If you charge a pocket comb by rubbing it with a silk scarf, 10 iuo i5easn,how can you determine if the comb is positively o s150,iaunei or negatively charged?

Why does a shirt or b+n .07a;v 0lvwnua qh0ob)i ewlouse taken from a clothes dryer sometimes cling to your bodyw0v0nah;a w0ob in+ .)v qlu7e?

Explain why fog or rain d .-ya)hbhi7n wroplets tend to form around ions or electrons in the airy hi.a-n)hw7b.

A positively charged rod is brought close jgc*. 7fa kbbpbks2)-to a neutral piece of paper, which it attracts. Draw a diagram showing the separation of charge and explain why attr- a fpgjbkb72 )c.bs*kaction occurs.

Why does a plastic ruler that6 wx m /q+do:hck,xcp5t:pk3f has been rubbed with a cloth have the ability to pick up small pieces of paper? Why is this difficult to do on a humid+w: kpxmt:c6pd 5h/fcxqo ,3k day?

Contrast the net charge on a conductor to the “free charges” in the conductor./ lviowi2q/. ysbz07;p.k s ks

Figures 16–7 and 16–8 show how a charges2glmlpsg8n;fz3-y 4 d rod placed near an uncharged metal object cf4p-ny38l lmssz g;2gan 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,hi jk -erxva:10;x*k w its two leaves repel each other and remain at an angle. What balances the electric force of repulsion:-10kkh x* ;irj vwexa so that the leaves don’t separate further?

The form of Coulomb’s law is very similar to that for Newton’s law of uniypbqz))t/5g4.3 / vwn nlwf ewversal gravitation. What are the differences between these two laws? Comparq) gzlwt5/ p/e4nbw fyw vn3.)e also gravitational mass and electric charge.

We are not normally aware of the gravitationn0g/ 6w.hhvr rpznm:aan3l42 al or electric force between two ordinary objects. What is the reason in each case? Give an example where we are aware of3gan0nz 4w6rv:lr/na p 2h.hm each one and why.

Is the electric force a conbab )x u(o,w -qzk+nj2servative force? Why or why not? (See Chapter 6.)

When a charged ruler **yz3 niroup )attracts small pieces of paper, sometimes a piece jumps quickl*3o iu *rpn)zyy away after touching the ruler. Explain.

Explain why the test charges wf -dr2l 7pl+/sn ,drxie use when measuring electric fields must be smalll7x+f / rrindds -p2l,.

When determining an electric field, must we use a positi;f i iar0tysk*fw, a.ux1.vlmx pe3plns+21*ve test charge, or would a negative one do as 3,2 en ps+u 0plry1*x fs* vit.1fl;akx.wimawell? Explain.

Draw the electric field lines surrounding two negawh9 + lbds.el+tive electric charges a distance l aparwl.++h edls9bt.

Assume that the two opposite charge (aypk-ch9*1uzsc2tc s 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 ac kpc 1h2*9- yzsu(tcright — is the electric field the strongest? The weakest? Explain.

Consider the electric field at points A, B, and C in Fig. 16–48. jmwsk-+2w; fy6*s9 pvno5d ktFirst draw an arrow at each point indicating the direction of the net force that a positive test charge would experience if-+wsk; sjt*w2kf p ym6on d5v9 placed at that point, then list the points in order of decreasing field strength (strongest first).

Why can electric field linesrc/ d;mf3 c9og/u-. sp j:kavm never cross?

Show, using the three rules for field lines given in Section 16–8, that the elezg qr.f i :/lh:b1:sdr7a0cm lctric field lines starting or ending on a single point charge must be symmetrically spa bmdz:./cq0a1r: s7ghlrf :l iced around the charge.

Given two point charges Q and 2Q, a distance l apart, is there a point along thene5.wmh6 5aqxs4 h.r gmh5x6rw n,r8h straight line txrme6,rm wgws6n 5ha5n5h x..4rh8h qhat 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 located on an electric field line at somex pt14 z)qttl4sn mp03 point, such as point P in Fig. 16–31a. Is the direction of the velocity and/or acceleration of the test c 0 q4s 14xppttzltmn)3harge along this line? Discuss.

Sketch the electric field lines for a uniform line of c fe4p +3-jmikbharge which is infinitely long. (Hint: Use symmetry.) Is the electric field uniform in-p +jmebi34 fk strength?

If the electric flux through a closem:jr o keyr,; 95;lhowepgufis-69.4u7ep pmd surface is zero, is the electric field necessarily zero at all :khm7fe9emu prpi ;e56l-.ow; j yg or,s9u4ppoints 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 spherical94z h1e)n osdu gaussian surface of radius r. If the sphere is replaced by a cube of side r, wi )41enozsduh 9ll $\Phi_E$ be larger, smaller, or the same? Explain.

  

  How many electrons make up a chargglk;ip9rcp xqe4h mp- 8 /x3-me of $-30.0\mu C\,?$   $ \times10^{ 14}\, electrons $

  What is the magnitude of the el5..wg jswl 2)uyilw*kectric force of attraction between an iron nucleu j* 2ugw5.l)iwsw.ylks $(q\,=\,+26e)$ and its innermost electron if the distance between them is $ 1.5\times10^{-12 }\,m\,?$    $ \times10^{-3 }N$

  What is the repulsive electrical f) )q fwl5f8 5gkqhl( eorw86bdorce between two protons $ 5.0 \times10^{ -15}\,m$ apart from each other in an atomic nucleus?    N

  What is the magnitude of the force g;cz:td.tb4 qa $+25\,\mu C\,C$ charge exerts on a $+\,3.0\,mC$ charge 35 cm away?    N

  Two charged dust particles exert a force of 5 5tl ,au1qo4apcftfp9 rbp) /$ 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.m k 18 g 1.vebf0js,ehme6wnj.45 cm apart. They are moved, and the force on each of them is found to have beenvk 1hb8, g.6wnejs. m0je1fe m tripled. How far apart are they now?    cm

  A person scuffing her feet on a wool rug on a dr w,a2 1t5 ag,+lpu.:syp ol nhd.tl-10nlqgkcy day accumulates a net charge of 1ohl.n51yksdqcp0ugt,t .l:la-g2n +ap l,w $-42\,\mu C\,.$ How many excess electrons does she get,    $ \times10^{14 }\,electrons$
by how much does her mass increase?    $ \times10^{-16 }kg$

  What is the total chh.rvvr054n0 k*3wjtn :nt blrarge of all the electrons in 1.0 kg of $H_2O\,?$    $ \times10^{ 7}\,C$

  Compare the electric force holding s+j4nyz fdej((me-)y zj2e/ hthe 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. The sum of wrbpvtcx(iy:p u;m 8tejmb x,9h.*,5kgc 2 n+their charges is What charge must each have in order ,( ;pn t: x.p8,*2jx5 uehmtkg m +9rcwiyvbcbto
(a) maximize the electric force between them,
(b) minimize it?

  Particles of charge : 8s uj-twt hwhwnle6- t.u,a3$+75$,$+48$ 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 eo2mjr 5z)p7lxv(6 kk ,a*dq nhqual 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 aciqbf ;4gf-6each corner of a square 0.100 m on a side. Dete-b6iacfqgf ;4rmine the magnitude and direction of the force on each charge.
$F_4$ =   $ \times10^{ 7}\,N$
$\theta$ =    $^{\circ}$

  Repeat Problem 14 for the c7 kb a39gcsit*ase when two of the positive charges, on opposite corners, are rep9* ib3asc7 kgtlaced 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 a5: xtsnwweq 0+re point charges of magnitude Q, 2Q, 3Q, and 4Q (Fig. 16–52). Determine the force on (a) thwew5+ :x0sn qte 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 cgy* d:b5;1mj-gvv x nk2zpw2 jorners of an equilateral triangle of side 1.20 m (Fig. 16–53). The charg1g- w*bvvd :m5j; jnyk22p xgzes 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 h0g imzvc4an764ts e*,3l1p(a wxhnc 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 spheres have a total cl 3vn ) h4kzby1q-coc/ag/v e.harge 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 plastictkk;ubhs / ./w; g0yuj ball to an identical ball 12 cm away. The force of attraction;sjgh0ykwb; u/k./ tu is then 17 mN. How many electrons were transferred from one ball to the other?    $ \times10^{ 12}$ electrons

  What are the magnitude and direction of the electric force on an electron i+si mpjj*19 vmn a uniform electric field of strmjs pimj*1+9vength $2360\,N/C$ that points due east?
   $ \times10^{ -16}\,N$
 ----待选择----westeast 

  A proton is released in a uniform electric ,s-:t z(q: loj3junt u2k4upkfield, and it experiences an electric forcjk(k u:, u23osu-jznt :q p4lte 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 exert(i xy h5rnv9(tahy68 n6atld+ed 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 elect2djt8*qfu4qv ric field 20.0 cm directly above an iso*d28t4fq uq jvlated $33.0 \times10^{ -6}\,C$ charge?    $ \times10^{6 }\,N/C$ ----待选择----updown 

  What is the magnitude of the9w48+wgnzr txo7gb5zh + jc(e acceleration experienced by an electron in an electric 74xjn+gz betg95 +wh8ozw( rcfield 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 point midway betm/.eas bfz*; m*ht71 pojun -lween -t.nhop1ej 7ba* m ;s/f lz*mua $-8.0\,\mu C\,$ 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 poin0sxgnwc ta l9((*s.jgt charges, $+Q$ and $-3Q$ which are a distance l apart.

  What is the electric fie(co;g nycb a-ts c:w,(kop. k.ld strength 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 release6ja6x,6u3 ufjn 3 6vuc)vpnxad from rest in a uniform electric field and accelerates to the north at aj6x6 vj,nxapf6u)u36av 3c nu 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 oppositejy0+ zjz5l wlr3hb8emb2q )p- 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 th5z: 5 mao7uhm dq(rp.4ss-)2lddn rid/ml w)te center of a square 52.5 cm on a side if one corner is ocw /mr- s 7to )z)dsu.mqd2r 5a(pm4 d5nldl:hicupied 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 oftvt;tdr ,9 7md a square 1.00 m on a side if the other three corn97 ttvtrd;d,mers 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 electric field at the po0k;8igu:plhn 8 8ewqg int 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 Q, x, a, a8ne hgwuq;kl8 g8:pi 0nd 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 f2 v22qsb)v hq qzygwol*0 zj.:z a(d/jield $\vec{E}$ 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 determinek .cz v9i4 ey+d9/ep8jw9pf5q.ydj ws the magnitude and direction of the electric field at points A and B in Fig. e9ce .4/wp i5 wz+pdf 8qkv d9ysjjy.916–57 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 4nik ;toc99as0a+bjd 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 mag06vbvxzj rv5j+ 18ffuty6/aynitude of 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 bet 8ua0f1 +r vj6x/by56 yfzvjtvween 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 entersndk1*d*qrf5n94z fbv -8bx ov a uniform electric field parallel to -1o*8n59xn*zf d4v rbvkfdbqits direction of motion. 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 bo) /zly 2cq*bcax 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 pl yw.0;vs:a ;z7o3zma2rsvju 4 y)ypsaae) q0taced in a uniform electric field of magnitudemy03e;s 2 j70uzaptsyv a;warz o:)4yq v.sa ) $ 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,/dme2er* 1+zr ox 3xse $O_1$ 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 unig+ccq:zo*k 8zform 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 wfz+ jzjk8q:, pdg)d zy 37ky6(tiiv 1plates is The plates are 1.0 m on a side and are separated by 3.0 ciw)jy+(p 1i 8t6: z ,kfgzjkdvyd zq37m. What is the charge on each plate (assume equal and opposite)? Neglect edge effects.    $ \times10^{-9 }\,C$

  The field just outside a 3.50-cm-radius metal ball i 43 yadn5in*hjohr;/e s $ 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 chatln tqziider .)f934: rge 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 thrv+reae +dsiu 2l wux-k, ;v0.in 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 ofv-axve;du l k02 rrw, +ei+us. 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 mop b;d+ m2gdo.qlecule 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 indicat.p2;modgqb +ded 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 de8na al, (7jzbe if the electric force between them is equal to theeza jnald8 (,7 weight of either at the Earth’s surface?    m

  A 3.0-g copper penny has a positive charge of e k/-8ijt-8d ut0z wtd$38\mu C$. 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 f35fl k yi7c qe-suq.877km8iamkt5ffield surrounding the Earth. Its 5k5flaskf7 q emq88kfm3-c7iui 7 ty.magnitude 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 gq eqlv/3vdle j4 594vexperienced by an elecl lvq/4 v9ed4j3g5eqvtron near the surface of the Earth?    $ \times10^{13 }\,m/s^2$, ----待选择----updown 
(b) What about a proton?    $ \times10^{10 }\,m/s^2$, ----待选择----updown 
(c) Calculate the ratio of each acceleration to $g\,=\,9.8\,m/s^2$ For the electron: $\approx$    $ \times10^{12 }$ For the proton: $\approx$    $ \times10^{9 }$

  A water droplet of radius 0.018 mm remains stationary in the air. If the down6ns4hzt9ck)1vh 9,uu auq kz*ward-directed electric field of the Earth iskh kzc1 *)96u avuh,uz nts49q $150\,N/C$ how many excess electron charges must the water droplet have?    $ \times10^{ 6}$ electrons

  Estimate the net force between the CO group a-em 0hc9 nkh2g yxd)h5nd the HN group shown in Fig. 16–62. The C and O hag 9dxh2 cy5)nhhk -0emve 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 electronbb oqxj mu3* njc-i1,9 revolves in a circular orbit around the proton with anjxuobb-q* 3,1i c9mj 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 responsible rm0 yu*b+t/mmfor holding the Moon in orbit around the Earth. If equal and opposite charges Q were placed on the Earth and the Moon, what should be the value of Q to maintain the present orbit? Use these data: masst/m *my+rmb0 u 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 speedj* dhxm.oz r8.mui5by 6u;2w:jvt 9lr $v_0\,=\, 21.5\times10^{6}\,m/s$ 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 charg36..gc uheulue $Q_1\,=\, 2.5\times10^{-5}\,C$. 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 plast+g/1 nbnr 9b7j8ditvwic and suspended vertically from an ideal srb/ j89nb1w n7i+t dvgpring $(k\,=\,126N/m)$ 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) ki30mqkey8u is made with “leaves” that are 78-cm-long wires with tiny 24-g spheres at the ends. When charged, nearly all the charge resides on the spheres. If the wires ea 3eyik mq8)k0uch 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 electric*y(ao qat h5.q field exceeds about.q qh5ao(y t*a $ 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 ch;got.m3 ws2*lzwt( iyarge $+0.340\,\mu C$, 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 electr 1jmpl51tg rpb/, 2 (besf)tkions 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 condui 4lvpn h64i93hmyj;pcting 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 ij43 pyh9 iim6nvp;h4ldentical 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 2kbc8dru d54s shown in Fig. 16–68, at what position(s) x is the electric field zero? Is the field zero at any other pob2kcsu485 drd ints, 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 charge;pbqcsrcef1 .p6e-g-kim v7 5s, 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?