If you charge a pocket qzntkec 74 xfq 2rw9) 29pzd;acomb by rubbing it with a silk scarf, how can you determine if the f)ket danzwq9rp;2c472xqz9 comb is positively or negatively charged?

Why does a shirt or blouse taken from a clottbo6e mf3/9b jhes dryer sometimes cling to your bodyfo 9b/eb m6tj3?

Explain why fog or rain droplets tend to 5zslfs29 t gl m7y*yhhsh6z* .form around ions or electrons in the air.shm. lhzt57h9z6fs 2**ly gys

A positively charged rod is br3is 7o0k1jk mrought close to a neutral piece of paper, which it attracts. Draw a diagram showing the separation of charge and explijrosk31m 0 k7ain why attraction occurs.

Why does a plastic rujgc7l 9y w ehc43,kd2qler that has been rubbed with a cloth have the ability to pick up ,ghj dw 7kqlc cey4392small pieces of paper? Why is this difficult to do on a humid day?

Contrast the net charge on a conducto:f: dgwsbbjrs+ v/ /2tr to the “free charges” in the conductor.

Figures 16–7 and 16–8 show how a charged rod(; g h)o7xo8pf1t8a ttga6oo h placed near an uncharged metal object can att)h ;o(txg6 ao 1hof7 8tapgo8tract (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 remacgmr28vb+t vgi,s0(j .tl(dlin at an angle. What balances the electric force of repulsion so that the leaves don’t separac m dv(l rgligt,tvj (8b+02.ste further?

The form of Coulomb’s law is very similars* )k fbsfo/,k to that for Newton’s law of universal gravitation. What are the differences between these two laws? Compare also gravitational mass and,/so) *bkk fsf electric charge.

We are not normally aware of go.k*piq88 6hjjbb 8v the gravitational or electric force between two ordinary objects. What is the reason in each case? Give an example where we are aware of each one a b*o h8.8gjbj8kqiv p6nd why.

Is the electric force a )bdam.swlsrqpg9rw) h ihqn0,3 ;cq*9 j8*xzconservative force? Why or why not? (See Chapter 6.)

When a charged ruler attracts small pieces of paper, so2tp:/6iik hl: 8dkmh vmetimes a piece jumps quickly away after touchm vkd6kh2h:l/i: pit 8ing the ruler. Explain.

Explain why the test charges we use when measuring electric fiervb cw hf654u7lds must be small.57fwcubhr4v6

When determining an electric field, must we us.ro7 f;p2budh e a positive test charge, or would a negati bou.h7pr d;2fve one do as well? Explain.

Draw the electric field lines surrounding two negative elecrly)skc 6c0+ * nnser0tric charges a distance l apart.rley +60k*rnn s0sc c)

Assume that the two opposite charges in Fig. 16f/m+xqsetugq 40 ; xx:–31a are 12.0 cm apart. Consider the magnitude of the electric field 2.5 cm from the positive charge. On which siuxxm gtx+0e4 /fqs :q;de of this charge — top, bottom, left, or right — is the electric field the strongest? The weakest? Explain.

Consider the electric field at py+ a+h 6ax/ww- s3fezpoints A, B, and C in Fig. 16–48. First draw an arrow at each point indicating the direction of the net h3zapswyf +- +xe/6awforce 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 li9v* aby;ea /ulnes never cross?

Show, using the three rules for field lines given in Section 16–8, that y0 r- nwv8zojr- qf1a98tdk9ethe electric field lines starting o9k8 z8r-endq0yvorw 1 jft-a9r ending on a single point charge must be symmetrically spaced around the charge.

Given two point charges Q and 2Q, a distance l apart, is dz8qkw+fnd:b8ymp+b g7(q i2there a point along the straight line that passes through them where E=0 whendwn8qk8m g(d2f yip:z b +7+bq their signs are (a) opposite, (b) the same? If yes, state roughly where this point will be.

Consider a small positive test charge located o y.a2 vcdy8x0pn an electric field line at some point, such as point P in Fvay d2.x 8yp0cig. 16–31a. Is the direction of the velocity and/or acceleration of the test charge along this line? Discuss.

Sketch the electric field lines for a uniform line of charge which is infinlbx: n(uz4z6 litely long. (Hint: Use symmetry.) Is the electric field unif:z4 xn(ublzl6 orm in strength?

If the electric flux through a closed surface is zero, is the electric field necb-s04wt m ot6) hdmjzq:9ck-cessarily zero at all points on the surface? Explain. Whmmc)9ztt06 oqdbj -c:s4kw - hat about the converse: If $\vec{E}\,=\,0$ at all points on the surface is the flux through the surface zero?

A point charge is suj go/,bqvq/lnu a,-m -xdr22a rrounded by a spherical gaussian surface of radius r. If the sphere ij,rga a- /vn/-qdb2lmq2xu,o s replaced by a cube of side r, will $\Phi_E$ be larger, smaller, or the same? Explain.

  

  How many electrons make up a charxn*9st/lh8 1a u( ,obk(*hglu had8 poge of $-30.0\mu C\,?$   $ \times10^{ 14}\, electrons $

  What is the magnitude of the electric force of attraction bmp2jel1c gb93irr 0 z4etween an iron nucleus ce0bzj 4gi3p291rlmr$(q\,=\,+26e)$ and its innermost electron if the distance between them is $ 1.5\times10^{-12 }\,m\,?$    $ \times10^{-3 }N$

  What is the repulsive electrical force betwes* b*)b x ha*c4)jgvapen two protons $ 5.0 \times10^{ -15}\,m$ apart from each other in an atomic nucleus?    N

  What is the magnitude of the force a 7e+x+poudfw- $+25\,\mu C\,C$ charge exerts on a $+\,3.0\,mC$ charge 35 cm away?    N

  Two charged dust particles exert a for0.l1jk pr1)wfyehp/cg l 8t;ddm-jg., 8zaxuce 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 8.45 cm a*cy vnc3mbr e;e0xr m;a8cg(-:m u*ijpart. They are moved, and the force on each of them isy0 m3xej*e (mbgc;urrciv8;m:-*acn found to have been tripled. How far apart are they now?    cm

  A person scuffing her feet o3hce n/4o0b5 ur 2ujvn*ol0szm58 zbjn a wool rug on a dry day accumulates a net charge of e5 sju5*lov u z820n b3bm0h/4 crjnoz$-42\,\mu C\,.$ 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 nsuzq: (gm/te2x35 f mo 0jm71qsrs(zthe electrons in 1.0 kg of $H_2O\,?$    $ \times10^{ 7}\,C$

  Compare the electric fo 67eibnsyf (c x(y6jv15nc k5 4dpi/csrce holding 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 diyad 3px 89f1ycstance apart. The sum of their charges is What charg13fxyd8 c pya9e must each have in order to
(a) maximize the electric force between them,
(b) minimize it?

  Particles of charge g8zs lix69biot:/z 2k.oa (rr$+75$,$+48$ 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 charge sg265b8e)mr:kmqj xw * kav)q, $+11.0\,\mu C\,$ 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 0.10kvs60(ovq 7zqd. w8gsc)ze3z 0 m on a side. Determine the magnitude and directis (wzvz7kev qo .30q8gzd)c 6son of the force on each charge.
$F_4$ =   $ \times10^{ 7}\,N$
$\theta$ =    $^{\circ}$

  Repeat Problem 14 for the case when two of the posiwy g,)ik-l+se,z9 mddtive charges, on opposite corners, are replacede-)zglm,k d ,sy9wd+ i 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 point charges of magnitude Q, 2Q3 6*mk*+ri2v l vgtadt3x5psf, 3Q, and 4Q (Fig. 16–52). Detrtvv5t m 6s+*i *lakgf x332dpermine 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 triangle of 2ws95z v,dl uasidwzda 2 v9sul5,e 1.20 m (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 tkei9jgy)e (3 i7fasr9 5 cnvkvz *czgef/ 8c+8otal 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 charg du4b61 d9tpyne 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 unctic28x prl7e:harged plastic ball to an identical ball 12 cm away. The force of attraction is cl 8:7xti2 perthen 17 mN. How many electrons were transferred from one ball to the other?    $ \times10^{ 12}$ electrons

  What are the magnitude and direction of 4 r qv3: wfnfoweggft-tp./*;the electric force on an electron in a uniform electrf4g;ow re q:n pt3-t wf/vgf.*ic field 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 experiences o8z gxv ue2m/:r7zct)an electric forcer8) mz/2 vtze xgc7u:o 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 e1xsiwjh,awk (y). .guxerted 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 ec41 f 0eppmmo53 dzw0wlectric field 20.0 cm directly above an30150 4fpdc pzmow wem isolated $33.0 \times10^{ -6}\,C$ charge?    $ \times10^{6 }\,N/C$ ----待选择----updown 

  What is the magnitude of the acceleration experient n/wyl *dhz,jfy/g ;v3a)t2igu2v8hced by an electron in an electric t h dz8) uywfgl2,v/tni;yv*/a2 3gh jfield 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 elp y6jg;i* 9rlsb*9ybfectric field at a point midway betweebyg*l; j9i9f* py6b rsn 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 t8bno,qela1 0(n/.ik drbn j /iybr3v ;+xv+eo wo point charges, $+Q$ and $-3Q$ which are a distance l apart.

  What is the electric field strength at a point in space where a-kjg.jp 7exugeoh 13 7 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 in a u*/43:gm0twvp 8jl7 cweatm x9idy(fu niform electric field and accelerates to the north avald w jiy8tem07/:c9*up 4t w(3 mgfxt 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 cha,(zl5nht x*e12 a w,dqlngx,f rges 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 center1y7; 7pzib4 fv;sp w -9jbcnbc of a square 52.5 cm on a side if one corner is occupied by a p4ncfpj;;1cvy7i9 -zb7bb ws $+45.0\,\mu C\,$ charge and the other three are occupied by $-27\,\mu C\,$ charges.    $ \times10^{6 }\,N/C$ at    $^{\circ}\,$

  Calculate the electric field atsaw.*tg+ i7 bd.rb 7e6.uuooh one corner of a square 1.00 m on a side if the other three cor7b.bta7iseo 6r*o wuhu+gd. .ners are occupied by $ 2.25\times10^{-6 }\,C$ charges.    $ \times10^{4 }\,N/C$   $^{\circ}\,$ from the x-direction.

Determine the direction and magnitude of1i; k(ak4b3rl k5vpli the electric field at the point P in Fig. 16–54. The charges are separated by a diski1ra5k4(vilp 3bl ;ktance 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 el 4 b *41y.gihd mns97scwizom gz2f)w,ectric 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 direcwv(a+cf hso9q s0f6f 80ipi62x5 xhbftion of the electric field at points A and B in Fig. 16–57 due to the two posipf 6x(hff o68+vx9s 2q5bcwfh0i as0 itive 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 charge9ozy(4d +vq7kdsjg5h + 5likys, $Q_1$ 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 0 7sycp hzoskzf2:.f ;xv;7bg5gib2wof the electric field at the point P shown in Fig. 16–59. The two charges are separated by a distance of 2a. Point P is on the perpendicular bisector of the line joining the charges, a distance x from the midpoint between f0 7;bzs2bvk;sczgg 5p.h2 7iyo x:fwthem. 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 thkq3hpmyv8je2ef- v t) k50i*oxv)vy;e right at 1.0% the speed of light enters a uniform electric field parallel to its direction of motion. If the electronmh;vkp2-8e vy qf5y0tvjov)*3 x)ei k 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 t pf4 mge)z7pzo+5:rw from a cubical box 28.0 cm on a side is $1.45 \times10^{3 }\,N\cdot m^2/C$. What charge is enclosed by the box?    $ \times10^{ -8}\,C$

  A flat circle of radius 18 cm is placed in a ed9 )cea /*q*duu3yz .ugvo-uuniform electric field of magnitude u*aee d/-vou*gyuqcu39 )d . z$ 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 o. xz8lvs uo7i3bjects, $O_1$ 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 plafhc 5f (v rt8ie/ 9xl s.m38a6xzrj.pzced in 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 between two square metal plates is The platescypvnu x1bleemf.6x ,k+ a/47 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)? Negle cmvfupk4.axeb y+le6n/ x,71 ct edge effects.    $ \times10^{-9 }\,C$

  The field just outside a 3.50-cm-radius metal bqrn5k3 c vt adxlb+/* ,:9tupjall 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 yx(.mr p+2wm dm 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 thi e7s:5p iblr1.ek52s3aakv zon spherical conducting shell. (See Fig. 16–33.) What is the electric field E as a function of r (a) for r less ta.ve2br s3:e o z57 1ikks5alphan 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 her0qg,*up 3 z0uhn. reclix-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 .zqn0g0 rrheucu3*p ,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 electric988b 4du*.fqulp-z 2t1md rlvsdf7 np force between them is equal to the weight of either at *fp ud48vsmp d8nlt7q 9z1r-du f.b2l the Earth’s surface?    m

  A 3.0-g copper penny has a positive charge ofe 0ci.vf.d4uk $38\mu C$. 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 anosfn,b o4 8r.c 4lok3)y6uaih electric field surrounding the Earth. Its magnitu,yin 4 coask64).o8ofru blh3de 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 acceler : c.wm; p1 eixi4iduu+2;rqun:c2thb ation experienced by an electron near the surface of the Ea.i: 1uwnbihce 2d ;2x+ipruqc;4t :murth?    $ \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 05w1 i 8up+axktpb r9 *lv-rbp4.018 mm remains stationary in the air. If the downward-dir prw blxi59+8u pa-4k*bv1rp tected 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 (ej7za x6w6sj1 ewx88(cccoaHN group shown in Fig. 16–62. The C and O have1wa 8ea7( cxj 6s(jecx86zwco 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 g8m;esdf4k rw7:*5dx.uq -xg 2pfjm4 bpy ,yy electron revolves in a circular orbit around the pro j;pdempqwxg 52bksygy4 4.d :7r*8ym- ufx, fton 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 gravity, were responsibrp:36 9vryqd ale for holding the Moon in orbit around the Earth. If equal and opposite crpd 36a9 yvqr:harges 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 spec7s9 7 c wf:o/mdh 6*crxerb8ued $v_0\,=\, 21.5\times10^{6}\,m/s$ is traveling parallel to an electric field of magnitude $E\,=\, 11.4\times10^{3}\,N/C$.
(a) How far will the electron travel before it stops?    m
(b) How much time will elapse before it returns to its starting point?    $ \times10^{-8 }\,s$

  A positive point charge (1a gu)m)kk;vzj7) q mih/z/lar.fun$Q_1\,=\, 2.5\times10^{-5}\,C$. 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 suso8nssuf q,s53pended vertically from an ideal spring3qfs n5su,o s8 $(k\,=\,126N/m)$ 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 dz/f qfvh )axuc5jzm5,6wk 88 with “leaves” that are 78-cm-long wires with tiny 24-g spheres at the ends. When charged, nearly all the chaf hwck8 qz5)/ ,d5v8 zum6jfxarge 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 if the el+m4wmid9a8b 8uu 2 euoectric field exceeds about 8w42mi8oad9u m u+ube $ 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.da ly9ng z30oy u(cq k/ze5mr3b;i;4 b210 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 bariovt; 4jkp po.m0zq :: 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 pw 3 86t1mwvhrand 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 hvm6 83r wp1twidentical 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 positid8d pc1hsp:* mg 87kw4jfln3jon(s) x is the electric field zero? Is the field zero c8k8 d3jl4ng j1*shf7pdmpw: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 charfmo .a 5al1*,l1i cyauges, 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?