If you charge a pocket comb by rubbing it with a silk scarf, how can you dete( m8v )+v3pu f5rpgyovrmine if the comb is positively or negatively ch v(f8)rgvp+movu 3py5 arged?

Why does a shirt or blouse taken from a clothes dryer sometimes c:zu01wipbkw/) lyfm ( ziy5n3ling to your bodykpi muizn1yf5 y30 /(lw:bz)w?

Explain why fog or rain dropletf9hyybsgv y4( y (so59s tend to form around ions or electrons in the air.sg5 f((9yyy yvhb94so

A positively charged rod is brought close t1usk1yggc)x b)w1 c y8o a neutral piece of paper, which it attracts. Draw a diagram showing the separati1 kgubyc1xc) 1swg8 y)on of charge and explain why attraction occurs.

Why does a plastic ruler q h(tx0et)jg(that has been rubbed with a cloth have the ability to pick up small pieces oe(tj)hg(0qx t f paper? Why is this difficult to do on a humid day?

Contrast the net charge on a conductor to v;d+mulc0 j2f 8.i ):btbpnfa the “free charges” in the conductor.

Figures 16–7 and 16–8 show how a charged rod placed near3b pwvf.8 rtp6f4kyp412 1eb8sgs xx k an uncharged metal object can attract (or repel) electrons. There are a great many electrons in the metal, yet only some of themks.vts3pr2481p x64b 8fxygbf1kpw e move as shown. Why not all of them?

When an electroscope is charged, its two lea6o)v4an5yp2 pn ujup) ves repel each other and remain at an angle. What balances the electric force of repulsion so thaoa)yuvj5pn64p) npu2 t the leaves don’t separate further?

The form of Coulomb’s law is very similar to that for Newton’s it8,x g*znrh at 4(6- usjbw(qlaw of universal gravitation. What ar -(trq4h ub,njxzaw6s( gi8*te the differences between these two laws? Compare also gravitational mass and electric charge.

We are not normally aware of the gravitational or electric force betw.nzg shgt,a x,9xut0dlm28 a 5een two ordinary objects. What , tnz0t25am u.xgx8,lsha9dg 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 nou vah4no:7ym2m. 1ihft? (See Chapter 6.)

When a charged ruler attracts /yry5xg5)97 at ac fjssmall pieces of paper, sometimes a piece jumps quickly away after touching the ruler. Explain.j9cf s)5ag5 ryxyt7/a

Explain why the test charges we use when measuring electric fields muhaje8ku3 0 uf3 d/cus-xl;r) kst be small03k 8fa)u/-rkhe3 xj;dcu sl u.

When determining an electric field, must we use a positive te geub 7i1tw6hd8x7 /cu,a)djest charge, or would a negative one do as well? Explain.,1a7w bu)i7 d xuej6etc 8gdh/

Draw the electric field lines surrounding twopwx,-lb1mlyf*u*dxu+d i,- c negative electric charges a distance l apart *cm 1xldf, +-udpu- ybw,l*ix.

Assume that the two opposite charges in Fig. 16–3x,l yce) z9*gqevw fv:bo.g 621a 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 the electric field the strongest? The weakest? Ex)bv eex9gz :2oqwfcg,yv *.6lplain.

Consider the electric field at points A, B, and C in Fig. 16–48. Fid .x;a1w7zp airst 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 wzad;pa7x.1i list the points in order of decreasing field strength (strongest first).

Why can electric field lines neveruyq(wn2vw nl+h gae7 2:xr+ y1 cross?

Show, using the three rules fjxlf;)yv3fzof02 16- rf cgueor field lines given in Section 16–8, that the electric field lines starting or ezfuf e06 gf)ly ;r1vox2- cj3fnding 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+ vpb.e;6ykxrha11h4 mt 1tyb along the straight line that passes through them where E=0 when kh 1v;h +1m4t.1prxeb6yytab their signs are (a) opposite, (b) the same? If yes, state roughly where this point will be.

Consider a small positive test charge locatq a 8 uwcvy5/a()u.j .cwflea x0ia :obw,,3obed on an electric field line at some point, such as point P in Fig. 16–31a. Is the direction of the velocity and/or acceleration aa b 5c:,i oa/0b)fwul.x(ju3vw, 8eqaw.oycof the test charge along this line? Discuss.

Sketch the electric field lines for a uniform line of charge which is in(gjzx +*g+oeqfinitely long. (Hint: Use symmetry.) Is the electric +g*oz(q+ejgx field uniform in strength?

If the electric flux through a closed surface is zero, is the9 ye b1(6/ p( ewisecgbufmt8. electric field necess8e69sme b.(1 cetpu(b y /gwfiarily 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 surroundnmb/9zx ww0*xed by a spherical gaussian surface of radius r. If the sph x*bxzn/w 09mwere is replaced by a cube of side r, will $\Phi_E$ be larger, smaller, or the same? Explain.

  

  How many electrons ma-xghfh uaae )opkis855/h7o4ke up a charge of $-30.0\mu C\,?$   $ \times10^{ 14}\, electrons $

  What is the magnitude of the electric force of f m9s676.lb idxw3iijattraction between an iron nucleusi7b wxsidfimj669. l3 $(q\,=\,+26e)$ and its innermost electron if the distance between them is $ 1.5\times10^{-12 }\,m\,?$    $ \times10^{-3 }N$

  What is the repulsive electrical force aecl +jn)h-uryio7a d7 .v1 6rbetween two protons $ 5.0 \times10^{ -15}\,m$ apart from each other in an atomic nucleus?    N

  What is the magnitude of the forcenez3a 5r0b 5w4 -fjsnn a $+25\,\mu C\,C$ charge exerts on a $+\,3.0\,mC$ charge 35 cm away?    N

  Two charged dust particles exert ;du8d5g - ibmwa 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 ar6djv :. m6u8nbd dgl,re moved, and the force on each of them is found to have been tripled. How far apart are they ludjb6 6v:,ddm8r gn.now?    cm

  A person scuffing her feet on a wool rug on a drztf7ev:kh2.6.n e b rvy day accumulates a net charge onvvk. 2 fr:tz6 h7bee.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 charge of alv ka8cz s5dkrz2ch;cmx1k *jrzw/i9kb0, 7m4l the electrons in 1.0 kg of $H_2O\,?$    $ \times10^{ 7}\,C$

  Compare the electric 7ih wxbmr mf.908 zz/c6pnf g1force holding 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 the 2 1y1c vd21opjmgjs.uir charges is Wh2 yvu1pdmo2 j1s1 c.gjat charge must each have in order to
(a) maximize the electric force between them,
(b) minimize it?

  Particles of charge /x2sc)/jpd 167fbwqgu r8ik p$+75$,$+48$ 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 particleshd,9:gh)wa2lekwj) e;j vd )k 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 u44fhk;bht*p63 n, fg+cj6i/ bzuma t each corner of a square 0.100 m on a side. Determine the mb 64t z*3kgctn ump+hfja4,i;bh/6ufagnitude and direction of the force on each charge.
$F_4$ =   $ \times10^{ 7}\,N$
$\theta$ =    $^{\circ}$

  Repeat Problem 14 for the case whe-d+m)ywk:w6j3ny5ez ojd +jc n two of the positive charges, on opposite corners, are replaced by negative charges of the same magnitude (Fig wom+:dk3+5y)n-ecd zj6w jyj. 16–51).
$F_4$ =   $ \times10^{ 7}\,N$
$\theta$ =    $^{\circ}$

  At each corner of a square of side l there are point c2bd pjth812ae,iakky a .n g:, maa1;mharges of magnitude Q, 2Q, 3Q, and 4Q (Fig. 1jkhy;itnaga8aa2kbm, . 1:pm 21da ,e6–52). 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 anj7v/y5c*ke mr m(tue qg6 -kd, equilateral triangle of side j5kemeguc tymqv(dk,* -/67 r1.20 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 have a total charge(txub b;p+ 0fi 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 nonconducti zg5e93 xgsrf2ng spheres have a total 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 ux22 vq0lkqs-z ncharged plastic ball to an identical ball 12 cm away. The force of attraction is then 17 mN. How many electrons were transferred fro0ks2vq-lzq 2x m one ball to the other?    $ \times10^{ 12}$ electrons

  What are the magnitude and direction of the electric force on an electron in ahy4ply,lsmi;t0lyrk )v1+b 6 uniform electric field of stb t+lr;4sl)ky6y l pi 1y0h,vmrength $2360\,N/C$ that points due east?
   $ \times10^{ -16}\,N$
 ----待选择----westeast 

  A proton is released in a um dsynavw1p3 6u- 2e:tniform electric field, and it experiences an electric force o e:y um6stpd2 1wvn-a3f $ 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 p+qf uhb6j6nilx()15y ax 8z6 +qhlpt $-8.8\,\mu C\,$ 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 dwou4 n8t ukjf6r, ye13xb6v+ tp8b8at irection of the electric field 20.0 cm directly above an isolated w 4tu 81x8ve,t tpb fok38a6 jyr6+nub$33.0 \times10^{ -6}\,C$ charge?    $ \times10^{6 }\,N/C$ ----待选择----updown 

  What is the magnitude:nzp*5qu9 qb2lc)ay a of the acceleration experienced by an electron in an electric fu5yal *z q9:2na p)qbcield 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 ) 8hd3i9lbij *issal)0ril s) the electric field at a point midway bet) adirb ) )0isi38his*j9l llsween 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 f605 rhgot) 9e(c+io+haoqqdi ield lines about two point charges, $+Q$ and $-3Q$ which are a distance l apart.

  What is the electric field strength at a point in suoo3qhak6c y.,e .3 xrpace 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 resy1d)vnp 3z2 kat in a uniform electric field and accelerates to the north at nadkvz2 31y)pa 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 is . 5cfnll: ens/1r7bsj$745\,N/C\,,$ 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 agsu;hgm 7 ku h ydkqj5-i/8/k(q0kzi+t the center of a square 52.5 cm on a side if one kk/(h8+7yiukg-0/ms 5z qihdkq;g jucorner 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 em 9k)9wyceyhm37f0b1.00 m on a side if the other th7w9 0kcym b m)9y3feehree 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 th6jtv+ nmgsctrh+l-. 5e point P in Fig. 16–54. The charges are separated by a distance 2a, and point P is a distance x f6v5s .gc+-l h+t nrmjtrom 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 electe/6 kw0hmo+u gvqnbo/; 94qpwric 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 ek 67mvjb* pl3xwmi+/jj7 y 6ahlectric field at points A and B in Fig. 16–57hjyap 7w *mi/l+ x jk67vj6bm3 due to the two positive charges $(Q\,=\,7.0\mu C\,)$ shown. Are your results consistent with Fig. 16–31b?
$E_A$ =    $ \times10^{6 }\,N/C$
$\theta_A$ =    $^{\circ}\,$
$E_B$ =    $ \times10^{7 }\,N/C$
$\theta_B$ =    $^{\circ}\,$
(16-51)
(16-31b)

  You are given two unknown point charges,*nku8n ksg ,;c $Q_1$ 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 e8e*3b,lx uyr*;igw at lectric 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 midpoine*y;t xwl ,8b3ui*gart 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 r.rq:pv,p l9xxsph7o:5mir-9rsmtc7r l,7 j uniform electric field parallel to its direction of motion. If the electron is to be brought to rest i7 9vx7rsl,:-qhrxm ,l jro9m:scp 7.ip t5rprn 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 fmg2r) cw.x6 yz:bmr 5bhs7zi (-h*fxqrom 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 t 5+h;ksybn3o cm is placed in a uniform electric field of magnitude ot+3b5ys; hnk $ 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 obiitpd5*ivic4j- us 8 -w+ )tfmjects, $O_1$ 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 fiel:p1yhyg 1l h+/s-osesd $ 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 twxa4fb-nr070ho kjgwe:ip3 (ho square 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 opposite)? Neglect edge efwkhfpb xn4ie0o -a (:hgj3r0 7fects.    $ \times10^{-9 }\,C$

  The field just outside a 3.50-cm-radio,x345(ugqwy / ygprjus 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 chargeo ;-y,g kpc *mmjdthd b6-7wr7 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 thin2w1he *pnsnf5. 9rdtm spherical conducting shell. (See Fig5*f9rmn dp2seht1.w n . 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 the shell?

  The two strands of the helix-shaped DNA molecule are he2cbpukrf7)y l3 ng7w .3h 3mykld together by electrostatic forces as shob73 f2mu lkky.ngrc)3wh 3py7 wn 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 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 t(*lp0yijov-ph hqz (7u7k.s 6bblg 5 zhem is equal to the wlzhp(l76 oqji(- 7 kgzvp5h*bbs 0uy .eight of either at the Earth’s surface?    m

  A 3.0-g copper penny hmo z+xqzu,y: (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 surrour,b+f uk,pu4bl54s ruj; fzo.nding the Earth. Its,+r; lu ,5fj. 4ofpkubs4ubrz 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 n iam6 kxx9.q-p8ai9 e what is the acceleration experienced by an electron near the surfa-i9 ainapk9.x6q8x mece of the Earth?    $ \times10^{13 }\,m/s^2$, ----待选择----updown 
(b) What about a proton?    $ \times10^{10 }\,m/s^2$, ----待选择----updown 
(c) Calculate the ratio of each acceleration to $g\,=\,9.8\,m/s^2$ For the electron: $\approx$    $ \times10^{12 }$ For the proton: $\approx$    $ \times10^{9 }$

  A water droplet of radius 0.018 mm remains stationary in the air. If the d6xq*vi io f-jyya0-9townward-directed electric field of the Ea9 6ijyitv xy0-a*oqf -rth 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 thelfvdx 24r 4jn( HN group shown in Fig. 16–62. The C and O have charge4(vx j rdlf4n2s $\pm0.40e$, 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 elect zkqy- nkicj28 (87sotron revolves in a circular orbit around the proto(yqck t8-joz 27s8kinn 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 ,s54jcb kp6z vgravity, were responsible for holding the Moon in orbit around the Earth. If equal and opposite charges Q were pla6 4zsv,5 pbkcjced 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 spe8gc7l7 52 smx (lztr3ei pxk1ked $v_0\,=\, 21.5\times10^{6}\,m/s$ 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 char(m7c:owyg hi)zuo+pl h z90+e ge $Q_1\,=\, 2.5\times10^{-5}\,C$. 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 iza .d2czsh-+ds encased in insulating plastic and suspended vertically from an ideal aszcd-.2+ hzdspring $(k\,=\,126N/m)$ 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 pp- q:lt0gjd :made with “leaves” that are 78-cm-long wires with tiny 24 lppqg:0 dt:-j-g spheres at the 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 (4f :cqtr vmr*8jn l+lgenerate a spark if the electric field exceeds aboutljtn r*8f:m(c rq4 +vl $ 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 chrkn5i,4 tc x4warge $+0.340\,\mu C$, 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 ilf8 qf2u gbe u,z+o+k3n a 15-kg bar of aluminum?    $ \times10^{8 }\,C$What is the net charge of the bar?    C (Aluminum has 13 electrons per atom and an atomic mass of 27 u.)

Two small, identical conducting spheres A and B are a dist,l)xgclz w;7 u/d3t41tb bb fyance R apart; each carries the same charge Q. (a) What is the ,tt;lc)w 1ylb dxuzg3b74f / bforce 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 Fig. 1rgyv0 l)4ub,a6–68, at what position(s) x is the electric field zero? Is the field zero at any other points, not a,0l4yug br)von 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 char 7un,mp+pyr-pe) k( scpiylv+/0pm-q ges, each of charge $8.0\,\mu C$ are at the corners of a square of side 9.2 cm. What charge should be placed at the center of the square so that all charges are at equilibrium? Is this a stable or unstable equilibrium (Section 9–4) in the plane?