If you charge a pocket comb by rubbing it with a su5+n2ivvt xu52 4dpqw t0p y1silk scarf, how can you determine if the comb is p5wp2t2+ i 5n q1xu0v4s dtpvuyositively or negatively charged?

Why does a shirt or blouse taken from a clothes dryer sometimjik7f cor:,rgf0gss )) s 4d5hes cling to your bog, rdf7)0 o5)s gihjskc:f 4srdy?

Explain why fog or rain droplets tend to uvx1(cjn;/wb)t p5k uform around ions or electrons in the air1;pjxu( wv)ut nb5c/k.

A positively charged rc3zyp7 /wd s)wod is brought close to a neutral piece of paper, which it attracts. Draw a diagram showing the separation of charge and explain why aw3 c/s7dpy z)wttraction occurs.

Why does a plastic ruler that has been rubbed with a cloth have the ability r76m84ly:aai4:mz:ey j 3waol0cmb ij gvm*: to pick up small pieces of paper? Why is this difficult to do on a hum3iw:l:vy:7*armmzl b :8myoj6c0 ia4 gema4 jid day?

Contrast the net charge onlqe vsq* 26-8xnihq9w a conductor to the “free charges” in the conductor.

Figures 16–7 and 16–8 show how a charged rod placed near v ,h3uq;jd1*p dd( sjny*a;dkan uncharged metal object can attract (or repel) electrons. There are a great many electrons in the metal, yet only some of1;ap(d k qvn*d3d,yd*jh js; u them move as shown. Why not all of them?

When an electroscope is charged, its two leaves rep 0;w.vvb, inuzel each other and remain at an angle. What balances i v0.,uwzv nb;the electric force of repulsion so that the leaves don’t separate further?

The form of Coulomb’s law is very similar to that for Newton’s laweaa1gmr +i(a,m1 w6,mn 2lequ of universal gravitation. What are the differences between these two6m qgr(1,amnma+ aee1lw ui,2 laws? Compare also gravitational mass and electric charge.

We are not normally aware of the gravitational or dlx 6dp3dk iztgf5:71electric force between two ordinary objects. What is the reason in each case? Give an example where we are xfik56:1l td zdd3gp7 aware of each one and why.

Is the electric force a conservative force? Why or w13;ar )idazpkcmy0z j ;x. .cdan9no ;hy not? (See Chapter 6.)

When a charged ruler attracts small pieces of paper, sometimes a piecel0 nlvt3)it2uomj zfabt:.u9t+ w+r6 jumps quickly away after touchurtot+mv ln)3tw 0l :az2 i+.9ubjft6ing the ruler. Explain.

Explain why the test charges we use kef)ftv0ryv+vz ki1gy yr-81t1+ x ( .gnb+yjwhen measuring electric fields must be small0jet gy+ytxyf(n1rrv81-1yizv f gk+) kvb+. .

When determining an electric field, must we use a pos0j,1z cih( 3+pwmjv: tv qv:m+wsdz7aitive test charge, or would a negative one zsat:++3 7mvwq mz:vch pjdjv,0iw1 (do as well? Explain.

Draw the electric fielcl m)c0wbtyp,08 0ftxd lines surrounding two negative electric charges a distance l apart.c pf,lctx0w0ytb 0m8)

Assume that the two opposite charges in Fig. 16–31a ar3fbu ltu(,e3e e 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, bottom, left, or right — is the elec e(u3fuelb3 ,ttric field the strongest? The weakest? Explain.

Consider the electric field at points A, B, and C is4ie+rz/ 8i 2k9xrt3k mu:lastjcr : 7n Fig. 16–48. First draw an arrow 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 firstmszusr3j8l e7 2r 9:rt:i/ kx+ktac i4).

Why can electric field li *qx w4ky+0whbnes never cross?

Show, using the three rules for field lines given in Section 16–8, e fxi4uk8 x2opuod3 qy.du ;wk3y4- w4that the electric field liny;4-o 83 dx. u4euqyf 32wuod4kxpwikes starting or ending on a single point charge must be symmetrically spaced around the charge.

Given two point charges Q and 2Q, a+pg- 6apd/yq k distance l apart, is there a point along the straight line that passes through them where E=0 when their signs are (a) opposit6yp/qg a kpd-+e, (b) the same? If yes, state roughly where this point will be.

Consider a small positive test charge; 99ul)wxi xefw(; uzu located on an electric field line at some point, such as point P in Fig. 16–31a. Is the direction of the velocity and/or accelera)x u; wf9;e(izxwuu 9ltion of the test charge along this line? Discuss.

Sketch the electric field lines for a wwg d9y.+y tbfz90)c9ewydh: uniform line of charge which is infinitely long. (Hint: Use sze gc9t9bf wywd)9yh+0d:y.wymmetry.) Is the electric field uniform in strength?

If the electric flux through a closed surface is zero, is t z uc: 575/*ul zzph 80h )mtonwiihgc3i;mhh+he electric field necessarily zero at all points on the surface? Explain. What about the convers;hzl mpnh c3 u)ih78z5hh i+:*i uct/ 0ogzwm5e: If $\vec{E}\,=\,0$ at all points on the surface is the flux through the surface zero?

A point charge is surqtcy rehl)l7mb1rc *4:lxf. ;*i b7 berounded by a spherical gaussian surface of radius r. If the sphere is replaced b4by:e;e *xqlb.l*b ir f17c7mhc )rt ly a cube of side r, will $\Phi_E$ be larger, smaller, or the same? Explain.

  

  How many electrons make up a charge of a o0 j fav79ij1alfn9sfr.99l$-30.0\mu C\,?$   $ \times10^{ 14}\, electrons $

  What is the magnitude of the electri5:dw2 p1xezgzus ;da6 c force of attraction between an iron nucleus:dasu6d1 52zgexw;zp $(q\,=\,+26e)$ and its innermost electron if the distance between them is $ 1.5\times10^{-12 }\,m\,?$    $ \times10^{-3 }N$

  What is the repulsive electrical forc1lz ):uv:ate2s s5hlg e between two protons $ 5.0 \times10^{ -15}\,m$ apart from each other in an atomic nucleus?    N

  What is the magnitude of the force au --f76u yfmnw 7rzqr8 $+25\,\mu C\,C$ charge exerts on a $+\,3.0\,mC$ charge 35 cm away?    N

  Two charged dust particles exert a force ij9sa2 :6xggc 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. They are moved, and the for9 q xayx2)fed22b7vudg ev9 )hce on each of them is found to have been trih)ex2dgy )bvvu9 2qd7e xa2 9fpled. How far apart are they now?    cm

  A person scuffing her feet on a wool rug on a dry day accumulates aol9u0 0np vj5y net charge ou09ovp nl5yj 0f $-42\,\mu C\,.$ 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 in 1.0ixa1 /hdstlc: :sh-tyb( e -d4wx:h;ho rl d*, kg of $H_2O\,?$    $ \times10^{ 7}\,C$

  Compare the electric force holding the electron in orb z os3d8y.06wko;z vtr4k-ses it $(r\,=\,0.53 \times10^{-10 }\,m)$ 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 ajqyy; 6 xaxsy)0ryxd -b 25ro..v+3f-mkrph fre a fixed distance apart. The sum of their charges is What charge must each have in opvdboyykym0rxf rsq.- 6x f.ja2 yr )x ;+5-3hrder to
(a) maximize the electric force between them,
(b) minimize it?

  Particles of charge *-/u1ab bczmsopfzj (p3i2g zt;vrz4 )2kz( x$+75$,$+48$ 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 ofhrzs//azn3 ( w 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 at each corner of a square 0.1002+va nwy.9i8g yr 1of)edn;he m on a side. Determine the m ne )igd;w ho9any8fy.r1v+e2agnitude 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 c h 7h2yw9qzdx9u7kn64-rk/o( iw xdazharges, on opposite corners, are replaced by negative charges of the same magnitude (Fig. 16–51). o7r(i4yxdxa6h/9 2kqk7w9dz nh z -wu
$F_4$ =   $ \times10^{ 7}\,N$
$\theta$ =    $^{\circ}$

  At each corner of a square of side l there are poinduycm8dg-uo vr e2r 1qc:/-*d;1 a qbpt charges of magnitude Q, 2Q, 3Q, and e8mvyg:*cu ur2/a1bq-rddo1 q -dc ;p4Q (Fig. 16–52). Determine 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 particlexct8 f k g4r. 8ply7k)czs4l6ts are placed at the corners of an equilateral triangle of side 1.k84gtkxfspyl7t.c z4c8r) l 620 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 chs(mr0*6 b tf qrkym1w:arge 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 ch ,e+4b73kengw4ffpzb arge 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 plasticwb g)dx +9mfyuezdbmd 792;)ol2 st6vaau39s ball to an identical ball 12 cm away. The force of attraction is then 17 mN. How many electrons were trans db ad7 )z6b ws;gysoa3 uvdxu9m2)lmfe99t2 +ferred from one ball to the other?    $ \times10^{ 12}$ electrons

  What are the magnitude and direction of the +yz ql 65p:mpjelectric force on an electron in a uniform electric f 5m:qlp+ 6jpzyield of strength $2360\,N/C$ that points due east?
   $ \times10^{ -16}\,N$
 ----待选择----westeast 

  A proton is released in a uniform elec /gjmfo52d//s*a j fttj.pu-m tric field, and it experiences an electric force fto /u.g/ -mpj*2jd /mjastf5 of $ 3.75\times10^{ -14}\,N$ toward the south. What are the magnitude and direction of the electric field?
   $ \times10^{5 }\,N/C$
 ----待选择----southnorth 

  A downward force of 8.4 N is exert;/h:xld5 wiu*ofuxb17 piu6m q9v8kned 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 a5 e (l9usmljagpp qyn:+iss ;t:9 yt:(bove an isolated m9iey 9pal( tl ysus;s:tnqpg+5j: :($33.0 \times10^{ -6}\,C$ charge?    $ \times10^{6 }\,N/C$ ----待选择----updown 

  What is the magnitude of the acceleration experiencd89 bs 9l-jdezed by an electron in an electric field of 8 sej-d bld99z$750\,N/C\,?$ 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 directiopj,7gl 4 n:bdjhqh)n ;n of the electric field at a point midway betwee 4hp;njg j)lhq,7 nd:bn 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 hu/c*77an2pogo js; gfield 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 where ae4 s(o+u gnp2m 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 e6ovy,/wqsvd d i69j9from rest in a uniform electric field and accelerates to the north at a ra6jyd9/qw96 id ,eovsvte of $115\,m/s^2\,.$ What are the magnitude and direction of the electric field?    $ \times10^{-10 }\,N/C$ ----待选择----northsouth 

  The electric field midway between two equal but opposite point bf d .k,,6aou+jydii(i9 fnz2charges 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 dmgq-u :n r- r.kqe3y-if one corne:q-uk emqd.-yn-3rrgr is occupied 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 s3enjz an+ 9;qkwk- 2.wvr2bbgquare 1.00 m on a side if the other thwz-q+ 9jg2abevk3nb r wn2.;kree corners are occupied by $ 2.25\times10^{-6 }\,C$ charges.    $ \times10^{4 }\,N/C$   $^{\circ}\,$ from the x-direction.

Determine the direction and magnitude of the ele ,jsv((tfey6d ctric field at the point P in Fig. 16–54. The charges are separ(t v,(sfyd je6ated by a distance 2a, and point P is a distance x from the midpoint between the two charges. Express your answer in terms of Q, x, a, and k.

  Two point charges, $Q_1\,\equiv\,25\,\mu C\,$ and $Q_2\,=\,+50\mu C\,,$ are separated by a distance of 12 cm. The electric field at the point P (see Fig. 16–55) is zero. How far from $Q_1$ is P?    cm

(a) Determine the eler ( c70kk rtg2f3qiv8vp dqks:g92b g5ctric 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 direction of the electric 1 qm+f*yp k5bbr4l3fbfield at poibr5*y4p1l 3qbb+m fkfnts 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 charges,8qthf/t b0 g58a/rgfyyzk f,(laj2d ( $Q_1$ 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 maatsed 5e4c *l2gnitude of the electric field at the point P shown in Fig. 16–59. The two charges are separated by a distance of 2a. Point P is on the perpendicular bisector of the line joining the charges, a distance x from the midpoint between them. Express your anstdc ae54sl2e* wers in terms of Q, x, a, and k.

  An electron (mass $m\,=\,9.11 \times10^{ -31}\,kg$) is accelerated in the uniform field $\overrightarrow{\mathbf{E}}\left(E=1.45 \times 10^{4} \mathrm{~N} / \mathrm{C}\right)$ between two parallel charged plates. The separation of the plates is 1.10 cm. The electron is accelerated from rest near the negative plate and passes through a tiny hole in the positive plate, Fig. 16–60.
(a) With what speed does it leave the hole?    $ \times10^{ 6}\,m/s$
(b) Show that the gravitational force can be ignored.

  An electron moving to the right at 1.0% the speed of light entersgupegb/ 8w:5b uy0oy , a uniform electric field parallel to its direction of motion. If the electron isp 0:/ywggu5u 8byb, eo 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 cub7-33sbl beiobical 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 pxkf0ah s3hnv:/lvd*1hyl9-xlaced in a uniform electric field of magnitudelv*1l-:n9xhy fx v03ksa h/dh $ 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 object 0ta 1:,du3j0pgnb-ce3 svojes, $O_1$ 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:yx6gpq :)o7 jlfl1i mniform 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 me1 mi6x pixxwwob-,tn+-8 ml,3xrhtx.tal plates is The plates are 1.0 m on a side and ni -w xxlm, 38 -wx+mb6xti ,orx1t.hpare separated 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 3.50/v cxon-t*zpm v+b9 .c6mx*tl-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 tota j)i4h jesm00uurz;s 3l 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 sphey yo:r(n( pqkd-r0g9l rical 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 th 0 yroyd(-nlg kp:r9(qe 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 molecule are held togeftnx3p: r3d;d ther by electrostatic forces as shown in Fig: pdrxdf3n3;t. 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 electr0c(z* s4ht oehons be if the electric force between them is equal to the weight of either at tte*(z oh04hsc he Earth’s surface?    m

  A 3.0-g copper penny hasg 1quk,rvh:o9 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 elect6p1k-l itkc 8,w) yhe+ zos/axric field surrounding the Earth. Its magnitude1zeho8)a,tli pc k6+/ -yx kws 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 6fxgvd-wai; f4,/ b v9v6upl macceleration experienced by an electron neb6dvfml,69- ugiw;f vvx /4pa ar 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 0.018 mkud 7f7 ao.o.b28gcyyl;w5bfm remains stationary in the air. If the downward-directed electric field ofdbf7g..lwoky f 27yaub ;8co5 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. 169hpqls j7dc zy 6y7cbu9cs (/)s5hhb 0–62. Thhjc 9 c9qz lpdu(7c/h65yb ys7b)hs0se C and O have charges $\pm0.40e$, and the H and N have charges $\pm0.20e$, where $e\,=\, 1.6\times10^{-19}\,C$. [Hint: Do not include the “internal” forces between C and O, or between H and N.]    $ \times10^{ -10}\,NN$

  In a simple model of the hydrogen atom, the electron revolves in a hsvq/ 1p r7z-;voktr zk10;xlcb2 rj n6mvm)4circular orbit around the proton with a ;j1rk 0/ ch1v x2 m6ovpns7lq4tzrzr;k-)mbv 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 a s;. 9+j-ybvia lkmekji1x*r1 ttraction, 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 and the Mova1;9 .jym k*bix 1ejsi-krl +on, 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 spe b :-7y qzbw*lsysfm8v a /0s,*pqvnl0ed $v_0\,=\, 21.5\times10^{6}\,m/s$ 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 chacjafeh/76 9cdp 7cc 2orge $Q_1\,=\, 2.5\times10^{-5}\,C$. 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 insue13wq ;ri(pj*to b ay7lating plastic and suspended vertically from an ideal spring wa (e1 ritbq j;y*37op$(k\,=\,126N/m)$ 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-cm-long ; ecds uyo:rpe3mc7tq)v8+: rwires with tiny 24-gmry;q78e+): teov 3:sdrp cuc spheres at the ends. When charged, nearly all the charge resides on the spheres. If the wires each make a $30^{\circ}$ angle with the vertical (Fig. 16–64), what total charge Q must have been applied to the electroscope? Ignore the mass of the wires.    $ \times10^{-6 }\,CC$

  Dry air will break down and generate a spark if the electric fiel-1sr zo:x5d.rx8brg,qbh ph6d exceeds abouthhzq xg 5d,pbrx8o-:r1s6br . $ 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 ma: f5mb pxme )kjco*h8d0 :/rqsss 0.210 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 all the electrons in a 15-kg bar o,07p a .xh/-xmcok h dt(tqn1wvkr:o/f 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 conducting3wgy7po* g973 jufn es spheres A and B are a distance R apart; each carries the s39gp 3fys7jguw* o 7ename 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 in this third case?

Given the two charges shown in Fig. 16–68, at what position(s) x is thdnu7e.:xf *t fe electric field *fxut.:e7 n dfzero? 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 charges, each o)o*nord: esd*v.g6 juf 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?