If you charge a pocket comb by rubbing it with a silk scarf, how can s ftc yfl1;a5 1:n-csdyou determine if the comb is positively or negn s;t51cy1fflad - s:catively charged?

Why does a shirt or blouse takh7kc r3s;+a qven from a clothes dryer sometimes cling to your bodq+ack; sr7v3h y?

Explain why fog or rain droplets tend to form around ions or electrons in thekrp7vc)n5f ,djlo */e ai )vn*lj/ckerp7 ,fdo5r.

A positively charged rod is brought close to a neutral pikzn6xe /e(o jqv pg()9ece of paper, which it attracts.kpenz9 o6( /q )exj(gv Draw a diagram showing the separation of charge and explain why attraction occurs.

Why does a plastic ruler that has been rubbed wi3g 0z(cnh. kgcth a cloth have the ability to pick up small pieces of paper? Why .hc znkg 0g3c(is this difficult to do on a humid day?

Contrast the net charge on a conductor to the “free chargesvo7 **me52 m +utsgows” in the conductor.

Figures 16–7 and 16–8 show how a charged rod placed near an unctn ya)/ -pccg-xd8 jf7y,aoq2harged metal object can attract (or repel) electrons. There are a great many electrons in the metal, yet only some of them move as728-c ) njxayc pygdo/qat,-f shown. Why not all of them?

When an electroscope is charged, its two leaves repel each other and rop :b*ib6*+/ n3nedhbiupc;lz0 s)s uemain at an:*unp6os+b ;sei 0c3l b)pbn/ d izhu* angle. What balances the electric force of repulsion so that the leaves don’t separate further?

The form of Coulomb’s law.(s0tpc:hwg u ; y8cg4xps uv/ is very similar to that for Newton’s law of universal gravitation. What are the differences between these two laws? Compare also gravitational mas0s8tg pcpuh:x./; s gwc(v u4ys and electric charge.

We are not normally aware of the gravitational or electric fororz+ upah)af)36g ur 5ce between two ordinary objects. What is the reason in each case? Give an example wher u h)r5fogza u)p63+are we are aware of each one and why.

Is the electric force a conservative force? Why or why not? (See Chappkr7jrf y :3 zk7x7en4ter 6.)

When a charged ruler attracts small pieces of p(n2 ,fz. dmu6gmufc2095 my4fzapn wyaper, sometimes a piece jumps quickly away after touching the ruleymm6 4nnp f2ug.2fyu, d5w(9c0 azfm zr. Explain.

Explain why the test charges we use when measuring electricj-k.p5v;q asl fields must be small.5.;jsqvkap- l

When determining an electric field, must we use a positive test charge,e.irp qkm0 b i99pke+1(o9io r or would a negative one di ri0 (mor o.kb1qke9 9pi+ep9o as well? Explain.

Draw the electric field lines surrounding2d r c+6ggs)gn two negative electric charges a distance l apag csn6d2g g+r)rt.

Assume that the two opposite charges in Fig. o,/n +urpl* 0:v(zv+f o 8fk stqte.fs16–31a 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? Ex0/v q(o+*lkefp ,nu fvt+tz s:fos r.8plain.

Consider the electric field at points A, B, and C in Fig. 16–48. First u7bo d g 10hlmagl1q*6draw 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 f mg*0lbdgoau 761q 1lhield strength (strongest first).

Why can electric field lines never c6b v9p9-sfhg 5 39n/ziy ygise gchf68ross?

Show, using the three rules for field lines given in Section 16–8, that zrhq: d5409 kc)ypq exthe electric fieldy:kqx 9dp r 504qz)hec lines starting or ending on a single point charge must be symmetrically spaced around the charge.

Given two point charges Q and 2Q, a di-o(tnczmc 6u,9s/w* h;wuu on j sq,/pstance l apart, is there a point along the straight line that passes through them where E=0 when their signs are (a) opposite, (b) the same? If yes, state roughly where this point n w/c, mpzuqnoh,/s;tu 6o suw9*j-c(will be.

Consider a small positive test charge located on an electri1xtc6 x x9w*mag,r)3b+w ge jgc field line at some point, such as point P in Fig.xx jmx9twc)a,b*3g+6 g r 1weg 16–31a. Is the direction of the velocity and/or acceleration of the test charge along this line? Discuss.

Sketch the electric field lines for a uniform line ofd r sp1: oepna)e0*3mz9ucby9 charge which is infinitely long. (Hint: Use symmetry.) Is the *1doce 9)n9s p:by 3 ua0pezrmelectric field uniform in strength?

If the electric flux through a closed surface is zero, is the electric fivb+yn+*/mx vweld necessarily zero wby v n+mx+/v*at all points on the surface? Explain. What about the converse: If $\vec{E}\,=\,0$ at all points on the surface is the flux through the surface zero?

A point charge is surrounded by a spherical gaussiimp4)gj mx jbbv84b6 8an surface of radius r. If the sphere is replaced by a6x8m pbjv )4j4 gb8bmi cube of side r, will $\Phi_E$ be larger, smaller, or the same? Explain.

  

  How many electrons make up7+npdb eiwcrg 5:s8e8 a charge of $-30.0\mu C\,?$   $ \times10^{ 14}\, electrons $

  What is the magnitude of the electric force of attraction between a4 pf avg(ql6w(fd/svi3w40bl n iron nucleusi qv6f4vp0/g3 (wdfbalw(4l s $(q\,=\,+26e)$ and its innermost electron if the distance between them is $ 1.5\times10^{-12 }\,m\,?$    $ \times10^{-3 }N$

  What is the repulsive electrical force be)-2j/owaw x bu1h :huctween two protons $ 5.0 \times10^{ -15}\,m$ apart from each other in an atomic nucleus?    N

  What is the magnitude ofhjcm f1n 1jr8j,qx o:: the force a $+25\,\mu C\,C$ charge exerts on a $+\,3.0\,mC$ charge 35 cm away?    N

  Two charged dust particles exert a force l e*ogp9gha(r/bg a zhlt5w9 2wk;, )sof $ 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 ahwm y ;34 vo),oepar gcc h3ohp79sd0.part. They are moved, and the force on each of them is found to have been tripled. How far apart are they 4hyo gcspm3w97da0c o,p.her) vh ;o3 now?    cm

  A person scuffing her feet on a wool rug on a dry day accumul6,r .b cibggw/ates a net charge of c6,gb/grbi w .$-42\,\mu C\,.$ 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 electroljmf, e9+ x.,u hv gp+q;easd0ns in 1.0 kg of $H_2O\,?$    $ \times10^{ 7}\,C$

  Compare the electric force holdingm dhf k/7 jy)ws 7s.mv) w7lc;6yx,rhz 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 chanxrkw- 8kt d v+v3v:j.rges are a fixed distance apart. The sum of their charges is What charge must each have in order todrv. v3vw x8n+k- :ktj
(a) maximize the electric force between them,
(b) minimize it?

  Particles of charge :5bm0.::u uf pfb/oqfo hg of0$+75$,$+48$ 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 equaw+3z1:k r gckql 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 each corner of a square 0.100 ot ) ;1.j+x 6s:mcgqzpc8ehe em on a side. Determine the magnitude and directi otcghsxe j8+:m1c ;e). pz6eqon of the force on each charge.
$F_4$ =   $ \times10^{ 7}\,N$
$\theta$ =    $^{\circ}$

  Repeat Problem 14 for the case when twz;1/9 mo. -hgr4rvq ti*oduam o of the positive charges, on opposite corners, are repmuv.ma ro/*zgoqdt4 1r-;9 ihlaced by negative charges of the same magnitude (Fig. 16–51).
$F_4$ =   $ \times10^{ 7}\,N$
$\theta$ =    $^{\circ}$

  At each corner of a square of sicezqpcq 8*j+4 cs, x.ide l there are point charges of magnitude Q, 2Q, 3Q, and 4Q (Fig. 16–52). Di4qc px. ej, z8s*c+qcetermine the force on (a) the charge 2Q, and (b) the charge 3Q, due to the other three charges.
$F_{2Q}$ =    $\frac{kQ^2}{l^2}$
$\theta_{2Q}$ =    $^{\circ}$
$F_{3Q}$ =    $\frac{kQ^2}{l^2}$
$\theta_{3Q}$ =    $^{\circ}$

  Three charged particles are placed at the corners of an equilateral triangld6u-)ccub +o cb,a:jce of side 1.20 m (Fig. 16–53). The chu - ,c6aj occb+cbu):darges 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 tota, or3gomyhhap4 4)ri 9fh m/4o g0rmu.l charge of $560\,\mu C\,.$ When placed 1.10 m apart, the force each exerts on the other is 22.8 N and is repulsive. What is the charge on each?
q = $ 5.54\times10^{a }\,C$ a =  ,
$ 5.54\times10^{b }\,C $ b =   
Q-q = $ 5.54\times10^{a }\,C$ a =  ,
$ 5.54\times10^{b }\,C$ b =   

Two charges, $-Q_0$ and $-3Q_0$ are a distance l apart. These two charges are free to move but do not because there is a third charge nearby. What must be the charge and placement of the third charge for the first two to be in equilibrium?

  A $+4.75\,\mu C\,$ and a $-3.55\,\mu C\,$ charge are placed 18.5 cm apart. Where can a third charge be placed so that it experiences no net force?    cm

  Two small nonconducting spheres have ajvau-vac- /wj1 n,u:ql;zu w2 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 ini j/ e3nel 5jufa4l dm(jkj/+a/tially uncharged plastic ball to an identical ball 12 cm away. Thf(5//3ul lj /ja jae4dn+mkej e 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 direction of the electri 6+47 z 9iypm4n7o l9 i5brkcwpz 3asw7orpzs.c force on an electron in a uniform electric field of ywzb9kr co z.m i+pwpio7 47l6 43paz7rs5s9 nstrength $2360\,N/C$ that points due east?
   $ \times10^{ -16}\,N$
 ----待选择----westeast 

  A proton is released in a unis5f05mvgb8y5 rsmvt s9,p7m dform electric field, and it experiences an electric force sf tmp0m59srbyg5,s8v v 5md7 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 h0 + t,rfpbppc-g9yp. 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 elec(o 7(l9ui yilwtric field 20.0 cm directly above au7(i owy(l9li n isolated $33.0 \times10^{ -6}\,C$ charge?    $ \times10^{6 }\,N/C$ ----待选择----updown 

  What is the magnitude of the acceleration experiencedku2os/yxsx-btcw90 h f kw,3: z6uhf 1 by an electron in an electric field/k0sf k9 u6t:x1hzyu x3bcfs2o ,h-ww 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 ff. 8mdli w7 iol/k2j)/yu/ jiaield at a point midway betweoiykw im/djal8l/f.u/ i) 2j 7en 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, )gq7 bji(h n yuqlkm(p:b;13a the electric field lines about two point charges, $+Q$ and $-3Q$ which are a distance l apart.

  What is the electric field scs+q:mcn6 59gj7xxwgtrength 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 and a9)gk-m2c jhm ot16yw rccelerates to the 1hgtjw c-2myor)m6 9k 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 cha,*rg j.2ne) cl+jldv drges 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 a9ha9t tx m1+brv4 g0or side if one cornerb9m rxt4 0 +gh9tv1aor 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 zwvt 4/y 2 figfz,yxq/+6ih0uat one corner of a square 1.00 m on a side if the other thre zfi,fvqy+i2y/w0/zuh t4 g6x e corners are occupied by $ 2.25\times10^{-6 }\,C$ charges.    $ \times10^{4 }\,N/C$   $^{\circ}\,$ from the x-direction.

Determine the directionkd.4 b19ev cvw and magnitude of the 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 midpd v4kvw b.9c1eoint 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 el(pfnx +x qi(x0ectric 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 dete ki((mqu9a :jfhs t+5nrmine the magnitude and direction of the electric field at points A and B in Fig. 16–57 due ts:tm ui(( n 5+khfq9ajo 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,6sc q*o xaycg4)7 eh(7b 7cidm $Q_1$ 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 3o u pvhi4cp(9jhc.q f44nqw3z+pp8e point P shown in Fig. 16–59. The two charges are separated by a distance of 2a. Point P is on the perpendicul.i qn+chow(49cj44up h f z3pqp8v3epar bisector of the line joining the charges, a distance x from the midpoint between them. Express your answers in terms of Q, x, a, and k.

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

  An electron moving to the right at 1.0% the speed of light enters a uniform ele4px9h6 aucw/h q4cgnmp : ruw5a++j3 octric field parallel to its direction of motion. If the electron is to be 49+ c5wahupuw +c3noa /j4r6q :hxgpmbrought 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 sideail( b80 g3csss4pw;;w.r,fe3oi bzqvu3d 9l 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 eldv/p/r3oc0 0wof qcq3ectric field of magnitude 0 q r/cfc3o3 dwo0p/vq$ 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 oj*mhoxv r; 52jbjects, $O_1$ 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 fielotxx4n akjpsik35d9:rx / k.dd0j8j0d $ 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 Theius(( .iv -pghuueqsl 9; hvhbmi .e -4.j(:ys plates are 1.0 m on a side and are separated by 3.0 cm. What is the charge on each plate (assume smb( (i ii4g.(v -h ;u sesul:veyhu.ph.qj-9equal and opposite)? Neglect edge effects.    $ \times10^{-9 }\,C$

  The field just outside a 3.5bvhx kc62jn 37-s +hvb0-cm-radius metal ball is $ 2.75\times10^{2}\,N/C$ and points toward the ball. What charge resides on the ball?    $ \times10^{-11 }\,C$

  A solid metal sphere of radius 3.00 mu c 3y ei9hxe:fzmhu+e/497 k;ipgp h3 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 sphericaf3sw.g 3x: ,sjptmny* l conducting shell. (See Fig. 16–33.) What is the electric field E as a function of r (a) for r less than the inner radius of the shell, (bp* gm:wn3x3sjt f. sy,) 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 held togethervb7i74f7 h2ezlhqft4n . s; :hjawz0e by electrostatic forces as s 4v;etlb:jsf7 e7zn07w2 .zqihfhh4ahown 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 them is equa jqs :llau zn5w2es6y:a2y +i nm-r)3il to the weight of either at the Earth’s surlj-:mu:nnyi2z iy s 3 a w6+rs5le)aq2face?    m

  A 3.0-g copper penny has a positi, : , 7lkf3 2zdwzrwkkhdqjx/)ve 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 electrte rs6 rh*q km7y3ve0/9y ti6 su6lbd.ic field surrounding the Earth. Its magnitude is abou.qr tv93 e d6ylr*emti yk6b/u 07sh6st $150\,N/C$ 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 oj/eo t:x psa;d:jv405yjb k/zx2 tew4-yfkn* f what is the acceleration experienced by an electron near the surface of the Eart::wkn0 - t44sbokea tfdez/x y 5;xpj/y2jvj* h?    $ \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 stationg6t1y w(rif6/j od*uotc k11b ary in the air. If the downward-dj/od*1(tyfkiwc6g 6r b11otu irected electric field of the Earth is $150\,N/C$ how many excess electron charges must the water droplet have?    $ \times10^{ 6}$ electrons

  Estimate the net force betwfx ,3px7zly) seen the CO group and the HN group shown in Fig. 16–62. The C and O have chap7yl3)x z,s xfrges $\pm0.40e$, 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 ld s)xrno5 qsx9815dpatom, the electron revolves in a circular orbit around the p 1s8 xn5r)lq5o9x ddpsroton 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, rat 29y4qb;y:dqys(xo prher than gravity, were responsible for holding the Moon in orbit around the Earth. If equal and opposite charges Q were placed on the Earth and the Moon, what should be the value of Q to maintain the present pq d(qo92y;s:xy4byr 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 speec ;icv 1tnhl-6am+7qhe+ksj.-8av fnd $v_0\,=\, 21.5\times10^{6}\,m/s$ 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 charget 7v/+ct, x ayd :e/mnan1;fzo $Q_1\,=\, 2.5\times10^{-5}\,C$. 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 verticanspt+p x m;yy4. /z. )no-twyplly from+ tw.ynp4 o/n;y pp)zxsym-t. an ideal spring $(k\,=\,126N/m)$ above a lab table, Fig. 16–63. The total mass of the coated sphere is 0.800 kg, and its center lies 15.0 cm above the tabletop when in equilibrium. The sphere is pulled down 5.00 cm below equilibrium, an electric charge $Q\,=\, -3.00\times10^{-6}\,C$ is deposited on it and then it is released. Using what you know about harmonic oscillation, write an expression for the electric field strength as a function of time that would be measured at the point on the tabletop (P) directly below the sphere.

  A large electroscope is made with “leaves” that are 78-cm-long wires with tm+ni 1fie d5w2 fdbs6-9n,a9bf 3i ywziny 24-g spheres at the ends. When charged, nearly all the charge resides on the spheres. If the wires each mafzi3n i9w-be i21 9d afymw6bn+5d sf,ke 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 fiel3 o1idgolp5 x+d exceeds about dox+o35pi1 gl $ 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 massg6nc fi,3vw5ir4wj8h lf4wga:d0/ v w(8ypzh 0.210 kg, and net 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 el0e+su cfir8nnn ps y n73p;8v(ectrons 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 condugv ge.1x ax)8lcting spheres A and B are a distance 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 sphere A? (c) Sphere C next makes contact with sg8.galv x)e 1xphere A and is then moved far away. What is the force on sphere A in this third case?

Given the two charges shown in Fig. 16–68, at what position(s) x is the a41rekmdv:p54y9+dh f s ,pjcp4h b9 melectric field zero? Is the field zero at any other points, not on the x axishepb 9 41:4d crp9vhjs 4y akd5m,+pmf?

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 charg rz//fd3r 2*2ir nsofces, 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?