If you charge a pockdfy. jpbr ,t:kh 0zf (x)l+v7yet comb by rubbing it with a silk scarf, how can you determine if the comb is positively or nega :j h7vfx )y.(0,ktzypflrd+b tively charged?

Why does a shirt or blouse taken from a clothesy 4wk*v0wzc a( dryer sometimes cling to your body? k4cw0yv*a(zw

Explain why fog or rain droplets tend to form around ions or e9ov gziep8 b3lp (ph,7c0pt7electrons in the ait,(po le7h9 b7c3pip pze80vg r.

A positively charged rod is brought close tom/(a 6aqdwhg 6(nc.yz a neutral piece of paper, which it a yq(n/6(d.achgmw6z attracts. Draw a diagram showing the separation of charge and explain why attraction occurs.

Why does a plastic ruler that has) aer f)9lctz4l c;3px been rubbed with a cloth have the ability to pick up small pieces of paper? Why is this difficult to dolar9ec ;x 4t )z3cfp)l on a humid day?

Contrast the net charge on a coqfu :te9vbm /r-qx t(0nductor to the “free charges” in the conductor.

Figures 16–7 and 16–8 show how a c ec// *uh6.xcvw1w uunfboa7*harged rod placed near an uncharged metal object can attract (or repel) electrons. Thubxw cuuwv/hnf c. *a67/*o 1eere are 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 leaveszn hs 0 t tvd mxj-loc69f3r*/(dqb86d repel each other and remain at an angle. What balances the electric force of repulsion so that the leaves don’t separate further?06fvo-jr/x*hq dd3csbn9lt t8 (m6 d z

The form of Coulomb’s law is very similar to that for Newton’c2w(60x s jmel.jw 0fms law of universal j0.s jm0we(wx26fm lcgravitation. What are the differences between these two laws? Compare also gravitational mass and electric charge.

We are not normally aware of the gravitational or electric forq ;tn4e;bkr /kt3dxrcd+ 03skce between two ordinary objects. What is the reason in each case? Give an example where we are aware ofk4 rxt 3s3ndct0+b;k q;erdk/ each one and why.

Is the electric force a conservative force? Why638lph2s ye p72xg uqb or why not? (See Chapter 6.)

When a charged ruler attracts small piqr nu:/nr/m ,zeces of paper, sometimes a piece jumps quickly away /ruq/,mzr: n nafter touching the ruler. Explain.

Explain why the test charges we use when measuring v qc1,(2(b etg8j ovmi04l/hdy rkw, telectric fields must be smallh dkqtgyi4vb( c(w lrtv28 /, ,meo1j0.

When determining an electric oeiqa* b(74 fly7py- dfield, must we use a positive test charge, or would a negative one do as welblyof-pi47* 7aeq(d yl? Explain.

Draw the electric field lines su3a yz)*3ky onqrrounding two negative electric charges a distance l apart.3 oanqzy) 3y*k

Assume that the two opposite charges in Fig. 16–310jxc2 gdlxp 48ik44 nca are 12.0 cm apart. Consider the magnitude of the electric field 2.5 cm frdix0 xgc 44 2l48jpnkcom 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)bjw 3i;fgk1 uxfx4c.pw7tp3. 16–48. First draw an arro ;74tg1kbx).w3 fx ip3cw fpujw at each point indicating the direction of the net force that a positive test charge would experience if placed at that point, then list the points in order of decreasing field strength (strongest first).

Why can electric field lines never eerafrx*q 7lv sn1: 8,cross?

Show, using the three rules for i6h13d1wg kszk-rc)u field lines given in Section 16–8, that the elecu1)k3siw1 6cr k-hdgztric field lines starting 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 44dew)90myb :pujth/ cxb m9ipoint along the straight line that passes through them where E=0 when their signs are (a) opposite, (b) the same? I0h u49 4/m9m)by ijtxpce:b dwf yes, state roughly where this point will be.

Consider a small positive test charge located on an electric field 5 e-qlit (zt()zaee -lline at some point, such as point P in Fig. 16–31a. Is the direction of the velocity and/or acceleration of the test charge along this(azze5te)le(i l-tq - line? Discuss.

Sketch the electric field lines for a uniform line of charge which isn:3ycyvgv g-y;zqoi*p 7 o-2j d+5 rys infinitely long. (Hint: Use symmetry.) Is the electric fiel yd3;sg *-nqi25:zypvyrv 7yo+-jgc od uniform in strength?

If the electric flux through a closed su8smig uefb 7r662s ol 6pp g+2bv)4veqrface is zero, is the electric field necessarily zero at all points on the surface? Explain. Wha 2fl664ib6e)svmp s ope7r8gv2q ug+ bt 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 g:9w ox auk-trdlp7:7cd 9 .sua spherical gaussian surface of radius r. If the sphere is replaced bycx9 :9kotr7s al.p-:dwguu d7 a cube of side r, will $\Phi_E$ be larger, smaller, or the same? Explain.

  

  How many electrons make up)5dkl5 yj jbf(. dlm *rpq/wc7 a charge of $-30.0\mu C\,?$   $ \times10^{ 14}\, electrons $

  What is the magnitude of the electric force of attraction between an iron nqe,-lq+2h q(qsof mu2pv2 ,tmucleup-2m+ omqts, (u,lqq2hfeq v 2s $(q\,=\,+26e)$ and its innermost electron if the distance between them is $ 1.5\times10^{-12 }\,m\,?$    $ \times10^{-3 }N$

  What is the repulsive electrical force bet;hz elg jx:*;4cs o9y 0hzu)uqween two protons $ 5.0 \times10^{ -15}\,m$ apart from each other in an atomic nucleus?    N

  What is the magnitude of u owfih(t+v*3,fx uht-6p.i uthe force a $+25\,\mu C\,C$ charge exerts on a $+\,3.0\,mC$ charge 35 cm away?    N

  Two charged dust particles zv rofm (+6ni8exert 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 b,tibxb, 8na88.45 cm apart. They are moved, and the force on each of them is foundt n 8,xba8bib, to have been tripled. How far apart are they now?    cm

  A person scuffing he fx18)q,fjq car feet on a wool rug on a dry day accumulates a net charge of,q cf 8xf)aj1q $-42\,\mu C\,.$ 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 alje:.hd3bebo/tl ,v9 c l the electrons in 1.0 kg of $H_2O\,?$    $ \times10^{ 7}\,C$

  Compare the electric force holding tnv6+gilx 1 ed2yf-r5 dhe 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 are a fixed distance apart. The sugu2ydy.- x 75 hcb dif1k*xd3xm of their charges is What charge must each have in oric- xxyd.k25 x hgy7fd*b u1d3der to
(a) maximize the electric force between them,
(b) minimize it?

  Particles of charge id-b8kcwz rg18(hu2r $+75$,$+48$ 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/d(e-d slc s vdz/ et 5/v54m+tkv cxjw)qa60ses 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 placed,jiizy7 a m-i, at each corner of a square 0.100 m on a side. Determine the magnitude and direction of the,-ai,iyz mij7 force on each charge.
$F_4$ =   $ \times10^{ 7}\,N$
$\theta$ =    $^{\circ}$

  Repeat Problem 14 for the case when two d4 kbmo j2n*8ri,hay0 of the positive charges, on opposite corners, are replaced by negative charges of the same magnitude (Fig o2jdr in, y8m0*hka4b. 16–51).
$F_4$ =   $ \times10^{ 7}\,N$
$\theta$ =    $^{\circ}$

  At each corner of a square of side l there are point charges of magnitubzo2c+wwgxq1+.f-d, p ck,wu de Q, 2Q, 3Q, and 4Q (Fig. 16–52). Determine the force on (a) the 1p.d cbww2fq+-+g wk zo, uc,xcharge 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 particlesibagvam4/ q.mm(.+ v u+sgd3 s are placed at the corners of an equilateral triangle of side 1.20 m (Fig. 16–53). The chargesigu.3+sd.mm+v( a bsqma4 /gv 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 charge8)e lk 0( 7h9vyzomkzq 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 chargeew+nz bks3gv;5 *uitc9 ,* pyy 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 plrmm:p 7aj0, ,m0qaov pastic ball to an identical ball 12 cm awm0ra pm,mav,7oq p:j0 ay. The 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 electric force onyu*mf p/ /5;f/dua9xd5umxvophq 1+k an electron in a uniform electric fiel u/15q/5fu mo/a*+xfpy du mhp;x9vd kd 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 eleo4g* 7 i-vkmilh ,9aructric force ugiiv,- hl7 o4*mk 9arof $ 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., 3 nk -dgs-6:m3gyk d 00pdhedavnv-j4 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 electric field 20.0 cm dire5p .ublota / ,m2ku 5diwo.n-xctly above an isolatbkl.n. -/puuid 2a5,m wo5 oxted $33.0 \times10^{ -6}\,C$ charge?    $ \times10^{6 }\,N/C$ ----待选择----updown 

  What is the magnitude of the acceleration experienced by an8-d jnz6nbf6:- jix:kira-x e electron in an electric field of : zbki-xn-i-6:6fd8 ajnjerx$750\,N/C\,?$ 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 electro 1p5sl9 .7c*6tfs folb -ihvric field at a point midway between ah.5 tlrsff7li- ovp*91bsc6o $-8.0\,\mu C\,$ 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 charges, 7f6w6w )6ntctym ni)q$+Q$ and $-3Q$ which are a distance l apart.

  What is the electric field strength at a pfc9a gbon2 1j)7kus/84v1dyg:pwg0 hqk cw /s oint 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 elect9ninu 8 /d5nwfric field and accelerates to then/ nw9udni85 f 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 biqf /9 atb mx(vfmy1bo4n7,4uut 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 at the center of a square 52.5 cm on a side if onoj/ - tbttqx-r2s.vk)e corner is occupi-r ./skq)b tv-j otxt2ed by a $+45.0\,\mu C\,$ charge and the other three are occupied by $-27\,\mu C\,$ charges.    $ \times10^{6 }\,N/C$ at    $^{\circ}\,$

  Calculate the electric field at one corneutp b7wj j,y6 34x(poar of a square 1.00 m on a side if the other three cornerto 4ap jwb6j(px, u73ys 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 at7e/t s .dvn, rs e)jkq/ q8xtxlr19n1m the point P in Fig. 16–54. The charges are separated by a distance 2a, and point P is a distance x from the midpoinlj7.e )sdrmt 9n1/xq/vn t1 xsk ,8reqt 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 fielyi)g *eiw s7i9d $\vec{E}$ 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 detxn+s ksce kl e97(py2*ermine the magnitude and direction of the electric field at points A and B in Fig. 16–57 due to the two positiv 7+2ksnxee* l(sckpy9e 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 un,eqzz brz gb8 cj yhle76:.,d3qdy)i8 known point charges, $Q_1$ and $Q_2$ At a point on the line joining them, one-third of the way from $Q_1$ to $Q_2$, the electric field is zero (Fig. 16–58). What is the ratio $Q_1/Q_2\,?$   

Determine the direction and magnitude of themy5ckrtp33r: g3m(i j electric field at the point P shown in Figc mk3ir3tmrpy35: j(g. 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 tyv2qr +z g.z:q2da e/of light enters a uniform electric field parallel to its direction of motion. If the electron is to be brought to rest in the space of 4.0 czvd/zqt.: y qag+ 2re2m,
(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)3mzg4 bqdlp*gs:wjn*9s p 9l box 28.0 cm on a side is $1.45 \times10^{3 }\,N\cdot m^2/C$. What charge is enclosed by the box?    $ \times10^{ -8}\,C$

  A flat circle of radius 18 cm is placed in a uniform eldr,k0wu6skmj- h+vk nu ;dr8vzmm :-6ectric field of magnitude+v jukw6d-0uvk -zkmnr 6,dr8sh;: mm $ 5.8\times10^{2 }\,N/C$ What is the electric flux through the circle when its face is
(a) perpendicular to the field lines,    $N\cdot m^2/C$
(b) at 45° to the field lines,    $N\cdot m^2/C$
(c) parallel to the field lines?   

  In Fig. 16–61, two objects,ervne48:lwu.b : u4i d9gp/tt $O_1$ 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 h ,tb;0,hi nyeu-:nol em)t z2field $ 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 plat 7om aaa5k:8iams0 1fbr0)mkhes is The plates are 1.0 m on a side and are separaio:k0 1bmf7hsk8 aa 0maarm5 )ted by 3.0 cm. What is the charge on each plate (assume equal and opposite)? Neglect edge effects.    $ \times10^{-9 }\,C$

  The field just outside a 3.5g*omk;fh0 db00-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 o(h hnd8-hzbzw2;l3 c;fba 1 om 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 spherical condups x31( exh)zgcting shell. (See Fig. 16–33.) What is the electric field E as a function of r (a) for r less than the inner radius 3( )gpex sxzh1of 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 DNA mt l,v18;w3 e ws( vac5fv 2wmhp0kvrv:olecule are held 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 O atoms is 0.4e. Assume also that atoms 2wwp(5r8v;lev khfsvc0vtamw:3,v 1on 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 equal9h f v;c ;f8mvn3,mswd to the wevm8;,mfds v;9 nf3hc wight of either at the Earth’s surface?    m

  A 3.0-g copper penny hd 8q ,2s(tpgu5t2)ku fk/nspkas 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 there is an electric field surrounding 7h lk+ 4v*lymdb53gxuthe Earth. Its magnitude is abouhl* 7ug+v bxkl54m dy3t $150\,N/C$ 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 is the j u 9/v 14xei/dqvxbe,acceleration experienced by an electron ne eq u41v9v/jxxdib, /ear 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 m8iw6 mndpo5eq.- nw-.018 mm remains stationary in the air. If the downward-directed electric field of theq8e.mnp m 6din-w w5o- 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 thel0.u 3 al,itmstvj ,y; HN group shown in Fig. 16–62. The C and O hasyvu, i,aj;t 3.lml t0ve charges $\pm0.40e$, and the H and N have charges $\pm0.20e$, where $e\,=\, 1.6\times10^{-19}\,C$. [Hint: Do not include the “internal” forces between C and O, or between H and N.]    $ \times10^{ -10}\,NN$

  In a simple model of the hydrogen atom, the electron revolc) 4 -9yh7b kejn.pci-;svpegves in a circular orbit around the proton with s7 jc.bchne4;9ykip- v p) eg-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 gravitvaq4w7lmib7; y, were responsible for holding the Moon in orbit around vbli;w747qam 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 speedp,xkcs4g,b ejhvs4) c(abj01,5 pgah $v_0\,=\, 21.5\times10^{6}\,m/s$ 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 char:/wbu qpp5ku3xipz+ g0hr:2r ge $Q_1\,=\, 2.5\times10^{-5}\,C$. 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 suspen5x q.(1lxn fpb kj)*kdded vertically from an ideal l5kdk.n j )1* b(xqfpxspring $(k\,=\,126N/m)$ 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 “leac6r8z.g jomxu3 + d tq2fi9vn*ves” that are 78-cm-long wires with tiny 24-g spheres at the ends. When charged, nearly all the charge resides on the spheres. If the wires each maketor. c2d q9fmgxz*6n3 8i vu+j 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 a 42 3neea9qjqu6nx2o 1fqbwy5 boutbe 2 39a wxonye1u5qnq2qj6 f4 $ 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 03b nx0of rz4*feq2 kinet charge $+0.340\,\mu C$, hangs at rest at the end of an insulating string above a large sheet of charge. The horizontal sheet of uniform charge creates a uniform vertical electric field in the vicinity of the point charge. The tension in the string is measured to be 5.67 N. Calculate the magnitude and direction of the electric field due to the sheet of charge (Fig. 16–67).    $ \times10^{7 }\,N/C$  ----待选择----updown 

  What is the total charge of all the electrons in a 15-kg bar of a 3 +4hxj60.fzqu qpszxluminum?    $ \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 spheresi+l0/w j *72q3q c dv s3mwiv(g1daucd 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 sphe/ ldqw13a3w2*vjc7dm+g uc(0dvi qisre 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 ivh4 w /z3yj-tjs the electric field zero? Is the field zero at any other points, not on the x axis?/z v4jy w-h3jt

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 w f4jo-go9.oecharges, 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?