If you charge a pocket comb by*,zevdl;7a8sc:vcyhcar/+n fsl, 6p rubbing it with a silk scarf, how can you determine if the comb is positively or negatively ca/;7 c,rnv6:,+8asde z*fcp csvlh lyharged?

Why does a shirt or blouse taken from a clothes dryer sometimes 7e;(z ax+2n wzu1f)8 hcvlqlpcling to your body?cw)qxpuzeh7l+l 2 az8( 1n;fv

Explain why fog or rain droplets tend to form around ions or elecc4iw 7zq5f8hnwwy30ys, f8j mtrons in the air.nw 5mjh3 fyfs 8w48 ci,qy7zw0

A positively charged rod is brought close to a neutral piece of paper, which itw.k( h,rr.qwd3 pls8i attracts. Draw a diagram showing the separation of charge and ex.ipr slw3d,k8 h.rqw (plain why attraction occurs.

Why does a plastic ruler that has been rubbed with a cloth have the ayg1gn x kd*3pm7e*fo :srf:* ability to pick up small pieces of paper? Why is this difficult to do on a humid day?ygfep1: * 3 m7fnskxa*rdo g*:

Contrast the net charge on a conductor toil30ibwm 7iw*uzoe7h w g +-7h the “free charges” in the conductor.

Figures 16–7 and 16–8 show how a charged rod placi1 qca*(tys )aed near an uncharged metal object can attract (or repel) electrons. *a s1iyt)(ca qThere 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, its2 tvzy+a we-k; two leaves repel each other and remain at an angle. What balances the electric force of repulsion so that the leaves don-v2zke twa;+y ’t separate further?

The form of Coulomb’s law is very similar to that for Newton’sklo4 z+5/mo nh law of universal gravitation. What are the differences between these two laws? Compare also gravitalz5n 4moh+/kotional mass and electric charge.

We are not normally aware of the gravitational or electric force betweejew -kgah +z-7 sor5g3 8zzq.;tco lg3n two ordinary objects. What is the reason in each case? Give an example where we are eg g8z.th+5;37ooq3 z- w gcakrz-jl saware of each one and why.

Is the electric force a conservative force? Why or whixu7k lvc9y ec3h- d31 y05mdjy not? (See Chapter 6.)

When a charged ruler attracts small pieces of paperye2aa0oo0 jo ;g0yhx1, sometimes a piece jumps quickly away after touchi a02 10ao;xohjegy0oyng the ruler. Explain.

Explain why the test charges we usn di8m,a qf01ye when measuring electric fields must be small.81,m0 adifn yq

When determining an electric field, must we use a positive test chargei)nr 7gjwuy2;7-g ;v 3r3qgdb4obzs o, or would34r;bgw3;go2 y nb i7s qz)g-dj7 vruo a negative one do as well? Explain.

Draw the electric field lines surrounding two negative +s ;t.zqvdq;relectric charges a distance l .;+z d;vr qstqapart.

Assume that the two opposite charges in Fig. 16–31a are 12.0 cm aplo 3:)dor1uux v vz4,kart. Consider the magnitude of the electric field 2.5 cm from the positive charge. On which si)vku lor o:x 3dvz41,ude of this charge — top, bottom, left, or right — is the electric field the strongest? The weakest? Explain.

Consider the electric field at poldzd++zz h.yt 6sq.u7ints 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 placed at that point, then list the points in order of decreasing field strength (z szhdq6ty.+ +.ludz 7strongest first).

Why can electric field lines never cr,3yya tf,s9pk(qu 5taafe4 j (x sga2(oss?

Show, using the three rules for) * ;i8:zowm6oe lp fh1jiq*vm field lines given in Section 16–8, that the electric field lines startiizo;*jqf m*:lovwi )h ep618mng or ending on a single point charge must be symmetrically spaced around the charge.

Given two point chargtq skcp0o,5 (s)rlwo)es Q and 2Q, 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? Isr5skcl)(tq)o 0 p,wof yes, state roughly where this point will be.

Consider a small positive test charge located on an electric fi8f8 wdquy/u220uox/, ahxenqeld line at some point, such as point P in Fig. 16–31a. Is the direction of the velocity and/oyx,x8/a/n0dweu 8o2h u qquf2r acceleration of the test charge along this line? Discuss.

Sketch the electric field lines for a unifb/s()m0kvlmgs *)hq z f vo((dorm line of charge which is infinitely long. (Hint: Use sbv((kvo f)0g s*/h (slmm qdz)ymmetry.) Is the electric field uniform in strength?

If the electric flux through a closed surface is zero, islh5;+ aq5c2v6gvvse n the electric field necessarily zero at all points on the sur65c 5qnhlv+ sv2vge; aface? Explain. What about the converse: If $\vec{E}\,=\,0$ at all points on the surface is the flux through the surface zero?

A point charge is surrounded by a spherical gaussian surface of radiusa-qjaro(ar7:l4, 8fgmh gk*f r. If the sphere is replaced by a cube of side r, will-ga*fh(jagq7 aof4lkr:8r ,m $\Phi_E$ be larger, smaller, or the same? Explain.

  

  How many electrons make up a cc,0 1vodusuaa xd*9 4i*o5shuharge of $-30.0\mu C\,?$   $ \times10^{ 14}\, electrons $

  What is the magnitude of the electric force o7n kky el2gttmch/ea5:,8 x.if attraction between an iron nucleuc. ate /x,nmkil: 5htyeg782 ks $(q\,=\,+26e)$ and its innermost electron if the distance between them is $ 1.5\times10^{-12 }\,m\,?$    $ \times10^{-3 }N$

  What is the repulsive electrical forcew 8pf4 kdpqsek3( +w2h between two protons $ 5.0 \times10^{ -15}\,m$ apart from each other in an atomic nucleus?    N

  What is the magnitude ok /qe+dh/adpb p 3b+s2f the force a $+25\,\mu C\,C$ charge exerts on a $+\,3.0\,mC$ charge 35 cm away?    N

  Two charged dust particlkk05 p 2;yyib 6*ohwv 6ycg*fnc+1juees 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 moves 24v5 a02vtkh,j( p8sjvcvbr qy/2g yd, and the force on each of them is found to ha2,j84/yyj qvpv5s 2t0kbsv ( rcgvah2ve been tripled. How far apart are they now?    cm

  A person scuffing her feet on a wool rug on a dry dai .(jcrf-m zqyk1q15ay accumulates a net charge ofmqy5faq cr (i-1z1 jk. $-42\,\mu C\,.$ 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 ofok/8p 0 8b0cap9l)6goe xcant all the electrons in 1.0 kg of $H_2O\,?$    $ \times10^{ 7}\,C$

  Compare the electricob i:,llx2t7 tv. k,bd force 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 distw;:ea 89wi 2ayjzxb4ho g:9piance apart. The sum of their charges is What charge must each have in order i4 ox;wwjy e29ba z::9ig8pha to
(a) maximize the electric force between them,
(b) minimize it?

  Particles of charge s6 njn .:ci)cg5 )wgy 8-vjlft$+75$,$+48$ 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 particlel j;,zttp-q y u:s*;ncs 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 0.10kp8lod.tzaq x g2 q*9/z/ -sdx0 m on a side. Determine the magn- * p/ l8qo.dzgd/ k9qs2atxzxitude and 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 charges, on opposiy;uckxy - 9bn4te corners, are replaced by negative charges of the same magnitude (Fig. 16–51). ;-yu yn4b9cx k
$F_4$ =   $ \times10^{ 7}\,N$
$\theta$ =    $^{\circ}$

  At each corner of a square of side l there are point charjto /a;xl;kf3:+od6w pofj(;t av ;lvges of magnitude Q, 2Q, 3Q, and 4Q (Fig. 16–52). Determine tlpowjdft;j;/( ka vfolv +:;6o t3x;ahe force on (a) the charge 2Q, and (b) the charge 3Q, due to the other three charges.
$F_{2Q}$ =    $\frac{kQ^2}{l^2}$
$\theta_{2Q}$ =    $^{\circ}$
$F_{3Q}$ =    $\frac{kQ^2}{l^2}$
$\theta_{3Q}$ =    $^{\circ}$

  Three charged particles are placed at the corners of an eqds 3y3/o,hpj vuilateral triangle of side 1.20 m (Fig. 16–53). The charges arpdyh,3s/jo3 ve $+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 charz l(aw-5nf-(rr va9at .l-wdwge 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 sphe+hiw9( po k)via:h2i fres have a total charge of $90.0\,\mu C\,.$
(a) When placed 1.06 m apart, the force each exerts on the other is 12.0 N and is repulsive. What is the charge on each?    $ \times10^{ -6}\,C$$\;\;\;\;$    $ \times10^{ -6}\,C$
(b) What if the force were attractive?    $ \times10^{ -6}\,C$$\;\;\;\;$    $ \times10^{ -6}\,C$

  A charge Q is transferred from an initis+4od y;8 g(mh/sjqxmz78*c kbpstg9ally uncharged plastic ball to an identical ball 12 cm away. The force of attraction is then 17 mN. How many electrons were transferred from one ball to the other?;m+g7 q4y s8j bs s8g hcpd(xo/k9z*tm    $ \times10^{ 12}$ electrons

  What are the magnitude and direction of the electric force on an electron ohw jp5d 2ub-8in a uniform elew-pd8 ob5jh 2uctric field of strength $2360\,N/C$ that points due east?
   $ \times10^{ -16}\,N$
 ----待选择----westeast 

  A proton is released in a uniform-tsr7r3u 7otrb + 3bzm electric field, and it experiences an electric force o ro7ru tz-sbmt33r+7b f $ 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 e-jnvm c40rfn.xerted 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 euz 6p+ la2nj 23craxj.lectric field 20.0 cm directly above an isolatedxn ac36a2 j +rjpzu.l2 $33.0 \times10^{ -6}\,C$ charge?    $ \times10^{6 }\,N/C$ ----待选择----updown 

  What is the magnitude of the acceleration experienced by an electron in an electpybz ny p(csd6jgvd )* 4ei7dk:r07w (ric fie w7d )d6grs0ycdzp:bkepj*iv(7y4(nld 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 field at a pjl0j9 jlg- 2 cs-6sbn wfl4ye;oint midway betweengy 69sl fej n-40ljb2l -;jcsw 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 fienqqxsh4t * ph+69 0brhld lines about two point charges, $+Q$ and $-3Q$ which are a distance l apart.

  What is the electric field strength at a point in space where a proto vo3r1pe.5dc in $(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 elscm79ul./.s + z pvwpzectric field and accelerates to the norl w v9ppsz. msc7uz+/.th 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 oppos1a*i mt myv4:6c cvzf:ite 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 ae yagju4oiwb*3l* f23mjr g)w9q7nn. square 52.5 cm on a side if one corner is occ4qownewy 3 rgig)*m9abu3*f.l 72 jnjupied 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 electric1s2tmxgub/q 42/ jbar field at one corner of a square 1.00 m on a side if the other /4/1a2gbu smbjx 2qrtthree corners are occupied by $ 2.25\times10^{-6 }\,C$ charges.    $ \times10^{4 }\,N/C$   $^{\circ}\,$ from the x-direction.

Determine the direction and magnitude of the electric field at tk i*x9igdhy 7v 13dd5 dw*g)axhe point P in Fig. 16–54. The charges 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, x7)gd9 d kighwv y*a35dix*1dx , 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 electr 8; 7vrmn4h*huj zcye4pr3tbt,pb2t 7ic 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 ano7kv o,fvg))nd direction of the electric field at points A and B in Fig. 16–5nfkovg v)o ,)77 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 poio,a ; hps(sx(k t c*9bmm0s8m5t5kjqt nt 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 poin)l7y (4a i zyrue7,uh8dj(moxt P shown in Fig. 16–59. The two charges are separated by ajy,ihdx(y 7 8( zum7er u4)lao 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.ttd7qp.z jl5 x86( yol0% the speed of light enters a uniform electric field parallel to its direction of motion. If the electron is to be brought to rest in the spacpd(lt6o75x.8 zql y tje 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 8d+ru1oki2)upru-r ca /mcllb,/4lh 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 placed in a uniform elehz v;p c6)1nzyctric field of magnitude 1zphn)v;ycz 6$ 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 objectu: 6)jyp:v q2ijvt+vu ;lhjc 9z+* lnqs, $O_1$ 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 place98yh q cvjbb/111mt vhd in a uniform field $ E\,=\,6.50\times10^{3 }\,N/C$ with edges parallel to the field lines.
(a) What is the net flux through the cube?
(b) What is the flux through each of its six faces?

  The electric field between two square metal plates v-e sd28 /dswvis The plates are 1.0 m on a side and are separated by 3.0 cm. What is the charge on each plate (assume equal and opposite)? e-/8d svsdvw2Neglect edge effects.    $ \times10^{-9 }\,C$

  The field just outside a 3.50 1 b:/z2xxgezj-cm-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 radiuswx 0m c4s.aa;t 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 an9w9+g: gpw , wjtl0rrer +iro3s66jht the center of an uncharged thin spherical conducting shell. (See Fig. 16–33.) What is the electric field E as a fuw3j:ip+ nte, jh ror rl6+rw9ws0 69ggnction of r (a) for r less than the inner radius of the shell, (b) inside the shell, and (c) beyond the shell? (d) Does the shell affect the field due to Q alone? Does the charge Q affect the shell?

  The two strands of the y p .pn4rx:3rlhelix-shaped DNA molecule are held together by electrostatic forces as shown in Fig. 16–44. Assume that the net average charge (due to electron sharing) indicated on H and N atoms l.n3prpx4yr: 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 elxx5 g immm55/2bg0 l9spd3eqoectric force between them is equal to the weight of either at the Earth’s surfac2smgxoeg03 p9lm5mdq / x55bie?    m

  A 3.0-g copper penny has a positive charge of;tr3x)eu io19 rswou/ $38\mu C$. 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 tokp, 0o(unc -n: +hhl8mfynu)hat there is an electric field surrounding the Earth. Its magnituc)umhpln0k+8y: , nnou(h-ofde 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 fiel31-wnlc- sv bu)ebs6 ld of what is the acceleration experienced by an electron -6ln-v sl) bsc1be3uwnear 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 0.018 mm remains statij+x. r7q nlaxq :k*/fmonary in the air. If the downward-directed electrqf j.n7xrk maxq :+*l/ic 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 th1p tq-k-;mjtd ldhv*, e CO group and the HN group shown in Fig. 16–62. The C and O havet lk-thj dp;1dq* v,-m 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 atom, .he/qjbo 9rsakg1(( bthe electron revolves in a circular orbit around the sbrh(jk /1(aq9 .goebproton with a speed of $ 1.1\times10^{6 }\，m/s,$. Determine the radius of the electron’s orbit. [Hint: See Chapter 5 on circular motion.]    $ \times10^{-10 }\, m$

  Suppose that electrical attraction, rather tmc+ vo nt67j r: v,chv86 0or3rtgmb2rhan gravity, were responsible for holding the Moon in orbit around the Earth. If equmom87cg+r26tb 6nh, ot: c3jrr vv0rval and opposite charges Q were placed on the Earth and the Moon, what should be the value of Q to maintain the present orbit? Use these data: mass of $Earth\,=\, 5.98\times10^{24}\,kg$, mass of $Moon\,=\, 7.35\times10^{22}\,kg$, radius of $orbit\,=\, 3.84\times10^{8}\,m$. Treat the Earth and Moon as point particles.    $ \times10^{13 }\,C$

  An electron with speed; w2i itam4t7ee7yx; h $v_0\,=\, 21.5\times10^{6}\,m/s$ 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 char4k/ym y6 iq7xige $Q_1\,=\, 2.5\times10^{-5}\,C$. 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 susp wkti.b. f+z,5e o8apnended vertically from an idizb.8pk 5 ,f ewo.ta+neal 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 “ (+y.qxi3dsgkjf cmzt g(-w ;1leaves” that are 78-cm-long wires with tiny 24-g (i gy j;qx-sd 13+mktg(zfw.cspheres 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 *v m6pa95ubo7,e stls 6md 6itgenerate a spark if the electric field exceeds about m, da6l6* uv msb5e9tsi7p6to$ 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 5xlgv+n6ev g1s 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-kg bar of alum.kt v f:;;lgt-yjlom 4inum?    $ \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 conduc0+ ./kmacpfv xting 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 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) S0 akv+ .p/mxfcphere 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 the elec: *x:t 3 7artvkqb3cm; ean9ditric field zero? Is the field zero at any other poict;*97n avtdqia:bmx3e r 3k :nts, 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, pbdc,5i3j z d*h7jj.)h. wgvseach 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?