If you charge a pocket comb by rubbixhn.25mj( bmpx/rf y:4 ti92(o mpqvung it with a silk scarf, how can you determine if the comb is positively orup(qf ( ohn m5 .:m 2mi4trb9v/xpxyj2 negatively charged?

Why does a shirt or blouse taken from ag n p:d d;4j)l8qldzkcf p9-g; clothes dryer sometimes cling to your boj 9df)lzn;;g:d-8qdp ckl4pgdy?

Explain why fog or rain droplets tend to form around ions or 6 jfcpvn8uues9e z;;8l,z eg7electrons in the aiv9zpn7uez j;6 ;ecf8 8ge,lusr.

A positively charged rod is brought close y3v1gv) -lihpto a neutral piece of paper, which it attracts. Draw a diagram showing the separation of charge and expvy1h ivg3-)lplain why attraction occurs.

Why does a plastic ruler th)ftwzh 3 g +c(rf3t)jnat has been rubbed with a cloth have the ability to pifnj3c+f 3 )hwtgt r()zck 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 chaevj6sh-z0y-a,j :) psvxk r*urges” in the conductor.

Figures 16–7 and 16–8 show how a charged rod placed nearp. yhzuec fn.ql5ds 30(*je 5g an uncharged metal object can attract (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? jue*fdz0( 5 ne.gqclsh3p.y5

When an electroscope is charged, its two leaves repel each oth lzr+ub0(u;e ter and remain at an angle. What balances the electric force of repulsion so that the leaves dor(zu;0uelt+ b n’t separate further?

The form of Coulomb’s law is very similar to that for Newton’s l:dno, ql,zp;m ,ha4aco73gz taw of universal gravitation. What are the differences between these two l3lt ,ap zo74z,;acgdmq :h,o naws? Compare also gravitational mass and electric charge.

We are not normally awar.r;f8pm xx tgn/tks66 e of the gravitational or electric force between two ordinary objnkm .8xf 6gxrt6p/;tsects. What is the reason in each case? Give an example where we are aware of each one and why.

Is the electric force a conservative force? Why or why not? (See Cha/+uyyt) ra(qumt0 z -- uxqe2tpter 6.)

When a charged ruler attracts small piecesm y4t5w rn+/zi of paper, sometimes a piece jumps quickly away after touching the ruler. Exp+tnw 45 /myrizlain.

Explain why the test charges we use when measuring electric fields must be smal ..osp:dgwc c0l.oc:d c0gs..w p

When determining an electric field, must we use a positive test charge, oxs ajwn1t f5d sl.y5i2 /56uzc: jl0zar would a negatijsjdax. 6 1licfz:ny5/0lt25s wu5 za ve one do as well? Explain.

Draw the electric field lines s8zvec9be z 93x1n7b qzurrounding two negative electric charges a distance l x3e7 vbb zz 8eqc9z9n1apart.

Assume that the two opposite charges in Fig. 16–31a are 12.0 cm apart. Consider x;t gvz717ax wthe 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 strong1g7 z7av;x twxest? The weakest? Explain.

Consider the electric f3+ll kr+5ftkj1) rp vsield 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 test charge would experience if3sr+1+jfl5vpk) rlt k placed at that point, then list the points in order of decreasing field strength (strongest first).

Why can electric field lines never croszjtwnet/w*e9) l 81 ad8 /z7ibxqn2th s?

Show, using the three rules for field iar:ecyjsxq.g +,4u 7lines given in Section 16–8, that the electric field lines starting or ending on a single point charge must be symmetrically spyaec gx4.isq u+r,7 j:aced around the charge.

Given two point charges Q and 2Q, a distance l apart, is there a poin.:v psfwx6q8f0yyef0 t along the strai8xf0.eyfps6 0y: vfq wght 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 onaxc :k+59s:qnw ecg r; an electric field line at some point, such as point P in Fig. 16–31a. Is the direction of the velocity and+ xec ;c59qn: wsarkg:/or acceleration of the test charge along this line? Discuss.

Sketch the electric field lines for a uniform lin ugw( c:kzq*.+es3ehce of charge which is infinitely lsk*:cw+u(hg.3z eq ce ong. (Hint: Use symmetry.) Is the electric field uniform in strength?

If the electric flux through a closed surface is z i,cwc.w2,bde1s- mlc ero, is the electric field necessarily zero at all points on the surfac s ccbd,ci1e2-.wmw, le? 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 r. If2:rkog yo 0cf lyx//) l/mid6zfk52ox the sphere is replaced by a cube of side yc/ 5oo:xk2/xkf ld0ifloy62r m g z)/r, will $\Phi_E$ be larger, smaller, or the same? Explain.

  

  How many electrons make up apz4ip u his,ye0,8s -th10wkt charge of $-30.0\mu C\,?$   $ \times10^{ 14}\, electrons $

  What is the magnitude of the electric force of attraction between an iron nuclkm.h f879 td,cbnta*seuf,7t sm bknd t8.9*hcas $(q\,=\,+26e)$ and its innermost electron if the distance between them is $ 1.5\times10^{-12 }\,m\,?$    $ \times10^{-3 }N$

  What is the repulsive electrical forcpe;:o. p u 1b1et9vbine between two protons $ 5.0 \times10^{ -15}\,m$ apart from each other in an atomic nucleus?    N

  What is the magnitude of the force a ig3bi mcw6:6t97nqmi $+25\,\mu C\,C$ charge exerts on a $+\,3.0\,mC$ charge 35 cm away?    N

  Two charged dust particles exert vs ezu *3*eft+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. They84ypckb 6y+/iflk/uc5sr + vl1l ufx* are moved, and the force on each of them is found to have been tripled. How far aparr*lf1l8/ u+py46li cbkc/s yk +v xuf5t are they now?    cm

  A person scuffing her feet on a wool rui7gc )gls *n2z/mn1az 7 igck4g on a dry day accumulates a net charge okcngn7a217zil) g zi m4*g/scf $-42\,\mu C\,.$ 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 elecs 0mvikxur2v3we 9m.*trons in 1.0 kg of $H_2O\,?$    $ \times10^{ 7}\,C$

  Compare the electric fo x a*k,elqr3apk9z8a p(do6k27o ric ;rce 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 their chaehfxxu qbw,10es/: dkc(u ;9i4o 9zmhrges is What charge must each haveo0 ;fhcu4(, s9ibw: u1dx /z9hk exqme in order to
(a) maximize the electric force between them,
(b) minimize it?

  Particles of charge 16 vredy/ldu 8$+75$,$+48$ 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 chdg pkkt gc95udq4:-3 yarge, $+11.0\,\mu C\,$ 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 side. Det dvgplkzd1y::;j1 f 0dvvn5g*ermine the magnitude and direction of the force on each charge.:*5 p:kfgd nvv1 jd1dv0l;gyz
$F_4$ =   $ \times10^{ 7}\,N$
$\theta$ =    $^{\circ}$

  Repeat Problem 14 for the case when two of theqw1 m8, kyeee, positive charges, on opposite corners, are replaced by negative charges of the same wem,ey81e kq, magnitude (Fig. 16–51).
$F_4$ =   $ \times10^{ 7}\,N$
$\theta$ =    $^{\circ}$

  At each corner of a square of side lhhs ejflhwbosa iipvwo z3 f3 .65s30;/+ l38o there are point charges of magnitude Q, 2Q, 3Q, and 4Q (Fig. 16–52). Determine the force on (a) the charge 2Q, and o3zfhsw 3 p+w3i solsh;vo/3je68.alifb 0h5(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+spjg8me ..hb )yek:e3 cw+rk equilateral triangle of side 1.20 m (Fig. 16–53ckegjskme+ :+p. ) .b erwh83y). 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 c f-./rqv7c0 mb boe1ivharge 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 chargaf (qm04htr(7rp ct23 e/qlykit,j *ge 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 lxkjb 6oro o33l*s1ly(pd4f2ball to an identicabp1lx *43o fjkodyo2ls36(lrl ball 12 cm away. The force of attraction is then 17 mN. How many electrons were transferred from one ball to the other?    $ \times10^{ 12}$ electrons

  What are the magnitude and directior 5s- :m7szx:bqz/3yb2f eyk zn of the electric force on an electron in a unifb2zm3/yf:5 rykzz7s- xbe qs: orm 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 electrz6q8)hz ykc5 qic field, and it experiences an electric force6k) yq5z8czqh of $ 3.75\times10^{ -14}\,N$ toward the south. What are the magnitude and direction of the electric field?
   $ \times10^{5 }\,N/C$
 ----待选择----southnorth 

  A downward force of 8.4 N is vdoeut bm 0hq+4x7a*k z+jz42exerted 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 x8bdq(hm 4n 3 n*l-.xdzihh6ythe electric field 20.0 cm directly above an isod8-.dbnxi3mq ln6hhyh4 x(*zlated $33.0 \times10^{ -6}\,C$ charge?    $ \times10^{6 }\,N/C$ ----待选择----updown 

  What is the magnitude of the ;/ agg (ksftzy-x12m.lecn /1/a dad bacceleration experienced by an electron in an electric fie. gebntkyd l1fzd; //-acax2 asg/m(1ld 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 field at a point midway f)2wz49q -hj ed h;uxxh/u-tobet9hzju o x -qhuh/xw;d4)f2 e-tween 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 l4 h2yzwqw8: 9g1rwwn8,in ejnines about two point charges, $+Q$ and $-3Q$ which are a distance l apart.

  What is the electric field strength at a point in space wherear b n-3hy:ym h8 qh0v7c/3d5j6p ykgj 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 electric field and accelerates * 6)uskknte9q to tn)u6e t*qskk9 he north at a rate of $115\,m/s^2\,.$ What are the magnitude and direction of the electric field?    $ \times10^{-10 }\,N/C$ ----待选择----northsouth 

  The electric field midway between two equal but opposite point chargezxw ai,h*b :f-s 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 centewb7bqzcc w 8-6r of a square 52.5 cm on a side if one corner is occupied bcqww 7-6c8bz 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 h nb:l x*in/d xvnk 8j..-56wuwbg ck/corner of a square 1.00 m on a side if the other threlv uh6..*i8gx/nk-/c nkx5wbnb jdw :e 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 e3e0(pq. q, rnk( znm5-esb qzalectric field at the point P in Fig. 16–54. Thqne,3n5qrb0k ea(p.-z m(zs qe 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 eltmak;16 e +kjvectric 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 magnitud8-euv u,xleo(byi3 0i jv 1(hge and direction of the electric field atjeluvigy x30 bo8(u-h 1v,i e( 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 unknown point charge7n/7ys h7djgz s, $Q_1$ 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 point7w2dsv;/ jsyc P shown in Fig. 16–59. The two charges are separated by a distance of 2a. Point P is on the perpendicular bisector of 2sdycvw;/7s jthe line joining the charges, a distance x from the midpoint between them. Express your answers in terms of Q, x, a, and k.

  An electron (mass $m\,=\,9.11 \times10^{ -31}\,kg$) is accelerated in the uniform field $\overrightarrow{\mathbf{E}}\left(E=1.45 \times 10^{4} \mathrm{~N} / \mathrm{C}\right)$ between two parallel charged plates. The separation of the plates is 1.10 cm. The electron is accelerated from rest near the negative plate and passes through a tiny hole in the positive plate, Fig. 16–60.
(a) With what speed does it leave the hole?    $ \times10^{ 6}\,m/s$
(b) Show that the gravitational force can be ignored.

  An electron moving to the right at 1.0j4:lklyxv5vv ** jk. s% the speed of light enters a uniform electric field parallel to its direction of motion. If the ex5*vy:sjlvk l. v 4kj*lectron 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 ssou+f0h8slaucys8 xz1 xka ))r9 ;5hxide is $1.45 \times10^{3 }\,N\cdot m^2/C$. What charge is enclosed by the box?    $ \times10^{ -8}\,C$

  A flat circle of radius 18 cm is placed in a uniform electric field of magnitud m o*sw6,)jxedejsm,) oxe*6dw $ 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 objecb mus qoo92m m:,e ss*)19rfemts, $O_1$ 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 pr(t +fy :b9cyacre 9g-laced in a uniform 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 squareoq tcz6u 2;-klp2v ihi)36nxid62ifm 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 p6 nvdikiu2ixomtl p3f 6c 62;q2-z)hilate (assume equal and opposite)? Neglect edge effects.    $ \times10^{-9 }\,C$

  The field just outside a 3.50-cm-radius metal bh 8;vqry u-1nball 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 radihst ;m (w yutif.tkbu78i8z37us 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 (p; h;*t5 nbzm+gwr xhspherical conducting shell. (See Fig. 16–33.) Wha*xbhwn+m h;g ;z( 5trpt 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 heln8 *b-df 5q8j0vn)s r0syhgp dix-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 a80j8bh*py 0 -qndnssf )drg5vtoms 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 - h4a,nt:qx(1 omp* :fwqrv apthe electric force between them is equal to the weight of either at the Eartn:a r q h:m* p1vf,4pow(taxq-h’s surface?    m

  A 3.0-g copper penny has a0e.xi)gsi-p vefo4 7x positive charge of $38\mu C$. What fraction of its electrons has it lost?    $ \times10^{-10 }\,$

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

  Measurements indicate that there is an electric field surrounding tt4g m4yc2mhu5ktlf-)nh7z r7he Earth. Its magnitude 7g cm k yn-t72r4ulhzft4)5 hmis 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 ek. i ct;elbf5f+ (cb,flectric field of what is the acceleration experienced by an electron nea ,cbkibf+.e5;t(c lffr 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 statriq8mpbhw. 3;ionary in the air. If the downward-directed electrhwr8 ;ipm3 b.qic field of the Earth is $150\,N/C$ how many excess electron charges must the water droplet have?    $ \times10^{ 6}$ electrons

  Estimate the net forcan f;sl:u+fp 4lo84mce between the CO group and the HN group shown in Fig. 16–62. The C and 8f;p:smalcuf4 no4 +lO 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 fgx/urft 5 r(lnn1: -a.m- dqqthe hydrogen atom, the electron revolves in a circular orbit around the prrt:u n-(a5-q md/lxgq .f r1fnoton 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 responsible for ho( rn9 vew2oqtjj /ai9r4+ub a*lding the Moon in orbit around the Earth. If equal and opposite charges Q were placwu9e t a9 rjqb+(4n/ior*2jv aed 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 7 cz*,rl2 vonzwt+kkd.k:xq;f0 .xtt$v_0\,=\, 21.5\times10^{6}\,m/s$ 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 charglvt ckz;5 )mns (cd9n5hs -wnxk 70(awe $Q_1\,=\, 2.5\times10^{-5}\,C$. 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 verk720 n:ecn.nq sb,;n 1v hskm: sid:pmtically from an ideal spring 7;m1 :cs 0 kibs:sp:kvn2qnhn e.d,nm$(k\,=\,126N/m)$ 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 “leav4xcg( ul xcnw0qc.(m1es” that are 78-cm-long wires with tiny 24-g spheres at the ends. When charged, nearly all the charge residesl m(4ccuxxcw.qg (1n0 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 r 7hnxu ovu7vb12t-. h1ek,c t+ o2zmaa spark if the electric field exceeds about2-+1.ohe2z xmt7u7 tcuhvk r,b vano1 $ 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 charg6 )t1:wib rkhdj-x0jte $+0.340\,\mu C$, 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 ele p bpngx 8(cn9ybi z9iovoxf3+e +10v88:bfexctrons 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 conducting spheres A and B are a dmh-gz- h s 49-*mrejazjgf7k/ istance R apart; each carries the same charge Q. (a) What is the force sphere B exerts on sphere A? (b) An identical sphere with zero charge, sphere C, makes contact with sphere B and is then moved very far away. What is the net force now acting on sfa 4r*mz/hkjgs j9- -zgh7 e-mphere 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. 16–6)cyi- o,o/7g,1eijjzcg- nvf 8, at what position(s) x is the electric fiel/nigfig coo 7cj-j-e yz,1)v ,d zero? Is the field zero at any other points, not on the x axis?

Two point charges, $+Q$ and $-Q$ of mass m, are placed on the ends of a massless rod of length L, which is fixed to a table by a pin through its center. If the apparatus is then subjected to a uniform electric field E parallel to the table and perpendicular to the rod, find the net torque on the system of rod plus charges.

Four equal positive point0a8 jyp+jbx p9 charges, 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?