If you charge a pocket comb by rubbing it with a sil; l62xwfq8(g( 3 xnz.f bkxatmk scarf, how can you determine if the comb is positively or negatively chargx x3 zg6xwt(m.k qal28;n b(ffed?

Why does a shirt or blouse taken from a clothes dryer sometimes cling to yourt 2etm2fht,* t body*t,22 mttth fe?

Explain why fog or rain droplets tend to form around ions or electrons in tht z s,j u3syb;kjt18jybz5w+(e air.ubj,wj kyt(1z;j3+zs8 ybs t5

A positively charged rod is brought close to a neutral;bspl.scv6+ sof *q0a nm0r1g piece of paper, which it attracts. Draw a diagram showing the separation of charge and explain why atqmv+ln1 ;*s 0fsr0 .cspbo6agtraction occurs.

Why does a plastic ruler that has been rubbed with a cloth have th+ b-fyi-pkwz4 e ability to pick up small pieces of paper? Why is this difficult to do on a hum-y-4 z f+ibkpwid day?

Contrast the net charge on a conductor to the “free chargx uchce))(n6fgd(5k t iwjs 85es” in the conductor.

Figures 16–7 and 16–8 show how a charged rod plaq* w iyuj+6rtrs6lxfrr+4 * 2cced near an uncharged metal object can attract (or repel) elecs+ l*r24wc j *x6ri6qrrufy +ttrons. There are a great many electrons in the metal, yet only some of them move as shown. Why not all of them?

When an electroscope is charged, its two leaves repel h91u)full )do each other and remain at an angle. What balances the electric force of repulsion so that the9fuo ldl )u1)h leaves don’t separate further?

The form of Coulomb’s law is very similar to that 5rtc4w 38 rdlhq*;smzfor Newton’s law of universal gravitation. What are thech5;84l3zwqd sm*rrt differences between these two laws? Compare also gravitational mass and electric charge.

We are not normally aware 5dt :sujd(x,h of the gravitational or electric force between two ordinary objects. What is the reason in each case? G(d :xh usjd5t,ive an example where we are aware of each one and why.

Is the electric force a conservative force? Why or why not? (See Chapter t 9 s2ocaou-z*6.)

When a charged ruler attracts small pieces of paper, sometimes a f,k 93s3zuuu hlunu s 4/4dje3o siymu83 zj+;piece jumps quickuey,fi3 43/szuum u sh;8s+kj49 3zonul 3dj uly away after touching the ruler. Explain.

Explain why the test charges we use when measuring electric fields must be smt(-qz/flc q/a3wnr8x allz-r/ xw8tnl(qf/q3ac.

When determining an electric field, must we use a postvwh(r a3hpj; pt x6).itive test charge, or would a negative one do as3 atw6)h.ph j ;pvtrx( well? Explain.

Draw the electric field lines surrounding two negative electric vkt3 .os42co kcharges a distance .kk 3s 4ovoc2tl apart.

Assume that the two opposite charges in Fig. 16–3csik60r7ky a8 /qp+ k6ye2btc1a are 12.0 cm apart. Consider the magnitude of the electric field 2.5 cm from the positive charge. On which side of this charge — top, botpct/ ysk 7kq6yb6ki +02ae8crtom, left, or right — is the electric field the strongest? The weakest? Explain.

Consider the electric field at points A, B, and C in Ffce19ydj 0-d v9vv-nvu f mo6/ig. 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 strengt1udmjoce v 9- y6vf fdnv0-9v/h (strongest first).

Why can electric field lines ne;5 gfxo;gsohywm n; ek*ow7/9ver cross?

Show, using the three rules f 6zzrh un:r3;mor field lines given in Section 16–8, that the electric field lines starting or ending on a single point chaz3 :rmrzn6hu; rge must be symmetrically spaced around the charge.

Given two point charges Q and 2Q, a distance l apart, is there a point along thbzl tp *jolw)0f ku8s*4h(a0oe straight line that passes through them where E=0 when their signs are (a) opposite, (b) the same? If yes, state roughly where this poiw0t0bsuz*oaj *4lok lf (8h )pnt will be.

Consider a small positicwth7w z069 n.n, 3mxlljw3trve test charge located on an electric field line at some point, such as point P in Fig. 16–31a. Is the direction of the velocitln6 t30xhzt93cj,w.n w7 mlwry and/or acceleration of the test charge along this line? Discuss.

Sketch the electric field lines for a uniform line of charge whicsic icdch+/;u, a)( joh is infinitely h (u+dcaco)jiic, /s; long. (Hint: Use symmetry.) Is the electric field uniform in strength?

If the electric flux through a clost8ybcfi g5 tc (/:vpv3s; dj4ned surface is zero, is the electric field necessarily zero at all points on the surface? Explv i:(pgjysf;3cb4vn t/dc8 t5ain. 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 radius r. If thme)bu :;ifp hre:e3(de sphere is replaced by a cube;)i(fdbe :hp :reum3 e of side r, will $\Phi_E$ be larger, smaller, or the same? Explain.

  

  How many electrons make up u b lfq)c+jh7c dc-: *ipmev.(a charge of $-30.0\mu C\,?$   $ \times10^{ 14}\, electrons $

  What is the magnitude of the electric fore. (m.ym z :xgvpfl-na+3c mw9ce of attraction between an iron nucleus ze xnm:3w g.vpm a.+mc9y(lf-$(q\,=\,+26e)$ and its innermost electron if the distance between them is $ 1.5\times10^{-12 }\,m\,?$    $ \times10^{-3 }N$

  What is the repulsive electk143pcn5mb z 2dtmd/frical force between two protons $ 5.0 \times10^{ -15}\,m$ apart from each other in an atomic nucleus?    N

  What is the magnitudemi(gyl/ht6p/ucc+xx-d n */n of the force a $+25\,\mu C\,C$ charge exerts on a $+\,3.0\,mC$ charge 35 cm away?    N

  Two charged dust particles exert a forwy4qa, 8g kb7 izz98winzo5jo8l5yf8 ce 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. jtzgg.zk /.9yThey are moved, and the force on each of them is found to have been tgzy9j. /kt gz.ripled. How far apart are they now?    cm

  A person scuffing her feet on a wool rug on a dry day accumulates a net chanhxad8 3uc7 nm+th 70zrge ozu cat7 38nhx d+nmh07f $-42\,\mu C\,.$ 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 in 1.0 kg of 9izcv7) 2f p gwfes;cq;s;kz /8xl;da$H_2O\,?$    $ \times10^{ 7}\,C$

  Compare the electric force holding the electz 2 ovpr o--m+.8lefphron 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 dist*vw yp6lgd/kr dbbt, ) 4r52weance apart. The sum of their charges is What c,*6tdw5p4l/d gwy e 2 rkrbb)vharge must each have in order to
(a) maximize the electric force between them,
(b) minimize it?

  Particles of charge dkyz 6(z89wf-/0o)lpzbag jj$+75$,$+48$ 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 hm hp84m7gsg xx,1ae*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 squ s+3f/zslk5j sare 0.100 m on a side. Determine the magnitude and ds5flsz k+j 3/sirection 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 opp5)zp 0oej/hv posite corners, are replaced by negative charges o)z vhp/peo 5j0f the same magnitude (Fig. 16–51).
$F_4$ =   $ \times10^{ 7}\,N$
$\theta$ =    $^{\circ}$

  At each corner of a square of side l there are point chargx+ttqakq36 g 2es of magnitude Q, 2Q, 3Q, and 4Q (Fig. 16–52). Determine the forc3+6tq2akt gqxe 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 equilat )cah80l 05pggr.biwceral triangle of side 1.20ccgb ).hg 0l5 rpia08w m (Fig. 16–53). The charges are $+4.0\,\mu C\,,$$-8.0\,\mu C\,,$ and $-6.0\,\mu C\,.$ Calculate the magnitude and direction of the net force on each due to the other two.
$F_1$ =    N
$\theta_1$ =    $^{\circ}$
$F_2$ =    N
$\theta_2$ =    $^{\circ}$
$F_3$ =    N
$\theta_3$ =    $^{\circ}$

  Two point charges have a towe 8vy0)xz:2p r fzwg669xkbqjt6vp3 tal 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 ha3ui k, t3ddl ,gi qa;yow wneu)m+74o4ve 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 fro-n(oc,kk 0dshps.w5.3i :lkekco ar 4m an initially 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 thpnl-k,kr0skodws: c 4( 3 . ieh5ca.koe other?    $ \times10^{ 12}$ electrons

  What are the magnitu:z52l/ r9guikyqcpr1 de and direction of the electric force on an electron in a uniform electrirk5clz pgr 1/9u:2yqic field of strength $2360\,N/C$ that points due east?
   $ \times10^{ -16}\,N$
 ----待选择----westeast 

  A proton is released in a uniform electric field, and it experiences an elect(cxiu og8a:osb) i39 kric force oaibi9 u)xc :83 k(oosgf $ 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. w02rpxuw0f;5aaoyyeny t(,x 26h.c j4 N is 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 dir 3n*q-jlokg:uqtu 2 7xection of the electric field 20.0 cm directly above an isolaukl2-j g7t*: nxq3qouted $33.0 \times10^{ -6}\,C$ charge?    $ \times10^{6 }\,N/C$ ----待选择----updown 

  What is the magnitude of the acceleration experiencd*ssc0 4n w5e/z,tmwqed by an electron in an electrsm, szt4ww/*nc50q edic 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 ponju/j6p08 ff zcg*o 0vint midway between a/6nj8zc jgu f00p*ovf $-8.0\,\mu C\,$ 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; docbcb, l4c/t 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 protoregg(q h.4l j.ov*lz 5n $(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 accelerates vk+jg8rk 5 d2nto the north at a rate ofkgrk5 8 j2vn+d $115\,m/s^2\,.$ 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 oppost9u p7u9,y qt9 eu t7(v9rkyebite 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 centerlqg1j cdh ; bjwlulus.;*;3g+ of a square 52.5 cm on a side if one corner is occupg cw*gh;j .lu+j l; 1sq;b3lduied 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 .huqcaf3t:i1wveaj( 22 qv p (one corner of a square 1.00 m on a side if the oth2vv1(fj:hcq t3.2p w(aauqi eer three corners are occupied by $ 2.25\times10^{-6 }\,C$ charges.    $ \times10^{4 }\,N/C$   $^{\circ}\,$ from the x-direction.

Determine the direction and magnitude s g7ueax4r9 2jof the electric field at the point P in Fig. 16–54. The charges are sepaxr472eug 9s jarated 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, 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 fi45lr;vrd 7j0y ezm4ijeld $\vec{E}$ 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 m68+ xf3eo*k ksu 41( n7puslvzq .ualhagnitude and direction of the electric field q*8lo( v4nu3s+6x1pkazel.u k husf7 at points A and B in Fig. 16–57 due to the two positive charges $(Q\,=\,7.0\mu C\,)$ shown. Are your results consistent with Fig. 16–31b?
$E_A$ =    $ \times10^{6 }\,N/C$
$\theta_A$ =    $^{\circ}\,$
$E_B$ =    $ \times10^{7 }\,N/C$
$\theta_B$ =    $^{\circ}\,$
(16-51)
(16-31b)

  You are given two unknown poinago 58 w0.kzdsuvu7 2 (ifk-()uwjtxmt 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 sh ye*yrwl j9hlk*9j)j/ own in Fig. 16–59. The two charges are separated by a distance of 2a. Point P is on the perpendicular bisector of the lh e) j9rywljjk9/* ly*ine 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 entccvnv(6h /t( 06w rtecers a uniform electric field parallel to its direction of motion. If the electron is to be brought to rest in the space of 4.0nc( wt(60vtvhc c re6/ 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 o umir )k56j5wahx8ry/n 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 eledqdg5:tq :ztyqhh3 8, ctric field of magnitude :qtqh3h8zt: dd5ygq,$ 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 object/ 4uymhgy6e3 l lch)7kbl(7lns, $O_1$ 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 pl 4cbf1av:1z5)fiu u pyaced 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 is Thzmw wtth;0w3zm8d4)h 2nnyaj2z : +a te plates are 1.0 m on a side and are sepw):2 j4y zz0 8hm2;3amtndt hww+tznaarated by 3.0 cm. What is the charge on each plate (assume equal and opposite)? Neglect edge effects.    $ \times10^{-9 }\,C$

  The field just outsideb2. q.08zihyi(u no*mscs,i e a 3.50-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 r-qp-w z8 emd4carries 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 spherical conducting ssr..jn+ke zl (f/rbojq-i niog-3 +8mh,y g)z hell. (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 thes3 gg yzbfehl/o8 (nmrj+.,z noir)ik-+ .qj- shell? (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 togethe h1bc1w keu3y:6v.oalr by electrostatic forces as shown in Fig. 16–44. Assume that the net average ch:e .1cwuk16 l vh3abyoarge (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 electrons be if the electric force between them is equal to h4s2e +5os(1ref/g w h laveb;the weigh1goh5lar; eb/ (4+svs2 e wefht of either at the Earth’s surface?    m

  A 3.0-g copper penny ha o:gww+g,-gwe-k)s7u jm jqx2s a 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 dwfph1i(g 3hs (7ym 2gfield surrounding the Earth. Its magnitude is giphw mh2 3(yf17(sdg 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 ezy xho *zl1me*em8; w0lectric field of what is the acceleration experienced by an l0 z81 *yx mwoe*e;hmzelectron near 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 stationarx*aevqzka cv( 3 /y/j) 7za+bly in the air. If the downward-directed electric fieb(zcav j/lex)y3vzq 7a+/*ak ld 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(h btn.d90v )juqd. po+p6cgou .0ary in Fig. 16–62. Th9+pjp.o d)0 (6 tubna0qo .udy ghrvc.e C and 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 hydrogd,z hs*+7io aven atom, the electron revolves in a circular orbit around the proton with a speed o7 dho s+*ivza,f $ 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, rathio11lg6z s n2il -eelph8thp54t8 rce( om8g0er than gravity, were responsible for holding the Moon in orbit around the Earth. If equal and opposite charges Q were placed on the Earth and the Moon, what should be the value of Q to maintain the preseip-ztll16om ( i0olheng1ep48c he85g 2 tr8snt 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 speo lbu)z/a .moo+up9q 0tc4ini(9/pcyed $v_0\,=\, 21.5\times10^{6}\,m/s$ 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 chargj- s kkf51+ t9ngjswk3e $Q_1\,=\, 2.5\times10^{-5}\,C$. 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 vertge hnvd 0hg)x0t qh;8bmy*z 1cmv,o 1)ically from an idec1ghv,1o8bztm0* ;)yh)m 0gnqv exdhal 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 lc r; bf2l 7xs-j2iynwfbm*t11vl31 b“leaves” that are 78-cm-long wires with tiny 24-g spheres at theflv7yf 1*-3cn wrb ll2;b2sit1xm1bj 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 the electric fopu7b w fqt1:5ield exceeds aboutptw:o7 q1 ub5f $ 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 net chaas8 7es4c0o dxrge $+0.340\,\mu C$, 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-wwc- pibqf 5q(om/oczk- 35+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 v6n /+5v7 zrjefr9ydgand 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 idedg fyz+95 rr/v nvj6e7ntical sphere with zero charge, sphere C, makes contact with sphere B and is then moved very far away. What is the net force now acting on sphere A? (c) Sphere C next makes contact with sphere A and is then moved far away. What is the force on sphere A in this third case?

Given the two charges shown in Fig. 16–68, at what position(s)oct a r/./j3k *ehytj* x is the electric field zero? Is the field zero a*.rt/*ck e oajt/ y3jht 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 c: rewiu2re22 pharges, 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?