If you charge a pocket comb by rubbingf .ma vpd;9dxy5 ) 28p3gmrril it with a silk scarf, how can you determine if the comb is positively or lar m) fxpgm.d3;8 ri5v92ypdnegatively charged?

Why does a shirt or blouse taken from a clothes dryer sometimes cling to jo5 .6 a5iyxyeyour boa ix.e o56jyy5dy?

Explain why fog or rain droplets tend to form arou7s-6xdeomz f 0nd ions or electrons in the ai0mo-z s f7xd6er.

A positively charged rod is brought close to a neutral piece of pa 9r. x +07ie-gfuvm)a /piafreper, which it attracts.i+rfr7ev0aixpf .9/m)-g e ua Draw a diagram showing the separation of charge and explain why attraction occurs.

Why does a plastic ruler that has been rubbed with a cloth have the ability to pinapx 7on0u(, ick up small piecoa xnun,i(7p 0es of paper? Why is this difficult to do on a humid day?

Contrast the net chardhrw32h ,os5 qa+ r6gtge on a conductor to the “free charges” in the conductor.

Figures 16–7 and 16–8 show how a charged rod placed near an uxg+/ n*c;iuqfmkv, v5 yc8 (s (1pkldgncharged 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 allk/d1,ymnpg(c v ks clui;x +* 5vq8g(f of them?

When an electroscope is charged, its two leaves fuys;h+q4p,m repel each other and remain at an angle. What balances the electric force of repulsion so tp+ym4fu,sh ;q hat the leaves don’t separate further?

The form of Coulomb’s law is very similar to that for Newton’s law nm9agzz:er(q;9 lq ;td72dmo ef2pf; of universal gravita;o n2zq dfq7me2z9;tfgdm:9 ep r;( lation. What are the differences between these two laws? Compare also gravitational mass and electric charge.

We are not normally aware of the gtnc2d1i4l v /3)swig sravitational or electric force between two ordinary objects. What is the reason in each case? Give an example where we are aware of eacv23l/g) cn ts14dwsiih one and why.

Is the electric force a conservative force? Why or why n;+/ks0 f;yw1ou w (vbenoht)wot? (See Chapter 6.)

When a charged ruler attracts small pieces x f71aaj*q7aqof paper, sometimes a piece jumps quickly away aft*xq7qaf a7 1ajer touching the ruler. Explain.

Explain why the test charges we use when measuring electric fielk h*h h 08c8qbzh*rpq m d73hd7n/y;vzds must be smallr/chq7 *h38d dzz0*;qhn ym 7hphbvk8.

When determining an electric f2wulaw hj1)ap)a a(0x0 uz3ltield, must we use a positive test charge, or would a negative one do as well? Explain axu3 wt2(p j 1auah00)az)llw.

Draw the electric field lines subnrm 7d:g0b(qts ne fit686,wrrounding two negative electric charges a distance l apatwisdt(r eb n 6bn678f:q,0gmrt.

Assume that the two opposite charges in Fig. ccgq 3/ee,wyv(kehk9d20s .s 16–31a are 12.0 cm apart. Consider the magnitude of the electric field 2.5 cm from th0 wshq.vg,2ek/e(9kccs e3yde positive charge. On which side of this charge — top, bottom, left, or right — is the electric field the strongest? The weakest? Explain.

Consider the electric field at points A, B, and C4.-wpcz/mm sp, lm ni0 in Fig. 16–48. First draw an arrow pmnsic0- lp.zw4/m ,m 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 (strongest first).

Why can electric field lines never crw/w iwx3m+wcf *+.cugoss?

Show, using the three rules y94( gc b xbju1-gqor9for field lines given in Section 16–8, that the electric field lines starting or endingbu99gry q(-j4g bo1c x on a single point charge must be symmetrically spaced around the charge.

Given two point charges Q and 2Q mgppiv/3z7w1:ak fu (0xhddz5i0 -sk, a distance l apart, is there a point along the strai/w(gak53x0 7v zmifdspu ihdpk:z-1 0 ght line that 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 loctjjp wk p;6qq+wq9 :w2ated on an electric field line at some point, such as point P in Fig. 16–31 +qj2k 6w;wwpq:9pqjt a. Is the direction of the velocity and/or acceleration of the test charge along this line? Discuss.

Sketch the electric field lines for a unnsurpi(**4o b 6 1qvqyiform line of charge which is infinitely long. (Hint: Use symmetry.) Is the electric field uniform in str iupv (qoybs n**q614rength?

If the electric flux through a closed surface is zero, is the electric fwo c+,:lcigbn0 jsq; )ield necessarily zero at all points on the surface? Explain. What about tg;+i):sw0jcbnl cq, o he converse: If $\vec{E}\,=\,0$ at all points on the surface is the flux through the surface zero?

A point charge is surrounded by az((o2 u d .s-pskwicpjvopo2b45x)v( spherical gaussian surface of radius r. If the sphere is replaced by a sspixpk u2(cpj2)vo (z d .o-v w(45bocube of side r, will $\Phi_E$ be larger, smaller, or the same? Explain.

  

  How many electrons make4 lxe9sbp++ cj up a charge of $-30.0\mu C\,?$   $ \times10^{ 14}\, electrons $

  What is the magnitude of the sz6 yhfu0i 5b8n ,uo0oelectric force of attraction between an iron nucleus0uhzy8oi50 f6nbo u,s $(q\,=\,+26e)$ and its innermost electron if the distance between them is $ 1.5\times10^{-12 }\,m\,?$    $ \times10^{-3 }N$

  What is the repulsive electrical ford:f8dmcutv0-9 omr z2ce between two protons $ 5.0 \times10^{ -15}\,m$ apart from each other in an atomic nucleus?    N

  What is the magnitude of the forcqt :n:2 gn2exu5v72mwf ) xtmfe a $+25\,\mu C\,C$ charge exerts on a $+\,3.0\,mC$ charge 35 cm away?    N

  Two charged dust particles exert kg y 5u2z4b6mr bn1y2ca 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 thy9ob f3p9cr u5f b*u7le force on each of them is found to have been tripled. How far apart ap7 5cubb3royfl9f 9* ure they now?    cm

  A person scuffing her feet on a wool r*f i*m 6oyn9fl 2u4tqeug on a dry day accumulates a net charge oyemf*4i6 2ulo*tn q9f f $-42\,\mu C\,.$ 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 electrons f pz7 ri*cdb+7q,*efmin 1.0 kg of $H_2O\,?$    $ \times10^{ 7}\,C$

  Compare the electric force hol tcvb7l7e 4f7dding 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. T*w cwmwv hc681he sum of their charges is What charge must each have i*c6 cw 81wwmvhn order to
(a) maximize the electric force between them,
(b) minimize it?

  Particles of charge q84zpe9hli5b f+et1 w$+75$,$+48$ 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 particlepkobe)eu :* 1aik7.iy s 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 0.100q+n4 mp0liya n *p/ps6 m on a side. Determine4q+* nsiyp6n l/p apm0 the magnitude and direction of the force on each charge.
$F_4$ =   $ \times10^{ 7}\,N$
$\theta$ =    $^{\circ}$

  Repeat Problem 14 for the case when twob z1ru6z,ld)+yl,yt c of the positive charges, on opposite corners, are replaced by negative charges of the same magnitude (Fig. 16–tzd+,)yy,lr cub 6 l1z51).
$F_4$ =   $ \times10^{ 7}\,N$
$\theta$ =    $^{\circ}$

  At each corner of a square of side l there are point charges of magnitude Q, 9 :hkzf rf2sa;1y vre92Q, 3Q, and 4Q (Fig. 16–52). Determine the force on (a) t9f9 :2zhfk s1ey;rva rhe 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 equilateral triangleqht g 9;1rek4+x-; gw:wd.t ada j(kug of side 1.20kdr +h gxe4uqk:jt;awgd( t;9 1g aw-. 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 hav.mxsp wv.ep48.i r2: idr irh+e a total charge of $560\,\mu C\,.$ When placed 1.10 m apart, the force each exerts on the other is 22.8 N and is repulsive. What is the charge on each?
q = $ 5.54\times10^{a }\,C$ a =  ,
$ 5.54\times10^{b }\,C $ b =   
Q-q = $ 5.54\times10^{a }\,C$ a =  ,
$ 5.54\times10^{b }\,C$ b =   

Two charges, $-Q_0$ and $-3Q_0$ are a distance l apart. These two charges are free to move but do not because there is a third charge nearby. What must be the charge and placement of the third charge for the first two to be in equilibrium?

  A $+4.75\,\mu C\,$ and a $-3.55\,\mu C\,$ charge are placed 18.5 cm apart. Where can a third charge be placed so that it experiences no net force?    cm

  Two small nonconducting spheres have a to/crrm0om* *uo tal 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 plasticd:a u1 gzhgkd9:a ou3/ ball to an identical ball 12 cm away. The force 1da93 odu zua khg/:g: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 fot(q )jtosskk2d 3; 9vhrce on an electron in a uniform electric field of stre; h2stkkjvso(3d tq)9ngth $2360\,N/C$ that points due east?
   $ \times10^{ -16}\,N$
 ----待选择----westeast 

  A proton is released in a lp0 ych3)k 0w5n s(vwt(xdgq8x )-ticuniform electric field, and it experiences an electricws0l-3iy(nq5pxgw c dx8 c( vt t0))hk force 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 is exerted on a 8ive m2boqz.- $-8.8\,\mu C\,$ 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 f0eu *r av0pk evf9u9snr4edwy( ;:-zdirection of the electric field 20.0 cm directly above n ;vfapvesk -uf*0w90(zdeu ry :9re4an isolated $33.0 \times10^{ -6}\,C$ charge?    $ \times10^{6 }\,N/C$ ----待选择----updown 

  What is the magnitude of the acceleration experienced by an elephxo v;)-f. wy wmd10wctron in an elect vh1wf) dpy0 m.ow;w-xric field of $750\,N/C\,?$ How does the direction of the acceleration depend on the direction of the field at that point?    $ \times10^{ 14}\,m/s^2$  ----待选择----opposite to the field in line with the direction of the field 

  What are the magnitude and direction of the electric field at a point m9d+jcx 0obr p-idway betwodjb -9r0c+px een 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 eh9d4sd/ybg8pgx k+) 3g *fit electric field lines about two point charges, $+Q$ and $-3Q$ which are a distance l apart.

  What is the electric nn9xp6r -lrgh;7dv,n4 aybdx ;yk75p field strength 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 field and accele82 n-grqd q(u tb(.qutrates to the north at a r 2t(.-tgq(u8n bdr uqqate of $115\,m/s^2\,.$ What are the magnitude and direction of the electric field?    $ \times10^{-10 }\,N/C$ ----待选择----northsouth 

  The electric field midway between two equal but opposite point chargesfd9j8nfen5j5;h* inx 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 square 52.5 cm on a side if 3lcsomqpu :yp9v(ir6+ x5 /ot* zoq2sone corner is occu*zyciq(lot:+s 5p vs29o6 ux3 /omprqpied 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 1n7t uy)y,zfyupe/vq f5sf*7 a square 1.00 m on a side if the other three coup5f*vy t fes/71qyy,nzf) u7rners are occupied by $ 2.25\times10^{-6 }\,C$ charges.    $ \times10^{4 }\,N/C$   $^{\circ}\,$ from the x-direction.

Determine the direction and magnitm9q9 ze:.kvw fgb*anow j)++ hude of the electric field at the point P in Fig. 16–54. The charges are separated by a distance 2a, and w .n9g*9mf+o jekhbzq+)v w :apoint 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 electric field1gm yi)omtr z.98c8 w:n6seb u $\vec{E}$ 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 z0 pz6 6g;u3y3jswad.menz*ldirection of the electric field at points A and B in Fig. 16–57 due to the two posi gjpamzuz6 e *w60yln.33dzs ;tive 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 chabrxv; y- u5h-vrges, $Q_1$ 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 magnitudeh5 )i79 us6zs9qtv iux 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 the charges, a distance x from the midpoint between them. E75vi9 xzistu )h9qsu6 xpress 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 suw6 k92dlfj-c peed of light enters a uniform electric field parallel to its direction of motion. If the electron is to be brought to rest in the space o dk- wu629jlfcf 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 c71 cp (+d lb4jcvm.d8yrh )fplubical 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 electric field o u/7z8 ls9 0efpz;qoimf magnitude e iozl98 q;f 7mus0/zp$ 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 objecwh bms1l.;bh+ts, $O_1$ 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 placedtef wsj, mx;nn,/ m6j*n.z )os 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 sx t4vxyaj4oa.* nm ej46r3 euoq+,j0onj s6(two square metal plates is 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)? N0j+*xomaojvsrj3t6 xq64n(u.os44ejeyna ,eglect edge effects.    $ \times10^{-9 }\,C$

  The field just outside a 3.50-cm-radius metal q p ;ic( w bq;iziwfhnw/))omn7.) im4ball 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 carri b5yf;is xw7y+5(cmj bes 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 sphero2aa17;bckhou0snkekm2 .y6fob(f 1 ical conducting shell. (See Fig. 16–33.) What is the electric field E as a function of r (a) for r less than the inner radius of the shell, (b) inside the shell, and (c) beyond the shell? (d) Does the shell affect the field due to Q alone? ok0b k2(nb.7cao6 ymh2e f 1;sofak1uDoes the charge Q affect the shell?

  The two strands of the helix-shaped DNA molecule are held t1og x x 6m)xcvfo1rj5+.cn cm8ogether by electrostatic forces as shown ic +g8c1x5x .rovfm njom)c6x1n Fig. 16–44. Assume that the net average charge (due to electron sharing) 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 electronsrhn k(byr*0+ csgc/3 f be if the electric force between them is equal to the weight of either at tf hc+b y/k0gn(s3c*rrhe Earth’s surface?    m

  A 3.0-g copper penny has a poa+b,jlz m fa81 7r/vtositive 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 y0 nu /qqb ta5lr;/ju(wqay3)field surrounding the Earth. Its magnitude is ab u3r/yq) a/wt0q ( 5b;juqalynout $150\,N/C$ 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 experk;le*ctbx zkdjvk muf:1/7,p2m: k,oienced by an electron ne,:1mj2:dkf c u kpelkzx;kt/,m o7*vb ar 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 stationa drp ,)d(d4sf byp,oi0ry in the air. If the downward-directed electric field ofp,i)rf ,s (ydbodd 0p4 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 sl z,cup a1a;8rc-4 v2y z;h4w zejxc7khown in Fig. 16–62. The C and O have rak7 44c zj2pv;ch x yau 8zzl;1,w-cecharges $\pm0.40e$, 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 a circular orbmf z2nje0 zv/9k bpz+*it around the proton with a speem zzfk2bz9v0*p+en /jd 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 attroacsd bwl257(action, rather than gravity, were responsible for holding the Moon in orbit around the Earth. If equal and opposite charges Q were placed on thesacbd 5( 7wo2l 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 spee43 ma bs3;d34je r pn*6csegled $v_0\,=\, 21.5\times10^{6}\,m/s$ 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 r/ 8z;wtf 9xla$Q_1\,=\, 2.5\times10^{-5}\,C$. 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 verticallaaq,v ;)p*rp /qo 6xgwy from an ideal sprx6 gq;,p p)/ *avowqaring $(k\,=\,126N/m)$ 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 “le(r+r 0cnca 5w q5xgt8haves” that are 78-cm-long wires with tiny 24-g spheres at the ends. When ch0+rat85 5crcn qhg(x warged, 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 generateyd fn+3d.p.-7 rmga8u 4gag ge a spark if the electric field exceeds aboutgyg.g-nma4g+78 d era3 pf .ud $ 3\times10^{6 }\,N/C$. How much charge could be packed onto a green pea (diameter 0.75 cm) before the pea spontaneously discharges? [Hint: Eqs. 16–4 work outside a sphere if r is measured from its center.]    $ \times10^{-9 }\,C$

  Two point charges, $Q_1\,=\,-6.7\mu C$ and $Q_2\,=\,1.8\mu C$ are located between two oppositely charged parallel plates, as shown in Fig. 16–65. The two charges are separated by a distance of $x\,=\,0.34\,m$ Assume that the electric field produced by the charged plates is uniform and equal to $E\,=\,73,000\,N/C$ Calculate the net electrostatic force on $Q_1$ and give its direction.    N  ----待选择----right left 

  A point charge $(m\,=\,1.0\,g)$ at the end of an insulating string of length 55 cm is observed to be in equilibrium in a uniform horizontal electric field of $12,000\,N/C$ when the pendulum’s position is as shown in Fig. 16–66, with the charge 12 cm above the lowest (vertical) position. If the field points to the right in Fig. 16–66, determine the magnitude and sign of the point charge.
   $ \times10^{-7 }\,C$
 ----待选择----positivenegative 

  A point charge of mass 0.210 kg, and zt pg*ph+hf1 p m+ pf o19*-ivnv)mpj27.urklnet 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 chargz y w nl4j5t6an;0q9eke of all the electrons in a 15-kg bar of aluminum?    $ \times10^{8 }\,C$What is the net charge of the bar?    C (Aluminum has 13 electrons per atom and an atomic mass of 27 u.)

Two small, identical conducting spheres A and B are a distance R apark80o) u kfhy)pw fdc04xgke 0:t; 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) Sphere C next makes contact with sphere A and y0fcd x )):wp oefh08uk 0kk4gis then moved far away. What is the force on sphere A in this third case?

Given the two charges sh/p0mt6 ynr7 ot2qc8ew own in Fig. 16–68, at what position(s) x is the electric field zero? Is the fqony8e7 rmtp02wct6 /ield 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 ofqrgu+ ,k.f ):r bopq,:cro:3d amojc8 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?