If you charge a pocketqz0hys 7 pemn)2d n/cxa**0ve comb by rubbing it with a silk scarf, how can you determine if the comb is positively opahcens n*7e * 0 ym/d)x0z2vqr negatively charged?

Why does a shirt or blouse taken from a clothes dryer sometimes cling +s.k.:rfk( kf2cu an 6js wfl(to your body?afj(kusn ..c l6k2ffs:r( w+k

Explain why fog or rain df*k xeqe8cx45u 4 ivc/ o1,;wlm)lfcv roplets tend to form around ions or electrons in the air. 1e5 wv/;fc xxi4f,uoelcv)4cqk8m*l

A positively charged rod is brou8i y 62+iwmjydght close to a neutral piece of paper, which it attracts. Draw a diagram showing the separation of charge and explain why attrac 6y8iwj 2yi+dmtion occurs.

Why does a plastic ruler that has been rubbed with a cloth have the ac: dxz 7 n*udoptd:+ f31lws;zbility to pick up small pi*oz3t +z n;su d17lpc dxf:d:weces of paper? Why is this difficult to do on a humid day?

Contrast the net charge on a conductor to the “fre +wjped4+bzkvo jt4*9e charges” in the conductor.

Figures 16–7 and 16–8k;; roc9 jw1i u00whhw show how a charged rod placed near an uncharged metal object can attract (or repel) electrons. There aru0 i hh;0w1ock;wr j9we a great many electrons in the metal, yet only some of them move as shown. Why not all of them?

When an electroscope is charged, its two leaves repemh( qx 0 ntxr-db: 7wahxa:y55l each other and remain at an angle. What balances the electric fox5hnq armba xw(yxd507-t: :h rce of repulsion so that the leaves don’t separate further?

The form of Coulomb’j78tglkwo zdk 97um/0s law is very similar to that for Newton’s law of universal gravitation. What are the differences between these two laws? Compare also gravitational mass and electric chao0 w/mu7 l78kgjdzk9 trge.

We are not normally aware ori0 wwu tj4b))h,g5 yjf the gravitational or electric force between two ordinary objects. What is the reason in each case? Give an example where we are aware of each one an05)tw u bj4y)jh wg,ird why.

Is the electric force *sa c4nd) -zegafk5 a6a conservative force? Why or why not? (See Chapter 6.)

When a charged ruler attracts small pieces of paper, sometimes a piece jum*,,tjqx g. osrps quickly away,x so *tj,g.qr after touching the ruler. Explain.

Explain why the test charges we use when measuring electr 2v- gsmu)xbl+5/hdcjic fields must be smallc-+us j/hmbxd )5gl2 v.

When determining an electric field, must we use a positive test chargty+th 2eyuxh5p 2rhf/6, og)fe, or would a nega fh65u2/tgyrt hehx2, )+yfop tive one do as well? Explain.

Draw the electric field lines surrounding two negative8r 3/:au jnwie:yf; zlamv 50z electric charges a distance l ap 3jv i azw08:a;: y5e/zunrmlfart.

Assume that the two opposite charges in Fig. 16–31a are 12.0 cm apart. Consi6z xize1xv1bn,w64i) gn5 s9uwo we(b der 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 stronei1,zbs( nb w6 n46e5vgwouxiz1xw)9 gest? The weakest? Explain.

Consider the electric field atk gwyts ks zc1a/6m o,es9-.v; 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 poss1 -y/g cv;sk6o ,w9k stm.ezaitive 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 c am/i7l sv:zdk y/un6*ross?

Show, using the three rules for field lines given in Section 16–w i; 7kvpztm:/we v)k,8, that the electric field lines starttv/ivm ;:k7)kepzw ,wing or ending on a single point charge must be symmetrically spaced around the charge.

Given two point charges Q and 2Q, a distance l apart, is there a pointbj5fst lm:4a1z drimh +,a 43t along the straight line that passes through them where E=0 when their signs are (a) opposite, (b) the same? If yes, sta lh+d fj3ai: t rat,b4mm145zste roughly where this point will be.

Consider a small positive test charge located on an j kjk+ vur:-*dn8kjc1j0 ckf8electric field line at some point, such as point P in j:kfj0ck-kr njdu 81+8* kjcvFig. 16–31a. Is the direction of the velocity and/or acceleration of the test charge along this line? Discuss.

Sketch the electric fieami ( g;llf/r5ld lines for a uniform line of charge which is infinitely long. (Hint: Use symmetry.) Is the electric field(l5a;/gi rf lm uniform in strength?

If the electric flux through a closed surface is zaor 4.v)c(ax zero, is the electric field necessarily zero at all points on the surface? Explain. What about the converse:4v( x ).aacroz 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 radiust5(fr; fg)m) dpgr5wk r. If the wrfm tfp d5)r(k5);gg sphere is replaced by a cube of side r, will $\Phi_E$ be larger, smaller, or the same? Explain.

  

  How many electrons make up a chargez8ce8eh+m1i2) 2hkxt/v w 4xmo4 kvc l of $-30.0\mu C\,?$   $ \times10^{ 14}\, electrons $

  What is the magnitude of the electric force of attraction between a6ci*d,)f fy.sj z9 zuy1zv4ohn iron nucleususf649 zdho yjzcy*z1)vi,. f $(q\,=\,+26e)$ 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 75wb:w(x,rfbjc) zog evv+n-two protons $ 5.0 \times10^{ -15}\,m$ apart from each other in an atomic nucleus?    N

  What is the magnitude p+efjz y71j sf,gth79 of 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 of ikb 17u 0j)ahd$ 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 ad7vqgo(lr 3n-re 8.45 cm apart. They are moved, and the force on each of them is found to have been tripled. How-od(rqln g7v 3 far apart are they now?    cm

  A person scuffing her feet on a wool wbi4 5u :ocwgkp 4q*;prug on a dry day accumulates a net charge o *pkw4: pwug;5obcqi4f $-42\,\mu C\,.$ 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 all5 xp o0 wn7fd;zif,nk* the electrons in 1.0 kg of $H_2O\,?$    $ \times10^{ 7}\,C$

  Compare the electric force holding (kb+9zx w2 yw ufv0bmztv1ps5/yfrk (la(+ 7n 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 chnbs rzw5ve;q w: w3f7:u/,zjiarges are a fixed distance apart. The sum of their charges is Www:z,qe 5;vfn3: u riw7/sbjzhat charge must each have in order to
(a) maximize the electric force between them,
(b) minimize it?

  Particles of charge 1nt-h t+5qqux 5 6fg-a16gr-u bzlqcz $+75$,$+48$ 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 particl 8cg de)ppv(p 85xj8bbes of equal 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 plec3d-7 t vzsx6aced at each corner of a square 0.100 m on a side. Determine the magnitude and d7x3dz6s t-vce irection of the force on each charge.
$F_4$ =   $ \times10^{ 7}\,N$
$\theta$ =    $^{\circ}$

  Repeat Problem 14 for the case when two of th ec2d)4dioq.*fb z6q3,k pmvge positive charges, on opposite corners, are replaced by negative charges of the same magnitude (Fig)2qd. o z3dm,iekbg6 p*c4fqv . 16–51).
$F_4$ =   $ \times10^{ 7}\,N$
$\theta$ =    $^{\circ}$

  At each corner of a square of side l there are point oz6yvm)6o4n7 p iy; ircharges of magnitude Q, 2Q, 3Q, and 4Q (Fig. 16–52). Determine the force on (a) the charge 2Q, and (b) the charge 3Q, due to the zo6 ;i)nm74r6i pyv yoother 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/oe*,z qvtcamq-78(h u .qyq+ssk /tm the corners of an equilateral triangle of side 1.20 m (Fig. 16–53)q 7 ,8yu *+q -s.qemsm za/tvc/(oqkht. 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 bfgwpaf puo)c1s * 23*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 qk gj-m3:y 1gttotal charge of $90.0\,\mu C\,.$
(a) When placed 1.06 m apart, the force each exerts on the other is 12.0 N and is repulsive. What is the charge on each?    $ \times10^{ -6}\,C$$\;\;\;\;$    $ \times10^{ -6}\,C$
(b) What if the force were attractive?    $ \times10^{ -6}\,C$$\;\;\;\;$    $ \times10^{ -6}\,C$

  A charge Q is transferred from an initially uncharged plastic bawrb2y zn:2)vsm3 * fpuzdg0l8ll to an identical ball 12 cm away. The force of attractiod) b:fl mr3uz svpzn202*g8wyn is then 17 mN. How many electrons were transferred from one ball to the other?    $ \times10^{ 12}$ electrons

  What are the magnitude and d-sb,:y 1 grk l7pkb.juirection of the electric force on an electron in a uniform elerk j: .-sluk1b,pyb g7ctric field of strength $2360\,N/C$ that points due east?
   $ \times10^{ -16}\,N$
 ----待选择----westeast 

  A proton is released in a u. a23 1eqskhcvd*7mqcniform electric field, and it experiences an electric foc*1e3 2.haq 7k vsdqcmrce 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 exe5lmb;2aa3k1d7 vci m arted 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 magnituwu0-czf;f -xdde and direction of the electric field 20.0 cm directly above f-;cx0wzud-f an isolated $33.0 \times10^{ -6}\,C$ charge?    $ \times10^{6 }\,N/C$ ----待选择----updown 

  What is the magnitude of the accel nr5 7ek,a6:+ig:g d vm xtgxqhez)0(peration experienced by an electron in an electegg)5a e h6(nvxg d,7+irm pqk: :tz0xric 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 and dip *1lime;lf.e 9t t.ut9aw 6hyrection of the electric field at a point midway betweet 69t ;.l1t9.mhaeuwpif* lyen 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 point chargv vqkt8x.3t0yvn: smp2ta-s ;-c tw 6ges, $+Q$ and $-3Q$ which are a distance l apart.

  What is the electric 5vyx +zl c1kbb7d*r6yfield 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 g+zpunrw0o8- rest in a uniform electric field and accelerates to the nor zpogru8nw 0+-th 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 po cc/gsa/(vf.h59qykmta sa1 9 int 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 one0q)jvrfo/h uku w 3(yl:z.vk5 corner is occ)lyuh/(:5q rv3jok0uf zkw v.upied by a $+45.0\,\mu C\,$ charge and the other three are occupied by $-27\,\mu C\,$ charges.    $ \times10^{6 }\,N/C$ at    $^{\circ}\,$

  Calculate the electric 82/ 1cja bsefpuk)t0 j yxsl60field at one corner of a square 1.00 m on a side if the otyt 8e a/pxc2u 1blf6)k0s0 jsjher 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 electric field at the point P in s /i2yb6pd 9kgFig. 16–54. The ckdgs6 i9 2bp/yharges 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 electric f kxf-2 rxh76 winaya,vp7 witf a4ylwka81903ield $\vec{E}$ 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 electrtu)m)+5)akpa- qkpn lic field at points A and B in Fig. 16–57 due t)-t)p+n m5kukl aa pq)o 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 chakl -dg 6/ih;f;bagi3 zrges, $Q_1$ 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 f okw,pnqb:p1) ield at the point P shown in Fig. 16–59. The two charges are separated by a distance of 2a. Point P is on the perpendicular bisec p1wobnqk,p:)tor 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 elecnl;vfi e5; cz4tric field parallel to its direction of motion. If the electron is to be brought to rest in the space oi4lef;c5 ;n zvf 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 cbdpec -)9ip z+ubical 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 18oxa 5:r3e:*4o ) zkvkivi0poy cm is placed in a uniform electric field of magnitudeo3irk4oiyp*0 v: ko5vx)zae: $ 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 obj.myu: kjb;fj /alx)fgl 1q -.qects, $O_1$ 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 s6*guk,nwpus; w-3h8mxbu8mjt4 cc( 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 are 1.0hbi62x.qw uv 5 t3ahg1 m on a side and are separated by 3.0 cm. What is the charge on each plate (assume equal and oa263gq 1wb.xi5vhtu hpposite)? Neglect edge effects.    $ \times10^{-9 }\,C$

  The field just outside a 3.50-cm-radim/ po0iw; 8mcq/y v-ljus 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 x umehz7g (2ebn.sx 8286w bwy3.00 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 ucr6)5c.qn5wrq/d ; ja jfur3fncharged 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 q)/jan5w 5 rcf6 qu fd3;r.crjof 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 helix-shaped DNAf7l2+r g-zw gs7 )owc0fm mog+ molecule are held together by electrostatic forces as shown 7mwcgol7z2g sgfm -+wfo)0+r 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 themdvjaof) *0 rg(j1rv/z is equal to the weight of either at td(/)j*ag0 1r jorv vfzhe Earth’s surface?    m

  A 3.0-g copper penny has acqcblb*.; c p)/swk i+5xhy1 a 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 su bzh3vf/oo**u5 c ,cthere is an electric field surrounding the Earth. Its magnfos*uuzb3o/h*v c,c 5 itude is about $150\,N/C$ at the Earth’s surface and points inward toward the Earth’s center. What is the magnitude of the electric charge on the Earth? Is it positive or negative? [Hint: the electric field outside a uniformly charged sphere is the same as if all the charge were concentrated at its center.]    $ \times10^{5 }\,C$  ----待选择----positivenegative 

  (a) Given the local electric field of what zi;i;* okfc )pis the acceleration experienced by an electron near the surface of the Earti )oz fc;;i*pkh?    $ \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 0.018tha 6cha; mjn2-jrw 74tdpe/7+ml 8o(maek3p mm remains stationary in the air. If the downward-directed elm26lr ;w8-p3+(m/nop7a takch ad m4 tejhj e7ectric 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 between the CO group and the HN q3n2m.bis7*g p+np+otifzi m/ t (mm1group shown in Fig. 16–62. The Cmgf +iqtnot i 1.2+s7pi3mmbz(pn / m* 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 hydrogev8 *4;k+gzcwk+wl/a l oo c5 zak;.idjn atom, the electron revolves in a circular orbit around the proton witio j;ld;k4kza .*lk cw+5a gc8 /vw+zoh 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, ratht 7/ al:u8drqmer than gravity, were responsible for holdim a/ur:tq dl78ng 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 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 speexk ob,w d(k .s32pzj-kh*m9 cqd $v_0\,=\, 21.5\times10^{6}\,m/s$ 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 chargekfa87 hct) wlhq45mfx ck) q:- $Q_1\,=\, 2.5\times10^{-5}\,C$. 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 plastici e6eey+ dh/zbj*z9w3 and suspended vertically fromi9e6+zj be*yzh /w3e d 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 ar/v0b m,bg8uo he 78-cm-long wires with tiny 24-g spheres at the ends. When charged, nearly8,b ug/b0ovh m all the charge resides on the spheres. If the wires each make a $30^{\circ}$ angle with the vertical (Fig. 16–64), what total charge Q must have been applied to the electroscope? Ignore the mass of the wires.    $ \times10^{-6 }\,CC$

  Dry air will break down and generate a spark if the electric field exceeds ab 60ztjv9vx q n/w.+sa, xjbjy1out x0az9y/ x b6,1j. nqtwsvjj+v $ 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 chargl j4+g -(y,90ffdmqn.ak9 8qkzd djuoe $+0.340\,\mu C$, 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 t,x pqj( qu8fq-he electrons in a 15-kg bar of aluminum?    $ \times10^{8 }\,C$What is the net charge of the bar?    C (Aluminum has 13 electrons per atom and an atomic mass of 27 u.)

Two small, identical conducting spheres A and B are a distance R am2-lisn * nh)opart; each carries the same charge Q. (a) What is the force sphere B exerts on sphere A? (b) An identical sphere with zero charge, *-h2 )nmlnsio 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 shown in Fig. 16–68, atgy8xjt d4 ,af4 what position(s) x is the electric field zero? Is the field y8adfg,jt 4x 4zero 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 pd4 vmx )s+8quaoint 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?