If you charge a pocket comb by rubbing it with a silk scarfbpva,exvl tiv ;x8o,k-m6;3 a/xy k+ t, how can you determine if -bi;mxx8o, yxlav/;evtkt ,3 v6+akpthe comb is positively or negatively charged?

Why does a shirt or blouse taken from a clothes d92p m jb*jxz.sb jdf-.ryer sometimes cling to your bod jp bxmb.9 sj.j-*2fzdy?

Explain why fog or rain droplets tend to form around ions or electrons in th boeu-tpgodnl0icy c28x/ t)1)vc ,g-d)3xmve airm yb3 c/)ge, dp xtt 0))n8vci1-ogduovx-c2l.

A positively charged rod is brought close to a neutral piec)(lp:vz3:r es/yj 3h jsxwv: je of paper, which it attracts. Draw a dij z::: /vjyej(p rvhsws3xl) 3agram showing the separation of charge and explain why attraction occurs.

Why does a plastic ruler qzvs kem sm:)c9 2.xenaod)y37 xvd9-that has been rubbed with a cloth have the ability to pick up small piecesomdn9)2skz3 .- xx vac:vsem 79edq)y of paper? Why is this difficult to do on a humid day?

Contrast the net charge on a conductor to the “frkqfp pde3 2/uw6q) bm0ee charges” in the conductor.

Figures 16–7 and 16–8 show how a chqesyy) fy(/nk74b i ;jq1is:garged rod placed near an uncharged metal object can attrack1sis4ey gfy/:q y ;nj)7 ib(qt (or repel) 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, nh5*- ltd;h7o6l jkmwits two leaves repel each other and remain at an angle. What balances the electric force of rep*k -on6jwl;d l5m 7thhulsion so that the leaves don’t separate further?

The form of Coulomb’s law is very simil82;2)0ofwdf irzw 9sn un4jfmar to that for Newton’s law of universal gravitation. Wha2 4is9ff; djnmww)z 2uf0ron 8t are the differences between these two laws? Compare also gravitational mass and electric charge.

We are not normally aware of the gxp.env 1i)wws,s:63-sg o ymsravitational or electric force between two ordinary objects. What is the reason in each case? Give an example whersvoe n)iwss,-s:g p.w3m6x1ye we are aware of each one and why.

Is the electric force a conservative force? Why or why not? (See Chapter wrw+: xwji- h9h .e,i( xczj;x6.)

When a charged ruler attracts small pieces of paper, sometimes a piece jumps qi-0g5j1 fu ga7t laod/uickly away after touching the ruler. Ex aagu g-ji0o/7tf5 d1lplain.

Explain why the test charges we use when measuring electric fields(a*. q 25dtjlsg)srzs1w or ;v must be small.v(t5j )* la;sgsd2o1. rz rsqw

When determining an electric field, must we use a )jy)/)*)2e b dsdrfv(bccohp5:u vl 4yuwv. e positive test charge, or would a() pc )yb*w vj)e uuody4d5fcrv.b2) vsl h/:e negative one do as well? Explain.

Draw the electric field lines surrounding two negative electric char5lo- t gxe-6tmges a distance l apartego6-t xt l5m-.

Assume that the two opposite charges in Figi8cma2gj (b1 qe1v 5zi. 16–31a are 12.0 cm apart. Consider the magnitude of the electric field 2.5 cm from the positive charge. On which side of this charge — top, bottom, left, or right — is the electric field the strongest? The weakest? Explai bg1c5ji1 2e8vamzi(qn.

Consider the electrije 3r+p*h*z9 +fmzcqrc field at points 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 te pq jrr*+m* zef3cz+9hst charge would experience if placed at that point, then list the points in order of decreasing field strength (strongest first).

Why can electric field lines neverj g.:fi-:wrlsswz sn1 c fp,,0 cross?

Show, using the three rules for field lines given 4 3i-h3 nwm7phej(symsi2g. din Section 16–8, that the electric field lines starting or ending on a single point charge must be symmetrically spaced around the charg 4hm37 3e-(jw.dhpnsm s iiy2ge.

Given two point charges Q and 2Q, a distance l apart, is there a point alonikbf u-b6zd a rd;-j1j fz-u0;g the straight line that passes through them where E=0 when their signs are (a) opposite, (d a fbuk1d-zj6;bui- 0f;j rz-b) the same? If yes, state roughly where this point will be.

Consider a small positive test charge located on an ele.zy .kclj )ppvq;,ufeo3r htt +4 5(toctric 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? Discupt(;4) rcp3euz5t jo f. qvtoyhk,+.lss.

Sketch the electric fieldwfe :c 0x;y5io lines for a uniform line of charge which is infinitely long. (Hint: Use symmetry.) Iiy; 5 0:wcfxoes the electric field uniform in strength?

If the electric flux through a closed surface is 8d- yg/hl4ocz zero, is the electric field necessarily zero at all points on the surface? Expzy8o/l d4-hgclain. 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 gaussicr11ia, y g*nean surface of radius r. If the sphere is replaced by a cu,1 cr1gany *eibe of side r, will $\Phi_E$ be larger, smaller, or the same? Explain.

  

  How many electrons make up a charglkg;tk7j(5jt **e8a 2nq7tvk d9m vqwe of $-30.0\mu C\,?$   $ \times10^{ 14}\, electrons $

  What is the magnitude of the electric fopm6g+c d6 g+pyrce of attraction between an iron nucleusp+ 6myg6 +gdpc $(q\,=\,+26e)$ and its innermost electron if the distance between them is $ 1.5\times10^{-12 }\,m\,?$    $ \times10^{-3 }N$

  What is the repulsive electricp2 b4pp, , 1bcwse*epmgz r:n,al force between two protons $ 5.0 \times10^{ -15}\,m$ apart from each other in an atomic nucleus?    N

  What is the magnitude of the f ndfy,bce+z(aotq,x 1+1azx 7orce a $+25\,\mu C\,C$ charge exerts on a $+\,3.0\,mC$ charge 35 cm away?    N

  Two charged dust particles exert .82s;fxyo/myad s-c s 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 9 jfukox7t54mare moved, and the force on each of them is foun4mo5 97utfxkj d to have been tripled. How far apart are they now?    cm

  A person scuffing her frxvc:vqfi0 *0dh z19meet on a wool rug on a dry day accumulates a net charge of z 0:hfmivcxq*1v dr09$-42\,\mu C\,.$ 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 t j2;ibbpb*uc0gzywdry o 0.,+he electrons in 1.0 kg of $H_2O\,?$    $ \times10^{ 7}\,C$

  Compare the electric force holding the electron in orbit jecibk.7 :o:p na:0j w1fwp) u$(r\,=\,0.53 \times10^{-10 }\,m)$ 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 arcoq2f;; :m +q (oltomae a fixed distance apart. The sum of their charges is;:oa +oltf qcq2;mom ( What charge must each have in order to
(a) maximize the electric force between them,
(b) minimize it?

  Particles of charge md(7lnw3xah1b zq8k.u1k :g7+tlff v $+75$,$+48$ 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 equal j6 mjd:;*( lll2hokrpcharge, $+11.0\,\mu C\,$ 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 ofz/q: sroy t.bza2 ve41 r8hyz2 a square 0.100 m on a side. Determine the magnitude and direction of the forczsv 18yy/2z .aqz bho r2rt4:ee on each charge.
$F_4$ =   $ \times10^{ 7}\,N$
$\theta$ =    $^{\circ}$

  Repeat Problem 14 for the case when twi gobja7e v6l4ng9/ p(o of the positive charges, on opposite corners, are replaced by negative chaa7b 9(6npgjvl4o g/ eirges of the same magnitude (Fig. 16–51).
$F_4$ =   $ \times10^{ 7}\,N$
$\theta$ =    $^{\circ}$

  At each corner of a ls;yp:r cvol*0w jk; 9square of side l there are point charges of magnitude Q, 2Q, 3Q, and yl*rpovc0 w;sk;9:l j 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 cor4i8lo:h hxq+kkq*b.n ners of an equilateral triangle of side 1.20.bk k8*+qoh h4:xnilq 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 of ha sc;1 -1)4mg6gdq.3dcfrer4r 5vxcsos x n/$560\,\mu C\,.$ 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 spheruk4q3zm49aj .klw5q7jlg0pz ,gen r3es 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 uncharged plastic balku,vc)/r ) xgjbxnt;- l to an identical ball 12 cm away. The force o-, txcvr;g)b kuj x)/nf attraction is then 17 mN. How many electrons were transferred from one ball to the other?    $ \times10^{ 12}$ electrons

  What are the magnituyw1z (9xj0baj de and direction of the electric force on an electron in a unif(9ya1zj0 jxwborm 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 an el059clb1h wmv uectric fcmb19wh v 50ulorce 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 isb0;r1bfh*uk x oyaa,+ 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 electrlq eour*8f0sr1f -*nnic field 20.0 cm directly above an iso**s0n - l8r1ofunfqrelated $33.0 \times10^{ -6}\,C$ charge?    $ \times10^{6 }\,N/C$ ----待选择----updown 

  What is the magnitude of the acceleration experienced by an elh6i2+vn y(u 0o; dmuhjectron in an electric field odu6;v hn2im+uoj y h(0f $750\,N/C\,?$ 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 ia9umdjt) +m*6 .i sjwfield at a point midway between a*i9w6ud).j ma+ sijtm $-8.0\,\mu C\,$ 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 pcxc:+ dv0 sib1 oa37cf we;di*oint charges, $+Q$ and $-3Q$ which are a distance l apart.

  What is the electric field strength at a point in d-0uyhtfs0 ,cq1nqe6 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 l7r*gomq*g -xrest in a uniform electric field and accelerates to the north at a ratm 7-q gogr*l*xe 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 o k 2f8iejk6,dbut 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 square 52.5 cm on a side pjq,93;xqqg u if one corner is occ;qxqq,jpu 39g upied by a $+45.0\,\mu C\,$ charge and the other three are occupied by $-27\,\mu C\,$ charges.    $ \times10^{6 }\,N/C$ at    $^{\circ}\,$

  Calculate the electric field at one corner of a square 1.00 m on a side ifggq.9q y sbj(a*q*h7t* q h-cn the other three corne*csq7(j*q-y *qh9 g n .taghbqrs are occupied by $ 2.25\times10^{-6 }\,C$ charges.    $ \times10^{4 }\,N/C$   $^{\circ}\,$ from the x-direction.

Determine the direction and magnitude of thehkls o h9ekkwb47:1l9 electric 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 in terms of Q, x, a, ank: k4 91b7kw9 lshehold 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 fieldyvmizp iui94c tsky 4a 2y.02; $\vec{E}$ 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 magnitr jto+0u1fj2cude and direction of the electric field at points A and B irf j 0utoj+c21n 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 unknowxbou 9f0adfw960cdz6+it zxmb ; l(/bn point charges, $Q_1$ and $Q_2$ At a point on the line joining them, one-third of the way from $Q_1$ to $Q_2$, the electric field is zero (Fig. 16–58). What is the ratio $Q_1/Q_2\,?$   

Determine the direction and magnitudei jdc(6 *gaza21ntsdi *rf f5/ 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 betw1 gi/frjand ac2 zifdt**65(s een 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 elecr ap9zu3gx4u 3tric field parallel to its direction of motion. If the el3x943gra uupz ectron 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 box 28.0 cm on a side i;xa3t .-br o4 tmvn7oqs $1.45 \times10^{3 }\,N\cdot m^2/C$. What charge is enclosed by the box?    $ \times10^{ -8}\,C$

  A flat circle of radius 18 cm is placed in a uniform electric field o, ( ef9zb yci,yg*r5amf magnitude yze gy(amfcir*,5,9b $ 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 objects1o g: l5r6r:ncfvse6 *1lglcb , $O_1$ 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 unif voy 77plv8,roorm 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 4bwef ;a4zc0m rs9k)g 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 edw c);mr9abfks e 0zg44ge effects.    $ \times10^{-9 }\,C$

  The field just outside a 3.50-cm-radius g lv/7zmpt7r 4metal 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 raddu,cj a/ j;.loius 3.00 m carries 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 thin spherical conductiny0xozam l0:ng 3y2j kw8jlh4+4wf ;m rg 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) insi40jlykhmam0 lx: g+w23 owj8n4zrf y;de 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 hel4w ri8;dt9qmyh t8xc/ix-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 indicatedy;9wc dimt/q8r ht4x8 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 elo7hva orh;4 wzxi x.:;ectrons be if the electric force between them is equal to the weight of eoxi:4w ;xhzrh.ov7a ;ither at the Earth’s surface?    m

  A 3.0-g copper penny has a positivnxh(lju2q o(i + cb(k2e 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 fiel5nu chun 9.p -flf:in r::d9izd surrounding the Earth. Its magnitupi-: 9uc:.ldf9n hf nn5urzi:de 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 acceleration experienced byf5m)e5olg :0y-ty vuy an electron neal:5teg)o muy 5yf 0yv-r 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 0.018v0x b1 1x1eg8oye0di g mm remains stationary in the air. If the downward-directed electric field of the Earth is0yo divg1 1e80exg1bx $150\,N/C$ how many excess electron charges must the water droplet have?    $ \times10^{ 6}$ electrons

  Estimate the net force between the CO group and the HN g dbv*t8k(0jwa m 69dsmj3 j)pt1g6 gctroup shown in Fig. 16–62. The pv1g6m( 98)s mtj 3cda dgtbtj 6w0kj*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 hydffy2oaj; nq.6ts )8by rogen atom, the electron revolves in a circular orbit around thenyjs 26tb y8;aqffo.) 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 nxb9o7/ukv5 f responsible for holding the Moon in orbit around the Earxk /b9o 7nf5uvth. 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 speoelv 803 d- nq2dj/tj xax0;toed $v_0\,=\, 21.5\times10^{6}\,m/s$ 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 cha4dmyx3yl- -q v 6sht)trge $Q_1\,=\, 2.5\times10^{-5}\,C$. 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 vertic)iawsvgjbc0x(4+y .eally from an ideal sprisgv)+jyxe a wib. 40c(ng $(k\,=\,126N/m)$ 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 wiresy2x itn y crh;z2;bm 6tq)v;ov1t 1q(r with tiny 24-g spheres at the ends. When charged, nearl)o26h;mctvn1q tz;r y i vy1qbr(t;x2y 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 spark if the electric field exceeds ae 9o+5 c vuawssz;skl6l6acfkbf6) 91 bout skcflo9 eu bl66zf); 1a9w+ssc6 v a5k$ 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 charge a0c 2ja70ux wl$+0.340\,\mu C$, 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 thlw er2q..5kdwe electrons in 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 condubgs7 cr7n yr5 )p5l*ldcting spheres A and B are a distance R apart; each carries the same charge Qrcrbpslg n7d)5 l7y5*. (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 moved far away. What is the force on sphere A in this third case?

Given the two charges8t khtrzdpml2+v2y*5 shown in Fig. 16–68, at what position(s) x is the electric field zero? Is the field zero at *+y mkp t258 ltrhzvd2any 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 chargesp0sgp6/2 wc ou tpjul 2hks5*;, 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?