If you charge a pocket comb by rubbing it with a silk scarf, how cant8 kaey. fng kbsm k5xo,04b+5 you determine if the comb is positivel y.0m5,xaeb nks8kf 5g+obk t4y or negatively charged?

Why does a shirt or blouse taken from a clothes dryer sometime f(i yr yxv48+nv;(mpful ((ozs cling to your bodmoyxv((;nl(+8f(uz v ifp ry 4y?

Explain why fog or rain droplets tend to form around ions or electrons lbiav / *co:*,djiy l.dc)d7yin the aird:.ldcii oc/,b)7*yl djyv *a.

A positively charged rod is brough4+ o*t yhg6fv6fuwcl :g(evw- t close to a neutral piece of paper, which it attracts. Draw a diagram showing the separation of charge and explain wh*owv vegguy +ht-c6 4l: wff(6y attraction occurs.

Why does a plastic ruler that has been rubu evjg7ub 7cj.y0(oqt;tq2 3l bed with a cloth have the ability to pick up small p.lyj3t o2j(c0bqgqutu 77v e ;ieces of paper? Why is this difficult to do on a humid day?

Contrast the net charge on a con ,2ui5kh /ezrzductor to the “free charges” in the conductor.

Figures 16–7 and 16–8 show how a charged rod placed neat lzl0 gc 6e)uf/jlw.j0-zmy voo01 g6r an uncharged metal object can attract (or repel) electrons. There are a great many electegy/mwolo zl0j6j z vf0u-61 .gt 0cl)rons in the metal, yet only some of them move as shown. Why not all of them?

When an electroscope is charged, its two .l 2di0 )p q(wduw:ww m5fpcp(leaves repel each other and remain at an angle. What balance:wp lw(.u05qfwm2did )(pcwp s the electric force of repulsion so that the leaves don’t separate further?

The form of Coulomb’s law is very similar to that for New*5hm*n w glv -irk1la) cm-l2uton’s law of universal gravitation. What are the differences between these two laws? Compare also gravitational mass andkhlmaln l5 *v1m w2c)i-ug-* r electric charge.

We are not normally aware of the gravitationalaq gp4ky )rp:s)r;( et)rtos8 or electric force between two ordinaryrr:pye )4 ap oks ()trqg);ts8 objects. 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 ;2 sdj3 yx0 fruv)k .3nd*hj -1blvdfsforce? Why or why not? (See Chapter 6.)

When a charged ruler attracts ;,q:nuj hd6k 0drhx,z small pieces of paper, sometimes a piece jumps quickly away after touching the ruler. Expln;q0 ,6hu ,k r:xhddzjain.

Explain why the test charges we use when measuring electric fields must be smallo8u ;wrfb5n0fo7mee /.70en/5 fumowefr; ob8

When determining an electric field, must we use a positive test charg6lxv6xy0*1qr )qfxj m e, or would a negative one do as well? Expla1 )fr6 q6 0xqjmlvxxy*in.

Draw the electric field lines s p9mj d3q*g-kuurrounding two negative electric charges a distance l apar -d k*q3gmp9jut.

Assume that the two opposite charges in Fig. 16–31a are 12.0 cm apart. Consido:hua9smc . 29b x+vouer the magnitude of the electric field 2.5 cm from the positive chargeo.hsv+ 9 oc2mau:b9ux. On which side of this charge — top, bottom, left, or right — is the electric field the strongest? The weakest? Explain.

Consider the electric field at points A, B, and C in Fiv) fetwu,990 +(bcwcoljf8 ojg. 16–48. First draw an arrow at each point indicating the direction of the net force that a positive test charge would experience if placed at that point, then list the points in order of decreasing field strength (stronges9col wje08vf9 o),wb+ t(uf jct first).

Why can electric field lctp+jz7go4z: :l nfnsn.8x/ yines never cross?

Show, using the three rules for f+w+ a uajhx ru2gz9:2xield lines given in Section 16–8, that the electric field lines starting or ending on a single point charge must be symmetrically spaced around the zhrug9+ jaw:x+ u2 2xacharge.

Given two point charges Q and 2Q, a distance l apart, is there atx r(,(qa8 nuc point along the straight line that passes through t 8u(,n xcqtar(hem 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 czcg)b743r1pqvjk c1(7w jqy r harge located 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 of the test charrwcy74 z c17q(gqj)kv3 prjb1ge along this line? Discuss.

Sketch the electric field lines for a uniform line of charge wtjcz qa;-v32hhich is infinitely long. (Hint: Use symmetry.) Is thavj2cqz t h;-3e electric field uniform in strength?

If the electric flux through a closed surf-:ddmf e*:nx race is zero, is the electric field necessarily zero at aedrfn:m-d* :x ll 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 byfpj73hyya j,7 a spherical gaussian surface of radius r. If the sphere is replaced by a cube of side r, willpjya7f yh j,37 $\Phi_E$ be larger, smaller, or the same? Explain.

  

  How many electrons make up a charge o qy(8g3: gph+ls pe3ntf $-30.0\mu C\,?$   $ \times10^{ 14}\, electrons $

  What is the magnitude of the electric force of attraction between an iow3r qylf5p-nyk0 6 9bron nucleu3 lyqk wpb9-5r60yon fs $(q\,=\,+26e)$ and its innermost electron if the distance between them is $ 1.5\times10^{-12 }\,m\,?$    $ \times10^{-3 }N$

  What is the repulsive electrical force between two protol. cjwm:g)pww, s)w u8ns $ 5.0 \times10^{ -15}\,m$ apart from each other in an atomic nucleus?    N

  What is the magnitude ofgg4cfm .qh(y) the force a $+25\,\mu C\,C$ charge exerts on a $+\,3.0\,mC$ charge 35 cm away?    N

  Two charged dust particles exervp4 - vse8/c0)vvg2;;lr ozyn ,lgjx gt 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 moved, a:b fg52 )us0zh7kq mwwnd the force on each of them is found to have been tripled. Hosfw h :wgu7 z5mb2)0kqw far apart are they now?    cm

  A person scuffing her feet on a wtf7: tbeb4h f8ool rug on a dry day accumulates a net charge of 4 ftte:b7 fhb8$-42\,\mu C\,.$ 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 elt u;1l/st ovr-ectrons in 1.0 kg of $H_2O\,?$    $ \times10^{ 7}\,C$

  Compare the electric force holding the electron in o7n a c+b xd(0+wcn+xasrbit $(r\,=\,0.53 \times10^{-10 }\,m)$ 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 tha 2a*tbnevxq 2n)p;kb udn-4:eir charges is What charge must each have in orderq) neu2-btp a: 2vx*4nabd k;n to
(a) maximize the electric force between them,
(b) minimize it?

  Particles of charge bhj5mc62b p9 h$+75$,$+48$ 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 equaifk1pwipn gv e (z:9goah/47kn33f8el 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 ph:mo,so ,(9aqxb8 wb is placed at each corner of a square 0.100 m on a side. Determine the magnitude and direction(hoo,am b , 98bs:wpxq of the force on each charge.
$F_4$ =   $ \times10^{ 7}\,N$
$\theta$ =    $^{\circ}$

  Repeat Problem 14 for the case when two of the positive charges, on opposite 802hn-unhlo gcorners, are replaho2hnl 8-n 0guced by negative charges of the same magnitude (Fig. 16–51).
$F_4$ =   $ \times10^{ 7}\,N$
$\theta$ =    $^{\circ}$

  At each corner of a square of side l there are point charges of ggjur 9.-; 8u-tnuf7 tli(rcf magnitude Q, 2Q, 3Q, and 4Q (Fig. 16–528r.-(;ujtl -n9 cg7igt rfu fu). 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 m7(/.m ,h ghif dfxv)tthe corners of an equilateral triangle of side g7fi,)vmxtm.(hdh/ f 1.20 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 ckn9dheik 219aharge 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 ofytceqo ;g -iodn24nzz) w4e;4 $90.0\,\mu C\,.$
(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 ball b7,;xvvgr4 5yxx * gzjto an identical ball 12 cm away. The force of attraction is then 17 mN. How many electrons were transferred from 7g*v5yxgz jxv 4xr ,b;one ball to the other?    $ \times10^{ 12}$ electrons

  What are the magnitude and direction of the electric fx+-k5hdg yg4j orce on an electron in a uniform electrixhk5gy -g+4j dc field of strength $2360\,N/C$ that points due east?
   $ \times10^{ -16}\,N$
 ----待选择----westeast 

  A proton is released in a lo 9indf72ru ac90khn/w9j9mng t n9*uniform electric field, and it experiences an electric forcenn*kn9tf0m2j /9lau 9n r9hw7i9o c dg 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 exerted onczu -.n,n07,sk pqgcl a $-8.8\,\mu C\,$ charge. What are the magnitude and direction of the electric field at this point?    $ \times10^{5 }\,N/C$ ----待选择----updown 

  What are the magnitude and direction of the electric field 20.0 cm directly abov5mgcz67mam (wyytr w9e;2 kz1e ayc7m5rzage21; wtw mmyz 9(k6n isolated $33.0 \times10^{ -6}\,C$ charge?    $ \times10^{6 }\,N/C$ ----待选择----updown 

  What is the magnitude of the acceleration experiencespgvq/+z8v a2cs /u,gd by an electron in an electrz gv, v/pas g2+usq8/cic 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 an , 8.5zqd,dazl* u rnrs2ldy.zd direction of the electric field at a point midway betd*5r,l2ylzrza.8uq.sd , zdnween a $-8.0\,\mu C\,$ and a $+7.0\,\mu C\,$ charge 8.0 cm apart? Assume no other charges are nearby.    $ \times10^{7 }\,N/C$ ----待选择---- towards the negative charde opposite to the negative charge 

Draw, approximately, the electric field lines about two pozr/0 -sy2tpq )jv1mmk-iyd.o int charges, $+Q$ and $-3Q$ which are a distance l apart.

  What is the electric fiela5;pyq):z j6krq yk d8;q-b gopx/ sn)d strength at a point in space where a proton $(m= 1.67\times10^{ -27}\,kg) $experiences an acceleration of 1 million “g’s”? $\approx$    N/C（Round it to one decimal place.）

  An electron is released from rest in a uniform electric field ajg gu,8ty9 b :/fw/gxand accelerates to txa 8y9:uwgg /bj,g/f the 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 poq4qcux1 n0rbl- qm +*uint 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 if one hjflyz6x7,xu i2yu- g66.yjgcorner -zjyfu76 h ,x.x i 62y6jgulygis 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 1.00 m on a v, ffojn1w qq1q uf9/.side if the other three corners are occupied .ujf9o qw/ n qv11q,ffby $ 2.25\times10^{-6 }\,C$ charges.    $ \times10^{4 }\,N/C$   $^{\circ}\,$ from the x-direction.

Determine the direction and magnitude of the electricy t7 *enw,/wtt field at the point P in Fig. 16–54. The charges are separated by a distance /t 7e ny*wtw,t2a, 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 elect c0)pmznnz gxo6/q)sva; (qe8 ric 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 determp-lyo o+ f:p-n*2 yoe4rpml-vine the magnitude and direction of the electric field at points A and B in Fig. 16–57 due to the-y lo-yn:ovprfm*4+2p l eop- 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 unknotr;gk(p/mv ri 9xo1p3 iu 1d0rwn 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 magnitude of the electric field at e(ugu ed68k-lt.b19c( s/g ;gdk oev othe point P shown in Fig. 16–59. The two charges are separated by a distance of 2seudt( b/ k.vgg8gk9o c;el -1e6od(ua. Point P is on the perpendicular bisector of the line joining the charges, a distance x from the midpoint between them. Express your answers in terms of Q, x, a, and 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 toe/upxa4ktq 0 1 the right at 1.0% the speed of light enters a uniform electric field parallel pkt4eaxu1q0/to its direction of motion. If the electron is to be brought to rest in the space of 4.0 cm,
(a) what direction is required for the electric field,  ----待选择----rightleft 
(b) what is the strength of the field?    N/C

  The total electric flux from a cubical bw83*ha:h bzt 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 cm is placed in a uniformlhty3 etu d3en, r*3h/ 4;zq zsao;b2o electric field of magnitude la,e oh4q; uz3ot3ey n2h /b*z;st3 rd$ 5.8\times10^{2 }\,N/C$ What is the electric flux through the circle when its face is
(a) perpendicular to the field lines,    $N\cdot m^2/C$
(b) at 45° to the field lines,    $N\cdot m^2/C$
(c) parallel to the field lines?   

  In Fig. 16–61, two objects, 9m)j c)rtq d m9ft0ck1$O_1$ 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 auc,o+tm- w 93wv:u5m6 dmemgn 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 square metal plates is The plates arez u-x3,yr 3/* 4qnlasixqtz g) 1.0 m on a siden xq 3it/)q-*yzug4r3 sxaz,l and are separated by 3.0 cm. What is the charge on each plate (assume equal and opposite)? Neglect edge effects.    $ \times10^{-9 }\,C$

  The field just outside a 3.50-cm-radius metal z0kwk9g ;h o b-;w brl.p*xeg,kpy;+s 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 carro18n g*h-q jfvph(.ga ies 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 spherw9zp :uhux4e1ical conducting shell. (See Fig. 16–33.) What is the electric field E as a1x9h 4epw:u zu 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 t( ixx . bc+tld+:/ic.clnax tc 5g/gsab6+:rbhe helix-shaped DNA molecule are held together by electrostatic for xci5:+ts+gbcnx./ic . +/ r l(:c axt6dabgblces 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 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 electr1ou bnuh4k2w*ic force between them is equal to the weight of e 2*uhon4bu w1kither at the Earth’s surface?    m

  A 3.0-g copper penny has a positive ch bi hh 3gc5mo38sso9+large 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 indicat2e:j1 0cosy ate that there is an electric field surrounding the Earth. Its magnia c1jyest2o 0:tude 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 electridbs k/r7tv7 s3sr9 zn:c field of what is the acceleration experienced by an electron ne 37/ssb:tkrsdn79z r var 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 stnjyt69 t ke4iqu8 02tax cmm*5ationary in the air. If the downward-directed electric field mt65y 2c iant q4m8etju9*0kxof the Earth is $150\,N/C$ how many excess electron charges must the water droplet have?    $ \times10^{ 6}$ electrons

  Estimate the net for 1l lns r4 u2 j)bftc/ia-2xzz594nhjsce between the CO group and the HN group shown in Fig. 16–62. The C aslt ni -nr1z2 4l fbhu/xzs 249j5cj)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 gs 5oryv5 a6ynww-o0 0revolves in a circular orbit around the a-goysr nwv0y6ow 055proton 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 responsibleez,1 8av /vlxk wxna3(cmjgx-( 7peb/ for holding the Moon in orbit around the Earth. If equal and opposite char ,a(plv w kxc/ezge1 83x jb-avn7m(x/ges 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 speeds h fa6ergf6z4c:)r4t $v_0\,=\, 21.5\times10^{6}\,m/s$ 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 cha) 2 uoqvw9p.xgrge $Q_1\,=\, 2.5\times10^{-5}\,C$. 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 plasti5c7 np.zby 6qbc and suspended vertically from an ideal sprib765qcnpyb z .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” tvk yqdz2cv8a +f(/q msjwqb2.j)/6 xwhat are 78-cm-long wires with tiny 24-g spheres at the ends. When charged, nearly all the charge resides on thdf2.ws) jx/ mqc z2(q8wy vjv/a+6bq ke 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 spat.x m 2,+f qk)xwo0kf.o0qbpr+kmhp 3rk if the electric field exceeds about q hpx)k0t+ x+m.0, kfpqow2mfkobr3.$ 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 netea8 r c)ch.n-z charge $+0.340\,\mu C$, hangs at rest at the end of an insulating string above a large sheet of charge. The horizontal sheet of uniform charge creates a uniform vertical electric field in the vicinity of the point charge. The tension in the string is measured to be 5.67 N. Calculate the magnitude and direction of the electric field due to the sheet of charge (Fig. 16–67).    $ \times10^{7 }\,N/C$  ----待选择----updown 

  What is the total charge of all the electrons in a 15-kg bar of alumibn4sj6o b/*p nnum?    $ \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 ap +z *e,o nsrsqisab/t*bn1 1e(art; 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 1*1zba(ns, soen+tbr* q es/ithe 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 whff 0n- y( ;c*wx xvn1r0)we2mh. ebxizat position(s) x is the electric field zero? Is the field zero n xyf i*r(fvm)ww1c;z0b-.0nhx2 xeeat 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 kft(u0gc.)zwfe3ev- y8- buz 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?