If you charge a pocket comb by rubbing it with a silk scarf, how can ywim zo.ju.i cc kly:,*r/)t; fou determine if the comb is positively , ;yri w/ku.cf: z tcom*i.)jlor negatively charged?

Why does a shirt or blouse taken from a clothes dryer sometimes cling tit0;kg xstpwxxp h/70l;zf )jsd+t 7jm f4/q6o your body?+x7 0 w m xsptzt;xgjf/fk0d/ qt ;shi)4j7pl6

Explain why fog or rain droplets tend to form aroum 9 1rmwbscht;mo31 d51jxot6nd ions or electrons in the air.wr 91m5;m3 x1cmt1hbj otd6so

A positively charged rod is brought close to a neutral piece of paper, w7 3a5 h*ehc; hptmq0gohich it attracts. Draw a diagq7 a0t ;5hh3pc mg*eohram showing the separation of charge and explain why attraction occurs.

Why does a plastic ruler that has been rubbed withp:ked8c j )e*v a cloth have the ability to pick up small pieces of paper? Why is this difficulvc8 pd:* ee)kjt to do on a humid day?

Contrast the net charge on a: vkd2t3xb; gozdt k4, conductor to the “free charges” in the conductor.

Figures 16–7 and 16–8 show h*ppz-ao;0c -a xlw ;dx-z 6cotow a charged rod placed near an uncharged metal object can attract (or repel) electrons. There are a greapo*0xa -z; co6xzwl-p tda-c;t 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 leaveq37(htf ; 6jvfsb+1h cu3bza ws repel each other and remain at an angle. What balances the electric force of repulsion so that the leaves don’t sepa aqb136 ;j+wz7h(ffctuvh s3brate further?

The form of Coulomb’s law is very similar to that for Newton’s law of universj72ee7rjwd57 s12zv/shwos h j, k 2bsal gravitation. What are the differences between these two laws? Compare also gravitational mass anbvws 17jsj2orw7kshs2,ee2z/ h57jd d electric charge.

We are not normally aware of the gravitational or electric force between two 6i5l6,kweb8z ktgz vm.pwx0 5ordinary objectz l,i58xm6wkkb we 5pv6z0.t gs. What is the reason in each case? Give an example where we are aware of each one and why.

Is the electric force a cowc4r vlpqedoth+v7*syp ,*) . vi6q1wnservative force? Why or why not? (See Chapter 6.)

When a charged ruler attracts small pieces of paper, sometimes a piece jqq6jhhp3 9, ytumps quickly awaq3 96jph ,yhqty after touching the ruler. Explain.

Explain why the test charges we use when measuring electric fields ikim m;7:wr z+must be small.z ;wmr:k7 mii+

When determining an electric field, must we use a positive nwtdm w/z8 ru/;93 onztest charge, or would a negative one do as weln8 ;wno/zrtu w93z/dml? Explain.

Draw the electric field lines surroundi1s3v6*u6xt6 ggza vhsng two negative electric charges a distance v63x6*s uza6v1sg hgtl apart.

Assume that the two opposite charges im-monyk:i i/brom)/nrt 11jbpyo - 35n Fig. 16–31a are 12.0 cm apart. Consider the magnitude of the electric field 2.5 cm from the positive charge. On which side of this charge — top, bottom, left, or right — is the electric field the sb r3 om1m/:n)b- 5noyyorp mj-t/ik1itrongest? The weakest? Explain.

Consider the electric field at points A, B, and C in Fig. 16–48. F jm bwqy d5j) : lr**j4t+rvje*j2svs+irst draw an arrow at each point indicating the direction of the net force tha2m54s dvjej* )jqs*jr+bj+ y*rvltw :t 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 linraq,rh+p h*n5w ) zhq,es never cross?

Show, using the three rules for field lines given in Section 16–8, tha1e1 j8e h q1:vwwpnut8t the electric field lines starting or ending on a single point charge must be symmetrically spn w188j1q1 wuh: epvetaced around the charge.

Given two point charges Q and 2Q,(x,assyz9 ojil/l/ 27-+j;aeq mk crw 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 where7/ jyxmq (lza r2+9-skowsl;ij aec,/ this point will be.

Consider a small positive test charge located on an electric field line at .67:hwo zg0jx : jlm .,qlit1xt ipof;some point, such as point P in Fig. 16–31a. Is the direction of the velocity and/or acc: 6j.170pwgx:jo;fm t.qt ,zihlixloeleration of the test charge along this line? Discuss.

Sketch the electric field lines for a un/sz9*nv/czj3jc 6t k (ow iv7xiform line of charge which is infinitely long. (Hint: Use symmetry.) Is the electric field uniform in stre9c/j i ov/ v*jxczs7t6w n3k(zngth?

If the electric flux through a closed surface ij h;dj 0 y8tl7pv gem9p*hmr2ls,z- tao601 rts zero, is the electric field necessarily zero at a*o19 26th pjtryd,-0mv0t gs ;7hez 8mpra lljll 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 gausm/qcd y8)pl.j 0,pojssian surface of radius r. If the sphere is replaced by a cube ,lyop/jq8sdp .j) mc0 of side r, will $\Phi_E$ be larger, smaller, or the same? Explain.

  

  How many electrons make up a chav yisng:+ nik y +p1b5d xm/xby9ig2;4u2vz+erge of $-30.0\mu C\,?$   $ \times10^{ 14}\, electrons $

  What is the magnitude of the electric force of attrac8s1.0am+ 1ga1pbhts rqs( qf.zkd7 sytion between an iron nucleus ss+(d s .01qzg b .mqyspf1a18tarh7k $(q\,=\,+26e)$ and its innermost electron if the distance between them is $ 1.5\times10^{-12 }\,m\,?$    $ \times10^{-3 }N$

  What is the repulsive electrical force bg8y:: tai7jzjknwq t vb:;eabl,33, s)gml 5qetween two protons $ 5.0 \times10^{ -15}\,m$ apart from each other in an atomic nucleus?    N

  What is the magnitude of th9xgh xaws 2,zb wfg02,e 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 cthr7z2qgr;+- :7 c :woq ou+b-ikmbxof $ 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 moy* qh0d* *nemived, and the force on each of them is found to have been tripled. *h*nie0d*qmy How far apart are they now?    cm

  A person scuffing her feet on a wool rug on a dry day accumulates a net chargekscb 3-/p-wpdl+g u( 3-yelg l ofl-yc3p-(ew u l3klg-/sd +gpb $-42\,\mu C\,.$ 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 eln c.4wn ,55wyjw*h+ tp jmkm8lectrons in 1.0 kg of $H_2O\,?$    $ \times10^{ 7}\,C$

  Compare the electric force holding the electron in orbit09 way ongq8fbr)1z2v $(r\,=\,0.53 \times10^{-10 }\,m)$ around the proton nucleus of the hydrogen atom, with the gravitational force between the same electron and proton. What is the ratio of these two forces?    $ \times10^{39 }\,C$

Two positive point charges are a fixed distance apart. The sum of their c,j wp/t4 pw(ddharges is What charge mu,p (wt4pdd/ jwst each have in order to
(a) maximize the electric force between them,
(b) minimize it?

  Particles of charge l3wqct+th+ f0f 4q lcxo-nt*8$+75$,$+48$ 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 eqjgs;-f7 b4thw ual 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 0.18zv /m*fwmjir 74fu1s) p7sy q00 m on a side. Determin f8/i7fs yu )1*74rmzwsqvmjpe the magnitude and direction of the force on each charge.
$F_4$ =   $ \times10^{ 7}\,N$
$\theta$ =    $^{\circ}$

  Repeat Problem 14 for the p43-x 6en9q wacley 5tcase when two of the positive charges, on opposite cornerspxlny-3e a 5t4cqe9w6, are replaced 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 u x8eo s.ud) /49:ga(r1tovhrctqvj 2point 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 other three chax1v/ta)9g srvruou dt28o4q c j:e(.h rges.
$F_{2Q}$ =    $\frac{kQ^2}{l^2}$
$\theta_{2Q}$ =    $^{\circ}$
$F_{3Q}$ =    $\frac{kQ^2}{l^2}$
$\theta_{3Q}$ =    $^{\circ}$

  Three charged particles are placed at the co0tx5f;h3c(ebs7 + bu fprvkd 1rners of an equilateral triangle of side 1.20 bv cp+tu;sfrdxf0k17h5e (b3m (Fig. 16–53). The charges are $+4.0\,\mu C\,,$$-8.0\,\mu C\,,$ and $-6.0\,\mu C\,.$ Calculate the magnitude and direction of the net force on each due to the other two.
$F_1$ =    N
$\theta_1$ =    $^{\circ}$
$F_2$ =    N
$\theta_2$ =    $^{\circ}$
$F_3$ =    N
$\theta_3$ =    $^{\circ}$

  Two point charges have a totalx+) z/a5 06cvd (-izfuhadukj (y cy6w charge of $560\,\mu C\,.$ When placed 1.10 m apart, the force each exerts on the other is 22.8 N and is repulsive. What is the charge on each?
q = $ 5.54\times10^{a }\,C$ a =  ,
$ 5.54\times10^{b }\,C $ b =   
Q-q = $ 5.54\times10^{a }\,C$ a =  ,
$ 5.54\times10^{b }\,C$ b =   

Two charges, $-Q_0$ and $-3Q_0$ are a distance l apart. These two charges are free to move but do not because there is a third charge nearby. What must be the charge and placement of the third charge for the first two to be in equilibrium?

  A $+4.75\,\mu C\,$ and a $-3.55\,\mu C\,$ charge are placed 18.5 cm apart. Where can a third charge be placed so that it experiences no net force?    cm

  Two small nonconducting spheres have a total char+;/9wp w wdpywge 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 initi (xng4 fokchjwakdf 2x2/;1r6ally uncharged plastic ball to an identical ball 12 cm away. The force of attraction is then 17 mN. How many electrons were transferred from onj cw;(n4kg d x2xkof2 ha1f6/re ball to the other?    $ \times10^{ 12}$ electrons

  What are the magnitude and direction of the electric force on an electron i-mq+6w:plyb n z yj)p ef5l7l,n a uniform electric field ol z p e7qn:yb-+6 l5w)ylfj,pmf 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 experiences lwi6b94 do nqi 3vmz*,.hqjx1 an electric force ov ,qiqmli314hoz bx6n.w*d9jf $ 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 b i u0lxfp h1l*5(as;cN 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 field 20.0 c 36l2d)uf 7fs ocsyo * *r,;mmhqn by*-3ijryvm directly above an 3 mfvn6 isf2;,bjyyr-)*3 *7rlcs*hqooydumisolated $33.0 \times10^{ -6}\,C$ charge?    $ \times10^{6 }\,N/C$ ----待选择----updown 

  What is the magnitude;r.8fj8bmj:tmx oe8q of the acceleration experienced by an electron in an electriomf8.m jq;ebtj8: 8xr c 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 directiow 46.ph7m uip xzy48aan of the electric field at a point midway betwex4pph 4a6m . uz78yawien 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 two point chargm(+9 yabkl3 jres, $+Q$ and $-3Q$ which are a distance l apart.

  What is the electric field strength at a po ea3x,xj u1xhe -vhe2;int in space where a proton $(m= 1.67\times10^{ -27}\,kg) $experiences an acceleration of 1 million “g’s”? $\approx$    N/C（Round it to one decimal place.）

  An electron is released from rest 0sljklhmv*- ;bn ,-sm in a uniform electric field and accelerates to the north at a ratlb lvmn* 0h;,sm s--kje 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 chu 2cs,te+ omu.j 1fww*arges 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 squart 8:-vrze olw*e 52.5 cm on a side if one - :t8 e*wzorlvcorner 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 revca*n,u902 rme-- 3 6iglm+srjxpf on a side if the other three vl2 x-mepa,+ fs- u*r36jnm9cgr 0ier corners are occupied by $ 2.25\times10^{-6 }\,C$ charges.    $ \times10^{4 }\,N/C$   $^{\circ}\,$ from the x-direction.

Determine the direction and magnitude of the electrtp.p/9d um kdlor. :-*;h zmdric field at the point P in Fig. 16–54. The charges are separated by a distance 2a, and point P is a distance x from the midpoint between the two charges. Express your answer in terms of 9pdhd/.;: m . ptmruk o*z-dlrQ, 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 fielf, f1 gqe5*w2zfx6l;l7tmx-+qkkgjt d $\vec{E}$ 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 electric fie1 hon..2s)hrt*sltt eld at points A tr21ss.eotl h. * nh)tand 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 pe *o4i bx0 ywcq*hr,g0oint 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 the point P showh9rw43h)3 k.b;isn tv j)io kx,m/chzn 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. Exprehwnrs;o j ,.c) hihbim zvk933x/kt )4ss 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 egnve.:mh 4 6lbnters a uniform electric field parallel to its direction of motion. If thv:glnmhe 4. 6be 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 on a *n dcxvfc32ww k1x xd7f8a1f;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 t9n+/n2yxfbg is placed in a uniform electric field of magnitude +nntf2 /b y9xg$ 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 objx )s2i :qtxbe*ects, $O_1$ 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 i7n u27v iczxi86u7w o*a-sdurn a uniform field $ E\,=\,6.50\times10^{3 }\,N/C$ with edges parallel to the field lines.
(a) What is the net flux through the cube?
(b) What is the flux through each of its six faces?

  The electric field betwee3;rft7zdslx /dp5 q-;l : johm/wa+mm n two 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 plate (assume equal and opposite)? Neglect zd;l+ q3almjpfm xs/m /; hrdw5to-7: edge effects.    $ \times10^{-9 }\,C$

  The field just outside,qui + 316sp9fvhio +yss b8q8dmi po4 a 3.50-cm-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 sphere7gy2au .bis, r of radius 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 theld :otan kv3n3e3 u50tvb 2bw8 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 less than the inner radius of the shell, (b) inside the shell, and (c) be3to3n8 5 v0kvbw dn3:bae 2tulyond the shell? (d) Does the shell affect the field due to Q alone? Does the charge Q affect the shell?

  The two strands of them65t q (-rlkzn helix-shaped 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 q-n km z5l6r(teach 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 electr 0 f 5aw3h43u8oyyn.h9nthclric force between them is equal to the weight of eithe 8tafnh .r5y y303ohnl94chwur at the Earth’s surface?    m

  A 3.0-g copper penny has a positive k(qjsd96*4h -m buw4 3qgg8daizjxu1 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 indicatdx czi+1lv l.c0*;udp4ictq8e that there is an electric field surrounding the Earth. Its m4lc i.t8 x;icdq0+ dpvu1c*lzagnitude 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 electriciszgrl+gbrs )g 7r* p:y2qg4) field of what is the acceleration experienced by an electron near the surface of tr7*) rq 4gspslg+)rb: ggzy2i he 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 the dowrh - v1f5h4ht .leriy 3ic2:nknward-dire :rh5c tev1n3lryfk4 hi.i- h2cted 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 andh0vowq, 4xp7g74 3 y/d0xwftonrsn:m the HN group shown in Fig. 16–62. Thefsoh w4 w4n /o0qd7r:7pnyg vmtx, 03x 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 circular o6/ q,j o:qg )uxpr(gpfrbit gq p(rfp )6 :qu,og/jxaround 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 mre.8k4 e c*xdv7e l3*uee3eeity, were responsible for holding the Moon in orbit around the Earth. If equal and opposite ke.8 cxd*elee *7mv34ree e3ucharges 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 spe3vglon lp /jfb2z)b36 ed $v_0\,=\, 21.5\times10^{6}\,m/s$ 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 chargeyf/:t ryyh1(j $Q_1\,=\, 2.5\times10^{-5}\,C$. 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 verticalllt 5jl uf(h4vhh8v73ubm*aey qi (;t6y from an v(l5 3me;lttfi4u7(8*auqh hy b h6jv ideal spring $(k\,=\,126N/m)$ above a lab table, Fig. 16–63. The total mass of the coated sphere is 0.800 kg, and its center lies 15.0 cm above the tabletop when in equilibrium. The sphere is pulled down 5.00 cm below equilibrium, an electric charge $Q\,=\, -3.00\times10^{-6}\,C$ is deposited on it and then it is released. Using what you know about harmonic oscillation, write an expression for the electric field strength as a function of time that would be measured at the point on the tabletop (P) directly below the sphere.

  A large electroscope is 0c budj,w(ws7 ;-v pwah08zbzmade with “leaves” that are 78-cm-long wires with tiny 24-g spheres at the ends. Whenbwwsbu- (cw,azjz0 h 7dp;08v charged, nearly 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 generate a spark ifawguq *+/zl7.qza x j2 the electric field exceeds aboutzlq/w 2zujaa g.x+ q*7 $ 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.b0swl32 tf g- tfzq5e $+0.340\,\mu C$, 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 fwr0a33/smo 2tjky: g of all 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 dist2i ;l wv,(aukqance R apart; each carries the k ,l;wvu q2a(isame 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 force on sphere A in this third case?

Given the two charges shown in Fig. 16–68, at what position(s) x y,+rjnp, h3:1e zk*li0zrakfis the electric field zero? Is the field zero at any other p1p0,i,z3l n*k z:k hrjrafy+e oints, 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 vv;g,(xxb,f y charges, each of 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?