m 0jb en two of the positive charges, on opposite cor7qo:qm bj)j 0f ,q3hwqners, are replaced 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 ,kqle4; ubm :s9r4.byi2z7cowjlp z-point charges of magnitude Q, 2Q, 3Q, and 4o;4zwu7z.y4llb m:ik,sb c2pj9re- qQ (Fig. 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 thebg*q1p0 /bmvb corners of an equilateral triangle of side 1.20 m (Fig. 16–53). Tgb/1*p0 q bbmvhe 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 charge orm-5x94 ivosv84zxvh f $560\,\mu C\,.$ 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 havea r w/ej8-l1jy 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 p r0n25 :.9q*(wz6caa/ prdkvmmcdpqf lastic ball to an identical ball 12 cm away. The fordr5 w/z(c rf6av0 nqppmc.*:mdqa 92kce 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 fo)sly .x/ t3pl) 3ojxeorce on an electron in a uniform electric fiej /y3x)lp.sext l3o) old of strength $2360\,N/C$ that points due east?
   $ \times10^{ -16}\,N$
 ----待选择----westeast 

  A proton is released in a uniform electrih/b)uprz2y: g8tf n )rc field, and it experiences an electric force g 8 )b/p:htfy)urn2zrof $ 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 exertedk ()pc,otdsi1 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 cmsf ebo 2h5y(uv- rn+v n.vvf58 directly above an isolat v(v-fu. enr+s5o8hnvyb2 f5ved $33.0 \times10^{ -6}\,C$ charge?    $ \times10^{6 }\,N/C$ ----待选择----updown 

  What is the magnitude of the acceleratis wj+je/k*i/y/pv, z5pj: jrmon experienced by an electron in an electric firjs/+p y* zkj /:,5jvwm/e ijpeld 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 electric fiel 1iq 3)0ijx )he:ky,wpyanlgh iu)w 47d at a point midway between a k0:iu1)) w ,hge7q lyh)i4xapy wi 3nj$-8.0\,\mu C\,$ 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 xeirgob+iiw6 m) 1:3r7zc9et field lines about two point charges, $+Q$ and $-3Q$ which are a distance l apart.

  What is the electric field stren3 cmxakw5jk;4 uis 8olx .e blj9(5q-ogth 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 inpq20qn*r1 ;c m e5tnldm:. pyjb+kizb m1zs // a uniform electric field and accelerates to jdr05i+y m*cq/p1nz kp1/bb zqtse.:lmn m ;2the 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 two3fqy8 2(kslvu 8m/s*yj 8izfj 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 electric field a e*4u(ivd2xvj t the center of a square 52.5 cm on a side if one corner is oc2 ivv4*je(dxu cupied 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 1.00 m on a side if the o 2an52jg8tcd athgdna2t8a c25jer three corners are occupied by $ 2.25\times10^{-6 }\,C$ charges.    $ \times10^{4 }\,N/C$   $^{\circ}\,$ from the x-direction.

Determine the direction and magt b5bde2i tp-9qif uv;lew83+nitude of the electric field at the point P in Fig. 16–54. The charges are separated by a distance 2a, and po 9t3 tbvqi5;eu2 fbd+pl-8w ieint 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 elw)cmeh/ )/9t/rfw ;;ux ax ztrectric 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 determin h.s q91lq-mnqo ,(a+z tlnr/fe the magnitude and direction of the electric field at points A and B in Fig. 16–57 / zqs,.qrtn 9a hl f-l+q(mon1due 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 p. i. du(vnxyr+oint 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 magnitude of the electric field at the point P mhr, 6us ;6g8e k*n.bzeatxs7shown 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 mirstsz bxmge* a.6 76u ,hn;8ekdpoint 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/bk9.j2qj xn v.0% the speed of light enters a uniform electric field parallel to its direction of motion. I xkjn/ b9qv2j.f 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 flux1/beb f brx+w/ 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 e mp,q,,.o:ha/ )/hf myustcnis placed in a uniform electric field of magnitude n.o a/h/,),:cye,qst pumf mh$ 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 olau9 go9* ge6ouq5az .e57gdebjects, $O_1$ 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 placed42 ifn;+elz6k1s+i 7vpc :q sbvp3mvt 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 s25 lc3e4kg yb;k,mi mdquare metal plates is The plates are 1.0 m on a side and are separated by 3.0 cm. What is2b5m3, m edic;gylkk4 the charge on each plate (assume equal and opposite)? Neglect edge effects.    $ \times10^{-9 }\,C$

  The field just outside a 3.50-cm-radius hyzua:d5 - k9 vxwke81metal 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 wk roe2u)mvoz lw-0ao 3-,:uxof radius 3.00 m carries a total charge of $-3.5\mu C$ What is the magnitude of the electric field at a distance from the sphere’s center of
(a) 0.15 m,   
(b) 2.90 m,   
(c) 3.10 m,    N/C
(d) 6.00 m?    N/C
(e) How would the answers differ if the sphere were a thin shell?

A point charge Q rests at the center of an uncharged tgc9:+ wk )dfoccf.l 9phin 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 she9)l. cp: f9d+ogwkfccll? (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 DNA molecule are held together bev.6glot :q;e dp8 n*lzj)qm)y electrostatic forces as shown in Fig. 16–44. Assume that the net average charge (due to electron sharing) indicated on H and N atoms is 0.2e and on thegem6)e*pt o lj:q).ld 8;vnqz 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 t)7g qx5 fy,ajbhem is equal to the weight of either7 j5x)bgfqy,a at the Earth’s surface?    m

  A 3.0-g copper penny has ae0ypq,bv7(hx* 7 gk nm positive 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 that there is an electric /io5 1+wj x7,2ua;y qcjql ilpfield surrounding the Earth. Its magnitude is ab;ol 5/cwx ,yqq21ua 7jpl+ji iout $150\,N/C$ 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 wh9/( oxbhirl +mat is the acceleration experienced by an electron near the sur 9oxhi(l /mrb+face 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 0.018 mm k 6,faf ioqu-4remains stationary in the air. If the downward-directed electric field of the Earth i q-6 ,fo4afikus $150\,N/C$ 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 in Fig. 1ixd z05awp2)zfp3 b6 f6–62. The C and 5)zaf3zpf2d x0biw6p 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 hh:- ipecd65r nydrogen atom, the electron revolves in a circular orbit aroundcdr5 e- pih6n: 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 attuil8o,6t) qhx raction, 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 u 6t,lhxqo8i)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 k e0i1t..ui7ysl,jgx$v_0\,=\, 21.5\times10^{6}\,m/s$ 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 chargy:w )9fkp fdc.23s1h yysi; iaswka 6-e $Q_1\,=\, 2.5\times10^{-5}\,C$. 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 s/.-jy5hdh wek2es*-0:tecs id w5xc xuspended vertically from an ite0-dwcwh se x* k j5c.ysd/h2 :-x5iedeal 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” that are 78-cm-long wires wi(qwemm4*paf.b *w/ yhth tiny 24-g spheres at the ends. When charged, nearly all the charge resides on the spheres. If *q(4w eb*fwmh m/ py.athe 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 excb8dkajg j-h2. eeds aboutaj8kj2b-ghd . $ 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 mas 4znpkk(y cqp271k(sss 0.210 kg, and net charge $+0.340\,\mu C$, hangs at rest at the end of an insulating string above a large sheet of charge. The horizontal sheet of uniform charge creates a uniform vertical electric field in the vicinity of the point charge. The tension in the string is measured to be 5.67 N. Calculate the magnitude and direction of the electric field due to the sheet of charge (Fig. 16–67).    $ \times10^{7 }\,N/C$  ----待选择----updown 

  What is the total charge of all the electrons in a 15-/kp7x1qj /tb z p4eq6ol evvu*f.t;3 ukg 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 apae2 4qrakwttcbe. ud0 ;rm7 82yq k*f2krt; each carries the same charge Q. (a) What is the force sphere B exerts on sphere A? (b) An identica t 20yfw8b*ktq4mce.ku; ek22rqd r7al 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–fxyyz7*; /r fk68, at what position(s) x is the electric field zero? Is the field zero at any other pointsxy*/k ;f fzy7r, 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, ehmrfwoyyi2xqbdomof q57a; wxl:6,; p 9(.q8ach 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?