If you charge a pocket comb by rubbing it with a silk sc- qg136 mr2 a 2v3s9meea3ppik- eohwqarf, how can you determine if the comb is positively or eqpm 1rqveama3hg-swp2i3 e3 6k-92o negatively charged?

Why does a shirt or blouse taken from a clothes dryer sometimes c 4 07u)kieg+ndfw4 mnv9u*xesling to your bo40fugnx+ 9d iv wneek*74m )usdy?

Explain why fog or rain droplets tend to form around ions or elwned ye5hl 7g). w/7m-mbs 0fkectrons in the air mm5./n0s ke)w7 e-bwgfldhy7.

A positively charged rod is brought close to a neutral piece of paper, which 3elc 92 ifz wddrwksgj6/e- .)it attracts. Draw a diagram showing the separation of charge and explain 6d jrki) dg/ce9e3w f. ws2-lzwhy attraction occurs.

Why does a plastic ruler that has been rubbed with a cloth ha3fgu; lrkr/kye2q x75ve the ability to pick up small piece lr3 eyf/5xg rqu2k;k7s of paper? Why is this difficult to do on a humid day?

Contrast the net charge on a conductor to thel t6ph xt6rj741n 0ab/wkwsfo560t kg “free charges” in the conductor.

Figures 16–7 and 16–8 show how a char9l 3vpvfhd c,4ged rod placed near an uncharged metal object can attract (or repel) electro9v4 vdlh ,pcf3ns. 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 i7)mbir - b0cr0bvf md9vhi/o3 kn1 h8js charged, its two leaves repel each other and remain at an angle. What balances the electric foriobdkr) 8c3h 0/0 -vnibf1b9 rvm7jmh ce of repulsion so that the leaves don’t separate further?

The form of Coulomb’s law is very similar to that for Newttvz3t). 85n 0vc-3jtzmpbxnn on’s law of universal gravitation. What are the differences between these two laws? Compare also gravitational mass and electric char vzvmn 5 tt )30.-nbtzp38cxnjge.

We are not normally aware of the gravitational or electric force betwee1v a l d1uul3w7i8t+cpn two ordinary objects. What is the reason in each case? Give an example where we are w 3tvll1ci8a71dp+uu aware of each one and why.

Is the electric force a conservative force? Why or why not? 5j f:*9po k;fm3lbsyw (See Chapter 6.)

When a charged ruler attracts small pieces of paper, sometimes a piece jumps quimz-n lcn93 -nhr,o(ukckly awaumrn (oz 9hlknn3-c -,y after touching the ruler. Explain.

Explain why the test charges we use when measuring electric fields must bv . 9p*zyhjh.de small.. .zj9d*hh vpy

When determining an electric field, must we use a positive test charg m0w1:yvl*+kk6bkjd we, or would a negd:jmkwlv 1* kk+w60y bative one do as well? Explain.

Draw the electric field lines surrounding two negative electric charges a diiar*l.b2,ng. llc//v ax4ao n stance l apa2v bxl a* . ./rani4lcl,n/oagrt.

Assume that the two opposite charges in Fig. 16–31a are 12.4cjjn84* f-6en c1 jbf g5ljict2vm n10 cm apart. Consider the magnitude of the electric field 2.5 cm from the positive charge. Ob f-*nc16tn4c vn4j5ifj j1 cjmel2g8n which side of this charge — top, bottom, left, or right — is the electric field the strongest? The weakest? Explain.

Consider the electric field at points A, B, and C in Fig. 16–48. First dq -al+/o)3ihmm 4 yytbxj1kbkn q 949araw 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 t k)mnj/ lqma9 4x o1bhakbt iy3q+9y-4he points in order of decreasing field strength (strongest first).

Why can electric field lines never croswfjk97 kt3h. ps?

Show, using the three rules for field lines fx47o k)n,iyft9 m rh6sgz/cw).pom 5given in Section 16–8, that the electric field lines starting or ending on a singles,oxyr) f.wmfh no )9g5cpk7/izt64 m point charge must be symmetrically spaced around the charge.

Given two point charges Q and 2Q, a distance l apart, is thsjz2 8uw9i8ptere a point along the straight line that passes through them where E=0 when their signs are (89tz 2us8jiw pa) opposite, (b) the same? If yes, state roughly where this point will be.

Consider a small positive test charge located on an electric field lins:au0 qc9l3yk 8lesw55 bnhe *e at some point, such as point P in Fig. 16–31a. Is the dirh q0* lwse9clnk3yueb 855:s aection of the velocity and/or acceleration of the test charge along this line? Discuss.

Sketch the electric field lines for a unifor, 9mv1 v/dpwymm line of charge which is infinitely long. (Hint: Use symmetry.) Is the electric field uniform in strengv v/w,m91y mdpth?

If the electric flux through a closed surface is zer87atfbl.4,mdeh z oe/u*(jtro, is the electric field nece tbr8(/fzlo 4j m*7ta,de hu.essarily zero 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 rj 3y3-fmbk6qf . If the sphere is replaced by a cubyk m6fbf3-3 qje of side r, will $\Phi_E$ be larger, smaller, or the same? Explain.

  

  How many electrons make up a chargzr 5ad,9t kn69m mdac/rj60hze of $-30.0\mu C\,?$   $ \times10^{ 14}\, electrons $

  What is the magnitude of the electric forcehi0+m +g2mmmb-tu2 n,ynm-vm of attraction between an iron nucleus himmv mub 22gy nm,-nm-t0++m $(q\,=\,+26e)$ and its innermost electron if the distance between them is $ 1.5\times10^{-12 }\,m\,?$    $ \times10^{-3 }N$

  What is the repulsive electt+en4si;z/9 );31fue ye /dciw hpejh rical force between two protons $ 5.0 \times10^{ -15}\,m$ apart from each other in an atomic nucleus?    N

  What is the magnitude of the for6 urcsi8fyx; 6vnc)m ljyy4(/ ce a $+25\,\mu C\,C$ charge exerts on a $+\,3.0\,mC$ charge 35 cm away?    N

  Two charged dust particles a jin1rum.-2:b k ,iawexert 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 8.45 cm apart. They are bi w ksr*j-+pqhz88f6 moved, and the force on each of them is fou 8*kw8p-qfiz+r s6b jhnd to have been tripled. How far apart are they now?    cm

  A person scuffing her feet on a w2 p l;f(1ngvagd e hwwd*c,jrcy2+* b-ool rug on a dry day accumulates a net charge orewdh-2 ja*1 ;nc+d2wbl(*,pcyfvg gf $-42\,\mu C\,.$ 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 o/)omd;./z7ybkt ntz v f all the electrons in 1.0 kg of $H_2O\,?$    $ \times10^{ 7}\,C$

  Compare the electric force holding the electron in orbiig6+0ddddpss2q uc3dlx2/ )lt $(r\,=\,0.53 \times10^{-10 }\,m)$ 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 oh 90;*knwxspx od1h /4yvnmo5f their charges is What ch0ym;9oh* n on5w1xdh p/xkv4s arge must each have in order to
(a) maximize the electric force between them,
(b) minimize it?

  Particles of charge hk;(yco38p xu $+75$,$+48$ 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 e d-jbgluevx5.q xo.z4f-+mi.n;y* zuqual 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 eachiikma2 b0)w y1so 0sl7 corner of a square 0.100 m on a side. Determine the magnitude and direction of the force on each 01syasm 07ibl )iwo2kcharge.
$F_4$ =   $ \times10^{ 7}\,N$
$\theta$ =    $^{\circ}$

  Repeat Problem 14 for the case when two of the positive charges, on opposite cork.5j)6 ow.qymhum;nv,h7y z dners, are replaced by negative charges of the same magnyhvzhd) ym.5w.q,mj; 6u ko7nitude (Fig. 16–51).
$F_4$ =   $ \times10^{ 7}\,N$
$\theta$ =    $^{\circ}$

  At each corner of a square of side l .sk:4 iehl/ bi+ca04k k01msn )rslre there are point charges of magnitude Q, 2Q, 3Q, a:k04/ c krke+nl4 ahib1r. ) ls0isesmnd 4Q (Fig. 16–52). Determine the force on (a) the charge 2Q, and (b) the charge 3Q, due to the other three charges.
$F_{2Q}$ =    $\frac{kQ^2}{l^2}$
$\theta_{2Q}$ =    $^{\circ}$
$F_{3Q}$ =    $\frac{kQ^2}{l^2}$
$\theta_{3Q}$ =    $^{\circ}$

  Three charged particles are placed at the corners of an equilateral triangle o6; ru80p oj k6t 2qzlo(i+dtskf side 1.20 m (Fig. 16–53). The charges are 60d8sol(u ;6qr2otkzijtpk+$+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 aviond ka -3qv2k 07+ra 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 charge of v oc;h40z /l h+7ajeqh$90.0\,\mu C\,.$
(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 frc *g0k)2+ nz cxu9+gdciw1bnv qn-:dh om an initially uncharged plastic ball to an identical ball 12 cm away. The force of attraction is then 17 mN. How many electrons were trugcdd:q gi1h vc +9 2n-+ 0c*znknbw)xansferred from one ball to the other?    $ \times10^{ 12}$ electrons

  What are the magnitude and direction of the electric force on xd,nd:lil uht/i.00 r an electron in a uni0ddh0nil, x il tur.:/form 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 experiences aur . ,ye:ix8tv8h a6hvn electric force o6 t8eyi8 u:avvh hr,.xf $ 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 o6;8n gif 9ulc jklsj35n 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 directionc 0zzk9. dwi78mztnv, of the electric field 20.0 cm directly above an.i zd9cn zmt 8kzw0v,7 isolated $33.0 \times10^{ -6}\,C$ charge?    $ \times10^{6 }\,N/C$ ----待选择----updown 

  What is the magnitude of the acceleration experienced by an electron ivr9 gxvj(w2r ,w2 z1smn an electr1 rx(9mg,s vvj2rwz2w ic 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 directio 8aea2+/ +rtn+utpk n)6osfrhn of the electric field at a point midway between aett n8 u+oa/a2fkrnpr h+6 )s+ $-8.0\,\mu C\,$ 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 8hplca2;c.+x;kb1 dn b;l hlxabout two point charges, $+Q$ and $-3Q$ which are a distance l apart.

  What is the electric field strength at a point in spn qen3 1vks2f6 kjz.xni9 8a1gace 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 uniform electri7aokre.kil *1* t9.etcjf 3 vic field and accelerates to the north at9.ri fa.jvck*to te*3le 7i 1k 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)8 r3xb9ll12k t:b kcf rvcz0up5z)pu 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 q p d66eisr*;fhga;w6center of a square 52.5 cm on a side if one corner is occupied bq6;we6d *i; gphar fs6y 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:9h tg-5 5yzr+zm b s1cuo+ylu 1.00 m on a side if the oth51 cy:z+y mt uz59hlsuogr+-ber three corners 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 point P in ;scfn+6g5d o 7zyt: jiFig. 16–54. The charges are separa oys5fg;+c6:djtzin 7 ted 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 electric o ;tl ;*n)nrhkct p,m*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 erh5o14;fd al electric field at points A and B in Fig. 16–57 due to the two positive chargho1f5a redl4 ;es $(Q\,=\,7.0\mu C\,)$ 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 charges,t ur7h(8 u;pfs $Q_1$ 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 the point 1mv tt)m,rerg wsdkvt;0j o0:-5af w5 P shown in Fig. 16–59. The two charges are separated by a distance of 2a. Poi05vvmgr,dk t1a- ojt f ;tr0wsw:e5m) nt 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 *,zy1tzmv k)zvw: b7rthe 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 *zkm,zw7)z1r: vyb vt 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 jeo 7bd3o+;gu 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 radiztu 9(l9 wtj4wn 6s1hqj k:z,6napo3yus 18 cm is placed in a uniform electric field of magnitudew(n s:p1ja9 6,9onw6tq 4hljzztuy 3k $ 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 objectaxe8r -71xhu/oht y4js, $O_1$ 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 a9xccc52c ;w nuniform 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 i jeqxvy:vg+83fposr 9, vl/ h+s The plates are 1.0 m on a side and are separated by vjyh +r/vlv83f q:g ,+9es pxo3.0 cm. What is the charge on each plate (assume equal and opposite)? Neglect edge effects.    $ \times10^{-9 }\,C$

  The field just outside a 3.w1n0fb:w) om m6 f,e d7c7q0duikfr h350-cm-radius 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 carries a total cha(kf5n5s b /medrge 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 cenz2ciha-edgn-h *- n2nter 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? (d) gd zn2 *-eaicnnh2--h 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 .jev9xh y0j8dmolecule are held together by electrostatic forces as shown in Fig. 16–44. Assume that the net average charge (due to electron sharing) indicated v e j8y9xhj0d.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 betwuq)eli8 o f ;skn.w,fle -(l/reen them is equal to the8rq(l;f slole -nf. i/ w)e,uk weight of either at the Earth’s surface?    m

  A 3.0-g copper penny h2yyzd7ikdtm j827ld 4 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 th, s lc-rcu8+io*7oh gfat there is an electric field surrounding the Earth. Its magnitude isgflc7 c- r,s*uoi+8h o 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 what3hm6id/ mqno/ is the acceleration experienced by an electron near the surfacen i6 /qd3moh/m 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 n* nsbq o6 y22gvbql1 jda6,p/the downward-directed el 2 dp6nnv* jbsbq1/ayog 26ql,ectric 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 grou*gvh3b owh-gqso,z,hnc+9 d ;p and the HN group shown in Fig. 16–62. Thezg, - s+9o b,*hn;woh3hgqcvd 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 electron rev lropxz 1n ;i;pb+g1z5olves in a circular orbit around the proton z r1boi1 ; ln;5gzpxp+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 ra6j 4phg u;yee ,f 1,clv,xk 4ezfn59yesponsible for holding the Moon in orbit arj,e e4aun ,9exyyk fpg;hc4 5l6,fvz1 ound 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: 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 spee6 s wpj jlk-dp;d8v:)xd $v_0\,=\, 21.5\times10^{6}\,m/s$ 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 pyohjgl:db6pin-a+mt4 3l61k av0 k ,$Q_1\,=\, 2.5\times10^{-5}\,C$. 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 encag3zc p gg) y9.2bv)*lday0dlxsed in insulating plastic and suspended vertically from an ideal g0 *yadvl yd2g39gb ))l.zcpx 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 with “leaves” that are 78-cm-long w7dd5/ wqv+mf uu-z a(rires with tiny 24-g spheres at the ends. When charged, nearly all the charge resideu(r/5-7vduf d qma+w zs on the spheres. If the wires each make a $30^{\circ}$ angle with the vertical (Fig. 16–64), what total charge Q must have been applied to the electroscope? Ignore the mass of the wires.    $ \times10^{-6 }\,CC$

  Dry air will break down and generate a spark if the electric field exceed wl9eg( s.fuj.s about.g.ej l9sf(u w $ 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 ne ,8l e5alo aodhhr424jt 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 barvdpt) ,ci g4f:lf/b q/ 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 a distance R apart; eacv s:(kp ) m-x-um+1hdv0obgti0i:vvyh 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 muvd)0vpv:oh +st-kv(i-i0 :gym x1b moved very far away. What is the net force now acting on sphere A? (c) Sphere C next makes contact with sphere A and is then moved far away. What is the force on sphere A in this third case?

Given the two charges shown in Fig. 16–68, at what posik)(xjn chw6y. tion(s) x is the electric field zero? Is the.jn6( ckwxyh ) 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 cha :h++t4 tqfjpirge $8.0\,\mu C$ 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?