If you charge a pocket comb by rubbing it with a silk scarf, how can yenw:cj r) 62qhou determine if the comb is positicj w:n6rh2eq)vely or negatively charged?

Why does a shirt or blouseecsq( eg.-3y eu n1p/scb e46q taken from a clothes dryer sometimes cling to your bodye /bn sq.sq(3 e4puee yc61cg-?

Explain why fog or rauov )56a1fg liin droplets tend to form around ions or electrons in the aiv16)luga5f oi r.

A positively charged rod is brought close to a neutral piece of paper, whi/i9 gjm y6j6trch it attracts. Draw a diagram showing the separation of charge and explain why at jt/iy6jg6 9rmtraction occurs.

Why does a plastic ruler that has been rubbed with a cloth have the ability h vyotrzs7r76 7e8tf: to pick up smt 7s6h z7e7 yv8:ofrrtall pieces of paper? Why is this difficult to do on a humid day?

Contrast the net charge on a conductor to the “fre;3ynr(w xk(xue charges” in the conductor.

Figures 16–7 and 16–8 show how a charged rod placed near an uncharged 0)ub7 c*+ tq.e mpianf3euw a g+ci)-smetal object can attract (or repel) electrons. There are a great many electrons in the metsieaec) .m7 3gupcqb t wafn0)++ui* -al, yet only some of them move as shown. Why not all of them?

When an electroscope is charged, ijjp wnqx(svu)iw2m7mr03m3.*c /zxsts two leaves repel each other and remain at an angle. What balances the electric force of repulsion so that the leaves donv2 3(m/jm .xi) s3pxm7*sr0 wqcj uznw’t separate further?

The form of Coulomb’s law is very similar to that for Newton’nkmy80dp s44f/q 8vur s law of universal gravitation. What are the differences between these two laws? Compare also gravitational mass and electric chvfpr4m 0 8qk8 /yn4usdarge.

We are not normally aware of thsy 1,w o0pqo,f- a+kape gravitational or electric force between two ordinary objects. Whk1 0wp aqy,p,os fao+-at is the reason in each case? Give an example where we are aware of each one and why.

Is the electric force a conservative force? Why or +oc4rq:atjd0 why not? (See Chapter 6.)

When a charged ruler attracts small pieces of paper,(trrg0 7 1pn/gpb m)e9rznz;upz9k 0k sometimes a piece jumps quitp9 n) neb9 rp0up ;/mkr 0z7rggz1z(kckly away after touching the ruler. Explain.

Explain why the test charges we use when measur)(tjv1 b *,+gixtgxxr63j kgp ing electric fields must be small xj 6k*tp1, j bx+ggxt)r(v3ig.

When determining an electric x+ n kt,9coawo4:+yig50hx) wlgm (qxfield, must we use a positive test charge, or would a negative on9 )40x 5c,wlqkto o iyg:+nxahgxw+m(e do as well? Explain.

Draw the electric field lines su+ms4pcue)i1r l18ols s3qp 5mj5pxk :rrounding two negative electric charges a distancesx e4m5s3+p8jpluops: 5 i1clq)1rkm l apart.

Assume that the two opposite charges in Fig. 16–31a arka0u6.+q me7:hu z6xbnitor br kv6.:e 12.0 cm apart. Consider the magnitude of the electric field 2.5 cm from the positive charge. Onbr xni:k ou67.u+. z tbhamq0rkv6e6: 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 afl; t0h ,(.y gq6txondrrow at each point indicating the direction of the net force that a positive test charge would experience if placed at that poil.n,hyt txdg 06f; oq(nt, then list the points in order of decreasing field strength (strongest first).

Why can electric field lines fnkzlcz r 8l tkv56*7g6v/d j7hcju1m3yz ,6 cnever cross?

Show, using the three rules for field lines given in Section 16–8, that the )jn 5k4n ,igqlelectric field li5kjq,n4g i)nl nes starting or ending on a single point charge must be symmetrically spaced around the charge.

Given two point charges Q and 2Q, avgk*wjgwkjdpy d*4 m4/mb 92aim4jh2/s55 s c distance l apart, is there a point along the straight line t w/m9bg g/445mmdy* 2d ikwh54vjjc sjas2 kp*hat 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 on.y/qk 1akp-th i cp52m an electric field line at some point, such as point P in Fig. 16–31a. Is the direction o1thk 5 apk/.yc-q m2pif the velocity and/or acceleration of the test charge along this line? Discuss.

Sketch the electric field linesu fgjl-1m. ho, for a uniform line of charge which is infinitely long. (Hint: Use -l.,1mugj ho fsymmetry.) Is the electric field uniform in strength?

If the electric flux through a closed surface is zero, is the-mg2.xw t ffb4p c.,om electric field necessarily zero at aloxm gptfbw,m..2f- 4cl points on the surface? Explain. What about the converse: If $\vec{E}\,=\,0$ at all points on the surface is the flux through the surface zero?

A point charge is surrounded by a spherical gaussian surface of ra8wz3) pu2wz mgdius r. If the sphere is replaced by a cube of ) pw3wgmuz82z side r, will $\Phi_E$ be larger, smaller, or the same? Explain.

  

  How many electrons make up a charge o6l (5ncv6g we9al.2 jvkytnf2f $-30.0\mu C\,?$   $ \times10^{ 14}\, electrons $

  What is the magnitude of the electric fotamuk 0mz w fbly)*,3f ti(-,srce of attraction between an iron nucleus mm, f* akwsuzy0lt f),(t3-bi $(q\,=\,+26e)$ 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 two protonso+pc4:1os.6xbgk dg98yim5y owcs r* $ 5.0 \times10^{ -15}\,m$ apart from each other in an atomic nucleus?    N

  What is the magnitude oe9.boi7 *oh9 p ra.ln ip(z.ov j1iz4pf the force a $+25\,\mu C\,C$ charge exerts on a $+\,3.0\,mC$ charge 35 cm away?    N

  Two charged dust particleo-rf,b g) )f ys 1(g aw*/ypz2twcvo(is 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 817ysam.yg5 ec .45 cm apart. They are moved, and the force on each of them is found to have been tripled. How far aps7cga5my .ey 1art are they now?    cm

  A person scuffing her feet on a 43 qtlzmya89n)crg ;0 f z;dvmwool rug on a dry day accumulates a net charge of mz8m9cdr 4zgf nq y;v alt;03)$-42\,\mu C\,.$ 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 e-h(3 mjdq,-m luz5ims an.zv )lectrons in 1.0 kg of $H_2O\,?$    $ \times10^{ 7}\,C$

  Compare the electric force holding the electron iy 3uia2 4y8j7dquccb8n 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 ar .v0-waydyvo2tdow,(8g0 ku xe a fixed distance apart. The sum of their charges is What charge musk t(d-dw,yw0y0go ao.8 2vvu xt each have in order to
(a) maximize the electric force between them,
(b) minimize it?

  Particles of charge jo2 7f(zvsovhm rjs)f6.g ojz w783a-$+75$,$+48$ 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 particew25 dzb.ga.r ppe7 e qw-ie20les 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 a/ j/x 6;2m nnezggs+hjt each corner of a square 0.100 m on a side. Determine the mahe6mxj s/jn;/ g2zg +ngnitude and direction of the force on each charge.
$F_4$ =   $ \times10^{ 7}\,N$
$\theta$ =    $^{\circ}$

  Repeat Problem 14 for the case when two of the positive charges, onxxl5yo n4jdw qa.,5;t opposite corners, are replaced by negative charges of the samna55w.;ltq yjx do4x,e magnitude (Fig. 16–51).
$F_4$ =   $ \times10^{ 7}\,N$
$\theta$ =    $^{\circ}$

  At each corner of a square of side l there are point chargey/ooam, 3mlk1aa t3, +7n- bk ofd n;0gfajv7ms of magnitude Q, 2Q, 3Q, and 4Q (Fig. 16–52). Determin7vma3 +/1jolof-bkmf,ymg0nn3,do aa kt7 ; ae 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 equilateralqi+l x9yw:9 mu:sq.b 6 kw,ktf triangle of sid :wybw96.tksf+lqx :k 9imq,ue 1.20 m (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 p5 ise8i w 9h)a9ft4riof $560\,\mu C\,.$ 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 spheof pb9*/*u wejres have a total charge of $90.0\,\mu C\,.$
(a) When placed 1.06 m apart, the force each exerts on the other is 12.0 N and is repulsive. What is the charge on each?    $ \times10^{ -6}\,C$$\;\;\;\;$    $ \times10^{ -6}\,C$
(b) What if the force were attractive?    $ \times10^{ -6}\,C$$\;\;\;\;$    $ \times10^{ -6}\,C$

  A charge Q is transferred from an initially uncharged plasy rpy34,o -lmgr5apc; tic ball to an identical ball 12 cm away. The for ;r5mg,r y4p-pyc3aolce 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 forct+-s sktc* n7ye on an electron in a uniform electric field ns+cst-ty 7*k 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 pxax ao/fi )+5oa 8.lian electric force ofxlxpoa8 i /i5 .)f+oaa $ 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 8.4bhlal-)w: 4(dn 1xnyp 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 directly ab4c s.gntm3 bq*wu5 6xzove an isola4w6uns3 gc ztmq 5.b*xted $33.0 \times10^{ -6}\,C$ charge?    $ \times10^{6 }\,N/C$ ----待选择----updown 

  What is the magnitude of the acceleration expencg ro6o1b e 2. vyxaw(z-ct01rienced by an electron in an electrt.b01y1c xnwz(oo -erva2g c6 ic 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 ankv jq5piiw;9tq5 7p) ld direction of the electric field at a point midway betwe9i )vp7 pwl5qi5tqk;jen 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 d,o n8e11-w iayki y7dcharges, $+Q$ and $-3Q$ which are a distance l apart.

  What is the electric field strength at a point in space where a uyar)sm+6hb8hs *k :(h p/regproton $(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 a( :/i wl4n8s0j aslzfelectric field and accelerates to the naswjs: /0 nlzali8f4 (orth 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 equald9alp b e*sy x/i.5ftlv 69mjttzl /5; 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 at the cente15c0 witct0m wyly q-2r of a square 52.5 cm on a side if one corner is occupied-w t2t5y 0yqlcm0c1 iw 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 corner wv-)d7t rh le-am ,tqw9r)ln: of a square 1.00 m on a side if the other three cornersn9 wtl)ql tm7rrda-)h -vw:,e 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 th.-) )pnwfptvb e 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 charges. Express you -b .pwp)n)vftr 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,mx;9mi; h 3)x7t ujxbkf5vi ptric 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 determine the magnitude and 7jy 2nh4+rosrfvht3) direction of the electric field tr hv+j74n2o)s3 yhf rat points A and B in Fig. 16–57 due to 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 cok. su;5exv( 41xy(q9drot k fharges, $Q_1$ 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 magnitunihaqxk8qrr+3k2:/w de of the electric field at the point P shown in Fig. 16–59. The two charges are h+irnqwx8/ kk32 r:a qseparated 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 c4oj8b d6eh 1hthe right at 1.0% the speed of light enters a uniform electric field parallel to its direction of motion. If the electron is to be brought to rest in the spaceo84eh 6d bjc1h 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 bm bd bul y:,9yg1x*c:cox 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 elei* qh .zyj1sa(ctric field of magnitudez(q j.ayihs*1 $ 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 ob3b)vq uh n3i84c/ra sb8dl* ryjects, $O_1$ 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 uni82, xhyc,zb4mkwqy 6 iform 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,y j mhq.gyog )5yqp;9 The plates are 1.0 m on a side and are separate yjo5,) gpqy;mgq. hy9d 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 3q8 e.q5tyx2 lh.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 3.00vxoygel t+ 4 bpl,5):z 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 uncharged thin sphericaneg zg0 fdu,//l conducting shell. (See Fig. 16–33.) What is the electric field E as a function of r (a) for r less than the inner radius of the shell, (b) inside the shell, and (c) beyond the shell? (d) Does the shell affe, zgdu//fgn0ect the field due to Q alone? Does the charge Q affect the shell?

  The two strands of the helix-shaped DNA molecule are qj zynu05q2q174mz yhqxp66 mheld 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 on each molecule are separpz16hm q 74x2 z0jynqqqy6mu5 ated 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;w5 -ury9*c+03gxisah ggb wx between them is equal to the weight of eitw+g- u gcaix x h0s3y9b;rw5*gher at the Earth’s surface?    m

  A 3.0-g copper penny has a positc;5:gq4fyruxe z-n h4 ive 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 tvk47y8zzufmokpzx82v p c ,2jm(. 8lwdaax9/ here is an electric field surrounding the Earth. Its magnitude i(x .ma/xvk2kv2a com8zu8,9wdp 8 lpzz4f yj7s 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 tzurd1wp, s3+ what is the acceleration experienced by an electron near the surface of the 3sup,t1zw d+ rEarth?    $ \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 re8bul58 k9ibsg 4wrv1/s9bo dtl w3xs.mains stationary in the air. If the downward-directed electric field s9lxvskw98 bsi53to l1b/ 8gw r4db.uof 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 grou6 bd0s:j p35 :guxturk;o r*uxp shown in Fig. 16–62. The C and O hav:spo 5x :u*ub0 ju6;rrd ktgx3e 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 revoeusooztpn5) n+e:mws* t15 3alves in a circular orbit around the proton with a speed a51tzesn p u*5 omt3en+ ):sowof $ 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 c s f,6i))nc0w -r6y 2,md)qjzcgksu lattraction, rather than gravity, were responsible for holding the Moon in orbit around the Earth. If equal and opposite charges Q were placed on the Earth as0 ))jru- 2cf, kzldn )iscg6 q6,wcmynd 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 ep 9-x7tb+xu c$v_0\,=\, 21.5\times10^{6}\,m/s$ 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 charge gh8iqs ;tz /te6117kjdkxm- 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 plastic and suspended verticab .qkd6ge4c( ully from an ideal .bd(egc ukq46spring $(k\,=\,126N/m)$ 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 we-sqm zos0k59 ith “leaves” that are 78-cm-long wires with tiny 24-g spheres at the ends. When charged, nearly s0omek 5sqz9-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 gene8vqxo)q 4 ,l/ ,eepzvjrate a spark if the electric field exceeds aboutp, j)x8e /ev,4lqqzo 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 charw5oe7hxa(9on 0qk0 rsge $+0.340\,\mu C$, 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 aluminu5qr. a osm4-;qg(f( vrd qnm:bm?    $ \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 jq2/p 4/a)1gs jioamj4z;ih l 1zx by3R 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 sphere A and is then moved far away. What is the force on sphere A 1hxj1ijsi4 zga/jm);ozbyl /qpa24 3 in this third case?

Given the two charges shown in Fig. 16–68, at whath;) 9l2b rrvli position(s) x is the electric field zero? blr 9ih)2 r;lvIs 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 poin05fp x9c tg;mjx4r 8 x0o1 s:avo4mlght 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?