If you charge a pocket comb by rubbing it vsew q sb0(l8+with a silk scarf, how can you determinebwlsev0(q s+8 if the comb is positively or negatively charged?

Why does a shirt or blouse taken from a clothes dryer sf4j,w(zzcu7 vh1 uyo1ometimes cling to your body?yhc 1z,(w147ofzuvu j

Explain why fog or rain droplets tend to form around ions or d.u /.bw(9pl6szk7 v jtp2wz xelectrons in the air.ju.p97vlz .pxwkt/(z 6s bdw2

A positively charged rod is brought close to a neutral piece s o45qvva3/:xe hkdl :of paper, which it attracts. Draw a diagram soh vkv/35d esa4x::q lhowing the separation of charge and explain why attraction occurs.

Why does a plastic ruler that has been rubbed with a cloth have 9j3gvb-f;xg;6/ok6 c.t3xh5 tlce xgtj alz 3the ability to pick up smalgk3lc 9 xj j-cohg3 / tx65xa6etfv3z ;t.;blgl pieces of paper? Why is this difficult to do on a humid day?

Contrast the net charge on a conductor to the “free charges” in the condzc6f): 4n4wzowigq7 b uctor.

Figures 16–7 and 16–8 show how a charged rod placed near an usmaub /v47 cx+mdn.p5ncharged metal object can attract (or repel) electrons. There are a great many elev/dm4s7p+nau b5x m.cctrons in the metal, yet only some of them move as shown. Why not all of them?

When an electroscope is charged, its two leaves repel each other and remai. 5z)fp. 6(aolive tu bf/d.npn at an angle. What balances the electric force of repulsion so that the leaves don’t separlb(udf n.pifz/o6)..e vatp 5 ate further?

The form of Coulomb’s law is very sim.w-6 z oyw:fup ysfhy2te;q*9 ilar to that for Newton’s law of universal gravitation. What are the differences between these two lay6pw.fyey9q*ws-u ;:t f z 2hows? Compare also gravitational mass and electric charge.

We are not normally aware of the gravitational or elepkobtr/r2w:u47 6 dljctric force between two ordinary objects. What is the reason in each case? Give ab: rk/rdp7lj6 o4t w2un example where we are aware of each one and why.

Is the electric force a conservative force? W ah*cd t77/tdzl5 hp50qrzh .ahy or why not? (See Chapter 6.)

When a charged ruler attracts smaboy706ppg m-s ll pieces of paper, sometimes a piece jumps quickly away after touching the ruler. po6ybmp-07s g Explain.

Explain why the test charges we use when measuring electric fields must be sm -,tz -pextx)mc3e4 fkallm etx4) cpxt,-f zek-3.

When determining an electric fiel.7/ jodld jj4vd, must we use a positive test charge, or would a negative one do as well? Expla4 7ljj.dd/ jvoin.

Draw the electric field lines surround2xk37 en3pftqfsv.g.ing two negative electric charges a distance l.nxp ek7vst qf. g23f3 apart.

Assume that the two opposite charges i7(ke leidsv w4zbc, v89v zduz40 0n4un Fig. 16–31a 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, bzu zs(nb4 d0v,z c09 vklew44vi7u8e dottom, left, or right — is the electric field the strongest? The weakest? Explain.

Consider the electric field at points zs 7jsq9zgio o2st/7 9A, B, and C in Fig. 16–48. First draw an arrow at each point indicating the direction of the net force that a positive test chars7oszjsitq2/99 g 7oz ge 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 crmat+y o xm ma5c)tukle1:(8tu, p07oloss?

Show, using the three rules for field lines given in n ;i5*xs rm56ense2ge Section 16–8, that the electric field lines starting or ending on a single point charge must be symmetrically spac;n2ies 5* rm65xseegned around the charge.

Given two point charges Q :s)/rmj7dp dvand 2Q, a distance 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/v)j 7sr ddmp: where this point will be.

Consider a small positive test charge located on an electric field line 0v4wbpvj*of fsy*3 /g at some point, such as point P in Fig. 16–31a. / p wybvj4vfo*f g03s*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 of charge which is iazf h xztsc:/.md6 o n(.gg,)lnfinitely long. (Hint: Use symmetry.) Is the electric field unifs6.zm zxtc n( / dfl.,h:g)aogorm in strength?

If the electric flux through a clomudf -r* ,qe3o/tbo 20uf6ur gsed surface is zero, is the electric field necessarily zero at all 0m r r2fu qeu/*o ub-f6go3d,tpoints 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 gaussian surface of radius r. 9mewz4f;rp*y c/uuxy,9b-e s If the sphere is replaced by a cube of si;94mxyecsp9e rbu z*,wu -yf/de r, will $\Phi_E$ be larger, smaller, or the same? Explain.

  

  How many electrons make up a charge of 5u/q9lk 4v4om.jr g o dd-1eor$-30.0\mu C\,?$   $ \times10^{ 14}\, electrons $

  What is the magnitude of the electric force of attraction s,4mf n+wgg6i between an iron nucleus g46fni ,wg+sm$(q\,=\,+26e)$ and its innermost electron if the distance between them is $ 1.5\times10^{-12 }\,m\,?$    $ \times10^{-3 }N$

  What is the repulsive electrica8oxf o*gy3pt 3l force between two protons $ 5.0 \times10^{ -15}\,m$ apart from each other in an atomic nucleus?    N

  What is the magnitude of tg*xv (kuok.. rhe force a $+25\,\mu C\,C$ charge exerts on a $+\,3.0\,mC$ charge 35 cm away?    N

  Two charged dust particles exert a o6kc(jxcd 0kn/g 9,ch 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. T9(ih 6o byetd)hey are moved, and the force on each of them is found to have been tripled. How far apart are they now?d thbeoi6(9y)    cm

  A person scuffing her feet on a wool rug on a dry day accumulates a net charge ohb3t9qty 40b) jhp, hn3:xlyxl y,bn 0h9t3ybxh:hpj4 xq)t 3f $-42\,\mu C\,.$ 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 electy+gqzn2 4brqyk+vq,2 rons in 1.0 kg of $H_2O\,?$    $ \times10^{ 7}\,C$

  Compare the electric force ho vg:hdicwx 4 g)5ftx8*75wjm nlding the electron in orbit $(r\,=\,0.53 \times10^{-10 }\,m)$ around the proton nucleus of the hydrogen atom, with the gravitational force between the same electron and proton. What is the ratio of these two forces?    $ \times10^{39 }\,C$

Two positive point charges arv/ n1qs 2*ojcse a fixed distance apart. The sum of their charges is What charge mus*qnv1ojs cs2 /t each have in order to
(a) maximize the electric force between them,
(b) minimize it?

  Particles of charge (.xf) fwdd pxe )rc.*u$+75$,$+48$ 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 charge)mdlw:a6 n b1( rlsrq*, $+11.0\,\mu C\,$ 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 o4hb6 .i6 ,t9v( deohf, nwvzmfn a side. Determine the magnitude and direction of the force on eac,f n6owhfmz ,teh9 d4(.6iv bvh charge.
$F_4$ =   $ \times10^{ 7}\,N$
$\theta$ =    $^{\circ}$

  Repeat Problem 14 for the case when two of the positive charges, on opgc0 sun 7o2 j;6fzg,ofposite corners, are replaced by7oggjcs6o f0, z2nf; u negative charges of the same magnitude (Fig. 16–51).
$F_4$ =   $ \times10^{ 7}\,N$
$\theta$ =    $^{\circ}$

  At each corner of a squa:l6r) x fp9-9f(tlfcbz7 ku0ziys i3zre of side l there are point charges of magnitude Q, 2Q, 3Q, and 4Q (Fig. 16–52). Detertri z:x90b9fki 6l73 -u(p fzyslc zf)mine 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 co yzr4m. )k;zsjrners of an equilateral triangle of side 1.20 s)r kzzjy m;.4m (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 charge g.d jlx93xip.::cu6rqh zl g: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 charg1;o zg x46d7lbp*pxcc e 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 gn/q e7m. cctrnq2i2w78g 2oxinitially uncharged plastic ball to an identical ball 12 cm away. The fog7q/wtqc2 n ox 8nr m2gic.e72rce 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 dn,5w8huk ikh kj+(s z(irection of the electric force on an electron in a uniform electric field hk((5juzw8 +hns,ik kof 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 experlq*ct+ 3x(o3g 3te0my spk: bgiences an electric force ofm goe *qctkxl b3p3t 0gs3y:+( $ 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 on aynxxm oobuwh 5+):bftk(8p,4 $-8.8\,\mu C\,$ 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 directin y bzo*zij/ti 2s )t*).l;fu y4innm4on of the electric field 20.0 cm directly above an is f)i*i4bm/.u znyjz t2nlo s;n4ti)y*olated $33.0 \times10^{ -6}\,C$ charge?    $ \times10^{6 }\,N/C$ ----待选择----updown 

  What is the magnitude of o4kj )nb8ub xfm4,e-y the acceleration experienced by an electron in an electric fbn jf ,-xybom eu8k)44ield of $750\,N/C\,?$ How does the direction of the acceleration depend on the direction of the field at that point?    $ \times10^{ 14}\,m/s^2$  ----待选择----opposite to the field in line with the direction of the field 

  What are the magnitude and direction of the electric field at pmv43,*xo n h g1ln(gra point midway betngh r *np mo,lg31x4v(ween 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 +v-) gnw*psr ad9j l0nfield 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 whe1)o ytdnwx4 0 d9i 0a;s2dianrre 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 fieldpbv 7d5z ou71edtj83u and accelerates to the north at a rate of tdo8177 epjzb53vdu u$115\,m/s^2\,.$ 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 om3- qbd,vke4 epposite 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 fieex/ m gkc.(r,ild at the center of a square 52.5 cm on a side if one corner is occupied bg (, xeircm/k.y 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 corn/ dgtc rw)oli/y:rs/+b)xwo6er of a square 1.00 m on a side if the other three corners are occud6)oxs b wi:+ rwrt /)gycl//opied by $ 2.25\times10^{-6 }\,C$ charges.    $ \times10^{4 }\,N/C$   $^{\circ}\,$ from the x-direction.

Determine the direction and magnitunsh.(,1 afl etde of the electric field at the point P in Fig. 16–54. The charges are separated by a distance 2a, and poinetl,( shf1a.n t 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 elec)t3 4w k li1wh7avgo;n(ms1/f ne;p betric 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 djuasf:)pkj 9 ke6k 8gh)8zcr- etermine the magnitude and direction of the electric field at points A and B in Fig. 16–57 due to the two pos) :ka8ku-s9krz)jfp6 g8 e hjcitive 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 poip9 ub -ky6 ;nxmp3bzmmq.vtj, ct) ;q5nt 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 the point P sho*f y8 vu)kzcdsvmvs)halr;+ *jiz +dhk) b112 wn in Fig. 16–59.z )8j yv;dd rhv*al+b)i zuf1k)+vk m1*ssh2c 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 , .hjxxia3u;xicl5-ddk c,u0 at 1.0% the speed of light enters a uniform electric field parallel to its direction of motion. If the x5x ahui3kcj xdu 0;i, l,-dc.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 28.0 cm onr5)0i)2l+9/v emhc),e kqf5hwt sijsjjfon 2 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 electrip; -s s277 idayr)txeg 0cd* rwftv(-fc field of magnitudeptrd*rx0(f7ewft; 7-civgdya s2s -) $ 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 objes7bn*z u wgjxoikm5/2-: 1ueali0- rdcts, $O_1$ 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 u l:zxyl 5ptr,86 vs h/n.uq4vdniform 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 T4k3 ik3 i2zv:qemcp8 dhe plates are 1.0 m on a side and are separated by 3p vik23q3dkmce:iz 84.0 cm. What is the charge on each plate (assume equal and opposite)? Neglect edge effects.    $ \times10^{-9 }\,C$

  The field just outside a c 6rl;r .zr4yt3.50-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 m carries a total char0n 5+ymd /p1:uy( ;jdfjbtywcge 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 spherical conducti ;i3cn ei+ o +.hcje*dr(pjw*ung 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) injn;+wc.ju odh* cie e3rip*( +side 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 0rv q6m,x0 rhbmolecule are held together by electrostatic forces as shown in Fig. 16–44. Assume that the net average charge (due to electron sharing) indqrvxm60rhb ,0icated 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 equ ry u;wz0ybgu*kax,d.p+a32i i iwb:)al to the weight of either at the+i3bg2y0a :b)a,w pyd*zi rk;.uwui x Earth’s surface?    m

  A 3.0-g copper penny has a positive charfnqi, t+;/k ug 8llob6ge 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 ele 8wbj) 7s*wdxoomx5w/ctric field surrounding the Earth. Its magnitu jxox8dm*/wobsw 7w5)de 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 e*m/ 1 gldpj-jxlectric field of what is the acceleration experienced by an electron near the surface of the Ear1dj/mp-*j g xlth?    $ \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 stationary in the air. If the kcfr56hc 72u g*(px brdownward-directed b rcr2*uf (k7g56c xhpelectric 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 group shown in Fig.mzrn:*7h(tc g;8ue b0u;cdek 16–62. The C and O have cc hz*8gn(; :k7t; e mredb0uucharges $\pm0.40e$, 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 electronhae3a9y: i, zx revolves in a circular orbit around,9zhx i3:yeaa 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, were responsible fgsz- 0cdjx(nhu8)qtrr. rd :lnnb 1/qm 04)vv or 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 pretd l8rs/nr xg juq.)z4(cn )0 mnq r1hvd:0v-bsent 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 spe1qfh sh -*2gd 3ychue3ed $v_0\,=\, 21.5\times10^{6}\,m/s$ 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 charga 6ja 99px0thce $Q_1\,=\, 2.5\times10^{-5}\,C$. 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 en8,u. kvlk r :) yg6rbwvs++yztcased in insulating plastic and suspended vertically from an bvy). 8 ,6vtrrwky :g+ lukzs+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 areufki/ -3fly*nw42dltg;m. e(ra j 1 mv 78-cm-long wires with tiny 24-g spheres at the ends. When charged, nearly all the y(4/amm3d ulltj.ffg riew v1kn 2 -*;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 elemm(g otw) u kg(lt: 1x;6f7bswx99 b;wxfoqa,ctric field exceeds about ok)x:bmxtfml; x;wgf( q (w6buw 9 ,s791ogta$ 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 0.2zi :fr 91em ;ac(ctszrt8 el +o(l1+hz10 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 a5 jb:.hzvp6o;q os4h oll the 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 distanc5qqimpg3 i/oct9 8ow 9e 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, sph9q3iito oq 9c8pwmg5/ ere 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, at whatvu.bn. o/vka6 e2 2ux/jp2pue ro*ne )(ea5tl position(s) x is the electric fiep*6nu/o/ve22 .2 vre) k auoj.ulpeaxnt(b5e ld zero? Is the field zero at any other points, not on the x axis?

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

Four equal positive point:jo2o, syvi ng -+6svl 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?