If you charge a pocket comb byl 2bog3 ge63px rubbing it with a silk scarf, how can you determine if the comb is positivel2 63pgg3boxely or negatively charged?

Why does a shirt or 8u.s4wapwlp ) zgxs5:1 feq1o blouse taken from a clothes dryer sometimes cling to your bod as.5q lxp1)1uwf :84owegzsp y?

Explain why fog or rain droplets . dp5.vfa.px.3( s5nv ldr isftend to form around ions or electrons in the air .xf5.( s5 3da.fl vvp.pindsr.

A positively charged rod is brought close to a neutral piece of paper, which 1y- (b7u nch9lb y-i)g9a.v rkvu hze3it attracts. Draw a diagram showing the separation of charge and explain why attraluyh 9by 7g-cr-n9 (bi.v)zek3auv 1h ction occurs.

Why does a plastic ruler that has bq hb-e-*q qcj.een rubbed with a cloth have the ability to pick up small pieces of paper? Why is this-qhe *.qj bqc- difficult to do on a humid day?

Contrast the net charge on a conductor to the “free chargesd/p+wwgb czb; a,zn:-” in the conductor.

Figures 16–7 and 16–8 show how a charged rodh fhz82phy5bg2-o-e6 2jdgo2zcr3lv placed near an uncharged metal object can attract (or repel) electrons. There are a great many electrons in the metal, yet onl-d2he6f r232hyhc5j- ogv2b zolp z8gy some of them move as shown. Why not all of them?

When an electroscope is charged, its two leaves q; zcdsy,,cfka o67b5 repel each other and remain at an angle. Wzy7;o ,5abccq k ,f6dshat balances the electric force of repulsion so that the leaves don’t separate further?

The form of Coulomb’s law is 7m14dhe fbg,emb)x,overy similar to that for Newton’s law of universal gravitatiof7eh xbm14d,b)g meo,n. What are the differences between these two laws? Compare also gravitational mass and electric charge.

We are not normally aware of the gravitational or electric force betwe gzv0iid.y6n9 en two ordinary objects. Whdn6 yzi 9gv0i.at 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? (See Chas lnm o+r5 3)b*q,aftppter 6.)

When a charged ruler attracts small pieces of paper, sometimes a piece 9s*r4gs kr3y9qw oy2t jumps quickly away after touching the rule39t9sryrog* yw4qs k 2r. Explain.

Explain why the test charges we u nk2s;) 0 msm0;vp4j h:kxcehise when measuring electric fields must be small cn s;:s)0khxmvi024ekm;phj.

When determining an i nggcbr 9a)/,electric field, must we use a positive test charge, or would a negative onean,igr9)c b g/ do as well? Explain.

Draw the electric field lines surrounding two negative electric charges a distk*w,o3xqjl r ,8; f+e4f:oclc eu6qv*cmfrv)an e c+emlj crfl k ov,84)ov;*qfx6*,uq3wfc r:ce l apart.

Assume that the two opposite charges in Fig. 1jl b0luy skb,k ),sv(86–31a 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 th(s 0k,b 8b)lv,lsu jyke electric field the strongest? The weakest? Explain.

Consider the electric field at points A, B, and C in Fig. 16–48. Fifeb*zfa3ol .zg 9b3t1 rst draw an arrow at each point indicating the direction of the net force that a positoztf3 fl.b19eg 3*zabive 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 lines never cros ;p--cyv lw7;q cjegj+s?

Show, using the three rules for field lines given in Section 16–8, that the2,qhl laqic .* electric field lines s.h2cq, * qlilatarting or ending on a single point charge must be symmetrically spaced around the charge.

Given two point charbz qz2p+)1t)0f jufbil:d.dk22w if zges Q and 2Q, a distance l apart, is there a point along the straight line that passes through them where E=0 when their signs are (a) opposite, (b) the same? If yes, j1wz ftzbd dz)f0f pi22)+.ikq2bu l: state roughly where this point will be.

Consider a small positive test charge lo;5rv mur *uk,w0eay.hcated on an electric field line at some point, such as w5u,.auv0erhk;r * y mpoint P in Fig. 16–31a. Is the direction of the velocity and/or acceleration of the test charge along this line? Discuss.

Sketch the electric field lines for a uniform line of charge whicwr-fr 3b,86fek ,pf6(w8yynj 7m w kgvh is infinitely long. (Hint: Use symmetry.) Is the electric field uniform i 8pyvfbf7n3w(6-m8g 6rk ,fw rjew,ykn strength?

If the electric flux through a closed surface is zero, is the electreu3ps)nq czaj*. dlg7fqs;00 ic field necessarily zero at all 3fq sg j7 ;0ucea.dsz)0n* lpqpoints 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 re 7 in lz)e:8w a n9(uao+64exxrmvbn/. If the sphere is replaced by a cube of side r, wilx6a bn/ee u oniae(:wn+m8lv9z4r )7xl $\Phi_E$ be larger, smaller, or the same? Explain.

  

  How many electrons make up a charge a+b kmuj+p 0b6of $-30.0\mu C\,?$   $ \times10^{ 14}\, electrons $

  What is the magnitude /3qts b-3pnwujqzdm8/b;t6k 9 dy 1grb/ do )kof the electric force of attraction between an iron nucleusb3q6k romzt ;dbkn yu3b8- 1wj/ p/ /9)sdtdgq $(q\,=\,+26e)$ and its innermost electron if the distance between them is $ 1.5\times10^{-12 }\,m\,?$    $ \times10^{-3 }N$

  What is the repulsive electrical force between two proton--r 1 crz/o h8ygrdhkyru t8,l b8r*w-jv2h/ns $ 5.0 \times10^{ -15}\,m$ apart from each other in an atomic nucleus?    N

  What is the magnitude of the nn d:vwi 4k)erd3j2w6force a $+25\,\mu C\,C$ charge exerts on a $+\,3.0\,mC$ charge 35 cm away?    N

  Two charged dust partii i33i48oa efkn*1sr na .oc-qcles exert a force 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 8qc- id);w qh6a l(bi(za4awi6.45 cm apart. They are moved, and the force on each of them is found to have been tripled. How far apart are they now? 6 )iazdl(-hcwawqq a ;4ii6b(   cm

  A person scuffing her feet on a wool rug on a dry day accumula escb6s2uqckpq x6 32+tes a net charge of qp+qscbkc3e 2626sux $-42\,\mu C\,.$ 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 w2xfh2oyk) mk0ce d b.nr .;1nhbr ;.nelectrons in 1.0 kg of $H_2O\,?$    $ \times10^{ 7}\,C$

  Compare the electric force wi.hgb;bn;k (qr rp43holding 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. The sum of their chargesrn*2y87 +d lcwlqff .8 j;blzl is What charge f+l l 8j;qfb8zly 2*wd.r7nc lmust each have in order to
(a) maximize the electric force between them,
(b) minimize it?

  Particles of charge 0(u2l/ mc8i)w okuabc $+75$,$+48$ 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 04oq.mgig: vsequal 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 i ,5wcc(bx (e4khb1dka square 0.100 m on a side. Determine the magnitude and direction 5ikc4d(b ,x e1( hkcbwof the force on each charge.
$F_4$ =   $ \times10^{ 7}\,N$
$\theta$ =    $^{\circ}$

  Repeat Problem 14 for the case when two of t)hjzmtx ybll 4 *ybn uf):p-b h..x6w/he positive charges, on opposite corners, are replaced by negative charges of the same magn)*) h6zunbb-yx .:flhywbjxm4l. t /p itude (Fig. 16–51).
$F_4$ =   $ \times10^{ 7}\,N$
$\theta$ =    $^{\circ}$

  At each corner of a square of side l there are 1 q5bs7( lzb-a2 j lf 4vrr1-sdmhjr.fpoint charges of magnitude Q, 2Q, 3Q, and 4Q (Fig. 16–52). Determine the frf1bhjj md5sr1qallb s-f2 7z-r .(4vorce 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 plaw oi b;:ox+yg(ced at the corners of an equilateral triangle of si g ;ox:ib+wy(ode 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 havetsw o,j lmc n2y+kf.3* 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 spheres have a total)72k c-y,u1xut gifvr 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 ;th ; 6lb8 wu8gwa,hjiplastic ball to an identical ball 12 cm away. The force of attraction is then 17 mN.8w a6h8 jwtgubi;;hl, How many electrons were transferred from one ball to the other?    $ \times10^{ 12}$ electrons

  What are the magnitude and direction ouy2);ena 7y(*u oomtwvd t 17of the electric force on an electron in a uniform electric field of stren2o)vwm1a utyytu; ode * n7(7ogth $2360\,N/C$ that points due east?
   $ \times10^{ -16}\,N$
 ----待选择----westeast 

  A proton is released in a uniform electric field, and it experiences an el)4zc*5)td nz, +k)lnj wbld hwectric f4nz) +wn,* bdk)l)zjcdwhl 5torce 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 exerted o+l 2w6m eqsw*gn 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 magnitud11e h3ii6 putie and direction of the electric field 20.0 cm directly above an isolatede3ti 1phiu6 1i $33.0 \times10^{ -6}\,C$ charge?    $ \times10^{6 }\,N/C$ ----待选择----updown 

  What is the magnitude of the acceleration experiei1im,n r7kx a*7t7ex ewzey52nced by an electron in an electric field o1 e2* xme75kxity , ze7ri7awnf $750\,N/C\,?$ 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 fimc5+zh:zr-ifh t( j yb.2w hu,eld at a point midway between wuhymtih- b2. h5:j (,fc rzz+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 abovyd0* glk4 wdwp9g9.e ut two point charges, $+Q$ and $-3Q$ which are a distance l apart.

  What is the electric field strength at a point in space where q1 96h-.aetjhnv m/sm 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 in a uniform electric fi g8i 6ybr;rs002) edttop-lpw eld and accelerates to the nort0 w-t y;drp)lo rb0i eg8ps62th 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 pdcmc4 n bc)0y z7i*jd)oint charges is $745\,N/C\,,$ and the distance between the charges is 16.0 cm. What is the magnitude of the charge on each?    $ \times10^{-10 }\,C$

  Calculate the electric field at the center of a square 52.5 cm on a side if on9(zep :wj yovdij55i6e cow5izievd5 9 (yo j6pj:rner is occupied by a $+45.0\,\mu C\,$ charge and the other three are occupied by $-27\,\mu C\,$ charges.    $ \times10^{6 }\,N/C$ at    $^{\circ}\,$

  Calculate the electric field at one corner of a square 1.00 m on a side if th(xll7lxz f8 2jr5pjcy+ z4v -6c5ddy te other three corners are occupied by 7cxxlpv l6 +zyc52j8d(5 r dyf4lz t-j$ 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 pnu;2izq: v/v xoint 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 tvinvz/ u:;xq2wo 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 elec 8 4*ae xm e8b,;ijkzoto.iqr9tric 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 theljwxu+j4o )8, 1ao mbc magnitude and direction of the electric field at points A amj1cx 4o) jwa+,ul8o bnd 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 unknow co;4llo 0om nxiue6ppb;k l)sx .,s6-n 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 electric field at fyrpr6o:ba58c te:0 mthe 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 mytf58:6cb0oa:rrpe line joining the charges, a distance x from the midpoint between them. Express your answers in terms of Q, x, a, and k.

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

  An electron moving to f;2ufahqa 5d/ the right at 1.0% the speed of light enters a uniform electric field parallel to its direction of motion. If the electron is to be brought uq 5a;fdh/2af 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 sidez2h5bwml w,n dth20v7 is $1.45 \times10^{3 }\,N\cdot m^2/C$. What charge is enclosed by the box?    $ \times10^{ -8}\,C$

  A flat circle of radius 18 cm is placed in a uniform electric field of mc5u3gwmy64 pmagnitude yup3gm6 c5wm4 $ 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 objec,*pt02rt lef;ve .erkts, $O_1$ 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 uniformo ixe/.y:4 2-8hhecivvagjqv mf9 +d, 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 ucv((krv:: z*8va 8.)f bs8ydmweef o The plates are 1.0 m on a side and are separated by 3.0 cm.zdv bu e )(mv*.8we:s 8fkfacyo8vr(: 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 lkupx6eu o4t-y):ue+u bu.)l 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 c0 xn /qyfxc ,kxh. qqpv*z(8.tharge 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 thin spherical c-3)fnd99r87 d lg6zorsq 3fl9fsduyx onducting 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) beyond the shell? (d) Does the shell affect the field due to Q alone? Does the charge Q affect thfg3yzd dfqd n3s99xl6 9-8so7rfu l)re shell?

  The two strands of the helix-shaped DNA molecule are held together by electrostsdi v.f9hdg/e n:cc+0dws 1h.atic 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 ath1:+en cs.fd0gc9hwvdd i s/. oms 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 fyrfz fdd4.p;(p l x600cprz /xorce between them is equal to the weight of either at the Eartrpd6fz p/pyxdf 0lr c;(0.z4x h’s surface?    m

  A 3.0-g copper penny has a positive charge o1oxfe ( 0im6i4wd l,ya2uh0eg f $38\mu C$. 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 a dkb:tldo8c5u r)0 t/in electric field surrounding the Earth. Its magnc:0u d8/b5rdt itk)loitude 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 accexspjad8t.kp,86qbso es;6ip7 urk6- leration experienced by an elect8b7xpd66k.u6s-sj 8t p sqe,pr ;oiakron 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 radiu9jix/k0zc gt+s 0.018 mm remains stationary in the air. If the downward-directed electric f c/iz0 gkjx+t9ield of the Earth is $150\,N/C$ how many excess electron charges must the water droplet have?    $ \times10^{ 6}$ electrons

  Estimate the net force be7)3wlpjobbf)skc h64 wd0 4detween the CO group and the HN group shown in Fig. 16–62. wcpf 4 sk3jebdh7o4 6)l) 0dbwThe 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 electq9,pafi lv / r4fnyyw2-1gip 1ron revolves in a circular orbit / 2v1ppqryfa9 i,wi4- ynlf1garound 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 gravity, were 7.c1jwn)hsjr7/o xbyresponsible for holding the Moon in orbit around the Earth. If equal and opposite charges Q were plac 1jhycbjw ox s/7rn.7)ed 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 speedbex+3)k0uh j s $v_0\,=\, 21.5\times10^{6}\,m/s$ 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 charl,hq 5hle;yf3lf9x- +g)ggvpve/d2 gge $Q_1\,=\, 2.5\times10^{-5}\,C$. 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 vertnohgl 1--w pi9ically from an ideal spro19g - n-ilhpwing $(k\,=\,126N/m)$ above a lab table, Fig. 16–63. The total mass of the coated sphere is 0.800 kg, and its center lies 15.0 cm above the tabletop when in equilibrium. The sphere is pulled down 5.00 cm below equilibrium, an electric charge $Q\,=\, -3.00\times10^{-6}\,C$ is deposited on it and then it is released. Using what you know about harmonic oscillation, write an expression for the electric field strength as a function of time that would be measured at the point on the tabletop (P) directly below the sphere.

  A large electroscope is made with “leaves” that are 78-cm-long wires ws ugtz 7uq2(c+ith tiny 24-g spheres at the ends. When charged, nearly all the charge re t7u+sug2q(z csides 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 a2 y3 xeo3q7fc uzoba)zt.f;;j spark if the electric field exceeds about7;t. x oy3 ;c3ffjeu baq)zzo2 $ 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 char*umn+2q:kt ph(f8ytv3i q c9 08hu liqge $+0.340\,\mu C$, 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 arl442p6x.l(8 gjqzzb80 waptmm cq km b*0.jwluminum?    $ \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 qm jm5 fe:po*a j9e;e.q*fuj5A and B are a distance R apart; each carries the same charge Q. (a) What is the force sphere B exerts on sphere A? (b) An identical sphere with zero charge, sphere C, makes contact with sphere B and is then moved very far away. What is the net force now acting on sphere A? (c) Spheree a5j e5*oqu:jj;p* meq.fm f9 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 chargesctcpriq/ -2t :kg( v/c shown in Fig. 16–68, at what position(s) x is the electric fck-/icpr(:t q/vc g 2tield zero? Is the field zero 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 charges, each of :6khy1xop v1d11cdwgg mad0z / qh)j+9p5ls n 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?