If you charge a pocket comb by rubbing u*+j0wgjo 91 *fusx neit with a silk scarf, how can you determine if the comwg9 jou 0 e*fuxn*js1+b is positively or negatively charged?

Why does a shirt or blouse taken from a clothes dryer sometimes cling0i+6tqsq: e:(04oyvq wc szts/ fi t6f to your body/0wfq 4o0z styqvssqf:t+(: 6i e6i ct?

Explain why fog or rain droplets tend to form around ions or electrons in the 2egsc)8zrri jus :5(2 e wz503lmzdahair 0asiu( 3de2r:z z)l5w 5zsemhj8 2crg.

A positively charged rod is brought clo4mho17:djoe kvj* l h.se to a neutral piece of paper, which it attracts. Draw a diagram showing the separatio4loe mhj o.jdv:1 k7h*n of charge and explain why attraction occurs.

Why does a plastic ruler txm mvwe51c9m4t62 vud hat has been rubbed with a cloth have the ability to pick up small pieces of paper1mm62uwtmv5 vd 4 c9ex? Why is this difficult to do on a humid day?

Contrast the net chaj)i;i4e* nxsra0 l:zyp1g, sx dp,4az rge on a conductor to the “free charges” in the conductor.

Figures 16–7 and 16–8sitne1h y sm1z- zt.z-j8 .k0n show how a charged rod placed near an uncharged metal object can attract (or repel) electrons. There arets.-z 01mzyn -tn1ek. j hiz8s 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 each other and remain ayml o0aa1:9 .h l:egbkt an angle. What balances the electric force of repulsion so that th k g:a.l1lbm9 o0:yaehe leaves don’t separate further?

The form of Coulomb’s law is very similar to that for Newton’s law d4afhl 0 .,)qqdv/pr sof universal gravitation. What are v 0f,ad.h ls) r/qq4pdthe differences between these two laws? Compare also gravitational mass and electric charge.

We are not normally aware n6mk0l q eb/ v9pp4c/wof the gravitational or electric force between two ordinary objects. What is the reason in each case? Give an example whm6cv0/ek /b4lw pqn9pere we are aware of each one and why.

Is the electric force a conservative force? Why or why not? (See Chapterc25 q -go1mxwvvzvj-ocz 82)n 6.)

When a charged ruler attracts small pieces b*nn; * kcq9a)1gkirp of paper, sometimes a piece jumps quickly away after touching thrki**; p)b1gacnn qk9e ruler. Explain.

Explain why the test charges we use when meas f:7 ut .tqxoagur zi02:7hlije7nk 04uring electric fields must be small.2x70r4 lfok:7j etiz 7gin0qu aht: u.

When determining an electric field, must we usw* :erm8hlr5eew f eh1:her*g)g +cjopp:n * 6e a positive test charge, or would a negaewnp* hejwmc)+:*5f:hgr1pelhe *r:e 6 g or8tive one do as well? Explain.

Draw the electric field lines surrounding two negative electri w-ip 3sgbeh(qm )n5;sc charges a distance l sw-);m( ehb gps5i3 qnapart.

Assume that the two opposite charges in Fig. 16–31a ar(pm 7r a1rpm8be 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, le18rb mpra (7mpft, 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. First draw an 7gw ozug4afu069 dd :sarrow at each point indicating the direction of the net force that a positive test charge would experie6o97sd:uuzad0 gfgw 4nce if placed at that point, then list the points in order of decreasing field strength (strongest first).

Why can electric field lines never cross+31o ze/outcz -poti(?

Show, using the three rules for field lines givx: zrq;c84-scvbp b 6fen in Section 16–8, that the electric field lines starting orrv:8 ;fbp6szb ccq4-x ending on a single point charge must be symmetrically spaced around the charge.

Given two point charges Q a a*+au r3iowg,oj)f b)nd 2Q, a distance l apart, is there a point along the straight line that passes through them where E=0 when their signs are (a) opposite, (b) the same? If yes, state roughly where this poioaw)ujrfb i)a,g*o3 +nt will be.

Consider a small positive test charge located on an electric field line at some k*kmzty+6o dfc8q:h 8point, +yzd ot*hqf8m6k:k8 c such as point P in Fig. 16–31a. Is the direction of the velocity and/or acceleration of the test charge along this line? Discuss.

Sketch the electric field lines +my kd k4*o+rmknnh3(for a uniform line of charge which is infinitely long. (Hint: Use symmetry.) Is the electric field unifoh+kdkkomy +* n4 (n3mrrm in strength?

If the electric flux through a closed surface ij 8+agos- 8nxg/vg:frzya*7p s zero, is the electric field necessarily zero at all points on the surface? Explain. What about the corf 7sg /-gjanozg p+*x8y 8av:nverse: 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 s13 qygh7atieo6;* xy,f ohe0sh9n 4luurface of radius r. If the sphere is replaced by a cube of sid 603txhlq17 inyooe9 , he;agufs4*hye r, will $\Phi_E$ be larger, smaller, or the same? Explain.

  

  How many electrons make up a charge ofd 71bn96rric e $-30.0\mu C\,?$   $ \times10^{ 14}\, electrons $

  What is the magnitude of the electric force of attraction between anmx5y0tr- wd)d5l1 h1eimckp6 iron nucleud6m1x5w- ek0)t5 rc1 yihmldps $(q\,=\,+26e)$ and its innermost electron if the distance between them is $ 1.5\times10^{-12 }\,m\,?$    $ \times10^{-3 }N$

  What is the repulsive electrical forniwm ztwe6;x7 439ny vwhi c,(ce between two protons $ 5.0 \times10^{ -15}\,m$ apart from each other in an atomic nucleus?    N

  What is the magnitude ofd qi,4)q* jg 1 *qosol+kudv5n 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 force9: bn)hgkj.1(nljmcf a*n5vg5zx2gv 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.yqr oe0jvs1ny b95 f*+45 cm apart. They are moved, and the force on each of them is founn+v0e * orqb91syy fj5d to have been tripled. How far apart are they now?    cm

  A person scuffing her feet on a wool rug on a dry day accumulates a nedvl/:b *eoem wm,o ;o2t charge o; *, /o ombomevld2e:wf $-42\,\mu C\,.$ 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 kv md4gxx5opsw 2:g gem(*de1+g of $H_2O\,?$    $ \times10^{ 7}\,C$

  Compare the electric force holdinybn bm m-/c:1se13 jwvg 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 yyr0)yo( tx +w4e h4n*y*xsq mmg e80iare a fixed distance apart. The sum of their charges is What char m*e0 e(tyihgy+n4sw0x4r*mo yy q)x8 ge must each have in order to
(a) maximize the electric force between them,
(b) minimize it?

  Particles of charge i 2at erc:t,qr8 u0gh0$+75$,$+48$ 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 particl:- d2cwztqlcd ;e 2bh-es of 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 square 0.100 m on a sihfn sgyf40b1jy *n-j 1de. Determine the magnitude and direction of the force on each chn 1 n4- bfjfsy0yh*j1garge.
$F_4$ =   $ \times10^{ 7}\,N$
$\theta$ =    $^{\circ}$

  Repeat Problem 14 for the case when hj dqrfh8qp4wnr91- z6u j)+ypf0h:i two of the positive charges, on opposite corners, are replaced by negati +h wjpyf j0-rnidz6: uqpq4h19hfr8 )ve 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 point charges of magnitude 2n5 7o t dpd-n4surdypml7m0(Q, 2Q, 3Q, and 4Q (Fig. 16–52). Determine the force on (a) the charge 2Q, and (b) the charge 3Q, due to the other th(2p7s0 doy5u rtl m n-dm47dpnree 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 equilateral triangle of9lvam +f:6s zsbw)bm2v* h i3e side 1.20 m (Fig. 16–53). T*b 9 zml)6+vsfea vmw:hi23b she charges are $+4.0\,\mu C\,,$$-8.0\,\mu C\,,$ and $-6.0\,\mu C\,.$ Calculate the magnitude and direction of the net force on each due to the other two.
$F_1$ =    N
$\theta_1$ =    $^{\circ}$
$F_2$ =    N
$\theta_2$ =    $^{\circ}$
$F_3$ =    N
$\theta_3$ =    $^{\circ}$

  Two point charges have a total charge4l si3d( hnw ,g* k bzt 2)x7enqu427ydjv7duv 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 u ;jg*1f .*jc6gccwgg a0re/ospheres have a total charge of $90.0\,\mu C\,.$
(a) When placed 1.06 m apart, the force each exerts on the other is 12.0 N and is repulsive. What is the charge on each?    $ \times10^{ -6}\,C$$\;\;\;\;$    $ \times10^{ -6}\,C$
(b) What if the force were attractive?    $ \times10^{ -6}\,C$$\;\;\;\;$    $ \times10^{ -6}\,C$

  A charge Q is transferred from an initially uncharged plastic ball +1be;( nd.e0fcbilrqto an identical ball 12 cm away. The force of attraction is then 17 mN. How many electrons were transferred fromlb ir .(n;de0+b1eq fc one ball to the other?    $ \times10^{ 12}$ electrons

  What are the magnitude and direction of the electric force ; )rk9dku-k( cr mea4von an electron in a uniform electric fieldmca)r4kk 9 ek-vdr; u( 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 e(u2k 02 :(satijedhraxperiences an electric force easu 2jiakr(dh02( :tof $ 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 8u.0s jk 11.vbi8 izi0xawi;c r.4 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 direction of the electric fieldi/ ckno ,f9;ju*l5g hd 20.0 cm directly above an isolag5lfku i cj;nodh/9*,ted $33.0 \times10^{ -6}\,C$ charge?    $ \times10^{6 }\,N/C$ ----待选择----updown 

  What is the magnitude of the acceleration exjh8tjb:gcde,: ep m9w d0(7uxperienced by an electron in an electric field o0wh87t(dgjx9eb:dp u c,: j emf $750\,N/C\,?$ 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 fidtd v8(wl6 xp*eld at a point midway bet vx*d(6wp8tl dween 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 about twom 7 e3,kiwou4ans,t32i kju1 p point charges, $+Q$ and $-3Q$ which are a distance l apart.

  What is the electric field stusep hw7*.qrvjs n9dde5j:/+ rength 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 gc3. xoqn3m 0grest in a uniform electric field and accelerates to the north at a ra3.nmx0cog 3gq te 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 oppos3* yix8 lpv7dsite 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 centy 4kq*si0t: tler of a square 52.5 cm on a side if one c*t 0tlsqiy :k4orner is occupied 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 therdobw+.u)k1sko+( d /s *m k7grdid.x other three corneb.rs+w.mk/dr*+kx k71g do dd o)isu( rs are occupied by $ 2.25\times10^{-6 }\,C$ charges.    $ \times10^{4 }\,N/C$   $^{\circ}\,$ from the x-direction.

Determine the direction and magnitud5oiu0t u1g4p1wlv+x ge of the electric field at the point P in Fig. 16–54. The charges are s0uxui l+pg1o54gt v 1weparated 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 electr yxh s*ts2h.q r4uc9nuk .k22cic field $\vec{E}$ at the origin 0 in Fig. 16–56 due to the two charges at A and B. (b) Repeat, but let the charge at B be reversed in sign.

  Use Coulomb’s law to determine the magnitude and direction of the electricrgzc w 6.lu-lfr6 c42p;.muzm field at pointur6lzc4 ;mm.2u.pl gf z rw-6cs 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 c1riyd 5)c-be zharges, $Q_1$ 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 t2 z*iemf-e t5n:twccypfb83 . he point P shown in Fig..pi3*8b c5e2z wtnftef my-c : 16–59. The two charges are separated by a distance of 2a. Point P is on the perpendicular bisector of the line joining the charges, a distance x from the midpoint between them. Express your answers in terms of Q, x, a, and k.

  An electron (mass $m\,=\,9.11 \times10^{ -31}\,kg$) is accelerated in the uniform field $\overrightarrow{\mathbf{E}}\left(E=1.45 \times 10^{4} \mathrm{~N} / \mathrm{C}\right)$ between two parallel charged plates. The separation of the plates is 1.10 cm. The electron is accelerated from rest near the negative plate and passes through a tiny hole in the positive plate, Fig. 16–60.
(a) With what speed does it leave the hole?    $ \times10^{ 6}\,m/s$
(b) Show that the gravitational force can be ignored.

  An electron moving to the right at 1.0% the speed of light en0/m fhsr/rdq0)bldde u1d0s8ters a uniform electric field parallel to its direction of motionmb/08d1d d0e l f0)qus rdshr/. 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 cubical box 28.0 cm xf) gizo++.iz 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 electric field of mebytorgr+ 98rrg (/h8agnitudere9o8hr+ 8gg/ (btyrr $ 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 objects, r8 (i-ibg (jx26 hrxyq$O_1$ 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 unypft49qu4) nyiform 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 2x6ixjcx+.f,+ x io1 th ep0ns 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 ijx2.pxei+t+6sxn1hfx, o c 0opposite)? Neglect edge effects.    $ \times10^{-9 }\,C$

  The field just outside a 3.50-cm-radius metal ball e m nocir92n(o,xa8,f 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 ra m8m,k j;+*lxg-kaxx qdius 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 resk9o4rel 2e3awykpr (8 ts at the center of an uncharged thin spherical conducting shell. (See Fig. 16–33.) What is the electric field E as a function of r (a) for r yea9eol 8(rp32wrkk 4 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 are held together by eja/k1uux3 j*w fk1sl9lectrostatic 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 f* ws1jxul/akk 13 9juthe 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 iwmn3/ )lm5i e3fx,nygf the electric force between them is equal to the weight of either at the Ea,3gi3nnlmm wy )fxe5/rth’s surface?    m

  A 3.0-g copper penny ha i .lx6o8.vv54gen bffs 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 field surrounding thgq1c si hgdg+ yk7 /savzms56+-g e3c6e Earth. Its mea +g+s71gsvy6g -6 5k/id3 cs mqzcghagnitude 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 experienced -6lnpof5yqoxsbjv(0-3xb li l+ n00g by an electr5 -l6 pyn 0qx0jsg(ib+ov-lx3 fl 0bnoon 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 tu2mx+ 0;zmxxh v eud1f6- o4 5j0zdksmhe air. If the downward-direcsz+x0f5u he zu0jod; 4xmmm6-vdx2k 1ted electric field of the Earth is $150\,N/C$ how many excess electron charges must the water droplet have?    $ \times10^{ 6}$ electrons

  Estimate the net force between the CO group and the HN group shown in 626st rvzore+Fig. 16–62. rvzre ot s2+66The 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 circulartow fu rw w 1e9,cjg:34(x8otm orbit around the proton with4 93wujo, xe(c r wtof1gt:mw8 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 attractionxia/e5k-9c n-q8equ sazpqu0m9 3 xx3 , rather than gravity, were responsible for holding the Moon in orbit around the Earthuxquxpi5e ka8qescaq03z m x/939-n- . 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 spee/anav / ic4m8i( cey:fd $v_0\,=\, 21.5\times10^{6}\,m/s$ 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 charkp:wq3 wc2o,e kf s l4je2;3tu7jx4 afge $Q_1\,=\, 2.5\times10^{-5}\,C$. 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 vertkmnj .yz/h9 k1ically from an idealzm./yh k1k9 jn 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 “leaves” that aog(d b5vlj5-v ln qafnr 8j7*3re 78-cm-long wires with tiny 24-g spheres at the ends. When charged, ne*f3 j8on v blda5jr(v7 5nl-qgarly 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 generatei/ :0nroykaa8 a spark if the electric field exceeds aboutaya:nr0i8/ ok $ 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-d7 *ct2i hfre, and 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 all the electrons in a 15-kg bar +t;da:-/qq col bb2azof 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-wg fms2iq83gq1i dwm,; 9ica spheres A and 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 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 foqsm ia;cimg9, 3gqww f18-i2 drce on sphere A in this third case?

Given the two charges shown in zhlkcnj 1x;g.f0 hvs9bq7x: 8Fig. 16–68, at what position(s) x is the electric field zero? Is the field zero at any other points, not on the x 91 z 0n7 h gxbjlsvf:8kxqh;c.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 ch0iw;n nbi 46jo-b s5xwarge $8.0\,\mu C$ 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?