If you charge a pocket comb byit.o00d:( h u7bz km1kw* vitt rubbing it with a silk scarf, how can you determine if the comb is positivel*hd k 1kv0bz i(u.mot: it0wt7y or negatively charged?

Why does a shirt or b58ilmh)er qycf)0ll,j 9dbky8, 1ubi louse taken from a clothes dryer sometimes cling to your body?m0ki 5,yc lfjqe1i8l8 9duhlb,r) by)

Explain why fog or rain droplets tend to form arot7ma :z 8qhzzni v.)4sund ions or electrons in the airh.qsm7:z4 z) nv8tai z.

A positively charged rod is brought close to a neutral z4 55r5u lbn:a// 2y(eu eydfzvvgs-wpiece of paper, which it aty 2 sgr5d/5lfvyb(z5aen4: /z wvu-eutracts. Draw a diagram showing the separation of charge and explain why attraction occurs.

Why does a plastic ruler that has been rubbdcv *ily2ok,.fa-mx;1gxf 3s ed with a cloth have the ability to p2v1magoxl , -*xcyk3i.ffd s;ick 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 charg yz6a 4od/irt7-una9t:4jpgppf+ e7h es” in the conductor.

Figures 16–7 and 16–8 show how a charged rod placed nv3opq,)hyzgl;r1 pp 7ear an uncharged metal object can attract (or repel) electrons. There are a great many electrongl;z,vhoypp3r pq 7)1s in the metal, yet only some of them move as shown. Why not all of them?

When an electroscope is charge :-ev 881q k7dl/,cmdo zvxwkad, its two leaves repel each other and remain at an angle. What1-:wxkv 8 z8md, cevoqldak/ 7 balances 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 Nerdm(6+ib * r pmgmth62 :idy*jwton’s law of universal gravitation. What are the differences between these two laws? Compare also gravitatiojm 6rhdmgiiy2mpt *r:6*( b+ dnal mass and electric charge.

We are not normally aware of the gravitational or electric force between tj 8 p7ibpbb*th:-ueu8 l,n.vpc )k)pt wo ordinary objects. What is the reason in each ptbun-k) pj hluv 8i pt)7,bb8:p .ec*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 -jpl26* 1h( 7za * cwonlomtsqChapter 6.)

When a charged ruler attracts small pbs*xbq:gqn2d f* - 1ehieces of paper, sometimes a piece jumps quickly away after touchingnsh: 1 *q f-eb2qbg*dx the ruler. Explain.

Explain why the test charges we use when measuring electric fields must be sm4k 0zd l+j+zxuall.z+duj zl +4xk0

When determining an electric field, must we use a positive t7-lva2q u, eptest charge, or would a negaeq t,uv-7lp2a tive one do as well? Explain.

Draw the electric field lines surrounding two negative electric charges a distg nfp-p /zl/*fancel f/g/* n-ppfz l apart.

Assume that the two opposite charges in Fig. 16–31a are xup0w* saeo*7+a l r1wf.ho5k 12.0 cm apart. Consider the magnitu5 s1haw o0 fu.7l+ wo*rpx*akede 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? Explain.

Consider the electric field at points A, B, and C in Fig. 16–48. First draw an a)2+ik mk5t3c3a im culrrow at each point indicating the direction oc k) k2u+i3 m3mlic5atf 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 (strongest first).

Why can electric field lines never 0)mi8xzhavfi : 1 gyw:cross?

Show, using the three rules for field lines given in S 9ljxbw 9b7 r0bp9remny46 a3kection 16–8, that the electric field lines starting or ending on a single point charge must be symmetric367 949bya9pr xnwe0jbbk m lrally spaced around the charge.

Given two point charges Q and 2Q, a byss qx 26e0x dpeb)3to5els c;i133gdistance l apart, is there a point along the straight line36)et20lcxq s3e; sydbx13gb5ei spo 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 onv7awb (tfp 6nw *pbu f48tv:k;as3r3o an electric field line at some point, such as point P in Fig. 16–31a. Is the direct f8:3 3b7btvu ;wf oaskawtrn4v p*6(pion of the velocity and/or acceleration of the test charge along this line? Discuss.

Sketch the electric field lines for a;-h.nsbegl j / uniform line of charge which is infinitely long. (Hint: Use symmetry.) .;eh -gslb jn/Is the electric field uniform in strength?

If the electric flux through a closed sur0qo ak7/:lkaoface is zero, is the electric field necessarily zero at all points o:aak/kl7 q 0oon 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 z2m /d2lm,smr xw7 g9va spherical gaussian surface of radius r. If the sphere is replace/s7dvm2w m ,mlr9zg2 xd by a cube of side r, will $\Phi_E$ be larger, smaller, or the same? Explain.

  

  How many electrons make up a c.*tqd exv(ge cjll 2))ntu6c+ harge of $-30.0\mu C\,?$   $ \times10^{ 14}\, electrons $

  What is the magnitude of the;*:.+lee1rop vn mmf+r,ind q electric force of attraction between an iron nucleus i+*ev:.pmrq;fl1 d, nom+rn e$(q\,=\,+26e)$ and its innermost electron if the distance between them is $ 1.5\times10^{-12 }\,m\,?$    $ \times10^{-3 }N$

  What is the repulsive electrical force b4yej 5tk+lkzw s19b x(etween two protons $ 5.0 \times10^{ -15}\,m$ apart from each other in an atomic nucleus?    N

  What is the magnitude of the force(76f83hhi mtmjh0ly b a $+25\,\mu C\,C$ charge exerts on a $+\,3.0\,mC$ charge 35 cm away?    N

  Two charged dust partax8jf9cr7r7n7. sn yun3)9 t qdees0ricles exert 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. The uusn1 y6+eh5t 4m6tyhy are moved, and the force on each of them is found to have bee6hm41ynuys+5tte h6 u n tripled. How far apart are they now?    cm

  A person scuffing her feet on a wool rug on a dry daye(f h 8es03m5xs jhx-k accumulates a net charge okes f8-e30xhxjsm5h(f $-42\,\mu C\,.$ How many excess electrons does she get,    $ \times10^{14 }\,electrons$
by how much does her mass increase?    $ \times10^{-16 }kg$

  What is the total charge o1t1wi .wyrndid-d8k f gnu-93oz3y 8df all the electrons in 1.0 kg of $H_2O\,?$    $ \times10^{ 7}\,C$

  Compare the electric force holding the e4i fvir 11yjz8x*dr h,lectron 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 b 6g0wt;m0a+0vr tq9pxswb 0 ,ovx)asapart. The sum of their charges is What chartv0b,w;0bv mog sw 6sxq)xtp r9+0a a0ge must each have in order to
(a) maximize the electric force between them,
(b) minimize it?

  Particles of charge :jt;pc 9yu xe5$+75$,$+48$ 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 chgw 8 oe;nl 9hpbavz;,,0f; jwiarge, $+11.0\,\mu C\,$ 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 sim*5 ;tyc rqtmq 6(t4mkoy+1u xde. Dete 5uy1k r;ymqmtqc 6*(mxo+4ttrmine the magnitude and direction of the force on each charge.
$F_4$ =   $ \times10^{ 7}\,N$
$\theta$ =    $^{\circ}$

  Repeat Problem 14 for the cas b-,6 a9t.bwy6qit nzee when two of the positive charges, on opposite corners, are replaced by negative charges of the same magnitude (F,b-6 tq9ytn .ib6 weazig. 16–51).
$F_4$ =   $ \times10^{ 7}\,N$
$\theta$ =    $^{\circ}$

  At each corner of a square of side l there are point charges of m(.sb4 :b jzwb6 dxe2lfj3(j ic b24equagnitude Q, 2Q, b : xu.s3b 42ej(dzq4ifljb6e (wc2bj3Q, and 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 corners of an equilaa0l qt )0qmslx(q,4w xteral triangle of side 1.20 m (Fsqx )twl, a(qq400ml xig. 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 hjulgtj jp -,p,gd;92a total 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 a total c) l(o6zaqoc -zu:py k3harge 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 ball to a wtbh) t4zgji(l3-5dnn identical ball 12 cm away. The force of attraction is then 17 mN. How many w(bjg itdh n5lz)3 -4telectrons were transferred from one ball to the other?    $ \times10^{ 12}$ electrons

  What are the magnitude and direction of the electric foit idn u.1f/x0qsaswj5* b 12irce on an electron in a uniform elecjfu1i5db1aisq. t*0nsxi w2 /tric 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 elecrm qs0v3 vzim*;t2;/k* ikm n0wk d8pytric force of mi /; rk i n*2wkk;y8*0qvz0mtdvmps 3$ 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.y e-ku bm-lk3k(nh3gc30+np t4 N is 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 e 04qy 2l3evjynlectric field 20.0 cm directly abovn3v2l ey0 4yjqe an isolated $33.0 \times10^{ -6}\,C$ charge?    $ \times10^{6 }\,N/C$ ----待选择----updown 

  What is the magnitude of the acceleration experienced by an electron i +ts8 znsrs4v.t u 1qq8x.vki6n an electric field o8 xq.ttsik.61sqvzs4n+r8 vu f $750\,N/C\,?$ 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 ,m zy:amkr*d7xp. + dhva.bt,d direction of the electric field at a point midway between a ,y k. .bx*drpm7zvd +:mtah,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 electriczs+ tx0nim uciz) .a a cr4c33m-jy(;g field lines about two point charges, $+Q$ and $-3Q$ which are a distance l apart.

  What is the electric field strength at a point in space where3gg: )s ;t aka09f iwgm+epht9 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 zb:abqpoo uh6 q (q7xys;-n2+ ecoc( ,field and accelerates tooh ;onpbczoe:q7q a 6+(c(2b sxq,y-u 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 midjii)f7v yo zn(0h yu5a-.gpp5way between two equal but 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 ab48 / wsnq8:vpxw fum3t the center of a square 52.5 cm on a side if one co88smub npx 34vwqf:w/rner 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 ataja*a t2 y0b(i one corner of a square 1.00 m on a side if the othetya j *i(2ba0ar three 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 electrj/td bag9erxtspz6*o f87 +e :ic 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 charo6at*d7 9jr gs8bx:tzf/e pe+ges. 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 electric fieldjbsq,v8 8uazw*t3z ) u $\vec{E}$ at the origin 0 in Fig. 16–56 due to the two charges at A and B. (b) Repeat, but let the charge at B be reversed in sign.

  Use Coulomb’s law to determine the magnitude and direction of the e jwa719 v8zvtalectric field at points A and B in Fig. 16–57 due to the two posiv7 8taw91za jvtive 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 charge, sukq)o kcvm.)i /6mu+a/t.rjdsz0rs, $Q_1$ 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 magni uw4s5nz(/z+5 1ves sz:nlkaaq s 89pitude of the electric field at the point P shown in Fiu lkezwipsv5n naaq85ss (41 +z/:s9 zg. 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 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 en/-r)mtt om (f)eu5evnjob o. ty(u+t5ters a uniform electric fietube(.)(5 tvont-o j/f m+t)ue y r5omld parallel 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 box 28.0b kdg kq4m, 7ckvtqn;31eql-/ 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 uniform electric fieljzp )jh363/5yqo9p p n z(tovrd of magnitudenjvqt539p3joz/ opy6()rz h p $ 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 objectsk8i gkd*kt f20, $O_1$ 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+x mec 6ogap)g-h,8t8j s pq)aorm 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 metaz vpjv:aqpg6 whl-d-2:vn68y+ frke5 l 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)? N 5g: p+jvrk-8l-d hzfw:66qvnvy ep2aeglect edge effects.    $ \times10^{-9 }\,C$

  The field just outside a 3.50-cm-radius metal ball is eh*. uzy4 spfcto+6.w$ 2.75\times10^{2}\,N/C$ and points toward the ball. What charge resides on the ball?    $ \times10^{-11 }\,C$

  A solid metal sphere of radius 3.00 m carries a total chargepqg i 9ajj 80,gre0lq6 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 a rc;i5hpcuzf-f, -3pl n uncharged thin spherical 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, (b) inside the shell, and (c) beyond the shell? (d) Does the shell affect the field due to -p;c z5uhfc lp- fi,r3Q alone? Does the charge Q affect the shell?

  The two strands of the helix-shaped DNA molecule are held tja 5jbz9bba5 ni6 n5;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 indicated C and ba956nzbb ;a5nti5j j 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 electrh4r76/bcowge w.h/dh rngr.)(im1g d ic force between them is equal to the weight of either at gihc/1orhb7g r/gdr.)m e(wd .wh64n the Earth’s surface?    m

  A 3.0-g copper penny has a posit eryb.w) ;0pp e8l+lbgive 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 the yu 3:/sq) g-d bpk4cfxvw; 3rfEarth. Its magnitudesu3 / bcf: 3wkpqf)yxdgrv-;4 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 ve wze0waz5.. t+opo;p )3kf xelectric field of what is the acceleration experienced by an electron nearw epexfpw) ;ozk . taz.3v05+o 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 reh4uuoi3p+ ii2vw p)(-ul tek1mains stationary in the air. If the downward-directed electric uu4puhv)ii(- lie3 1wokp2 +tfield of the Earth is $150\,N/C$ how many excess electron charges must the water droplet have?    $ \times10^{ 6}$ electrons

  Estimate the net force between the CO group and the HN groububfby rjq v; /+j)c*.p shown in Fig. 16–62. The C and O ha fv;) rbuqb.bcj /+*jyve 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 th;3 nkh,3i ( 2v5dvjkay utp5gxe hydrogen atom, the electron revolves in a circular orbit ar i ; 3gvtj,u(3hk5a5kd2nxpyvound the 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, wer8vt2id6q lz( v+mmx567 r8lerfs6sqke responsible for holding the Moon in orbit around the Earth v6l7t8+x8mskr2lr6di 6m z5ve (fs qq. 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 speed /d/* uym4 itqe2 j3rfj$v_0\,=\, 21.5\times10^{6}\,m/s$ 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 chac1kd+k 3sd8w ugc5a 8wrge $Q_1\,=\, 2.5\times10^{-5}\,C$. 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 6t,z-qu+7hu0 81ksg q3wuhiph ekfj ) in insulating plastic and suspended vertically from an ideal0qqk -f eu7uz)g+,w3 6iuh hth8 sp1kj 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 tin 857lejn tw1sqy 24-g spheres at the ends. When charged, neqwjtn78l 5 e1sarly 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 genera9aq.dw.m zpzyque;* +te a spark if the electric field exceeds about.+my9 z wzqe.qdpa;u* $ 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 0.2 qeo(rtfh+j93v3ib6 n10 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 electrons in a 15o7*:pz t tnh r5b1a*emwa. ym;-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 sp-e mk2* -cxl(znwh*mjhhn/ f1heres 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 i-fw*(/ x2hjck hzn*n- 1eml hmdentical sphere with zero charge, sphere C, makes contact with sphere B and is then moved very far away. What is the net force now acting on sphere A? (c) Sphere C next makes contact with sphere A and is then moved far away. What is the force on sphere A in this third case?

Given the two charges shvy5* :5ehv)zu sfub x7rq m1t2own in Fig. 16–68, at what position(s) x is the electric field zero? Is the field zero at any other poinb )1h5m z:fv2y5xu tq 7uv*srets, 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 of charge -u5tl kfk qn1o ;;yoe3$8.0\,\mu C$ 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?