If you charge a pocket gkoq 7: ise)e4t/0p zgiy 8dt)3q1fvdcomb by rubbing it with a silk scarf, how can you determine if the comb is)4itids yz1)kde7fpo/ge v83q 0:tq g positively or negatively charged?

Why does a shirt or blouse taken from a clothes dryer sometimes cling to y i( u rnbts-+cwhh6*s-our bo s(-c hwsnui-* hbr+t6dy?

Explain why fog or rain droplets t3atbl9 3hiu c+end to form around ions or electrons in the air.3 9au hb+lci3t

A positively charged rod is brought cln1* 4p-w xbxxs nn++blose to a neutral piece of paper, which it attracts. Draw a diagram showing the separation of charge and exl +wxbp-+ n*snn4x1xbplain why attraction occurs.

Why does a plastic ruler that has been rubbed with a kqu; vpxq p8:g 6gk:3gcloth have the ability to pick up small pieces of paper? Why is this difficu8qp;gqk36ugvx k:gp : lt to do on a humid day?

Contrast the net charge on a conductor to the “free charges” in the conzj37i)doh y-a8mp,otductor.

Figures 16–7 and 16–8 show how a charged rod placed neagu m nu/ e;0x+o2b-:g s-yscrar an uncharged metal object2 ery+c b :g -uo0m/xasgn;su- can attract (or repel) electrons. There are a great many electrons in the metal, yet only some of them move as shown. Why not all of them?

When an electroscope is charged, its two leaves repel each other and rexms (5yf,i 1uimain at an angle. What balan( iusfi5yx1 ,mces 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 New:w(9 j3ow r/ kfg2xotjton’s law of universal gravitation. What are the differences between these two laws?3/w kojrxf2jg:w( o t9 Compare also gravitational mass and electric charge.

We are not normally aware of the gravitational or electric force between t;5fvd,u-6bkyhz mq0 owo ordinary objects. W oz -b5 ;qvmkhd,fyu06hat is the reason 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? i rx9g5 2zh)l5esyb)-rqjv6 i(See Chapter 6.)

When a charged ruler attracts small pinh xce o056xjm/tgggg* 4xe2 )eces of paper, sometimes a piece jumps quickly away after tou6 g5e tn*4c/ xho20gxjggmxe)ching the ruler. Explain.

Explain why the test charges we u)i, i9ulyqdr2 chjs:*k1q6bo se when measuring electric fields must be smallul b q* 2 riidcq:6sojhy,1k9).

When determining an electric field, must we use a positive test charwk. 5j;8 hrf2dh77 cih8tdkrage, or would a nj;5k .ih7dr7whf2 ah cdr8 t8kegative one do as well? Explain.

Draw the electric field l6r6rd d gic8; :cwicuug*u: w9ines surrounding two negative electric charges a distanci:9 urg;c wu86c6r*g dwui:c de l apart.

Assume that the two oppo.tavc cfj;xny 3y)4 v2site charges 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 elec f); vjcyv3nay4t2 .cxtric field the strongest? The weakest? Explain.

Consider the electric field at points A, B, and C in F eqursaau/4/ xg6o; (tna7;g gig. 16–48. First draw an arrow at each point indicating the direction of the net force that a positive test charge would experi6u gn ge/7tg(aru;o;/ax4 qa sence if placed at that point, then list the points in order of decreasing field strength (strongest first).

Why can electric field q)1i znt lfv6z07md+e lines never cross?

Show, using the three rules for field lines given in Section 16–8, that the eleoccvzt/ i2m p ..wrd)7ctric field lines starting or ending on a single point charge must be symmetrically spaced art7 wzip..2d /c morc)vound the charge.

Given two point charges Q and 2Q, a distance2m03eluh pd7f l apart, is there a point along the straight line that2mf 7hu p3d0el passes through them where E=0 when their signs are (a) opposite, (b) the same? If yes, state roughly where this point will be.

Consider a small positive test charge locoaoh+k 6p ,bg+; uw/tdc/l3fgated on an electric field line at some point, such as point P in Fig. 16–31a. Is the direction of the vdgfo ; ,u/oa/chpwgl+t+b 63k elocity and/or acceleration of the test charge along this line? Discuss.

Sketch the electric field lines for a uniform line of charge whic.0vul5.m+ntk v +u ersh is infinitely v.e0lsv +r5.nk+utumlong. (Hint: Use symmetry.) Is the electric field uniform in strength?

If the electric fluxox ehg cuvwl),6(s4:x through a closed surface is zero, is the electric field necessax)lhw: u6sge(, covx4rily zero at all points 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. If thrmeknc .6-ejf )t h,8we sphere is replaced by a c mc6jh-t8., n wekef)rube of side r, will $\Phi_E$ be larger, smaller, or the same? Explain.

  

  How many electrons make up */4*x 1nem qtnrjv+k)5lx iy,mfg s zwxh*,0ga charge of $-30.0\mu C\,?$   $ \times10^{ 14}\, electrons $

  What is the magnitude of the electric force of attractionw(zo7 3 k2bty0nmtt0 q between an iron nucleus ty0t 0z3m(b7qk2wton$(q\,=\,+26e)$ and its innermost electron if the distance between them is $ 1.5\times10^{-12 }\,m\,?$    $ \times10^{-3 }N$

  What is the repulsive electrical fo6v8dat4 np4kxrce between two protons $ 5.0 \times10^{ -15}\,m$ apart from each other in an atomic nucleus?    N

  What is the magnitude of v2s;k ;er(ssp ,i 8p9ifffcfqn7n/,a 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 of3v ej5hs 8b391o isog/kt(n jm $ 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 7wiul 0xc b3l1apart. They are moved, and the force on each of thub 30lilc1w7xem is found to have been tripled. How far apart are they now?    cm

  A person scuffing her feet on a wo:sp98 t4ef rgqol rug on a dry day accumulates a net charge of gpte 4 9fr8sq:$-42\,\mu C\,.$ 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. ;ief6k btwoht-y-82 j0 kg of $H_2O\,?$    $ \times10^{ 7}\,C$

  Compare the electric force holhjo:yjutm; ;n* 0da+yding 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. Thef* (lpr8gmzym/c 3j t k/:lnw0 sum of their charges is What charge must eacmgmyckf/*ll (pn z83tr: 0jw/ h have in order to
(a) maximize the electric force between them,
(b) minimize it?

  Particles of charge v29)emtvryuk 3xe (9 s$+75$,$+48$ 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 eatchmgsuk).gsq ev 29 ) ;yg/-qual 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 n(:9mc bbs6 7twe btd(a square 0.100 m on a side. Determine the magnitudenc67bw:tbt( e9 (mdbs and direction of the force on each charge.
$F_4$ =   $ \times10^{ 7}\,N$
$\theta$ =    $^{\circ}$

  Repeat Problem 14 for the case when t- yf3 zfp,oyw .kk6l+ qo5q3wfwo of the positive charges, on opposite corners, are replaced by negative charges f,kwq5y3zkl +f 3o-qpfwy 6 o.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 charg* oa*dxq d6+n(o d)uwmes of magnitude Q, 2Q, 3qwa*o6mdo)(dx+ nu *d Q, and 4Q (Fig. 16–52). Determine the force on (a) the charge 2Q, and (b) the charge 3Q, due to the other three charges.
$F_{2Q}$ =    $\frac{kQ^2}{l^2}$
$\theta_{2Q}$ =    $^{\circ}$
$F_{3Q}$ =    $\frac{kQ^2}{l^2}$
$\theta_{3Q}$ =    $^{\circ}$

  Three charged particles are placed at the corners of an equilateral triangaw a5 s,q*p4ve1i;sadle of side 1.20 m (Fig. 16–53). The charges sd;w5as1q, iaepav*4are $+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 havepna0+en :x j(f a 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 spherc,y4nn wh x anq2n0z(l2 w3wl-es 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 to an idee ;yyxpu )5o5*)o gnlwntical ball 12 cm away. The force of attraction is then 17 mN. How many electrons were transfyu e;5*wopo5 )lgxny)erred from one ball to the other?    $ \times10^{ 12}$ electrons

  What are the magnitude and direction of the electd /rg;y /x vsh9/gokoz.o (k4eric force on an electron in a uniform electric f/h/ zk4.;gr9v(yoogk sxod e/ ield of strength $2360\,N/C$ that points due east?
   $ \times10^{ -16}\,N$
 ----待选择----westeast 

  A proton is released in a unif;4 , cjaaen-3 ivyf5m y+9r2p*ekatux orm electric field, and it experiences an electric j,y;etcvi amra 5 u+e* -yaxp3k 94fn2force of $ 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 exerps e4nm9q1 h.vted 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 ofp-5op3fkbyk9 rqe s bfnr)4e:;h/b*a the electric field 20.0 cm directly above an y4;*b b:bq k 9rn5-apropefh/)3k sef isolated $33.0 \times10^{ -6}\,C$ charge?    $ \times10^{6 }\,N/C$ ----待选择----updown 

  What is the magnitude of the acceleration experiencedkfzk- f,3 oe4a by an electron in an electric fz- kafo34e fk,ield 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 poin;udjq *(l w;hdf qia27t midway betwew2l; u jh* f;7ddi(qaqen 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 annwv94-toh h 4e)9yyx:2t.fir3 n zxibout 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 protonymius 5v56e5pmz (t/d $(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 electriugigcl* n4 ,ce/2w jx7c field and accelerates to the n 7x2el/gc4,wu*jgc in orth 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 charga8g(vsr;g9 1kwb i; qhes 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 vs ip iwpbgae-*))- 5gaqul: +on a side if one cor)i-: i e* wu-gl qvpsp)gaba5+ner 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 s c;vy chag+o:qob2v71quare 1.00 m on a side if the other three corners are occvybv h ;o72+1oc:agqc upied by $ 2.25\times10^{-6 }\,C$ charges.    $ \times10^{4 }\,N/C$   $^{\circ}\,$ from the x-direction.

Determine the direction and(n7lgv joaq 5e/bi21a magnitude of the electric field at the point P in Fig. 16–oagj7bl (/1niae5q2 v54. 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 electric fieldm nzt13n+r / ihvmlo fb25i0ff:5 *jdh $\vec{E}$ 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 magnituu 20ujlhctwj5p372uqh9x/: - lfbfjj de and direction of the electric field at points ftlhbu/qjp2-h:jf 97j w5x2c u lj30uA 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 unknownf9fh l--f.9yluyzeig *dj 6b- point 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 electri t(17(zjm qdhpc 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 o(q7tm 1hd(jzp f 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 o u .8yapeg1)d9jb jnvs0r-fm 0f light enters a uniform electric field parallel to its direction of motiyd0ajbnmv)1 0e gj98.uf-spron. 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 2 de-sr)vmp6 lp (,j)mb8.0 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 iszqgtuy/36)g l placed in a uniform electric field of magnitude ylzuggt)q/ 36 $ 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 ob.fo; pl/r*xbk ip:of jj05 t/tjects, $O_1$ 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 uniforx q fk0pp.phm*t*n(gdb xvy02 3a -mrdq+ *+rkm 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 platesly/nms9ny0 o do x8.9 wmgae6+r(-xtz 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 efm naow y(n 0odrmt+l6ez s-.x/89x9ygfects.    $ \times10^{-9 }\,C$

  The field just outside a 3.50- +.u9om4tm60(df a/ :yeojiqn5 qllwecm-radius metal ball is $ 2.75\times10^{2}\,N/C$ and points toward the ball. What charge resides on the ball?    $ \times10^{-11 }\,C$

  A solid metal sphere of radius 3.00 m carries a total c4ncek lzk76b .qht:p.harge 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 this+o k)5 yt:cuan 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) inside the shell, and (cty)s+ ocau5k :) 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 electr81 oq8 rnz-x cmyjn*3bk0y 7uuy-zf1xostatic forces as shown in Fig. 16–44. Assume that the net average charo *qn f-c3 8xznx7ybur8u 1y-0y1zkjmge (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 f(zakp3( xkqfg );d.no orce between them is equal to the weight of ein g z o(;3f)k(xdqkp.ather at the Earth’s surface?    m

  A 3.0-g copper penny has)bfunma94 gt* i;d4vrc6 c zedj0)xw3 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 s w0ffw5h34k k upcsu89urrounding the Earth. Its magnuc39hu0 k5p8 swkf4fwitude 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 uro79;l k/diwbarh2 )tbw3j9 what is the acceleration experienced by an electron near the surface 3bh ;or twl9ki29w7 )rj adbu/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 stat5zqjr is5+ 5qxhhd. u(ionary in the air. If the downwar5 ri jz +s(qqhu5d5x.hd-directed 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 ins a7;yf-)taf2 *s ei:f(jc pws Fig. 16–62. The C and O have chargest)fs( ip y:-;ef jsw csa*2fa7 $\pm0.40e$, 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 idcekshubs*56l0/rn tal,6 c g wad,51n a circular orbit around the proton with a speed of d,sc6au 61 lgal, w nr0b*t/h5dke5 sc$ 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, werptu9r e *by 87fs*,alde responsible for holding a7r*de* fs,8bt lyu9pthe Moon in orbit around the Earth. If equal and opposite charges Q were placed on the Earth and the Moon, what should be the value of Q to maintain the 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 spee93a- k0epkjzn 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 chaxps0 i 64x7p lpn 9lbk(1vgm9hrge $Q_1\,=\, 2.5\times10^{-5}\,C$. 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 a)ttc 68 zv62qqgy0sbbnd suspended vertically from an id6sz)yq 0bg6tct 8b2q veal 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 maw; bqqvjowt*,lv :2jc1mn.q 1de with “leaves” that are 78-cm-long wires with tiny 24-g spheres at the ends. When charged, nearly all the chargewwbq,ctq;j*n1:l2jo m1v.vq 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 andg;7a fzp1juh4 qpj9x . generate a spark if the electric field exceeds aboutaz17u4hjg9;.xjpf pq $ 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 kaguwh dq u r qw+7-w18qli74.kg, 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 of aluminum? kva; ht4p/r9el f,z-p    $ \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 R ajl x*x3xl0 ,ljpart; 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 jlx,xx0*jll3 contact with sphere A and is then moved far away. What is the force on sphere A in this third case?

Given the two charges shown in Fig. 16–68, at what position(s) x is the elecv,a;4kzi a wcjl2ucuy. 8,t4n nmou3 8tric field zero? Is the field zero at any onvc.n, it;yuu8z8 , m 3oulwc4 2akja4ther 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 of chargeazr ep1k84z0rg 2t9x( bsc/mr $8.0\,\mu C$ 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?