If you charge a pocket comb by rubbing iltnagw(5xn)jxl 8 8s/t with a silk scarf, how can you determine if the comb is positively or negatively char5xx 8 /ntglln(w8 a)sjged?

Why does a shirt or blousef5cu//y- fe gc taken from a clothes dryer sometimes cling to your body? f/fce/-cgy 5u

Explain why fog or rain droplets tend to form arou *ck-up 0zikohk35v 5ind ions or electrons in the ai hz3u5 5vip kk*co0ki-r.

A positively charged rod is brought close to a neutral pi1rs,y6el h/mh8e a n2aece of paper, which it attracts. Draw a diagram showing the separation of2h6ya/rm1nl,8he e sa charge and explain why attraction occurs.

Why does a plastic ruler that has been rubbed with a cloth have the ab z + 4 kcnt5y-nl/hfu:d)crnyxtdx2:/ility to pic tzntfync4c+ d-r5 u:xlx:k)hd/ny/2 k up small pieces of paper? Why is this difficult to do on a humid day?

Contrast the net charge on a conductor to the “free charges” in the conductor 3g0eleipgfv3 w-7yx7 .

Figures 16–7 and 16–8 show how a charged rz2*q e 5udv yykd*)2buod placed near an uncharged metal object can attract (or repel)5 ved *b2d)uyk2* uzqy 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 leave7 gq sgaf74nn 5sav9;us repel each other and remain at an angle. What balances the electric force of repulsion so that the leaves don’ts 59gs7nv4 aa7ufq;gn separate further?

The form of Coulomb’s law is very similar to that2vr trl 3;s+yrdl8*3cw clzd5q. qyn- for Newton’s law of universal gravitation. What are the differences between these two laws? Compare also gra3d *d +wrncz2tql3v cq; r.syly5 -l8rvitational mass and electric charge.

We are not normally aware of the gravitatio k sn.h/4 4be-m1t.czwb6 uz:6 jkrunonal or electric force between two ordinary objects. What is the reason itsc zzkek4w1on/u 6ubm jrn6-h4: ..bn each case? Give an example where we are aware of each one and why.

Is the electric force a conservative force? Why or why n.uwri *am h.;vot? (See Chapter 6.)

When a charged ruler ats0ith76y.jazy8;dxi tracts small pieces of paper, sometimes a piece jumps quickly away afh8xj d7.6iizysyta; 0ter touching the ruler. Explain.

Explain why the test charges we use when measurinql2a4 uht2w m/of-d6v g electric fields must be small.64tvwodl mh2a -q /uf2

When determining an electric field, must ;tzwyl). c bctwq-6t6we use a positive test charge, or would a negative oneb tt.c6 zq)tycl;w6-w do as well? Explain.

Draw the electric field lines surh 24iex zv:(qqk1c7b9vpyau 0k) fqq*rounding two negative electric charges a distance2 yx 1qacifp4qeb097h*(vkzk qv)q :u l apart.

Assume that the two opposite charges in Fig. 16–31a are 12.0 cm apart. nnb 76 xw) smabvn ap*;,uf +7hdfp)d.Consider the magnitude of the electric fie fn6 pa d*x7vbuw;7)f.bha snp,+n)m dld 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? Explain.

Consider the electric field at pointh8dy swad6jbq 7/z ))ss A, B, 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 pw )b/qyj ds)6s8ha 7zdoints in order of decreasing field strength (strongest first).

Why can electric field lines ns+vi) wb) v*d2ehp*b*z6w3odx g8 qjdever cross?

Show, using the three rules for field lines gikwf *pj 6h+vx11omzx 4z(sm 2hven in Section 16–8, that the electric field lines starting or ending on a single point charge must beo1 j4xmh+f wz(2s mv*pkx6zh1 symmetrically spaced around the charge.

Given two point charges Q and 2Q, a distance l apart, is ther f9th1r862q8shecwyqe a point along the straighy t hr1fc26sq wh8q89et line that 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 a7 piz a6znf-5pn+1sfo5tjf9hrc0-,b x zd/efield line at some point, such as point P in Fig. 16–3ro sp1f a90exinanz,j-/dz7t hpfb 5fz-56+ c 1a. 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 ofa5lv7tvi shhh ,m()m* charge which is infinitely long. (Hint: Use symmetry.) s* lh,t5ai )hvh(vm7mIs the electric field uniform in strength?

If the electric flux through a closed surface is zero, is the electric filp)h5o ,3md+ vmmry d6kgz, ;celd necessarily zerh) dp6;d y ,kmmm+c5z3 glv,oro at all points on the surface? Explain. What about the converse: If $\vec{E}\,=\,0$ at all points on the surface is the flux through the surface zero?

A point charge is surrounded by a spherical gaussian surface of radius ro:.lnw pl/ oz/ks(y i;. If the sphere is replaced by a cube of side r, w.yo/il;: szn l(/pok will $\Phi_E$ be larger, smaller, or the same? Explain.

  

  How many electrons make up a cklpoxq):0g2rh8 rpkzl. i bynz-:;y) harge of $-30.0\mu C\,?$   $ \times10^{ 14}\, electrons $

  What is the magnitude of the electric force of attraction be:km y8lxmak 2(tj mk7:tween an iron nucleusx:mtkky(m l827j k :am $(q\,=\,+26e)$ and its innermost electron if the distance between them is $ 1.5\times10^{-12 }\,m\,?$    $ \times10^{-3 }N$

  What is the repulsive eleu*uuh72 h*u +pjkm i,,m qthm9ctrical force between two protons $ 5.0 \times10^{ -15}\,m$ apart from each other in an atomic nucleus?    N

  What is the magnitude of the force akxsne* n+pms:mm g+. p4/a r)o $+25\,\mu C\,C$ charge exerts on a $+\,3.0\,mC$ charge 35 cm away?    N

  Two charged dust particles exert a fo)za8w+klex7;d f mm b2rce 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 apart. They are moved, and the force on each of 5xx8y;yb3dswwe,pdj1o - 5fy td5,81-jwex5y;dw3sxyo y bfp hem is found to have been tripled. How far apart are they now?    cm

  A person scuffing her feet on a wool rug on a dry day accum,o/ poff .ouhq;9f pp0ulates a net charge o ;o p0hu.foo pff,p9/qf $-42\,\mu C\,.$ 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 electrons in 1.0 kg ya.*ktr9rd 45ia7.hik8vt e pof $H_2O\,?$    $ \times10^{ 7}\,C$

  Compare the electric force holdingl9kg4qce17g y 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 distancg8u 4yym 2hsdfge. ds62l,gr+e apart. The sum of their charges is What charge muf,2g h 4dsr28u+esyl6d gmy .gst each have in order to
(a) maximize the electric force between them,
(b) minimize it?

  Particles of charge b7 ):j7t3xa1byc9k x kc zbda*$+75$,$+48$ 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 particxf,fd : f9nsk+les 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 a square 0.100 m on a stb)jzqmt .l+7 n3i:an ide. Determine the magnitude and dira)lqz:.+t7 n3njtb imection of the force on each charge.
$F_4$ =   $ \times10^{ 7}\,N$
$\theta$ =    $^{\circ}$

  Repeat Problem 14 for the case when two mqu s0d,jrhdp0 v,ej9 ob/q 6-of the positive charges, on opposite corners, are replaced by negative charges of the same magnitud- e b djs6q9r0qpujho ,/,dv0me (Fig. 16–51).
$F_4$ =   $ \times10^{ 7}\,N$
$\theta$ =    $^{\circ}$

  At each corner of a square of side l there are po:b6e kr80ia9s sfdcv0qbvm .2 int charges of magnitude Q, 2Q, 3Q, and 4Q (Fig. 16–52). Determine the force on (a) the charge 2Q, avab9:ive 0fs8k.bd 6s m0qr2cnd (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 equi 88vp/h5k svr9tk mm5clateral triangle of side 1.20 m (Fig. 16–53). The9s rh5p5mvv t8c k8k/m 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 total :l*tm9nj rt cb u/0-qucharge 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 tota*ej3p(xk6f(8g vts 0.q rxj ppl 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 f cjcqu8i0z p37rom an initially uncharged plastic ball to an identical ball 12 cm away. The force of attraction is thiz0c3pq 7 c8ujen 17 mN. How many electrons were transferred from one ball to the other?    $ \times10^{ 12}$ electrons

  What are the magnitude and direction of the electric5ft* ey;jp:qt force on an electron in a uniform electric fiel*e5q ;j:tytfp d of strength $2360\,N/C$ that points due east?
   $ \times10^{ -16}\,N$
 ----待选择----westeast 

  A proton is released in a uniform m*y n*fig),s2(xt gr- jc4qcg+z d xs)electric field, and it experiences an electric forxcidx+)js rf(g*nzsq*, 4mc) 2 gtgy-ce 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 8.4d4o -3c i8au-brrpfn. N is exerted on a $-8.8\,\mu C\,$ charge. What are the magnitude and direction of the electric field at this point?    $ \times10^{5 }\,N/C$ ----待选择----updown 

  What are the magnitude and direction of the electric field 20.0 cm dirahfukbn/ 2 +z8j9ynp08 j8vk0frj0q aectly above an is jan0fkjz v0h 9ubpa82nq+r 80 fj/8ykolated $33.0 \times10^{ -6}\,C$ charge?    $ \times10^{6 }\,N/C$ ----待选择----updown 

  What is the magnitude of the 7r.2v khm+)/brc lvcs acceleration experienced by an electron in an electr+klcvrcm )b7h.s r2 /vic 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 electric fielr8) )ltfc1 8a k2jedg 7tz 02+njqpidrd at a point midway betwee0jt nqkr8+ 2) lt1 )ddp2zijer7gca8 fn a $-8.0\,\mu C\,$ and a $+7.0\,\mu C\,$ charge 8.0 cm apart? Assume no other charges are nearby.    $ \times10^{7 }\,N/C$ ----待选择---- towards the negative charde opposite to the negative charge 

Draw, approximately, the electric field lines about two point chargesh*qd te-;c xuqu4 v20e, $+Q$ and $-3Q$ which are a distance l apart.

  What is the electric field strengt9 kr4a4b6 wj(4o tupnhh 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 releasewv+uf* qc8h c prjc+xiqy6a1. x8m8:yd from rest in a uniform electric field and accelerates to the north at haf8q8w.86ccm+p c*+i1ruyxx yq :vj 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 charges jll0(vyqb7; q 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 s h p*hac6uaq5j n(1r4nide if one corner is occupied by ac(1uqjr4*hp5n6a a hn $+45.0\,\mu C\,$ 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 6cpm gd2d3)eg ljh h6q94ob2jon a side if the other three cg)qop jl 3bhd2dcg4296 mhj6e orners 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 /j jsc,2mvn) (7seze v7zkgv; the point P in Fig.nvjv/szm (v7c7jge s)e2, ;kz 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, 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 ele0tq 3ge6b;q iqctric 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 magnitudewa+)z uhc q 2(x: xkex1xc7w4s and direction of the electric field uxxzcw e27axk (c w+:1sh) 4qxat points A and 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 unknokap 7-,ns u/j16l4ecwxls rz qyi.j/t ( t(jn6wn 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 ai)/v n6jst)v,ac 9 ocz::70ufidkjr qnd magnitude 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 between them. Express your answers in terms of Q, x, a, and :k6) o:jz r jia)i cv9/ tvduf,0sc7nqk.

  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% pj xx*d :;(qkqmi7t1ithe speed of light enters a uniform electric field parallel to its(qiidmxj tq*xp: k7 1; 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 bc)3j7x s st-xvox 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 isgyw3u(u mq ) /gw.s6qf 1mxca/ placed in a uniform electric field of magnitude 63xq .muu/g(sq w1g)amfc/ w y$ 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,t5* sehc l:u)h $O_1$ 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 uniform fi* 0uero,ul;kp eld $ 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 ss55jr9 3wkqs.9 thaqxquare metal plates is The plates are 1.0 m on a side and are separated by 3.0 cm. What is the charge on each plate (assume equal and oppqkxq 9.hj tw9sr53 as5osite)? Neglect edge effects.    $ \times10^{-9 }\,C$

  The field just outside a 3.50-cm-radius5:hcjwbd/ep9fzv; ;k0ey +qo metal ball is $ 2.75\times10^{2}\,N/C$ and points toward the ball. What charge resides on the ball?    $ \times10^{-11 }\,C$

  A solid metal sphere of radius 3.00 m carriefdin0m2*.1* 1p-xoe zn:up9gu lai up s 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 thinas//1c dzwa 8c spherical conducting shell. (See Fig. 16–33.) What is the electric field E as a function of r (a) for r le1 ds z/8a/cacwss 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 the shell?

  The two strands of the helix-shapek n*87qxzn u*:*md/u: xdewhbd DNA molecule are held together by electrostatic forces as shown in Fig xnnu /hb*:m7u8de*x *w:zkqd. 16–44. Assume that the net average charge (due to electron sharing) indicated on H and N atoms is 0.2e and on the indicated C and O atoms is 0.4e. Assume also that atoms on 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 /pooi*si,do 4is equal to the weight of either at the Earth’s surfacsopo/i 4di ,o*e?    m

  A 3.0-g copper penny has a positive+hpp qn r7b40aj6fyn 5 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 elp:6 ; jltih2huectric field surrounding the Earth. Itsu l2:j; hhipt6 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 accelebq 03az jh :lv8g1p4jjration experienced by an jh jgjbv30la: p1zq4 8electron 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 thpa/atew6q q d)g;c 4c0e air. If the downward-directe dc pqa6)/ct0 a4e;wgqd 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 th5izb1 *ldr9xnl6jr ;h e HN group shown in Fig. 16–62r;x6b*zi9 1j nld5 rlh. The 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, the0 cgcddu-:rvp,4 au1t y2xm:k electron revolves in a circular orbit ar-:41 rypdcudx2: mk u vgta0c,ound 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 l/t2 k( d16bgfraxq r/responsible for holding the Moon in orbit around the Earth. If equal an( kal/rb/f tdgxr21q 6d 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: 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 speed kv1 z0w1mvo o:$v_0\,=\, 21.5\times10^{6}\,m/s$ 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 charkdtr; dt 1vdmwl8hn/) +b4 *i 9i:qjtpge $Q_1\,=\, 2.5\times10^{-5}\,C$. 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 verticalymfs.( x1puh eou,uw*.n7h/uly from an ideal .,*7 m/h1s euux.hpfu (ounwy spring $(k\,=\,126N/m)$ above a lab table, Fig. 16–63. The total mass of the coated sphere is 0.800 kg, and its center lies 15.0 cm above the tabletop when in equilibrium. The sphere is pulled down 5.00 cm below equilibrium, an electric charge $Q\,=\, -3.00\times10^{-6}\,C$ is deposited on it and then it is released. Using what you know about harmonic oscillation, write an expression for the electric field strength as a function of time that would be measured at the point on the tabletop (P) directly below the sphere.

  A large electroscope is made wit/u2 qat)o/qhwi gs)* qh “leaves” that are 78-cm-long wires with tiny 24-g spheres at t2oa /)*qg s)ihq /uwqthe ends. When charged, nearly all the charge resides on the spheres. If the wires each make a $30^{\circ}$ angle with the vertical (Fig. 16–64), what total charge Q must have been applied to the electroscope? Ignore the mass of the wires.    $ \times10^{-6 }\,CC$

  Dry air will break down and generate a sparkpz6n+7 qjqe ltdo32a- if the electric field exceeds about 23 t7qoq-elapzn 6dj+ $ 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, aspau/guki+wjzl 6 5. 7nd 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 bar of aluminum/cfu;sl a .ha6 2rm .yxyf78ry?    $ \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 mw zjim7,3/8rg0fzae A and B are a distance R apart; each carries the same charge Q. (a) Wh8j 70mwz a/rei g,3mfzat is the force sphere B exerts on sphere A? (b) An identical sphere with zero charge, sphere C, makes contact with sphere B and is then moved very far away. What is the net force now acting on sphere A? (c) Sphere C next makes contact with sphere A and is then moved far away. What is the force on sphere A in this third case?

Given the two charges shown in +8i d-e bme41(gyyhr vFig. 16–68, at what position(s) x is the electric field zero? Is the field zero at any other points, not y h(r8b ge4+1-e dvmyion 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 bsc u1r2w. 9,)(t1 hmfjzxfarcharge $8.0\,\mu C$ 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?