If you charge a pocket comb by rubbing it with a silk scarf, how can you dete/ of08o59 fot h2+nvp0ung jrcrmine if the comb is p 2hu+po08vgjn5of 0rtcf 9/noositively or negatively charged?

Why does a shirt or blouse taken from a clothes dryer sometimes clin-nk b bxqu6k jq53k4v7g to your bo x6qb57k 4bvjq-nuk k3dy?

Explain why fog or rain droplets tend t5og js +clw/9y+ 7(7 .osvhlwbwb pnp;o form around ions or electrons in the air swbpgl. +(yvno 95;opc/7shb7jww+l.

A positively charged rod is brought close to a neutral piece pxf 2cfu5rz9 3zlpf:l ejk5c0a:+ 2tpof paper, which it attracts. Draw a diagram showing the separation of charge and explain why attractionz2x0:z3tp+ epf fp52l:c ural9ck 5f j occurs.

Why does a plastic ruler that haw-zo ms0ah yy+r- 5e:ds been rubbed with a cloth have the ability to pick up small pieces of paper?sh-zwma-:5dyr oe 0+y Why is this difficult to do on a humid day?

Contrast the net charge o7idkx6r5 9 q1m1ibmyhn a conductor to the “free charges” in the conductor.

Figures 16–7 and 16–8 show how a bc 7ki 5tut.5zcharged rod placed near an uncharged metal object can attract (or repel) electrons. There are a great many electrons in the metal, yet only some of5 bzt7tcuki5. them move as shown. Why not all of them?

When an electroscope is charged, its two leaves repel each y;t 8lh 1j8pbl8a -msjother and remain at an angle. What balances the electric force of repulsi; 1 b hsljtjl8m8-pay8on so that the leaves don’t separate further?

The form of Coulomb’s law is very similar to that for N fsrxi+8yqa: o o-3;pyewton’s law of universal gravitation. What are the differences betwe-s;8y fq3yo o:ix +paren these two laws? Compare also gravitational mass and electric charge.

We are not normally aware of the gravitational or electric fo d.*kdvpka8gn5u8r syd*egkbj;;. l: rce between two ordinary objects. What is the reason in eapseg nb dr8;5: k v*d*a.g kkujy.8ld;ch case? Give an example where we are aware of each one and why.

Is the electric force 5quk8/il 36 a.z6r09ujpi f-kmfjejga conservative force? Why or why not? (See Chapter 6.)

When a charged ruler attracts small pieces of paper, sometimes a piece jumps qud1iak dis0 p)4ickly away after touching the ruler. d)10kis ipda4 Explain.

Explain why the test charges we use when measuring electric fields must b16qj- vti 5zvbe small.1b ztj vi65vq-

When determining an electric field, must we use a positive test charge, or wosx576g p/mhtr uld a negative one do as well?r67/ gx 5mhspt Explain.

Draw the electric field linep a(;p:ukj :v2n xrem-s surrounding two negative electric charges a distance l apar:;(parmn x :ep2-vu kjt.

Assume that the two opposite charges in Fig. 16–31a are 12.0 cm ap a52mfdi;j f+qart. Consider the magnitude of the electric field 2.5 cm from the positive charge. On which side of this charge — top, bottom, left, or right — is the electric field the strongest? The weakest? Explain.i d5f2;qfm +aj

Consider the electricv p m0z6-;rse.6szhas field 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 placed at that point, then list the points in order of decreasing fie6v a -0psmhzz;s6.s reld strength (strongest first).

Why can electric field lines never crod ,6(gur*aoy k2+bjxh ss?

Show, using the three rules for field lines given in Section 16–8, tha ru twk s3ct(1apjdb1r;y;96 dt the electric field lines starting or ending on a single point charge must be symmetrically spaced around the chat 3p( buacdd6w;s1rt kyr;1 9jrge.

Given two point charg 4ymx/aczbm2.o h92a oes 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? If yes, state rob.y2 /aaz ox hcmo2m94ughly where this point will be.

Consider a small positive test chkk jy.w:;z :woarge located on an electric field line at some point, such as point P in Fzj :k;w:k.woyig. 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 ofw j:u1c7jl+rqgt u3p 4h9.b be charge which is infinitely long. (Hint: Use symmetry.) Is the electric field uniform in strengtjr9l7 gu+: wutpqe. h jc14bb3h?

If the electric flux through a closed surface is zero, is the electric fieldnn: veo 3b07j+ wek0 0o9olohr necessarily zero at all points on the surface? Explain. W:vr+3on0 9o 0on 0lob7jhw keehat 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 surfac l; *.bjmo 4spb9thvbm i60/;u4x nopxe of radius r. If the sphere is replaced by a cube ;b6/ 4;pn xv0hl ms4bojo9ti .pxbmu *of side r, will $\Phi_E$ be larger, smaller, or the same? Explain.

  

  How many electrons make up a charge o, +;oq pxf,80ol 6ye.b- la+ov rcqtuxf $-30.0\mu C\,?$   $ \times10^{ 14}\, electrons $

  What is the magnitude of the electric force of attraction between an iron nudb oy vp9xx)6/cleus6 xd/po yxv9b) $(q\,=\,+26e)$ and its innermost electron if the distance between them is $ 1.5\times10^{-12 }\,m\,?$    $ \times10^{-3 }N$

  What is the repulsive elecbood+y7d it7115h *4 ip ibekutrical force between two protons $ 5.0 \times10^{ -15}\,m$ apart from each other in an atomic nucleus?    N

  What is the magnitude of the f.7:tu . jzkb h:vfv11va75.nsgzzpzhorce a $+25\,\mu C\,C$ charge exerts on a $+\,3.0\,mC$ charge 35 cm away?    N

  Two charged dust particles exert a fclws9y r(ysi( (vadnp .6)c +porce 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. roxo 3m* 7 iq2rqiw8-(dlou;*jqz w1tThey are moved, and the force on each of them is found to have been-qo7(wz*u13r qlx*ditw2r; mo8ijqo tripled. How far apart are they now?    cm

  A person scuffing her feet on a wool rug on a dry day accumpu7f ,ass,(;o )lzdyg0h9 apqulates a net charge of,zgls;u ay,pf09dqs 7 )(aoph $-42\,\mu C\,.$ 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 cq5c jddq41-zg5owq 0+bhe /x the electrons in 1.0 kg of $H_2O\,?$    $ \times10^{ 7}\,C$

  Compare the electric force holding thekt u f -d1q/r5k -rk:2gfoblp: electron in orbit $(r\,=\,0.53 \times10^{-10 }\,m)$ around the proton nucleus of the hydrogen atom, with the gravitational force between the same electron and proton. What is the ratio of these two forces?    $ \times10^{39 }\,C$

Two positive point charges are a fixed distance apart. The sum of their cha znjg2dpnmisuv(c2u*y -7i:0rges is What ch sjz0mi n u27(ygun2-d:iv*cparge must each have in order to
(a) maximize the electric force between them,
(b) minimize it?

  Particles of charge k-mo-je 3hawr-e/e;te qw :*)v 6pu qv$+75$,$+48$ 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 chtp1(mu +mgik9s6d5pti :k 8cwarge, $+11.0\,\mu C\,$ 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 p,sk*1+h9*ud)jgk lpei77k d um,g j dsquare 0.100 m on a side. Determine the magnitude and direction of mji l, 7**k+juh79dp du g1dkp) gs,ekthe force on each charge.
$F_4$ =   $ \times10^{ 7}\,N$
$\theta$ =    $^{\circ}$

  Repeat Problem 14 for the case when two of the positive chargeynmpyn32ao 0r*wvz) (d xcx9 .zn5tu2s, on opposite corners, are replaced byzxrnn3 on.t*)va5 p y y9dcxm02zu2( w 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 poinl,:8ar72ht8bwx:tskcoly (w t charges of magnitude Q, 2Q, 3Q, and 4Q (Fig. 16–52). Determine( w27kh cabxt8or :: yslwt8,l 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 a 8ngv 4z1bhjwi87ie l:t the corners of an equilateral triangle of side 1.20 m (Fig. 16–53)g8 i4ljv18h7 ze:b wni. 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 chargeh:x 8smgij 6;/fxhki 5156gwpbk or6o 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 haveiy1:s rmu /uo7 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 plamc rdsb.0 k14tstic ball to an identical ball 12 cm away. The force o0 4c.tb1km srdf 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 force on an electron in w97k0uovh1 oo 44n vzua uniform electric fieuvvhnoo14z9 0 w7ko u4ld 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 itt +l+6wgcd9 fq experiences an electric for6twq++gf 9cdl ce 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 isiqo8 wfkfohq) r3(pu -vw 8c), 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 the electric fie6jzsd; l)lgpaq1mz:j zy ,k9)ld 20.0 cm directly abovy,d19l:skazgjz) lp j6;mqz)e an 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 electr8f3so oi qz.2yna)w ,zon in an electric field of )s o2,zy n.q i8ozfw3a$750\,N/C\,?$ 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 thex(16ud5nzuwy5/ooiw(5s zx ajb k7k0z/r .iy electric field at a point midway betwex 0 jbzki5 /wu(osdx6 u ry5az7ki5n (1o.zwy/en a $-8.0\,\mu C\,$ and a $+7.0\,\mu C\,$ charge 8.0 cm apart? Assume no other charges are nearby.    $ \times10^{7 }\,N/C$ ----待选择---- towards the negative charde opposite to the negative charge 

Draw, approximately, the electric field lines abou- iw -(sw5slmkf85p*yq;h l( ts5mcy ut 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 p w73 2nsonq4jog1)c ouroton $(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 a9ta (0 bahrumn,r c67zk-m:yw ccelerates to the nort w:(-umk6nbt r y,0z 97amchrah 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 oppos /)k)ltzbi+gw jjk9-oite 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 square 52.3rxbxa;d9:oo g adv/xxhrk d 2(9 7 jd5c+y+xa5 cm on a side if one corner is occupied byoxb7 3:da9g+o dxxj2x;d r kx/5d9aa hcry+(v 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 v y 8u,pnwq ao 9 bwq1tsv.;c+lb4*xt4if the other three corners arc4lb sp vxutb 49;.w8 oa,t*vn1yq+wqe occupied by $ 2.25\times10^{-6 }\,C$ charges.    $ \times10^{4 }\,N/C$   $^{\circ}\,$ from the x-direction.

Determine the direction and magr.zs7cn j0)s kosij,jl19 . nj2vgm/bgm +w, wnitude of the electric field at the point P in Fig. 16–54. The charges are separated by a distance 2a, and point P is a distanceck m2so7 j ggm,w+lsvz9n)1 ,b s.0.jjijnr w/ 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 elg gpnzfy/ogq;h7in 7e)p30 9 fectric 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 of2qe:b)imet4 g the electric field at points A and B in Fig. 16–5ee )t qgib24m:7 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 unklk1 zj rz pmm:7m1s- +dxpy- v6z0:rstnown point charges, $Q_1$ and $Q_2$ At a point on the line joining them, one-third of the way from $Q_1$ to $Q_2$, the electric field is zero (Fig. 16–58). What is the ratio $Q_1/Q_2\,?$   

Determine the direction and magninr j341 cjvn8t5 cv(hfta)ea6tude of the electric field at the point P shown in6hjvcn 8r(vatf3e t)14c n5 ja 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. 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 of light enters 0:i6sy i/hx) -duk ol ghnwc4.a uniform electric field parallel to its direction of motion. If the electron is to be brought to rest in the spayc64os)/ gu:n0xli k. hh-diwce 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 28.0 cm on a side is * u9e z:ed b,tpm;7hs,+ tqrks$1.45 \times10^{3 }\,N\cdot m^2/C$. 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 matxt;;emq* o 5 lu(tm,tgnitude;xoqm*eltmt tu;,5 (t $ 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 obg9+: ;z jabw2iji wz:ejects, $O_1$ 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 placeyj(ou k0nvhom5os; 23d 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 isnhj2bhf/ syb20i :6 ozgnu9 q,2upb.y 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 6z2/ybhq nu:29ius b j2pfgy0.ohnb, and opposite)? Neglect edge effects.    $ \times10^{-9 }\,C$

  The field just outside a 3.50h0x*1 . :.hd nevmhw 6t*wjjnc-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 radius 3.00 m c b6klzwz-9l9y arries 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 c0g+j blr,x.hjenter of an uncharged thin 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 shell? (d) Does the shell affect the field due to Q alone? Does the charge+jj.bg ,h0rlx Q affect the shell?

  The two strands of the helix-shape7 w;jas* /rpkvd 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 is 0.2e and on the ij* sp ;v/arw7kndicated 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 elec(z79 ez vm1waptrons be if the electric force between them is equal to the weight of either at the(zvmea1p7 9wz Earth’s surface?    m

  A 3.0-g copper penny has a posit pujih 8hb 42r43ljy;dir8b *tive 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 th /jkma 1ok2ne wh+7u7iere is an electric field surrounding the Earth. Its muo7e/ 27n1k kwijha+magnitude 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 elect6zoe u5-qj+)l /gzie oric field of what is the acceleration experienced by an electron near z6uo)q-ze /j+igo5e lthe 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 stationary in the air. Ij t.d6g t/fob-f the downward-gdbj. ottf -6/directed electric field of the Earth is $150\,N/C$ how many excess electron charges must the water droplet have?    $ \times10^{ 6}$ electrons

  Estimate the net force between the CO group and the HN group shown i sb0a2b2; vhi w4ytkfl; ds72un Fig. 16–62. The C and O have chaf;vb k id274aby22w;l0 su tshrges $\pm0.40e$, 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 electronyvd 1/j,,d ykn revolves in a circular orbit around the proton widjkvdn y, ,y/1th 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 attractdf* m1-uc;t ixwk8 dk5/-:n;yyyjy t wion, rather than gravity, were responsible for holding the Moon in orbit around the Ea jyt8uyd1ckw f/k xy:mt5n*yd-- ;iw ;rth. If equal 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 spe *g*vl y1/palwk n6 22p1ekls nxiol+3ed $v_0\,=\, 21.5\times10^{6}\,m/s$ 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 charg y/+mhd dg4tp,.u3n wje $Q_1\,=\, 2.5\times10^{-5}\,C$. 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 su3u.8cvxh 9hfjryy3kh8.pn 0 g spended vertically from an idg 3jr8 pfnchuvy. 3y. 9h8x0kheal 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 “leaveg-via6+i( z1l ge7mils” that are 78-cm-long wires with tiny 24-g sphereivg(m+i ea g6l7il1 -zs at the ends. When charged, nearly all the charge resides on the spheres. If the wires each make a $30^{\circ}$ angle with the vertical (Fig. 16–64), what total charge Q must have been applied to the electroscope? Ignore the mass of the wires.    $ \times10^{-6 }\,CC$

  Dry air will break down and generate a spark if cl(oqyk4te8.rc 8 mne ;hup11the electric field exceeds about rm(ltye;qc4ou p1.ck1h8ne8$ 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 nef1o )at 3p*zls eldn z2i8+0k-*othnyt 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 15o w chkt,q dgk,4r )z/k11t-own8oc9z-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 rk *w9-wp;f bjare a distance R apart; each carries the same charge Q. (a) ;-wr*jb9pw fk 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 is then moved far away. What is the force on sphere A in this third case?

Given the two charges shown in Fnmq m11m)u)3ebd omw7 ig. 16–68, at what position(s) x is the electric field zero? Is the field zero at any other p me 1m7om)qw1b3ndu)moints, 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 charge6y1 c 0fy tege) nd-)cs-e5exls, 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?