If you charge a pocket* k oi(cnn3*yqf/e ,pjrl1eu . comb by rubbing it with a silk scarf, how can you determine if the comb is positively or negapeji1ekrucn noql *f .,( 3/*ytively charged?

Why does a shirt or blouse taken from a clothes dryer sometimes cling to your q 7san k/c6/vaboksc va7n6q//a dy?

Explain why fog or rain drop4zmwjj o n;i+(lets tend to form around ions or electrons in the ai+; w(4zoinmjj r.

A positively charged rod is brsg tq)krnl9 k*+js 9/ybat61oa i(w/aought close to a neutral piece of paper, which it attracts. Draw a diagram showing the separation of charge and explainaa +o /99y*g6a( 1rb sn )skqtlkti/wj why attraction occurs.

Why does a plastic rffvid2d *1k km tost9m6oc-5x( kq8m ,uler that has been rubbed with a cloth have the ability to pick up small pieces of paper? Why is this difficult to do on a huxf(cm o812dqivfo t65-k tk*9msm ,kd mid day?

Contrast the net charge on a conductoy:g z eepl70j(8f0ywr r to the “free charges” in the conductor.

Figures 16–7 and 16–8 1enre u1dnx:(show how 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 alln(1 ud:rxeen 1 of them?

When an electroscope is charged, its two leaves repel each other(u1beup v7m+ s and remain at an angle. W s+veum71p( ubhat balances the electric force of repulsion so that the leaves don’t separate further?

The form of Coulomb’s law is very similar to that for Newt eqiyccrr923 0 ,dqx/eon’s law of universal gravitation. What are the differences between these two laws? Compare also gravitational q9 i yc,/r 3eqdexr20cmass and electric charge.

We are not normally aware of tz0gx5 :pn- db glvsz5/cw v(v*t;sv e;he gravitational or electric force between two ordinary objects. What is the reason in each case? Givs:v;nv *;gs z05wgtb 5xv lpc( d-zev/e an example where we are aware of each one and why.

Is the electric force a conservative force? Why or why not? (See Chapt ccu+p ,. i0g,v4nxcnser 6.)

When a charged ruler atti)u7* dz vslpjzy(4 )tracts small pieces of paper, sometimes a piece jumps quickly away zjs4d( *lyzt7vip )u)after touching the ruler. Explain.

Explain why the test charges we use when measuring electric fields must be small.tp52 ei a5hhd.h h.5e2itd p5a

When determining an electric field, must we use a positive test charge, ormdi/s .egvs/k8g y-+g+lns b/ would a negative one do as well? Expgl/+-dsv/ bsny/kes gm.+i8glain.

Draw the electric field lines surrounding tw; ja4c)s jmn18vh)bky o negative electric charges a distance l apartj s)jk;48ay)m c1nbhv .

Assume that the two opposite cf09fg8zl r ( qwf(no)bharges in Fig. 16–31a are 12.0 cm apart. Consider the magnitude of the electric field 2.5 cm from the positive charge. zfnrwo89fq(l 0) b(fgOn which side of this charge — top, bottom, left, or right — is the electric field the strongest? The weakest? Explain.

Consider the electric field at points A, B, and C in Fig. 16–48. F)oye 5 /ft:s:b/0odees vpc8dirst draw an arrow e)spy:dd05tve/8s /: c efobo at each point indicating the direction of the net force that a positive test charge would experience if placed at that point, then list the points in order of decreasing field strength (strongest first).

Why can electric field ldo bsg49m+)ix/ h/ t a2ybcu(uines never cross?

Show, using the three rules s 5uwhsj7t/o 33mrs5u for field lines given in Section 16–8, that the electric field lines starting or ending on a single point charge must be symmetm/ujrts 7 oshs53wu5 3rically spaced around the charge.

Given two point charges Q and 2Q, a dist v*.vvjj1/o7z qngp x8 vyl,f)ance 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 roughf j)v .j*vov qz/,7n8vxpl1 ygly where this point will be.

Consider a small positive test charge locateko-,wuk00aso.:ob mf9kyr:zu a8 0vrk3 kkq -d on an electric field line at some point, such as point P in Fig. 16–31a. Is the kkv-,8kq y0:kr-s u0mr zfoaak9oobk.0:3 wu direction of the velocity and/or acceleration of the test charge along this line? Discuss.

Sketch the electric field lines for a uniform la h vh/0uspp8o +9ho pfhg4 ::4pn4jamine of charge which is infinitely p/phpua:4h0 sgo j9hfm4vao+n8: ph 4long. (Hint: Use symmetry.) Is the electric field uniform in strength?

If the electric flux z (kcnd 5dn :9jhgep11through a closed surface is zero, is the electric field necessarily zero at all points on the surfacecn(dpdn159h :j1g ezk? 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 surroun1+d y5 :na*nj;bmkp bgded by a spherical gaussian surface of radius r. If the sphere is replaced by a cube ofd5m+nk1:jb; y ab np*g side r, will $\Phi_E$ be larger, smaller, or the same? Explain.

  

  How many electrons make ud(b+8u8bvti/cr) k,yd *lum p p a charge of $-30.0\mu C\,?$   $ \times10^{ 14}\, electrons $

  What is the magnitude of thi 0v5w1su exu94 aedy()1xg sse electric force of attraction between an iron nucleuxd ixs1sw 1e)u(yu90 4egvas5s $(q\,=\,+26e)$ and its innermost electron if the distance between them is $ 1.5\times10^{-12 }\,m\,?$    $ \times10^{-3 }N$

  What is the repulsive electrical force bbs u fuv99wro4g7yy1)j6 8 suletween two protons $ 5.0 \times10^{ -15}\,m$ apart from each other in an atomic nucleus?    N

  What is the magnitude of tha 713u9ngw)dq/:hsmrj c 6bdse 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 of ohzowy4f ,0)v $ 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 forch fzhd7t q;. 4i(a4t9dohr u)ne on each of them is found to have bit9fahd44 q 7 o) t;rdnuzh.h(een tripled. How far apart are they now?    cm

  A person scuffing her feet on a wool rug on a dry day accumulates a ne+:2d1kqugui cwqx0 n,k (ebkpl30s0 kt charge ofkeu0x: 0ib2l, 3 pgnc +u(1ks0dwkqkq $-42\,\mu C\,.$ 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 c.zx bxk6eg9)y0h)7peutxy :s(4yd g 1.0 kg of $H_2O\,?$    $ \times10^{ 7}\,C$

  Compare the electric force holding the eleh 85;y(jt/b9 ndsgdiz ctron 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 fhiaqj2b1 sss+9lil988cqm z 6ixed distance apart. The sum of their charges is What charge mui82j69shl z sb mq8qs+al 9ci1st each have in order to
(a) maximize the electric force between them,
(b) minimize it?

  Particles of charge koj jyz7t wsiq 081;ify1,q4r $+75$,$+48$ 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 c.yl +)n4ebkg8t;*hnr0 trfihharge, $+11.0\,\mu C\,$ 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 sq/ut b4lc-6,4itr./c rrkas i d iu+m7buare 0.100 m on a side. Determine the magnitude and direction of the force on each/4a 7r.b,itl 4 imsbu i+ccuk/dtr-r6 charge.
$F_4$ =   $ \times10^{ 7}\,N$
$\theta$ =    $^{\circ}$

  Repeat Problem 14 for the case when two of the positive charges, on oppositeggh uf3xdky5b b7)*7fdz:v i2 corners, are replaced by negative charges of the same magnitude (Fig. 1k hdv*2g b bdiu77x5fg):yfz 36–51).
$F_4$ =   $ \times10^{ 7}\,N$
$\theta$ =    $^{\circ}$

  At each corner of a square of side l there areqxu hh3v, .61mncr,)gblgju jz9vu 2 / point charges of magnitude Q, 2Q, 3Q, and 4Q (Fig. 16–52). Determine the forceh.ngcm,lu/u 9jj qvvh,3 6z)u 2g1r xb 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 aub;) +,rt, ol7 iri6sbsl1ukv n equilateral triangle of side 1.20 m (Fig. 16–53). The charges a ltru7vsb,;u )lb, os 1ik6ri+re $+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 t tfrgl.mr :r79/mosm, ,mbu) 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 ds5,7 xe*cvmr/3w lfra 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 fromq*w;,z; qu1o8jokqwb 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 tb*q1qo zu ;ok,w;qjw8he other?    $ \times10^{ 12}$ electrons

  What are the magnitude and direction of the electric force o75-ax oe36,kdvhec umte zoc j02f8g1n an electron in a uniform electric field - 5 jc3da08vf c6xutzg1omeeke7o,2h 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 experi/d:n od cei/0xaew 4zy2+hwt4ences an electric force wo z/nw:4 tdhxa4+/e2c id0 yeof $ 3.75\times10^{ -14}\,N$ toward the south. What are the magnitude and direction of the electric field?
   $ \times10^{5 }\,N/C$
 ----待选择----southnorth 

  A downward force of 8.4 N is exerted wag*5/: cp 9otwl3sepon 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 thez2dmf; (rjq mq :7/uqs electric field 20.0 cm directly above an isof2zjqmsq7d (qu;/mr: lated $33.0 \times10^{ -6}\,C$ charge?    $ \times10^{6 }\,N/C$ ----待选择----updown 

  What is the magnitude of :,vylhb*,l c nthe acceleration experienced by an electron in an electllv*h:,cy ,bn ric 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 amj-o bwb)nj qfm.l x(883d4t s point midway betwe8d3jlo)w8b x.fm n bt(m -qs4jen 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 abwc.tb ;skg:1s out two point charges, $+Q$ and $-3Q$ which are a distance l apart.

  What is the electric field s+spnh6 o3yjx) xj//y 3w8j kl6eoh bi0trength at a point in space where a proton $(m= 1.67\times10^{ -27}\,kg) $experiences an acceleration of 1 million “g’s”? $\approx$    N/C（Round it to one decimal place.）

  An electron is released from u7 ps (rb9,zn9a4ecn qrest in a uniform electric field and accelerates to the north at a ra a n(,bp4u 9ne9sqzrc7te 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 ztl* p.d lor1,two equal but opposite 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 9.f)n9 m1p()brdu9th q zixqysquare 52.5 cm on a side if one corner is occupithbn(i1 .d)9q uyrq xpm 9z)f9ed 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 fieuv 8h sx)8 lmpu3b4ls2egy-y7ld at one corner of a square 1.00 m on a side if the other three corners are )-lvl8p 7yg3xu y2 su8eb hs4moccupied by $ 2.25\times10^{-6 }\,C$ charges.    $ \times10^{4 }\,N/C$   $^{\circ}\,$ from the x-direction.

Determine the direction and magnitude of the electric field at the po pt*+fe g6g4cpw(4pwzint P in Fig. 16–p* e4+6fpcwz( gtgpw 454. The charges 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 electria5-fh4.o1 cajmm0 db.6twe fac 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 d(w0rn2py43 nj ,bwt tjzac.o2etermine the magnitude and direction of the electric field at points A and B in Fig. 16–57 due 0 23anpt,jwzt(orc j .by 4n2wto 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 po5r+jf3 iri8a w pc /i3gtp(uoj+80zk eint 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 theln40s:u f .2gfmt2 wdw 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 l:tfn2d u2w.0wmg 4fsmidpoint 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 xk n5vr+h7c0f 7zm(pethe right at 1.0% the speed of light enters a uniform electric field parallel to its direction of motion. If the electron is to be brought to rest in the s (c vren+xk7 hz0mf7p5pace 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 cub e,nw*rbd69czical 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 1g+g+te6l+bfxni 3y4 o1v kjr +8 cm is placed in a uniform electric field of magnitude+f3 jy+l6gbv+e+r 4 1nit kgox $ 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 objvh45 qptf8 8gjects, $O_1$ 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 uwvtfln p2hdp9*+e lpp3)x9v (niform 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 t bso5mtq4r (2i r9os z7dl8:htwo square metal plates is The plates are 1.0 m on a side and are separated by 3.0 cm. What is the charge on each prrs52 iz97(o84mq l:oshtdbt late (assume equal and opposite)? Neglect edge effects.    $ \times10^{-9 }\,C$

  The field just outside a 3.50-cm-radi* /9g. cc3snamqhe2yxus 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 radiusd :l3vre p*p+m 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 an uncharged thin spherical condu j b 3khwjvlk5;ym;zg)o).z7 scting shell. (See Fig. 16–33.) v;j3szm)og l k k;7y)jbw5z.hWhat 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 Q affect the shell?

  The two strands of the helix-shapet(y*rk w s8 4,0teknyid 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 indicated C and O atoms is 0.4e. Assume also that atoms on each*syy8 0 eritkk,t4w(n 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 elec9sfd jq:u.y5 js+tb: utric force between them is equal to the weight of eiths jufq .jydub+s9::t5 er at the Earth’s surface?    m

  A 3.0-g copper penny has a positive cha k bdgn02u5)wbrge 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 field surrounding the-ll. ,zskau9k s+s. ak Earth. Its magnitude is a s +l kz,-ua9sk..lksabout $150\,N/C$ 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 elemibh)fhv0l8bm7i/ 5b 4 -qy7 za e:thzctric field of what is the acceleration experienced by an el m 7bblhhia m/ie7v fzh4b8z5yqt:)-0 ectron 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 stationary in the air. If fm*8mezk rf+84fo v 4gthe downward-directed elek8gr4e* 4mffzo8 fm+v ctric 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 groucm4epln1hqkd8-b 2 g9 p shown in Fig. 16–62. The C and O 4mhqp2e8n-kb9gl cd1have 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 a0dn2)*cwwd h ctom, the electron revolves in a circular orbit around2cc*w 0h dwn)d 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 grav z6d 2.9v8qvso yaucp 2aj8+tsity, 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 o jq82 u2s9zdo+8y6.asvc p tavf 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 spee(hz on cyz/0t18 y6deg*eed+b d $v_0\,=\, 21.5\times10^{6}\,m/s$ 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 charg0tl 3m*aogty 78 eyk+te $Q_1\,=\, 2.5\times10^{-5}\,C$. 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 suspen **brstd2rhd/ ded vertically from an ideal spt rbd2** hdsr/ring $(k\,=\,126N/m)$ 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 w+ z* z;)y(lnzt-ji y7mgp (lbgires with tiny 24-g spheres at the ends. When charged, nearly all the charge resides on the spheres. If the wires eac pg mg(+iz)zn;yzy*ll t(jb7-h 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 electri5gpnd;tc0axc 3e/e.fc field exceeds about de tg0c/3afx;c pn5 e.$ 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 yu) mm*v3c.s fj3h ey3net 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 15-kg gz4xkso92zi lr1x )b- :+nerl 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 sphereu38pecd02c4xobp. vi e 7 *exjs A and B are a distance R apart; each carries the same charge Q. (a) What is the force sphere B exerts pxp2 xi4c .u0bejc7ev3e*o8don 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 Fig56u(u6sbo c*a xh( olc. 16–68, at what position(s) x is the electric fielcl (h*u us(b ao6c6ox5d zero? 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 ofsq1df5-olg /g8+ rpkyt jb5;w 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?