If you charge a pocket comb by rubbing it with a silk scarf, how can you de6;hq +721ovomxanuegr 3 f9qatermine if the comb is positively or negativ oq7h3agu; o+v9q2m6afnr 1xeely charged?

Why does a shirt or blouse taken from a clothes dryer sometimesu 0g 3k-a-tniy cling to your bod30ig u--ak ytny?

Explain why fog or rain droplets tend to form around ions or electrons in the ah sgs;b:pzc9 +a*f2e ksw :d2+bid(q air(c:d2hifp 9 gs+2qkda;bw *az :esb+ s.

A positively charged rod is bro+ m scc7+s/rzgst3 du,ught close to a neutral piece of paper, which it attracts. Draw z3srd /++ tcus,s cm7ga diagram showing the separation of charge and explain why attraction occurs.

Why does a plastic ruleaw6skjj qwd- uj6n 8l17m9k9x z2o*y kr that has been rubbed with a cloth have the ability to pickawqn7s*l9-k9 uw j2z6 kxj8ykj6 o1md up small pieces of paper? Why is this difficult to do on a humid day?

Contrast the net charge on a conduh6t+b+dode:gmo4 flc1 67r kmctor to the “free charges” in the conductor.

Figures 16–7 and 16–8 sho )4d wdqxfk -v/y coq;5ykku(2w how a charged rod placed near an uncharged metal object can attract (or repel) electrons. There are a great many electrons in the metal, -v4y/d qykq 5dk(xowcu k f);2yet only some of them move as shown. Why not all of them?

When an electroscope is charged, its two leaves repel each other a(9 wmvl6kkg tah7 2ds4nd remain at an angle. What balances the electric force of repulsion so that the leaves don’t separatevm h ( glka79swd4kt26 further?

The form of Coulomb’s law is very similar to that for Newton’s l-qd iv ;3x6sg o.6+ti xryn5jmaw of universal gravitation. What are the differences between these two la g3yjxiqv5no-;t .im6 6xr+sdws? Compare also gravitational mass and electric charge.

We are not normally aware of the gran4a6h ttjlw/: p5i+ wyvitational or electric force between two ordinary objects. What is the reason in each case? Give an example where we are aware of each oi+ja6 w/5hl4 ytpnwt:ne and why.

Is the electric force a conservative force? Why or why noder zd4 h;x;v:t? (See Chapter 6.)

When a charged ruler attracts small piece+v1icy z/rdg0aldn 0-x mq;3ys of paper, sometimes a piece jumps quickly away after touching the ruler. Expla;nl+xyvc1 zgqdd r0 -3/ym ai0in.

Explain why the test charges we use when measuring electric fields must bev)n. nkje0 v*.xopk4d small.opd) vv.nkk en40jx *.

When determining an ele-3tmch* xixk5c1 ox5ictric field, must we use a positive test charge, or would a negative one do as well?t*cxcix13k55 oi-m h x Explain.

Draw the electric field lines surrounding two nega+3phn3n *p4-cwu7 hh/hs ybdt.8 pelb tive electric charges a distance l apart.l8 *-n.3y/3hp hbch+ept4nu bdp hsw7

Assume that the two opposite charges in Fig. 16–31a are 12.0 cm apar86v urmj(i 1awt. 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 electric field t( m18w a6juvirhe strongest? The weakest? Explain.

Consider the electric field at points A, B, and C i3xs0h ft0f:t.2 x zzpvn 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 ppxv2 :xh0ft3sz.t z 0flaced at that point, then list the points in order of decreasing field strength (strongest first).

Why can electric field lines never cross?-mft:/ e hxuax )tmn.j-x*f 0a

Show, using the three rules 7okum9j pbmj 7 )0oub61lys bv) b(-imfor field lines given in Section 16–8, that the electric field lines starting or ending 0b- 6yi 917lj(u)m o b)7ummbovkjpbson a single point charge must be symmetrically spaced around the charge.

Given two point charges Q and 2Q, a distance l apart, is x;qd2fi) *lfxthere a point along the straight line that passes through them where E=0 when their signs are (a) opposite, (b) the same? If yes, state roughl*li 2 dxf)qx;fy where this point will be.

Consider a small positive test charge located on an electric field line yzh 3fe-)sjto(vd(-1k v:d gcat 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 line? Discuss.k vgty)( c:-vdz(o1fd e-sj3h

Sketch the electric field lines for 7nu7 jj*csi zl10+p0nx;1 lozd7ua k )czizw-a uniform line of charge which is infinitely long. (Hint: Use symmetry.) Is the electric field uniform in strength7upjj) ;zwcl +sl cu-*7oax17 nnzi1k z0z0id?

If the electric flux through a clzpji430 6vtyz*xz a y*osed surface is zero, is the electric field nece a x43*z6*ypj0zizyvt ssarily zero at all 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 surrounj,wd-f;h ogwxhj 1,d; ded by a spherical gaussian surface of radius r. If the sphere is replaced by a cube of oh;xh,1 ,d-dw;f wjgjside r, will $\Phi_E$ be larger, smaller, or the same? Explain.

  

  How many electrons make up a c74rln d:-q pggharge of $-30.0\mu C\,?$   $ \times10^{ 14}\, electrons $

  What is the magnitude of the electric force of attractio)3w n+tt) gng1s4dl pin between an iron nucleus +w t)lsgg 1pi nntd43)$(q\,=\,+26e)$ and its innermost electron if the distance between them is $ 1.5\times10^{-12 }\,m\,?$    $ \times10^{-3 }N$

  What is the repulsive electrical for t2lgh f3wnd-h qq 3r/29cv:m1qecdk2ce between two protons $ 5.0 \times10^{ -15}\,m$ apart from each other in an atomic nucleus?    N

  What is the magnitude of the forceyfvrk u n8hzhlda:.c8 i uj 1..825krk a $+25\,\mu C\,C$ charge exerts on a $+\,3.0\,mC$ charge 35 cm away?    N

  Two charged dust particles exert a f ,v :h3sot0gixorce 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 forcexrb:cez 4 m6f5 on each of them is found to have been tripled. How far apart ae4m6xr: c5zb fre they now?    cm

  A person scuffing her feet on a wool rug on a dry day accumulate:y3(cookzxe4iy1e h+aq1:6wu jqz q9 s a net charge of +61 z:exqkquzqh(o4y 3e9ic1yoa j: w$-42\,\mu C\,.$ 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 thx1.95 ocs ppyne electrons in 1.0 kg of $H_2O\,?$    $ \times10^{ 7}\,C$

  Compare the electric force holding the elect9ufvu) :6wzwkp 5j:gf ron 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 their chr;b25)y x bfffarges is What cyf;f5 )f bx2brharge must each have in order to
(a) maximize the electric force between them,
(b) minimize it?

  Particles of charge fx9.0ni9m2wgg4 jm eg$+75$,$+48$ 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 equnaqv e5bhow kbb8(5kq(45+,t.cbkl tal 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 isfqh -q3mk s1-kfi2m -j placed at each corner of a square 0.100 m on a side. Determine the magnitude3mhfm jk 2--i f-s1qkq 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 posgfnn mt1zp03 4itive charges, on opposite corners, are replaced by negative charges of the fm 0npn1 tg4z3same magnitude (Fig. 16–51).
$F_4$ =   $ \times10^{ 7}\,N$
$\theta$ =    $^{\circ}$

  At each corner of a square of side l there are poinj794 )o o zhwvtm,p:yst charges of magnitude Q, 2Q, 3Q, and 4Q (Fig. 16–52). Determine the force on (a) the charge,p js:v4wtoyomz9) 7h 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 corner0wqt*b-b3n*d wh a.kk0 qoj3os of an equilateral triangle of side 1.20 m (Fig. 16–53). The cwbahq-o*bk 3q.o 0wnkt3 d* j0harges 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 : o)zm hqgq845 ad5rqbof $560\,\mu C\,.$ 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 charg2- 1mw4sp o qynat8sx:e of $90.0\,\mu C\,.$
(a) When placed 1.06 m apart, the force each exerts on the other is 12.0 N and is repulsive. What is the charge on each?    $ \times10^{ -6}\,C$$\;\;\;\;$    $ \times10^{ -6}\,C$
(b) What if the force were attractive?    $ \times10^{ -6}\,C$$\;\;\;\;$    $ \times10^{ -6}\,C$

  A charge Q is transferred from an initia dhq0t9a a0 z/z-d5-qbakgdi3lly uncharged plastic ball to an identical ball 12 cm away. The force of attraction is then 17 mN. How many electrk-adt- qid09ba 5z /3 za0ghqdons were transferred from one ball to the other?    $ \times10^{ 12}$ electrons

  What are the magnitude 4/6ktoblg 0 (szg,bkk)zc a6a and direction of the electric force on an electron in a uniform eleo0/6z kk6)zltagbg s(,a cb 4kctric field of strength $2360\,N/C$ that points due east?
   $ \times10^{ -16}\,N$
 ----待选择----westeast 

  A proton is released in a uniform e8 z9z+hiq:y okvb8bc.lectric field, and it experiences an electriczk9i8yvq+: 8cbh zo.b force 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 wrz o666 negzi0brs69 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 fielt7h;3x+ lw r) c 298kryfryf55nkxxmrd 20.0 cm directly above an wr3c 8f; lr5x9x kht2rkyr)5mnf+7xy isolated $33.0 \times10^{ -6}\,C$ charge?    $ \times10^{6 }\,N/C$ ----待选择----updown 

  What is the magnitude of the acceleration experia a-sbgq0ij5wpn;-( fj/fudmvml 2;v 9i1i/h enced by an electron in an electric fiel a j/0;p2wili;i51mf -gm-uf/q9davvsjnb h(d 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 dip9-4hyy ecu8xee 8hi :rection of the electric field at a point midway betw:h4i -c8ye uhpex e89yeen 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 c oieqc0y:b:k4xnwy26q f 6l5eharges, $+Q$ and $-3Q$ which are a distance l apart.

  What is the electric field strength at a poq vs; i-ye+ k/1vpg6hzbj/al3int 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 electric field and accelerates x.hd i11oh.p nzswj60 bpng47to the north at a4j 6sn 1hoz1bpig7p.w.0 xdhn 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 equi 5dko83xj 5vky6gehdd- w9lo7 8g0-kg0 i crcal 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 center of a square 52.5 cm on a side if 7wq k1+zmux4done corner is occupied by aq wkz+m ud41x7 $+45.0\,\mu C\,$ charge and the other three are occupied by $-27\,\mu C\,$ charges.    $ \times10^{6 }\,N/C$ at    $^{\circ}\,$

  Calculate the electric field at onsv4qc bhm0f,mg 7 ;0im v61po zg3;zdne corner of a square 1.00 m on a side if the other three corners z1zs7 m dibp ; gofvn0vm ;gch3m64,q0are occupied by $ 2.25\times10^{-6 }\,C$ charges.    $ \times10^{4 }\,N/C$   $^{\circ}\,$ from the x-direction.

Determine the directionrt2yv) d31tg f0b (f7plrtl*u and magnitude of the electric field at the point P in Fig. 1tu 3 * t7t(vfgrd2lrl f1b)yp06–54. The charges are separated 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 eleckd,0m adm )7;4ngg1djnp b uh(tric 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 electri)pg mp cex,eu7it7l:t :8*oxmc field at points A and B in Fig. 16–57 due to the two positui:ep,8* pxml)xm 7 teo:7tc give 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 unknf 1k(fdz j5x,eu n9q0 5cbp(xsown 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 the electwsf99ya2r :4 e9p ih-qdrv+vfs 9hf y*ric field at the point P shown in Fig. 16–59. The two charges are separated by a distance of 2a. Point fp r-+* 9: hiv4say9sh2qy e9frfdw9v 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 rig4i q2 grvde*;:k cdt7hht at 1.0% the speed of light enters a uniform electric field parallel to its direction of motion. If the electron is to be brouh:d7citr d e;kq2*v g4ght 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 c* y1urh8bv06hucr 0oq ubical 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 h/q *zwl cv:lg)nh55scm is placed in a uniform electric field of magnitude h) *wgnlq v/5lz 5chs:$ 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 obje4lczady t+ ggkw+8m9 e) 5h+ ymo*/bqicts, $O_1$ 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 62asv0+fhtnb 9dq2 ugh b-5v kin a uniform 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 os jad(+ 29d q5bjcq4ctwo square metal plates is The plates are 1.0 m on a side and are separated by 3.0 cm. What is the charge on each pd 4qd(c5j+qj2co b9aslate (assume equal and opposite)? Neglect edge effects.    $ \times10^{-9 }\,C$

  The field just outside a f2 2o(suo mca.3.50-cm-radius metal ball is $ 2.75\times10^{2}\,N/C$ and points toward the ball. What charge resides on the ball?    $ \times10^{-11 }\,C$

  A solid metal sphere of radius 3.00 m carries a tot 8jb d 9:6s/b2vx qqz)7ggjibhal 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 centq-t4 ;3mb5lijsv vxq9at ardf3; p2 r/er of an uncharged 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?i;fjt s/qarvdtlp 3;mb4vqxa29-5 r 3 (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 together by electrostv30ga zfk2eclc 2b7r, atic 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 ato 2l3c7, c2vz fbragek0ms is 0.4e. Assume also that atoms on each molecule are separated by $ 1.0\times10^{ -10}\,m$. Estimate the net force between
(a) a thymine and an adenine;    $ \times10^{-10 }\,N$
(b) a cytosine and a guanine. For each bond (red dots) consider only the three atoms in a line (two atoms on one molecule, one atom on the other).    $ \times10^{-10 }\,N$
(c) Estimate the total force for a DNA molecule containing $10^5$ pairs of such molecules.    $ \times10^{-5 }\,N$

  How close must two electrons be if the electric force between them is08xle. ffj o8k equal to thefj8ef .08o lxk weight of either at the Earth’s surface?    m

  A 3.0-g copper penny has a positive charge rbe6g 7gopc *-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 tdq:w1 snf:u4b here is an electric field surrounding the Earth. Its magnituds unw f::1qdb4e 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 experienc:on*p p:3aq-r 5s sgm+s ge:wl-bhcf; ed by an eleh-ca*sb: ls+ 5nmg3wpq prseg:-;o: f ctron near 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 radi270ehjdi 3j 4p uyk0p5mc (kuhus 0.018 mm remains stationary in the air. If the downward-directed electri0pc up7kyj (h mde5u3204k hjic field of the Earth is $150\,N/C$ how many excess electron charges must the water droplet have?    $ \times10^{ 6}$ electrons

  Estimate the net force betwe1k hdpl.mn5 1.bb1kvx en the CO group and the HN group shown in Fig. 16–62. The C and p h.l15bdx.1km1 nkbv 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 atolzvs /np v(x8i4+rq, rk/p0 mcuey) 8om, the electron revolves in a circular orbit around the prokupxv s+4/ mrye i,/8q8l0)(pcznvorton with a speed of $ 1.1\times10^{6 }\，m/s,$. Determine the radius of the electron’s orbit. [Hint: See Chapter 5 on circular motion.]    $ \times10^{-10 }\, m$

  Suppose that electrical attraction, rather than gravity, were responsible fora w)383han)a+ r2 3lm .umjlt3 oekpzu holding the Moon in orbit around the Earth. If equal and opposite charges Q were placed on th3).8oaajw3et2 ak 3u zmmhl)n lu+p r3e 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 speed ue hy: zy6:luczw8 +o-6r:xwk$v_0\,=\, 21.5\times10^{6}\,m/s$ 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 cha)4u8 h-ct vzxoh c-ru(rge $Q_1\,=\, 2.5\times10^{-5}\,C$. 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 io .7ig(vem2uvn insulating plastic and suspended vertically from an ideal smgo.v27v i(eu pring $(k\,=\,126N/m)$ 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” th/tf2oi5 if osw8216 hlanj at*at are 78-cm-long wires with tiny 24-g spheres at the ends. When charged, neonfl28tfa ao /62 i* i1jh5tswarly 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 field exceehj3 cy8eus roq*;t:5m ds about*35q:s 8c hmuetyojr; $ 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 kmfr96 n-h,dmjqm 9(yi g, 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 hag8a ; 5lw6b-id7 s ay6d/phta 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 distance R aparc5j pi5t).loc t; each carries the same charge Q. (a) What is the force sphere B exerts on sphe)l.5 5ijtcoc pre 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 the electricye5yb 14*livi field zero? Is the field zero at any other points, not on the x axis*4 yy5lei1vbi ?

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 poini gfztxkus *7n*40c(7z nza:t t 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?