If you charge a pocket comb moevgt7e 5s (i*xh4* iby rubbing it with a silk scarf, how can you determine if7siv5 x **e4otg(hmi e the comb is positively or negatively charged?

Why does a shirt or blouse taken from a clothes dryer sometimes cling to you.f;w8oglk d 1jr bodk 1;d.jo8g lfwy?

Explain why fog or rain droplets tend to form around ions or electrons ih 5mfu8r v8pf5nig-, fn the ai8fimrv58fugh 5 p-n,f r.

A positively charged rod is brought close to ns:wja*d6;e rs31w grpk90x w a neutral piece of paper, which it attracts. Dra ;pn3 d0s9:*awrwwrks61exg jw a diagram showing the separation of charge and explain why attraction occurs.

Why does a plastic ruler that has been rubbed with a cloth have the abilityw )t9djt;(ga;g lgm1z to pic;t ljt; g(a)m1zdg gw9k up small pieces of paper? Why is this difficult to do on a humid day?

Contrast the net charge on a v5 zy1o4(bwlro4u8fuy5dno (u 7dy(dconductor to the “free charges” in the conductor.

Figures 16–7 and 16–8 show how a charged rod placed near a 0+.y f)dbmyf-cs f9qwn uncharged metal object can attract (or repel) electrons. There are a great many electrons in the metal, yet only some of them move f9 bqc -w+ .f0ydm)sfyas shown. Why not all of them?

When an electroscope is charged, its two leaves repovc;9 ;zr eckh,0;wua el each other and remain at an angle. W, ; uor ve09waz;hkc;chat balances the electric force of repulsion so that the leaves don’t separate further?

The form of Coulomb’s law sg: xvqw-)7 alis very similar to that for Newton’s law of universal gravitation. What are the differences between these tg-xq:7 lsavw) wo laws? Compare also gravitational mass and electric charge.

We are not normally aware of the gravitational or electric force betweenisu( 7u- (;x: tlazdol two ordinary objects. What is the reason in each case? Give an example where w:-s; u7 u(a(dioltxl ze are aware of each one and why.

Is the electric force a conservative force? Why or why not? (See Chapter 6.)8 jpot-auny ,zf5g-l4

When a charged ruler attracts smx bdqejg-(87+r9rssaall pieces of paper, sometimes a piece jumps quickly away aftes sabr8-d7j9r qge+x (r touching the ruler. Explain.

Explain why the test charges we use when measuricfu 6npy3v:sqqb*vy;-xu 0g3 ng electric fields must be small vy qc x:up yvq3bsn60fug-3*;.

When determining an electric field, mik (g)a: jquw(ust we use a positive test charge, or would a negative one do as well? Explaig( aqwi(kuj ):n.

Draw the electric field lines surrounding two negative electric chardm7mo-rkyfvv 3 - + 91cdzzqbhh2q -)rges a distance l apart2v3d-b - f )hdqz-y 1v+ chq7rrmo9kzm.

Assume that the two opposite charges in Fig. 16–31a are 12.0 cm apartwwom l mv 6vx7at 3o:jw)7f*5t. Consider the magnitude of the electric field 2.5 cm from the pof5jw:) 7movm7tl x63* towvawsitive 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 ioqt 7y0coj55cj.db-v 5cx9 dpn Fig. 16–48. First draw an arrow at each point indicating the direction of the net force that a positive test charge wd0cy5 qc5 5.9ojtx-odjv pb7c ould experience if placed at that point, then list the points in order of decreasing field strength (strongest first).

Why can electric field lines never ci19xczdo v+h mc22 e2qross?

Show, using the three w bddjj83pf3iq(c:(p rules for field lines given in Section 16–8, that the electric field lines starting or ending on a single point charge must be symmetrically spaced around t8fpqdp:dw bj3i ( (c3jhe charge.

Given two point charges Q and 2Q, a distance l apart, is there a point86zij9 g xum q .zob.cjs6,ml, along the straight line that passes. bxgl6i o6,jz9muzs ,8.qjmc 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 ccu -p(c+ ptw7charge located on an electric field line at some point, such as pcp7+ uwct-(p coint P in Fig. 16–31a. Is the direction of the velocity and/or acceleration of the test charge along this line? Discuss.

Sketch the electric field lineic )7zyk /vfp,s for a uniform line of charge which is infinitely long. (Hint:i vk) z7p/cfy, Use symmetry.) Is the electric field uniform in strength?

If the electric flux through a closed surface is zero, is the electric fir ww ,,xtca/uv)k(gcn *k0r/ neld necessarily zero at ar,x0 //vuarw ck nk)(,t gwnc*ll 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 surroundjaixk3rh *ya8 7d. pu mrm.;7qed by a spherical gaussian surface of radius r. If the sphere i xyrah8m.dr ma* 3.pk;uji 77qs replaced by a cube of side r, will $\Phi_E$ be larger, smaller, or the same? Explain.

  

  How many electrons makssm8 uu s1og;0e up a charge of $-30.0\mu C\,?$   $ \times10^{ 14}\, electrons $

  What is the magnitude of the elev;dq6. ,ex*hs kn, a siq4rl,mctric force of attraction between an iron nucleus ,sr.,hnldi4 ,k v e 6qs;x*amq$(q\,=\,+26e)$ 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 rr3zp w3* b/;1zw2ltn4ixme vtwo protons $ 5.0 \times10^{ -15}\,m$ apart from each other in an atomic nucleus?    N

  What is the magnitude of the 8vp8fc(4 s xrioa:f81 rma sy9force a $+25\,\mu C\,C$ charge exerts on a $+\,3.0\,mC$ charge 35 cm away?    N

  Two charged dust particles exert)t1v mqsu.)i4l /+p*foy/hr tw 7aubo a force of $ 3.2\times10^{ -2}\,N$ on each other. What will be the force if they are moved so they are only one-eighth as far apart?    N

  Two charged spheres are 8.45 cm apart. The/so of 9g)v1buy are moved, and the force on each of them is found to has/)9 bog1fvo uve been tripled. How far apart are they now?    cm

  A person scuffing her feet on a wool rug on a dry day accumulates a net chargvhj0ah4l- .zwe of a.h -v0j4wlhz $-42\,\mu C\,.$ 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 electrons i9;g 3mp3 drmvrn 1.0 kg of $H_2O\,?$    $ \times10^{ 7}\,C$

  Compare the electric force h8mfip+17k zd2 adu.pcolding 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 are a fixed distance apart. The sum of hca xp-3z qzp gm09nrza52- ht+:;hmp their charges is What charge must each have in o;9ax+0ng:tpz 2z p zp 5mqm-hh3hr -acrder to
(a) maximize the electric force between them,
(b) minimize it?

  Particles of charge cjr)sn)y: k6o j8d- oo$+75$,$+48$ 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 equbgxu ;/i*z;wc7qc 4v oal 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+/ r5 qzbda4eb/e7e qft each corner of a square 0.100 m on a side. Determine the magnitude a/dfqzq7be+/e are b45nd direction of the force on each charge.
$F_4$ =   $ \times10^{ 7}\,N$
$\theta$ =    $^{\circ}$

  Repeat Problem 14 for th(rcfe a. 5 rw5fops)0ze case when two of the positive charges, on opposite corners, are replaced by negative cha(cpfwe s05.o5zar) frrges of the same magnitude (Fig. 16–51).
$F_4$ =   $ \times10^{ 7}\,N$
$\theta$ =    $^{\circ}$

  At each corner of a square of side l there are point charges of magnitude Q, 2Q, w q;acywj(4ma6t *ie7 3Q, and 4Q (Fig. 16–52). Determine the force on (a) the charge 2Q, and (b) the chargeaqi(ce76yw4amt*w j ; 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 equiel4:azu:*,.+ ygb+wt md myj; elayr5lateral triangle of side 1.20 m (Fig. 16–:r5g .b *d:aaml ywtym+jy lu;ze4,+e53). 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 t9yykkk: pb *b8otal charge of $560\,\mu C\,.$ When placed 1.10 m apart, the force each exerts on the other is 22.8 N and is repulsive. What is the charge on each?
q = $ 5.54\times10^{a }\,C$ a =  ,
$ 5.54\times10^{b }\,C $ b =   
Q-q = $ 5.54\times10^{a }\,C$ a =  ,
$ 5.54\times10^{b }\,C$ b =   

Two charges, $-Q_0$ and $-3Q_0$ are a distance l apart. These two charges are free to move but do not because there is a third charge nearby. What must be the charge and placement of the third charge for the first two to be in equilibrium?

  A $+4.75\,\mu C\,$ and a $-3.55\,\mu C\,$ charge are placed 18.5 cm apart. Where can a third charge be placed so that it experiences no net force?    cm

  Two small nonconducting spheres have a total ch5au h5b -y z 2gwwjy 38m-f7vor1z ugno4/ll5uarge 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 initiallknand./f)g bvcryfjl 7* i0q/- a) cy6y uncharged plastic ball to an identical ball 12 cm away. v )dc 7a0/r-l6bj.ny)n f gfak i/*cqyThe 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 the1y ft nx-n0 atv;1+mwo electric force on an electron in a uniform ele1+ymv1at;t -fnn w0xoctric field of strength $2360\,N/C$ that points due east?
   $ \times10^{ -16}\,N$
 ----待选择----westeast 

  A proton is released in a uniform electric field, and it experiences ann4kf;6p 3m9l gy nlzu: electric force of k ;pn6ly3l9m:u gfzn4$ 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 exe sj9ogb ;jc*he) g8yn*rted 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 dirc vo wyf8*/rcophy31 evome.h)i* e)lu;to2 -ectly above an isoyo e/ c )1eo;w.l32hp)-*cv uyo8ihef*rov tmlated $33.0 \times10^{ -6}\,C$ charge?    $ \times10^{6 }\,N/C$ ----待选择----updown 

  What is the magnitude of the acceleration experienced by an electron in an elvx/ge(a i*+f ;7ag(lfhsn;ab4(kauv ectric fielaxla(i*b;ehnfu v a(4v a+gsg7f/ (;kd 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 fienk *hq0 4f*:q)k/hl slvc8ax qld at a point midway betwe0lx s)qq vncq:4k h*8ha/*l fken 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 c1r(rkl2j+, xgfwz n 9rharges, $+Q$ and $-3Q$ which are a distance l apart.

  What is the electric field strength at a point in space where a protos7ld(z:* .d rweh-ydwq/r(ku n $(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 field and x+81q,j+;6gocy p y gt ygxfnx)h 9,waaccelerates to qc8yya6,,g jp gh xyw1t+)x+ ;x9gnfothe 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 but opposz gxr )yw4g4lz( oj;,hite 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 ah*gor3)/.kwtwm n(l t t the center of a square 52.5 cm on a side if one corner is occmo 3.w (nl)*hwkrg/ttupied 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 of a )5i2(9iul/yp ek +2zv orovrk square 1.00 m on a side if the other three corners are occu 2rorz(il /ekokui)5 pvv y9+2pied 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 poinly8db32k1ok7 ; lvxlprs:hr: t 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 yoslv73:r 8 y 2xdlo;blk:1hpk rur 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 electrimmwaz .1 s*nimo 5*)gkc 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 thelqti-bfrq-( * magnitude and direction of the electric field at points A and B in Fig. 16–57 dulb q-ft(*qir- e 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 unknowqh ca/:*zt :oen 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)7b 5xb +4tp1hadyzym of the electric field at the point P shown in Fig. 16–59. The two chabxy zhytb17a m)5p4d+rges 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 ti/naypv es kbu6nd0njglf0y u4z0a-/) e 9w86he right at 1.0% the speed of light enters a uniform electric field parallel to its direction of motion. If the electroneb v/k0nnlf0j84 aus/auy-dny 0)6wz 9i6gp e 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 o9s-oq4v( b gocm 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 1 noqs+q8(0zty*/hv/ mm qt k3.;uhcjt 8 cm is placed in a uniform electric field of magnitude(mqt3n mty8h0h.tv+ q/ /ksoqj;*zuc $ 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 objectsl /s3x,puk/ ouw5 qib/, $O_1$ 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 b9 jr)-1 zs:pqgbmzx7niform 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 pl8db/(wdxodc9- l+gz avkl*15 1 znxr fates are 1.0 m on a side and are separated by 3.0 cm. What is the charge on each plate (assu(w-n1azlz fdx*k/+1r 8o c95dbgldv x me equal and opposite)? Neglect edge effects.    $ \times10^{-9 }\,C$

  The field just outside a 3.50-cm-radie7e o)q+9d j8dfmccm6 us 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 cavj vz;o3ldc.; xsg p03rries 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 unchargmz 2q-)xz6 dyied thin spherical conducting shell. (See Fig. 16–33.) What is the electric field E as a function of r (a) for r less than the inner radius of the shell, (b) inside the shell, and (c) beyond the shell? (d) Does the shell affect the field d)qm i 2zdx-yz6ue to Q alone? Does the charge Q affect the shell?

  The two strands of the helix-shaped DNA mole*1 tzx e13:o4ikqzw jbwxc4g)cule are held together by electrostatic forces as shown in k4jo1cbx4q ixg t 1ew*) :3zwzFig. 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 electronsyqpvf fppx;8u) wz h+p:p,m(n ;cc.,l be if the electric force between them is equal to the weight of either at the Efq pppcm c;xpuypf(nz:.,,w)vl;h8+ arth’s surface?    m

  A 3.0-g copper penny has:hkgu-i,t zfl2 tws. ( 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 trg otcjsmr+uxuipna);u3f (3) ,im, 7he Earth. Its magnptu,)jg 3+ifcsm;r7(, rau x iun 3om)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 is the acceleration experiencf stsyia5k:)2 mx t5n2ed by an electron near the surface of the Eart)inx yt:2stm5sa2 5kf h?    $ \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 bn1fjs3hiy wg , 31g3 4aaggak0uu,;w remains stationary in the air. If the downward-directe1jb;gufukh 3 na,i g33swgg0, ay4a w1d electric field of the Earth is $150\,N/C$ how many excess electron charges must the water droplet have?    $ \times10^{ 6}$ electrons

  Estimate the net forceg (1onu2r.qd ts(u ,bf between the CO group and the HN group shown in Fig. 16–62. The C an1qrsno(u(.,gud2 b tf d 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 hydrogbbv ,x1fz+0/qsmmksz-0 mkz.en atom, the electron revolves in a circular orbit around the proton,b0.zb/v m0xqs1m-mk +zksfz 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, r 3i7l ; 8evocy:p-fwujather than gravity, were responsible for 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 present orbit? Use these data: mass o uoyp:l;-iw8vc73ej ff $Earth\,=\, 5.98\times10^{24}\,kg$, 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 spea 2a ozbgm3h5y,*zd v6ed $v_0\,=\, 21.5\times10^{6}\,m/s$ 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 chahl4e2ujx7pwfeo1 66,4y2 i1i fwp +e7ho gbjbrge $Q_1\,=\, 2.5\times10^{-5}\,C$. 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 verti. 5iuluc+ 9(s cr8jfwpcu l6-wcally from an id fsw lcuupcl96-j c+5ir8u .w(eal spring $(k\,=\,126N/m)$ above a lab table, Fig. 16–63. The total mass of the coated sphere is 0.800 kg, and its center lies 15.0 cm above the tabletop when in equilibrium. The sphere is pulled down 5.00 cm below equilibrium, an electric charge $Q\,=\, -3.00\times10^{-6}\,C$ is deposited on it and then it is released. Using what you know about harmonic oscillation, write an expression for the electric field strength as a function of time that would be measured at the point on the tabletop (P) directly below the sphere.

  A large electroscope is made with “leaves” that are 78-cm2e zuin x-i u,d(7p3:g hrxbe.-long wires with tiny 24-g spheres at the ends. When charged, nearly all the charge resides on the sp7 3hb-(gz.enudepx ii:,u2r xheres. 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 downt; fw*der.st tx /5jt4u 6dn4g and generate a spark if the electric field exceeds about t;snj fd.ude4g* /64ttxw5 tr$ 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 n e14nl/ei)ekv et 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 s6npd a gr3tazw8 69f+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 o -m) 6pd +n9hbw *vqdrs9y6pldistance 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 sphdp6mr)ol y9 bds q6wp+hn-9v* ere 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.wq* g+ll/ b-hn arfeuzg24 32e 16–68, at what position(s) x is the electric field zero? Igl+ he3r-n/z *a2wlf4be qg2us 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 chptlb.zmh eam:m)xxy k.4 /6 h5arges, 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?