If you charge a pocket comb by rubbiah-l3htbxj(5 00tx st+e k4na ng it with a silk scarf, how can you determineaslthx0(htjat0e + 5-x bk43n if the comb is positively or negatively charged?

Why does a shirt or blouse taken from alg csqm44-6ct+p 0orgpq9ih0 e- k:he clothes dryer sometimes cling to your body:rl6g0h-qo-k9 +metg i0 qphpes 4 c4c?

Explain why fog or rain droplets tend to form around ions or electrons ig,fgm)o6t v1)(w a furn the ai)tr 1 6(fagu omf)gw,vr.

A positively charged rod is brought close to a neutral piece of pap6m1 ;.f(.vjgg wlj9vxsp z7raer, which it attracts. Draw a diagram showing the separationwv;m6vg.9f(xl1g7jp r js. az of charge and explain why attraction occurs.

Why does a plastic ruler that ibyj4e 4c18v z40ew;vircj c3has been rubbed with a cloth have the ability to pick up small pieces of paper? Why is zwb4iy8 rji4e3cc v;1jce4 v0this difficult to do on a humid day?

Contrast the net charge on a conductor to the “free / g f7/8ndyvel,b sv+lcharges” in the conductor.

Figures 16–7 and 16–8 show how a charged rod placed near an uncharged won ,2mun9lhqh0ym(-j-c4 pometal object can attract (or repel) electrons. There are a great many electrons in the metal, yet onlmoum(h nh-pqclo 2-wny9 ,j04y some of them move as shown. Why not all of them?

When an electroscope is charged, its two leaves repel each other and remain a x prgvnz vqm9pln181n 3r6:a4t an angle. What balances the electric foqg zr 9vv:3 ma1xnnl48n6p1rprce of repulsion so that the leaves don’t separate further?

The form of Coulomb’s law is v)fnsmzp (8 9ck: vnhv(s(cp1rery similar to that for Newton’s law of universal gravitation. What are the differences between these two laws? Compare alsn8) kcp vsrhvm(zn:1 9 ((fscpo gravitational mass and electric charge.

We are not normally aware of the gravitatiotf2h(2a pxb q/nal or electric force between two ordinary objects. What is the reason in each case? Give an example where we are aware ofqtx (p 22bha/f each one and why.

Is the electric force a neyjzt f2/ b:2rd4,jmd6j, spconservative force? Why or why not? (See Chapter 6.)

When a charged ruler attracts small pieces of paper, sometimes a piece jhk ju8-k- :mdbumps quickly away after touching the ruler. Exjkubm-d:8k -hplain.

Explain why the test charges we use when measuring electrics)l ,m7kyp ff. fields must be small, fk7mlpys).f.

When determining an electric field, must we use a positi +0a:-lwmvb)pq 2mo,djn2yz*e b 3ficve test charge, or would a negative one do as we+ 2mvqm2 pje)3oi, :alyn cb* zbfdw-0ll? Explain.

Draw the electric field lines surrounding two negative electriigc0,gi -3 wo qb;l:awc charges a distanceao: ; q gli3i0bw-cg,w l apart.

Assume that the two opposite + dk12t def4ppcharges in Fig. 16–31a 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, bottom, left, or right — is the electric field the s2ppetd fd 14+ktrongest? The weakest? Explain.

Consider the electric field at points A, B, and C in Fig. 16–48. bmi1wwc0. 1dvFirst draw an arrow at each point indicatin.cbw 110vmw dig 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 cros,ohp4sy* zi8cs?

Show, using the three rules for field lines given in Section 16–8, that m 2q6v) yszaap w)3v*bthe electric field lines starting or ending on a single point charge must be *3wsa)bav) zmvq p2y6 symmetrically spaced around the charge.

Given two point charges Q and 2Q, a distance l apart, is there a point along t;cgj2gwg 6w)a he straight line that passes through them where E=0 when their signs are (a) opposite, (b) the same? If yes, state roughly where thigcaw)2wgjg; 6 s point will be.

Consider a small positive test charge located on an e17yf kc qrmvk81b+7wu7):ki:pxbb eklectric field line at some point, such as point P in Fig. 16–31a. Is the direction of the velocityx)1mq:cv7y ikk7 b7+wbbk1ep 8ukf:r and/or acceleration of the test charge along this line? Discuss.

Sketch the electric field lines for a uniform line of charge which ic8ma(h4g f hd9s infinitely long. (Hint: Use symmetry.) Is the electric field uniform in strengtha(m9 hgfh4d8c ?

If the electric fluxpwqh 386do7tvo lfu in :-i62t through a closed surface is zero, is the electric field necessarily zero at all poti82vow3q toi 66f ul-:nh7pdints on the surface? 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 radius r. Iaisjt .zm 2)*(jxaor;is-bf qre5s;9 f the sphere is replaced b2m s -s9;x(sj*oii)t .j5 af;zrbqraey a cube of side r, will $\Phi_E$ be larger, smaller, or the same? Explain.

  

  How many electrons make up a char-vehi6ny:lm+ue hv 36p t. d b1+nou( ie4/swlge of $-30.0\mu C\,?$   $ \times10^{ 14}\, electrons $

  What is the magnitude of the elgi38khy2 bk dq2toc y2*m+vx8k7 gkt.ectric force of attraction between an iron nucleu*y2ty.3qi7k vx8b tckgk2g d+ 82k ohms $(q\,=\,+26e)$ and its innermost electron if the distance between them is $ 1.5\times10^{-12 }\,m\,?$    $ \times10^{-3 }N$

  What is the repulsive electrical fo+pcfvml.fs6*ucattvi: t:/r 9o:8 mqrce between two protons $ 5.0 \times10^{ -15}\,m$ apart from each other in an atomic nucleus?    N

  What is the magnitude of the f/1st5n ,r41urq9 malsvg cn6korce a $+25\,\mu C\,C$ charge exerts on a $+\,3.0\,mC$ charge 35 cm away?    N

  Two charged dust partica*cbowro: )z 8bn25hv 0xkc: 9zu.jsales 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. c/o)z:l0sd)-) vnne wt4 bvcpThey are moved, and the force on each of them is found to have beed- n4)):w ecvsotlbv/ 0 pcn)zn tripled. How far apart are they now?    cm

  A person scuffing her feet on a wool rug on a dry day accumulatetr1 27gy ijknjx ;l2t5s a net charge of2 lyk5;rj2 gtnt7 j1xi $-42\,\mu C\,.$ 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 th)gguu1 id( xo(e electrons in 1.0 kg of $H_2O\,?$    $ \times10^{ 7}\,C$

  Compare the electric force hold *4bh+6iwt spwikjd /c4.zm/i y(hse1ing 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. The sum of their chan 8tl :q.*,amd sb 8epnw:lfo3rges is What charge must each e8 al 3tmf8 l.:onqb*dw,np:shave in order to
(a) maximize the electric force between them,
(b) minimize it?

  Particles of charge t-x4fjnn8tq *t4j1s g$+75$,$+48$ 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 7oi d*(nog64glaa0e yequal charge, $+11.0\,\mu C\,$ are located at the corners of an equilateral triangle of side 15.0 cm (Fig. 16–50). Calculate the magnitude and direction of the net force on each particle.


the force on the lower left charge is of magnitude    N, and
will point    $^{\circ}$below the-x axis. The force on the lower right charge is of magnitude    N, and will point    $^{\circ}$below the +x axis.

  A charge of 6.00 mC is placed at each corner of a square 0.100 m on a side. Db5bf70i9nk 5la *7xm g;us lv lshmh92etermine the mal9g7ims bhu7b x*5kns290 l mlv5h af;gnitude and direction of the force on each charge.
$F_4$ =   $ \times10^{ 7}\,N$
$\theta$ =    $^{\circ}$

  Repeat Problem 14 for ty j;,r mtgle,8he case when two of the positive charges, on opposite corners, are replaced by;8ejym, lg t,r negative charges of the same magnitude (Fig. 16–51).
$F_4$ =   $ \times10^{ 7}\,N$
$\theta$ =    $^{\circ}$

  At each corner of a + 6q;k- d/lscdhhc5y xsquare of side l there are point charges of magnitude Q, 2Q, 3Q, and 4Q (Fig. 16–52). Determine the force on (a) the charge 2Q, and (b) the charglhxy/h-c;dk6 csdq+ 5 e 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 h 9g2l hhnsi) : ek4gvj::;akmequilateral triangle of side 1.20 sl9ik: ;)keg2 :4vanhghhmj: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 tot;vjtxsg76s 5ui-hu yf8 + qz3a3ti9tgal 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 total chargqw32ch: k+bcp sa+:jze 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 fromo alfun8ecv)1 ()* hnw an initially uncharged plastic ball to an identical ball 12 cm away. The force of attraction is then 17 m1)*eu)nf waonch 8(lvN. How many electrons were transferred from one ball to the other?    $ \times10^{ 12}$ electrons

  What are the magnitude a-x;hvb db- (xe-t 1wa:.polz rnd direction of the electric force on an electron in a uni1 bpl-xod.bwh:-z e;varx - (tform electric 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 fieldwx5bfzgq)om4w33w 8 k , and it experiences an electric force of 8)wwox b5fqzg3wk3 m4 $ 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 yfgv/(l(gw e,bqw *de.,6jhyis 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 an*nei wqwlb-- zj5hxij. ;(ls2d direction of the electric field 20.0 cm directly above an isoln.(*esq-;lbh ji -zjxw2lwi5ated $33.0 \times10^{ -6}\,C$ charge?    $ \times10^{6 }\,N/C$ ----待选择----updown 

  What is the magnitudg/zk k gz/p; 6h-mv4gomy0.e xe of the acceleration experienced by an electron in an electri kg/;g0gepkomy z4m z- 6./hvxc 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 midway bet c(y(9pmc3k+vo*;wn( o.ch.vmuziq zween a cz * hock((vcp qm. i mou.z39+;yvnw($-8.0\,\mu C\,$ 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 electri sdtz,2fmli/ ui- ccj9f2*vb 5c field lines about two point charges, $+Q$ and $-3Q$ which are a distance l apart.

  What is the electric field strength at:; -/s+) quiazfj yrgm 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 elr;u-3i776ismc)j pn qxm a2joectric field and accelerates to the northj 7miimx)u 6-r 7j3;qcpsona2 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 gl 1iz;bv6du(if1kj)1pb.y +yofm )gopposite 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 52.5 cm on amhl 2;8mvir o1 side if one corner is occupied bv;m2riho18 ml y 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 1.0a eafc6jir0e.s(g1 trvg ; 2;j zc56kc0 m on a side if the other three c;2k isc6j t r(;.0 arg 5ac6evfg1zjecorners 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 elecs:ow1b,4jxy8e9 .4 ybojgg na tric field at the 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 chargn8s j:b. w aggj4b91o4xey oy,es. 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 y79r pm :q;ktfzbhzg(1kl f*( 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 magnitudebvpo3+x vle lt.2,g v/ and direction of the electric field at points A and B in Fig. 16–57 due to the two positet.+ pgl/2,v3 vloxv bive 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 chh7 cv* d2(t (duyfwoj5arges, $Q_1$ 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 electrj :*bzyd:wfz4ic 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 xf:yjb:wz d4* z 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 thevxu lc9d nc9j:d/( 2oh right at 1.0% the speed of light enters a uniform electric field par j2l c(d9uc n/o9h:dxvallel to its direction of motion. If the electron is to be brought to rest in the space of 4.0 cm,
(a) what direction is required for the electric field,  ----待选择----rightleft 
(b) what is the strength of the field?    N/C

  The total electric flux from a c6 lwlb gr sz3 s0k:f5zba7hy:)a6yku( ubical 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 uniformzn9llo/suv mg6,) ozq. mjvat2*44 oq electric field of magnitudev)z gj oo,/mol46t*zqa.4svu9n2q ml $ 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 objn/ gx(tg 3:lfbects, $O_1$ 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 placed iaouw-1j+et )qvh+9q ln 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 plat:3dhyr kqi4* e,wpl-v es is The plates are 1.0 m on a side and are separated by 3.0 cm. What isd4rk- y*q vi:ple, hw3 the charge on each plate (assume equal and opposite)? Neglect edge effects.    $ \times10^{-9 }\,C$

  The field just outside a 3.50-cm-radius metal by 7c;tgk8wbuw/nlwb 6j3p vp10, rq-uall 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 carries a total chk2u /u9t.dpt garge 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 tilplmsvn1 c 9k:phi8odr3-(b ,+xue* hin 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) insid1p*n+u: v iblxm ehp3 dci9k,8-rsol(e 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 helix-shaped DNA molecule are he(uc tmeat/;.x rnry r q7db,2m5wh,f7 ld together by electrostatic forces as shown in Fbxyc7t ;m./ra,wu5nhmt edr72qr (,f ig. 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 electrons be if the electric force between them is equay-e 5i3vkx7kk4h . ncgl to the weight of either at the Earth’s surfvhk g5-x47kein3. kyc ace?    m

  A 3.0-g copper penny has a positive charge of 4zjk,pgjj 04x$38\mu C$. 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 field adhai0 5,/krk surrounding the Earth. Its ma5krh,akdi a 0/gnitude 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 field of what is the acceleration experiek5yn*d jj94c 2aq 9wwhnced by an electron near the s q2nj5 awkhjdw9c y9*4urface 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 statio6e5b fh ti/ixgr1t6,6t p bc5hnary in the air. If the downward-directed electric field of the Earthcb,x1br56it 5p f6e ih/t 6gth 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 hhmq;v3tzw :eh;e)a 4HN group shown in Fig. 16–62. The C and O h:vh;zm 3a)hqwt ;hee4ave 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, th+ v0 mcnobx77se electron revolves in a circular orbit a v0m cb77xnos+round the proton with a speed of $ 1.1\times10^{6 }\，m/s,$. Determine the radius of the electron’s orbit. [Hint: See Chapter 5 on circular motion.]    $ \times10^{-10 }\, m$

  Suppose that electrical attraction, rather than gravity, were responsible 9( -5eef/zwvgrh eh rk + xpa(sb07ii:for holding the Moon in orbit akr/b5xg ie:7ezh-v 9p+s(0rf heiw( 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 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 speggbkw 4- ,7he0n+mh msed $v_0\,=\, 21.5\times10^{6}\,m/s$ 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 z4noi8 h3p,7mtmeis sg09r 7p$Q_1\,=\, 2.5\times10^{-5}\,C$. 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 suspl)exu; )h,5ytp3q j wyended vertically from a3qy)l)eyh5txu ,w ; jpn ideal 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 +6 bnh) dsago880a6toidqos 9 is made with “leaves” that are 78-cm-long wires with tiny 24-g spheres at the ends. When charged, nearly all the chhdaso8+dt o86 )9as0gb 6nqoi arge 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 t xg*j.:5-,nfa hfcuk ihe electric field exceeds about :x.g *5cf ufk-,nhjia$ 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, an 0hsdf, oiy-y:d 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 o. g 2el5hxu6m,dp3saa,4 xcnall 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 j3dyn u yx.dngf1(2*z 1o9gzf 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 cont u*oyzf3j21gx1( n.fzgdyd9nact 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 charges5olntxw:v2*;kxqy /wpx)j s8 shown in Fig. 16–68, at what position(s) x is the electric field zero? Is the field zero at any other points, not on the 2:5ykt oqpj*lx nw8v/xws) x; 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 of charu*z 38iff 1.hg*be f ww/mx gu.ig84ucge $8.0\,\mu C$ 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?