If you charge a pocket comb by rubbing it with a silk scarf,7i**q44 c1 usetrv dps how can you determine 4std**qi v 7csr14ep uif the comb is positively or negatively charged?

Why does a shirt or blouse taken from a clothes dryer sometimes cling c6q t31xo8/8rlacge6*jhp:hq *t vsyto your bods1/q 3reh*8*ttc oygch vlpx 8:aj66qy?

Explain why fog or rain droplets tend to form aroundfd1 7yy -37clg hubgo jme s2i:590sm+x d+lhf ions or electrons in the aircdome+yh g d -bs+:7f9lh ix 05g12lsj73mfyu.

A positively charged rod is brought close to n/yemi9 )dzbun)z 0 9ra neutral piece of paper, which it attranr)yunem0 9/zdzi b)9 cts. 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 abi1bj-hiaho5h*a2xfv, lity to pick up small pieces of paper? Why is this difficult toi,axh5 fh2bjo1a * vh- do on a humid day?

Contrast the net charge on a conductor to the “free charges” ii lb ly+9f/2,pdd. o6tb5soazn the conductor.

Figures 16–7 and 16–8 show howsw u57pvtri: o1l*sy6 a charged rod placed near an uncharged 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 allur1syp:o 67l5s *t vwi of them?

When an electroscope is vylneqx .5p(v *f ,jt.charged, its two leaves repel each other and remain at an angle. What balances the electric force of repulsion so that the leaves don’t sepp .eyn(jqx ,v.flv t5*arate further?

The form of Coulomb’s law is very similarm/5k *vuh9.x( vxgbfi to that for Newton’s law of universal gravitation. What are the differences between these two laws? Cobmx* g iuxf/v.v k95(hmpare also gravitational mass and electric charge.

We are not normally aware of the gravitationar3xx n *k/a.iil or electric force between two ordinary objects. What is the reason./a i knx3*xir in each case? Give an example where we are aware of each one and why.

Is the electric force a conservative force? Why or why not? (See Chap9mp5 ky13eg,b;6hrlkqltc3wdm o)0z ter 6.)

When a charged ruler attracts small pieces ofp ,bsl 9b ;6sr+b l.skoyjq+e9 paper, sometimes a piece jumps quickly away af bp+9+ 9lsy;s.l6js ekqb b,orter touching the ruler. Explain.

Explain why the test charges we q19xq*a4-kqmk8cn l yuse when measuring electric fields must be small.qm8-qql 1x ykn*k94ac

When determining an electric field, must we use a8b h 7ht)bcwczb1g b-/ positive test charge, or would a negative onb17ghz8bh /b b-c)tc we do as well? Explain.

Draw the electric field lines surrounding two negative electric charges a distanr z8l ty**)jbuce )zur *y* j8lbtl apart.

Assume that the two opposite charges in Fig. 16–31a are y:2+0l xsaw my*2hqi-jh: zz+; utjeg12.0 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 electgjl y zq:+-sh hxj2a0y*2itm: ;wu+ezric field the strongest? The weakest? Explain.

Consider the electric field at po4i71qw; go4 qqzsqhtqlz( 07ggy 1lzhg 1.q r:ints 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 o s z1tg;lqizo q: 1wqqg4 0g(y.1lhh4z7gq7qrf decreasing field strength (strongest first).

Why can electric fielmgyu.germc7lc9rr- z85 r.y1d lines never cross?

Show, using the three rules for field lines given in Sectionx0dfbeh9w +c. rfp86r 16–8, that the electric field lines starting or enp hc. +ffr0x89er6 dbwding on a single point charge must be symmetrically spaced around the charge.

Given two point charges Q and 2Q, a distance l apart, is * oc.bjox l2tzjvo/5 ot-z 03ithere a point along the straight line that passes through the0z xzjt5o /bj3ol-oo2 v .c*tim where E=0 when their signs are (a) opposite, (b) the same? If yes, state roughly where this point will be.

Consider a small positi/ z bfx.0nu0ol 3iu3ck x qylf945jex:ve test charge located on an electric field line at some point, such as point P in Fig. 16–31a. Is the direction of the vejql:y 9/oik3u0nefb.x l4 zf ux5cx03locity and/or acceleration of the test charge along this line? Discuss.

Sketch the electric f;2x0v ,jqbmauo*z(t46uo pm oield lines for a uniform line of charge which is infinitely long. (Hint: Use symmetry.) Is the electric field uniform *0z,outm6uq jop( b4;2mox avin strength?

If the electric flux throchzcdm7wyn .tkpsq znr8r:8;p5c.sp r949i4 ugh a closed surface is zero, is the electric field necessarily zero at all points on the surface? Explain. What about the converse:p8pmh:s n dcc wn9; p85rk47iy t9rzs 4cqzr.. 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. I xhw6;gvelj+3 f the sphere is replacejh; xwl6v3g+ ed by a cube of side r, will $\Phi_E$ be larger, smaller, or the same? Explain.

  

  How many electrons make up a chaprlo;wy5xib7q6dqw(b7ff 2 p 7ab87o rge of $-30.0\mu C\,?$   $ \times10^{ 14}\, electrons $

  What is the magnitude of the electric force of attraction between an iron nucleuzv -mr0 *+ykx4jpw*wem epk+*0wv-yz*wj4rxs $(q\,=\,+26e)$ and its innermost electron if the distance between them is $ 1.5\times10^{-12 }\,m\,?$    $ \times10^{-3 }N$

  What is the repulsive electric9fw78 yxmai ,hal force between two protons $ 5.0 \times10^{ -15}\,m$ apart from each other in an atomic nucleus?    N

  What is the magnitude 9aws,l *5 2euiv1jfimof 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 force ozgpjy*88 j 5 kjupwu50f $ 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 the force on each olj yymk)-:h dcn2)s-cf they ld-cys -2)j:m)kchnm is found to have been tripled. How far apart are they now?    cm

  A person scuffing her feet on a woo+i6l,sa7ybsh2; ai , py*d9vdf:xpbkl rug on a dry day accumulates a net charge of *vd2as p b7yfs9hi;6pi:xb,+ aydk,l $-42\,\mu C\,.$ 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 electronsc+n4r ,8ja8fe 1se ya0)9w.sr haqo zs in 1.0 kg of $H_2O\,?$    $ \times10^{ 7}\,C$

  Compare the electric force holding the electron in or;izq pvrsh 3t impx3+9gu-3.nbit $(r\,=\,0.53 \times10^{-10 }\,m)$ 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 o vyjer)+pd5)q ,j lj8sum of their charges is What charge must each ,jj)vo5)ly+jrqe 8pd have in order to
(a) maximize the electric force between them,
(b) minimize it?

  Particles of charge bs-3 ju 5cv ih,,5mtle$+75$,$+48$ 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 chargbk:mhfo4 a8wsah+ j,.e, $+11.0\,\mu C\,$ 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 0.100c ogw2 tlzg(3* m on a side. Determine the magnitude ang(lwcog23 *ztd direction of the force on each charge.
$F_4$ =   $ \times10^{ 7}\,N$
$\theta$ =    $^{\circ}$

  Repeat Problem 14 for the case when two of the positive charges, on o)9zg :q 5pqlh+dwx)bqpposite corners, are replg+5zldxqph:w9 qq )b )aced by 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 pa b7e)-d+ayhpoint charges of magnitude Q, 2Q, 3Q, and 4Q (Fig. 16–52). Determine the force on (a) the charge 2Q, and (b) the charge 3Q, due to the otherd-ab +7ae) hyp three charges.
$F_{2Q}$ =    $\frac{kQ^2}{l^2}$
$\theta_{2Q}$ =    $^{\circ}$
$F_{3Q}$ =    $\frac{kQ^2}{l^2}$
$\theta_{3Q}$ =    $^{\circ}$

  Three charged particzpj1o4u7nf3af5 )uvj*, lqbg les are placed at the corners of an equilateral triangle of side 1.20 m (Fig. 16–53). The chal4zoq v j1)gpbf 3fun,ja*5u7rges 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 y.oawb40ng5haah :p;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 toonfujzp9 h3s0( b3gvw;ef9 ,atal 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 fcy.+ b4v e x*a.rtx*mprom an initially uncharged plastic ball to an identical ball 12 cm away. The force of attraction is then 17 mN. How manpav +.bmx tx*ce4y.*ry electrons were transferred from one ball to the other?    $ \times10^{ 12}$ electrons

  What are the magnitude and di r0*3d+roxbc prection of the electric force on an electron in a unixcbd+ op r*r30form electric field of strength $2360\,N/C$ that points due east?
   $ \times10^{ -16}\,N$
 ----待选择----westeast 

  A proton is released in ta0+edvh t 7k/wqcp)+ a uniform electric field, and it experiences an electric force of +d7cp) + v/kqtet0ahw $ 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 exmho2es+e.hr+0d2xch997dvm da/y emerted 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 field 20.0 cm directly ,ozlat, rk m(s.m;9glabovea(r klgl., sm9otz;,m 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 awesa77yy wws v5 j0q( .e1.jzrn electron in an electr 77 wqssjyayj wv(.5er z.w1e0ic 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 magnitud+ ;;jp7up x0sj 9vny8jj qvabs0vh :3we and direction of the electric field at a point midway between a:7wvvbpvjn y0u8 s9 j0+;x3pajj;hqs $-8.0\,\mu C\,$ 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 a o - c25rx.27 n8lyu 7u6hbfjjv:d1dg*sqeyan bout 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 pnu34a;4s0wumi p1rgk roton $(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 tq0ew,7ad*w+)nwx/x u mdh a2yfo4p8so th2 uxmq)+ah f,y*pxd/os4 0ewn7a8w wd e north 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 opposite point charges ) /q ns5v)rddzawqgf466 ye 8ais $745\,N/C\,,$ 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 the5j*r c-ljc9ns center of a square 52.5 cm on a side if one corner is oc-9n jscl 5rj*ccupied 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 a square 1.00 m on a side if the o(c;b btbk g38uz(r1 .vbv z5sother three corners abt3zbv.kbvsc15 bgo ;(zu 8 (rre occupied by $ 2.25\times10^{-6 }\,C$ charges.    $ \times10^{4 }\,N/C$   $^{\circ}\,$ from the x-direction.

Determine the direction and magnitud(r j6zx v:pxo3kjc /b3e of the electric field at the point P in Fig. 16–54. The cha/bxc( k xr: jov6zpj33rges are separated by a distance 2a, and point P is a distance x from the midpoint between the two charges. Express your answer in terms of Q, 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 electrla5 r87ec8-m*cetlr dic 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 delrpal9y v aih/k( pqp7*y w/-1termine the magnitude and direction of the electric field at poih1lpr qp * kapv9/(/-ay7lwy ints 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 point charnz;bu2y 1- iowges, $Q_1$ 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 mauy2n8wo -ii(k gnitude 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. Express your answers in terms of Q, x, a, anu-n82w(ioy ikd 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 yv2e4k /2tfqw :g1jufspeed of light enters a uniform electric field parallel to its direction of motion. If the electron is to4vytj1g2ef /:2f kwuq 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 cubicabn0 vai8j/z9fwva (e 0l 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;g oct(q sa9, .adodwbi:oo5q i* q+q5 electric field of magnitudeqd:db5.sqoq; ( g*9,atwoio ai qo5+c $ 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 objec 4y v.eeq-trzs,*r n0tts, $O_1$ 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 in a uniform fu /9+4s uupxj u:-w,llhwf0ahield $ 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 met:l *u,;d7v )uieves wral 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)? Neglect edge esv ;,u v 7)le*iw:dureffects.    $ \times10^{-9 }\,C$

  The field just outside a 3.50-cm-radius metal bah u enqd qai4yf4/2 :lh12j-xill 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 rad+vs4asx gr3 t53xy6 manyqb*hqj65 v8ius 3.00 m carries a total charge of $-3.5\mu C$ What is the magnitude of the electric field at a distance from the sphere’s center of
(a) 0.15 m,   
(b) 2.90 m,   
(c) 3.10 m,    N/C
(d) 6.00 m?    N/C
(e) How would the answers differ if the sphere were a thin shell?

A point charge Q rests at the center of rj2;bve2 :zvgg4 nk i7an uncharged thin spherical conducting shell. (See Fig. 16–33.) What is tzg: k;jirngb 4v7e22v he 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 Q affect the shell?

  The two strands of the helix-shaped DNA molecule kvbl4z67;,u g +pw-ix ukuob6are held together by electrostatic forces as shown in +7;ul 4iobwvukx ,bk-6zug 6p 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 eletm5i ;)fuq+xhy4 ng3actrons be if the electric force between them is equal to the weight of either at tx5;3hq +gfmn) y uita4he Earth’s surface?    m

  A 3.0-g copper penny has a 0xibnnxqp * 9kog/j8n:(j/c x 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 isi frsb* f n88bt*0herb83z68+ i giawy an electric field surrounding the Earth. Its magnitude is about tib*z3 sfn* 0yr eg8whb86rab8i8 + if$150\,N/C$ 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 wha;8am .9c tsdf2 czko5pt is the acceleration experienced by an electron near the surfa fo dcc8z.29;skat 5pmce 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 ul 9;vel*7knc tnh:x* wr++eg air. If the downward-directed electriclwxt**: 7n +g9e lckn+ruh;ve 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 in Fig.+ d3bdzu-k2th 16–62.htb zku d-+3d2 The 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 hydrogen atom, the electron revolves in a cir pnltf 4o6n01qcular orbit around the proton with a speed np1qn6 f 0lt4oof $ 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 -xlqd1r 6k 0iiosgx64 responsible for holding the Moon in orbit around the Earth. If equal and opposite charges Q were placed on the Earth and the M -1 x60iglkd4or6xi sqoon, 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 speeiaf f3iyq.- 1rd $v_0\,=\, 21.5\times10^{6}\,m/s$ 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 vhqv q8a7 mew-m7x iw(,v.ji:$Q_1\,=\, 2.5\times10^{-5}\,C$. 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 suspendeq9(* tgfssdb 1d vertically from an ideal sprids( t*1sb 9fqgng $(k\,=\,126N/m)$ 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 “leaves” that are 78-cm-long wszljbp q.aqt-q;b( n+q dg5cu 4 xf*5*ires with tiny 24-g spheres at the ends. When charged, nearly all the charge resides on the spheres. If thed jq t5* nalb+ s.gcpxqzf5u(q-b;4q* 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 55anbiln/ gg/ spark if the electric field exceeds aboutl55gi /bgn a/n $ 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 charge u65 q3ntlju(k$+0.340\,\mu C$, 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 bd+. oj; :twouall 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( /z*.8 /syu,rya t9 eram5wut h5iwzd 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 coneuz5 a8ryh5rtz /usyww(,.9i tm a/* dtact 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,tqb(c bxh 6mk nny2;;9 at what position(s) x is the electric field zerk;b(2nn q mb6chtxy ;9o? Is the field 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 oy;wb.5wg ln0lvu/,d pf 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?