If you charge a pocket comb by rubbing it with a silk scarf, how caippws(8 ;cx ,w cai6ik*vl2.g n you determine if ,x giiipkw6cas8*v 2l ;. cpw(the comb is positively or negatively charged?

Why does a shirt or blouse t )(wy(.cp ynn c;ua6gkaken from a clothes dryer sometimes cling to your boduanyy w .c(gn()kc;p 6y?

Explain why fog or rvv e7a770 mpzm,bey2aain droplets tend to form around ions or electrons in the aiaeme02v 77 7pm zvayb,r.

A positively charged rod is bro+onvp8+jsmn r04 n8iyught close to a neutral piece of paper, which it attracts. Draw a diagram showing the separation of charge and explain why attraction occujy 8i80rosnnp+vmn 4+rs.

Why does a plastic ruler thb7 px**moi-ftn+7i)oyb kt; q at has been rubbed with a cloth have the ability to pi;7*)k*nxpibftoybq i +m7ot- ck up small pieces of paper? Why is this difficult to do on a humid day?

Contrast the net charge on a b;8 j-z:bz8nrpwrz, fconductor to the “free charges” in the conductor.

Figures 16–7 and 16–8 ssmkl+)ps1zvmi,(0 bz how how a charged rod placed near an uncharged metal object can attract (or repel) electrons. There are a great many electrons in thembl , k)i ss0vp+zm(z1 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 remais-ho0 bgjci 4/n at an angle. What balances the electric fo4ghcjsoi/b 0- rce of repulsion so that the leaves don’t separate further?

The form of Coulomb’s law is very si+wbb0kf3yjsq wx3 a +di:z4 v6milar to that for Newton’s law of universal gravitation. What are the differences betwee kzwy+ia3 sqb x+d0:f6w4j b3vn these two laws? Compare also gravitational mass and electric charge.

We are not normally aware of the gravitational or electric 9 unrsj8ei;,f force between two ordinar8jrsuf in,e; 9y objects. What 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? (Se+t/nz+d p ug4n0, u isqsz(r1he Chapter 6.)

When a charged ruler attracts small pieces of paper, sometime o /ai)f80fpw*c,r5 zci9nkpx5mw (ods a piece jumps quickly away after touching the ruler. E/fp5pf9*0inwxkoa c ro 5 dmw,c z)i8(xplain.

Explain why the test charv7 v d.0uguufik;+tm2 r:w y5ages we use when measuring electric fields must be small.+mu7tad2 k:g v5y i0u r;fu.wv

When determining an electric field, must we use a positive test charge, or woul: -a9 4xskcihgd a negative ona49-:kscigh x e do as well? Explain.

Draw the electric field lines surrounding two negative electric +gc j8 e/ uo.vmz(,auucharges a distancemoe/uc8 u (uv+.jazg, l apart.

Assume that the two opposite charges in Fig. 16–31a are 12.0 cm apart. tw30qqbk1* tn 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 strongest? The weakest* t qbwknq013t? Explain.

Consider the electric field at points A, B,n/ta tg 5j iwmtm96h+3 and C in Fig. 16–48. First draw an arrow at each point indicating the direction of the net force that a positive test charge would experience if placed at that point, then list the p 5 6mjmt/thtn9gaiw+3oints in order of decreasing field strength (strongest first).

Why can electric field f*yu :ym.p3.pci 8e qglines never cross?

Show, using the three rules for field lines giv8ttkw0d5(cdfq;k.p :6 jey wlen in Section 16–8, that the electric field dkcjek:8w .p(tfl6tyd ;wq05 lines starting or 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 there a point along7*t7*o jp d*e mwxn2eg the straight line that passes through them where E=0 when their signs are (a) opposit7nw* jtpgemed 72**ox e, (b) the same? If yes, state roughly where this point will be.

Consider a small positive test charge located on an electr cw0eup4uek 6jo;b8f,ic field line at some point, such as point P in Fig. 16–31a. Is the direction of the velocity and/or acceleration of the test charge along this line? Discuss6o, ue fe jb4kw0uc;8p.

Sketch the electric field lines for a uniform li 3mz 9a ;bbrhts16:p/ip dox7ene of charge which is infinitely long. (Hint: Use symmetry.) Is the electric field uniform in stren;p:xedh7zi s1ort9 bmpa63 /bgth?

If the electric flux through a closed surface is zero, is the electric fie5w.rbquc to,kfc h/f+ i 0co*)ld necessarily zero at all points on the surface? Explac*/c+rqcfw )0bkf tu ohio, .5in. 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 surl+b 54hfee,8 iknr, duface of radius r. If the sphene58,irlfh+k beu, d 4re is replaced by a cube of side r, will $\Phi_E$ be larger, smaller, or the same? Explain.

  

  How many electrons make up ggt-7h490l6)k1l)po yu:jhunwlx gi a charge of $-30.0\mu C\,?$   $ \times10^{ 14}\, electrons $

  What is the magnitude of the electric force of attraction between an iron nucleem k8t ioif/6/us k/8 im/ e6ofti$(q\,=\,+26e)$ 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 3erz 746f k*l.lt jlrzprotons $ 5.0 \times10^{ -15}\,m$ apart from each other in an atomic nucleus?    N

  What is the magnitude oo;/9l8 l k/mexfa7+k a,yv qmgf the force a $+25\,\mu C\,C$ charge exerts on a $+\,3.0\,mC$ charge 35 cm away?    N

  Two charged dust particles exert a k x-jvg-tu u/hz,rk46 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 8.4ew; pe;ytbr +67zgmqtivi39 ,5 cm apart. They are moved, and the force on each of them is found to have been tripled. How far apart are they now? ti 9bvm67 e+;weg3i;,pry tzq   cm

  A person scuffing her feet on a wool rug on a dry day accumulates a net chg9/2tzg)z6et+jik sz arge ojz9gg+s2e t ztkzi) 6/f $-42\,\mu C\,.$ How many excess electrons does she get,    $ \times10^{14 }\,electrons$
by how much does her mass increase?    $ \times10^{-16 }kg$

  What is the total chargl kak qx9)*/vre of all the electrons in 1.0 kg of $H_2O\,?$    $ \times10^{ 7}\,C$

  Compare the electric force holding the electron ine 7h a-6ntwus lq.zqda6t*3v2 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 agq0pct1 4 ,a na5vh3+ccd.nycre a fixed distance apart. The sum of their charges is What cha5+q3c1gd t cvy a.ncp nhc04,arge must each have in order to
(a) maximize the electric force between them,
(b) minimize it?

  Particles of charge v2o f0es6; cxsx.t-z h$+75$,$+48$ 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 particles3c1pq;; 02 j8;kinoq lekazs4s2dtejshd 0c* of equal 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 zbe p v;+w0u,cpm9)uma square 0.100 m on a side. Determine the magnitude and direction of the force on each charg z e0,upvw9mcbu pm;+)e.
$F_4$ =   $ \times10^{ 7}\,N$
$\theta$ =    $^{\circ}$

  Repeat Problem 14 for the case when two of rc9t0s )*ka vu-7b0sb fo2fhks3/smbthe positive charges, on opposite corners, are replaced by negative charges of the same magnitude (Fvt0/03fmkos bkush7b- 9assb 2r*f)c ig. 16–51).
$F_4$ =   $ \times10^{ 7}\,N$
$\theta$ =    $^{\circ}$

  At each corner of a square of side l there are point charges of magnit(,-r3spjpro lude Q, 2Q, 3Q, and 4Q (Fig. 16–52). Determine the force on (a) the 3p-jr(l ro sp,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 ne/q7-c6vb n6i0 r aj/slpid0 placed at the corners of an equilateral triangle of side 1.20 m (Fig. 16–53). The chargei njla/0vrnq60sbd6 7 i-e p/cs 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(.xn g ,ofl4s- tsuz,y 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 totat)y l(uba t* d62iwa)al charge of $90.0\,\mu C\,.$
(a) When placed 1.06 m apart, the force each exerts on the other is 12.0 N and is repulsive. What is the charge on each?    $ \times10^{ -6}\,C$$\;\;\;\;$    $ \times10^{ -6}\,C$
(b) What if the force were attractive?    $ \times10^{ -6}\,C$$\;\;\;\;$    $ \times10^{ -6}\,C$

  A charge Q is transferred from an initially uncharged plastic ball to an identic 6k5cl a6968m1 9hiidjmp1 v:uh vwk(akk7uhval ball 12 cm away. hi1d(9 vvuc8kak6a iwu m 65:kh6k9h 7j 1plmvThe force of attraction is then 17 mN. How many electrons were transferred from one ball to the other?    $ \times10^{ 12}$ electrons

  What are the magnitude and direction o.4u *und,t7 cqtn0t b9.jtiy ff the electric force on an electron in a unifot07t. ctqy u.bun nt4d,*f9j irm electric 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 experienc9d:+qtn-xt7w8t sya (ddpjmq (pkt4 7es an electric f- y+7 :ds 84m pj9t(7(qaxkdntdpttwqorce 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 on a 34gwrgdu7 be( $-8.8\,\mu C\,$ 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 cm di7;re mdz-u zh0rectly above an -rh z;7due0m zisolated $33.0 \times10^{ -6}\,C$ charge?    $ \times10^{6 }\,N/C$ ----待选择----updown 

  What is the magnitude of the acceleration experienced by an electrre)ue o d4z4.yon in an electru4 .d yzre4)eoic 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 direction of the elect;nw 2y .26vuza2v7cow o o2zdmric field at a point midway betwevzooo6uw2ynz md vcw; 2 272a.en 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 abar xf672 4o1ukvxk lw6out two point charges, $+Q$ and $-3Q$ which are a distance l apart.

  What is the electric field str9o6 -bbnloq;z.b* o d f::bflhength 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 released from rest in a unifor1rqnsu0ylm x4k2 2w8 xivytuk5o .+*p m electric field and accelerates to the northmi12+p y42 n *kxsvwu8y5 qoru0.kxlt 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 equa)bgxm 9a;kj6ebv n.0ol but opposite 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 the center of a sa d.53,vl tk 7ovh)ozkquare 52.5 cm on a side if one corner is occupied byv,d3 ko v.o)lta5k7zh 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 cornero 8ajft wgd9,20f yjqzo di:,8 of a square 1.00 m on a side if the other three corners are occupied bygo ot 988 fw,:ayqddj0jz,f2i $ 2.25\times10^{-6 }\,C$ charges.    $ \times10^{4 }\,N/C$   $^{\circ}\,$ from the x-direction.

Determine the direction and magnitude of the electrilx a c(z3d2jo a7)v5:b des7occ 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 ida e(c ) 75odocsxa:7vblj23 zn 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 eledxfd;om wrm+ ,d5e,ka u;(ea9wc br *6ctric 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 direction of the elmeie- -wp3 tz/;owt1,s.nj c uectric field at points A and B in Fig. 16–57 due to the two positi-w- 1/cji mn3e e sotw;.,ztupve 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 paih(o2+uuq m .mv(i 1qc dwat-:p4ma( oint 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 a 7iibwgerzx 5rk5w)0. t the point P shown in Fig. 16–59. The two charges are separatekw5)i i5e7.zrbgrxw 0 d by a distance of 2a. Point P is on the perpendicular bisector of the line joining the charges, a distance x from the midpoint between them. Express your answers in terms 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 enters a uniform elez15wfu ; jfo5cctric field parallel to its direction of motion. If the electron is to be brought to rest in the space of 4fjfu51o ;w 5zc.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 fx*sny1w3 w-;d bbp2 yzlux 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, nf ,m5ypq.qp a uniform electric field of magnitude ,.pqpmn,5 qfy$ 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 x8h:.ga r6y hk:qyxi-, $O_1$ 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 uniformg i ,j ;qz0,q3f*kqbcg 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 platef 9+cy6m8 vxzhs 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 eqhf8x6+mvyz9c ual and opposite)? Neglect edge effects.    $ \times10^{-9 }\,C$

  The field just outside a 3.50-cm-radius metal ball -kd: dfcd,6iz 5pfqcu:w)yw3is $ 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 totalc4v/zoza3,u;eq x,e 7 6cyjal: mfds8 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 centekzt(8f h -r-nqr 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) beyond the shell? t- zqfk8r-n( h(d) Does the shell affect the field due to Q alone? Does the charge Q affect the shell?

  The two strands of the helixr)w1/n(vonx8 yx rt h7:aho5e;q,5ur j. gwic-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. n;ctxa e75j5hrx18(.w)i :o vn w,gyrhqo u/rAssume also that atoms on each molecule are separated by $ 1.0\times10^{ -10}\,m$. Estimate the net force between
(a) a thymine and an adenine;    $ \times10^{-10 }\,N$
(b) a cytosine and a guanine. For each bond (red dots) consider only the three atoms in a line (two atoms on one molecule, one atom on the other).    $ \times10^{-10 }\,N$
(c) Estimate the total force for a DNA molecule containing $10^5$ pairs of such molecules.    $ \times10^{-5 }\,N$

  How close must two electrons be if the electric force between them isi +z.mj wn:/,rp hyvc3 equal to the weight of either at the Earth’s surface? p+r:jcz n,3ihmy. /wv   m

  A 3.0-g copper penny h2 fli.74g nj6ynfhmhw6/6v13 qymy mm as a positive charge of $38\mu C$. What fraction of its electrons has it lost?    $ \times10^{-10 }\,$

  A proton $(m\,=\,1.67 \times10^{-27}\,kg)$ is suspended at rest in a uniform electric field $\vec{E}$. Take into account gravity at the Earth’s surface, and determine $\vec{E}$.    $ \times10^{-7 }\,N/C$  ----待选择----updown 

  Measurements indicate that there is an electric field surrounding the Earthop 4vk ,*;yn;tgan;1rul r x+gyyfj9+. Its magnitude ojn;k 1f yy*+punl+rxgt;g4v9r y;a,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 xu;dl qynz.pt j+3o7 ) +)skl/hh8qxmis the acceleration experienced by an electron xy3qk j+.tp d hms8/nxl+luq)7)o h;znear 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 sta(yw.sdw 8 j qig1;6obationary in the air. If the downward-directed ;wwi(qs1 b6.y8dj oagelectric field of the Earth is $150\,N/C$ how many excess electron charges must the water droplet have?    $ \times10^{ 6}$ electrons

  Estimate the net force between the CO group and the HN group shown in Fig. 16–62id80epu/ba 0 b g nq9(n:6chjklt-a0f. The C and O have char h0ugcal0 i0ban(68bkfd/-9etnjq p: ges $\pm0.40e$, 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 electa)fdtluf al: 0,spf 2t w3f(i1ron revolves in a circular orbit around the proton with a spee a)aswl2 u 1lttfi3,pff:(0fdd 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 attr:yez.u9 nky;d49, dmg9whiwo action, rather than gravity, were responsible for holding the Moon in orbit around the Earth. If equal and opposite charges Q were placed on the Earth and the Moon, what should w9 9.e oki4y,nygd:h;mz duw 9be 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 speg4w 9q 3ku(8:(ea9aq3u mkhswybyh)t 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 charge t e 6fuf4iwe;14-snqb $Q_1\,=\, 2.5\times10^{-5}\,C$. 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-zz aj ra5g z2s-twy7pk:( aa9 insulating plastic and suspended vertically from an ideal sprizza rajkpgw--:a (2a 7yzst9 5ng $(k\,=\,126N/m)$ 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 with i j2g2m 15y0t9hyubzjtiny 24-g spheres at the ends. When charged, nearly all the charge resides on the spheres. If the wires each mam g2 j50bj1ty9yu zhi2ke 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 an- ybno ;*w5:x qzx+ei; qmjq d)bmfh(4ml:yb4 d generate a spark if the electric field exceeds about *wq)o x;(fmjyhdb4;i4 :bylq: q eb n5z-mm +x$ 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 0.26+d7*kvrot hy1h h+jl10 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 15l oq :8p;.vwpv-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 a1d5*s i 0wxwllgrhcq 3e221/gxfsoy ) 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) Sphere C next makes contact with sphere A and is then movedlrf3hwy i2d wge2)qsxc/o* l 0s15g1 x far away. What is the force on sphere A in this third case?

Given the two charges m 4zlt3hmkg;5 shown in Fig. 16–68, at what position(s) x is the electric field zero? Ik3mlg54htm z ;s 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 chargnoxw - uz;u 0np46aq8re $8.0\,\mu C$ 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?