If you charge a pocket comb by rubbing it with a silk scarf, how can bs o: +78zpd)y 0/uiaupv cne5you determine if the comb is positively or negatively 8 /57pednubo0)yi:zsu acp v+charged?

Why does a shirt or blouse taken from a clothes dryer sometimes cling t*p + fqtgejrm8+w kt4.o your body? wkq4tjr 8m+ tg*+.fpe

Explain why fog or rain droplets tend to form around ions xxujy/q (v +7por electrons in the air.p(qx /u j+xv7y

A positively charged rod is brought close to a neutral piece of paper fou/g7 xp(/yt3km/ii , which it attracts. Draw a diagram showing the separation of charge tm 3/(i fop/ gxi/uyk7and explain why attraction occurs.

Why does a plastic ruler that has been rubbed with a cloe r-focy p8f64u lvf5*th have the ability to pick up small pieces of paper? Why is this difficult to 8rcffpy uf4v56ol e*-do on a humid day?

Contrast the net charge on a conductor to the: 43c4 q*czb( coo2phx opy8zo “free charges” in the conductor.

Figures 16–7 and 16–8 show how a charged i(n-5l fsf nwwf3do,caw0:a9rod placed near an uncharged metal object can attract (or repel) electrons. There are a great many electrons in the nf9 o:f 30-niaw,ld( w cswa5fmetal, yet only some of them move as shown. Why not all of them?

When an electroscope 9g7ve)um *rtgs by,+nis charged, its two leaves repel each other and remain at an angle. What balances the electric force of repulsion so that the leaves don’t separate further, g9m t r7gbs)*n+uevy?

The form of Coulomb’di cm8 hm/nu6(ymy1 d95r.rtjs law is very similar to that for Newton’s law of universal gravitation. What are the differences between these two laws? Compare also gravitational mass and electric myn r mi(cru .dj9y5m/6d18 htcharge.

We are not normally aware of the gravitational or electric force betwe+juqb+ fkl eqdeglemu63+(. 3en two ordinary objects. What is the reason in each case? Give an example where we are aware of each one and b(qe6+ lu++u .dj ekm3g3el qfwhy.

Is the electric force m6zx zm*wc764 h 2njera conservative force? Why or why not? (See Chapter 6.)

When a charged ruler attre9ym ul3l3rhs )rn wp.a7w.*k.g4pdd acts small pieces of paper, sometimes a piece jumps quickly away d7psl)wlae. udng krh.r34mw9* .py 3after touching the ruler. Explain.

Explain why the test charges lpj ur4r3+em w8zw+ a8we use when measuring electric fields must be smallz r4w++lu8 mw8a rep3j.

When determining an electric field, must we 8/ma gau y:/tfuse a positive test charge, or would a negative one do as well/ m:atf/8 guya? Explain.

Draw the electric field lines surrounding two negative elects3pdn1wdn8/9m hnol 5 ric charges a distance l apart. s8mln d1w395/onnph d

Assume that the two os(f g*ep6 bg(xpposite charges in Fig. 16–31a are 12.0 cm apart. Consider the magnitude of the electric field 2.5 cm from the positive charge. On which side of this charge —6bp(g*g(esxf top, bottom, left, or right — is the electric field the strongest? The weakest? Explain.

Consider the electric fielw(k;qa yo; e c jfs1xv2;lgz-*d at points A, B, and C in 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 lis * ;y gwj2 ;ef-aolzsk;q1v(cxt the points in order of decreasing field strength (strongest first).

Why can electric field lines nywnba49xlh73b *rtz + oz)rig :v 8f.iever cross?

Show, using the three rules for field lines given in Section (f/5z*4 uk5z dgqaryz 16–8, that the electric field lines starting or ending on a single point charge must be symmetrically spaced aroun* yuz(5akg 5 fd4qzz/rd the charge.

Given two point charges Q and 2Q, a distkwzj/2ds:y6g ,kp z.nance l apart, is there 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 roughly where this jyg.zkd,w s2/:pz kn6 point will be.

Consider a small positive test charge loc ) rz-ihi83;cph1sch yhk *q9lated on an electric field line at some point, such as point P in Fig. 16–31a. Is the direction of the velocity and/or acceleration of the test charge along this l8h;ycc qhs9p h*r i lzki-1)3hine? Discuss.

Sketch the electric fiefb1s *90xyo epld lines for a uniform line of charge which is infinitely long. (Hint: Use symmetry.) Is the electr*x yb1f e09ospic field uniform in strength?

If the electric flux through a closed surfa4m*c:wfo8 6 p ucnxgh3ce is zero, is the electric field necessarily zero at all points on the surface? Explain. What about the c6xwhcfo 8m3 u*pgc:n 4onverse: 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 surfac5(/ s1tv6bnp y+ezdfke of radius r. If the sphere is replaced by a cube of side r, wills kp+vyf1(6 /t endzb5 $\Phi_E$ be larger, smaller, or the same? Explain.

  

  How many electrons make uh6)s g0n5bxpk p a charge of $-30.0\mu C\,?$   $ \times10^{ 14}\, electrons $

  What is the magnitude of the electric force of attraction between an irwjk/.,ef7 gzmon nucleu f.jkzw7,/m ges $(q\,=\,+26e)$ 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 protom)z9 d4r*bn5xfsd 7t kns $ 5.0 \times10^{ -15}\,m$ apart from each other in an atomic nucleus?    N

  What is the magnitude of the force anrecga6,lw6 3t (254tt skygm $+25\,\mu C\,C$ charge exerts on a $+\,3.0\,mC$ charge 35 cm away?    N

  Two charged dust parts/ i*.h bsp*/hieqf 4ce9qb h5uai1;bicles 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 8.45 cmk dg9zqe5,)c- vmyxr 0 apart. They are moved, and the force on each of them is found to have been tripled. How far apartkgq m-r0y,z5d) v9exc are they now?    cm

  A person scuffing her fejf )imx va.h72et on a wool rug on a dry day accumulates a net charge oh27m faj .)xivf $-42\,\mu C\,.$ 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 electron rr.xn3 ht)pc*s in 1.0 kg of $H_2O\,?$    $ \times10^{ 7}\,C$

  Compare the electric force holding the electl(9w ws-m zkvla:; t7zron 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. The4v 6pk;z gp1yn sum of their charges is What charge 46zp nkv 1g;pymust each have in order to
(a) maximize the electric force between them,
(b) minimize it?

  Particles of charge p8jzrna /yv z9+gc,0k$+75$,$+48$ 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 eqy/2 7igxmt0h.e5ksc8z 7rpdr ual 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 nm v if81-rx5bgy7n3no7wzi1 placed at each corner of a square 0.100 m on a side. Determine the magnw zim1 brn-iyo71g5n vx87 f3nitude and direction of the force on each charge.
$F_4$ =   $ \times10^{ 7}\,N$
$\theta$ =    $^{\circ}$

  Repeat Problem 14 for the case when gn omrwcs6-p:bgcn;(7 o8ok7 two of the positive charges, on opposite corners, are replaced by negative charges of the same magnitude (Fig.mop8;n-7ng gc6r7oo b(wsc: k 16–51).
$F_4$ =   $ \times10^{ 7}\,N$
$\theta$ =    $^{\circ}$

  At each corner of a square of side l there are point chlz9*ga)a t*(hl f.nta arges of magnitude Q, 2Q, 3Q, and 4Q (Fig. 16–52).t) az lg9*(a*.hfaln t 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 particles are placed at the corners of an equilateral triangle v dbcn0 hu5(5;b rfi0rof side 1.20 urf;d 0i5( rhbvc5n0b 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 chugd fi 7 g/uy0s/*eay-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 )so 6 wdpsdmf;p;ifqt5nsb t (6u*r*6arge 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 transfer yzpl 8u ;z,x*avylw+2red from an initially uncharged plastic ball to an identical ball 12 cm yz2;v*+p la,zxu 8wlyaway. The force of attraction is then 17 mN. How many electrons were transferred from one ball to the other?    $ \times10^{ 12}$ electrons

  What are the magnitude and direction of the electric force on an electronuk4gh-; : bgm-hsz 0as 1phew0 in a uniform electric field ofhs-1g0h4puh 0em;zk - g baw:s strength $2360\,N/C$ that points due east?
   $ \times10^{ -16}\,N$
 ----待选择----westeast 

  A proton is released in a uniform electric field, and it experiences an electri.c p igcxwm9ms3: m64cc force oc4mxpicmc:w3 9m6 gs .f $ 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 exerted o.h*7on y bo r*6txuz8en 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 zr6t1 r(k-i 9rxuo 7kvof the electric field 20.0 cm directly above an iztxi(r- r9okr k671v usolated $33.0 \times10^{ -6}\,C$ charge?    $ \times10^{6 }\,N/C$ ----待选择----updown 

  What is the magnitude of the acceleit5zr7,m6a gc ration experienced by an electron in an electt7r 6img az,c5ric 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 and directioo*3g t34ggsh5urttr+ n of the electric field at a point midway betwrrt5* ustth4go gg3 +3een 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 electricuvfbodvsf)./* b j )(d field lines about two point charges, $+Q$ and $-3Q$ which are a distance l apart.

  What is the electric field strength at a pzy , 7cxx )qyjt9q1u)coint 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 unifor )y+r7a bt qa,b9ske6gm electric field and accelerates to the north as aa e)6b+byrqk9 t,7gt 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 equac)bxlm 0uxo ho:y-1+el 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 sqs5q3 :0wz,kmrfnh vn vf;5ut 5uare 52.5 cm on a side if one corner is occupiedvq5un,0; h3k5 :sv mtnf5 wzfr 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 o+ ioc,+lf- rruf a square 1.00 m on a side if the othe oul, frc-+i+rr three 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 electric field at the point P in Fi9t ctujg7i4 mqmr+(f .g. 16–54. The charges are separated by a distance 2a, and point P is a distance x from the+ tuf(94.mq tgm7ir jc 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 eleep/fd5o +e-0 apleoh7ctric 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 o3nio b86i 9d8fjt3 akzf the electric field at points A and B in Fig. 16–57 due to the two positive chargeid a9i8fz6bk3j n 8to3s $(Q\,=\,7.0\mu C\,)$ 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 unknov0ecwb z3 a,31j,x dczwn 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 electric field at the point z9v 7zbm (f:wpP 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 fromvp zm7zf(w:b9 the midpoint between them. Express your answers in terms of Q, x, a, and k.

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

  An electron moving to the right ata;7 zinxxxa* 6 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 spaxx x6 i7a;a*znce 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 frr (aam.(o odw:om a cubical box 28.0 cm on a side is $1.45 \times10^{3 }\,N\cdot m^2/C$. What charge is enclosed by the box?    $ \times10^{ -8}\,C$

  A flat circle of radius 18 cm is placed in a (c s iaaa33tcb8:a 5y2n(5xv/sz dnqsc(jz1a uniform electric field of magnitudeazv3ci jsb(1s(za 3ct2a:c sx(nay5qda8 n /5 $ 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 objb:fs67cin*: goj+ wwxf5qm5o ects, $O_1$ 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 pli372gn*0)k t kj9iueqidf4 c naced in 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 bn1e tx.t4k/ vcetween two 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 plate (assume equal and oppotnk t /.e4vx1csite)? Neglect edge effects.    $ \times10^{-9 }\,C$

  The field just outside a 3.50-cm-radbzejm;;ah2uz w06rehm 6 bp48 ius 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 total .gyb z3( phyqx, g(gmn4tb4-ucharge of $-3.5\mu C$ What is the magnitude of the electric field at a distance from the sphere’s center of
(a) 0.15 m,   
(b) 2.90 m,   
(c) 3.10 m,    N/C
(d) 6.00 m?    N/C
(e) How would the answers differ if the sphere were a thin shell?

A point charge Q rests at the center of an uncharged thin spherical con7pj l dl8+lv 9lm.og-tducting 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) D +vl7-l.l jol9gdm8tp oes 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 heb n sq*o47fvogu 3v,-lld 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 ind 4b o-uolf3*v,7gnq svicated 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 electrons be if the electric force betwbs s8 +yq)qr-mh ygh+il77;lqj l).zo een them is equal to the weight of either at +8 i)gqbor m.ls h7;l+qyjqs 7-lhzy) the Earth’s surface?    m

  A 3.0-g copper penny has a positihnfp4//a zft 5b 0xqj.ve 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 surros8/xi q ls;zs:unding the Earth. Its magnitudeis; sx:/8q lsz 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 acceles 06qduw4e1qf,xv*kf5i0qrm ration experienced by an electron near the surface of the E0sff64q1qmqirde 50vwx*, uk arth?    $ \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 remains stationary injv c.i cum.*2y the air. If the downward-directed electric fc icjv2 *uy.m.ield of 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 xy)0n a*u)e9/hn (t szud m ugep5.pp4and the HN group shown in Fig. 16–62. The C and O haveh uptu) ) .a 5*s9d(0xyn4mznepuepg/ 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 circula fi0r 64l1mnz3d;l0hn,qo g hpr orbit around the n,hi;np30h dg0l z1foql4m6r proton 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, rat:u4 dwb hn lnukq7ku7,9o*u ruq0ih39her 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 m h9wd k 7 : nnu40u7q3o,9*uhqluuibrkaintain 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 sped -0.6jpwgd 7)mir fd0 qw5ozsed $v_0\,=\, 21.5\times10^{6}\,m/s$ 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 chardg gt67lt5 9rdnik2eans 1n*/ zpeg41ge $Q_1\,=\, 2.5\times10^{-5}\,C$. 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 vru:/h/ncc:haq xh9 u-): i ycsuspended vertically from an i vyuh/a-xr :qhh/icn :9c:uc)deal 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-cm-lony;r.u. bfkq ;-+dqqtwg wires with tiny 24-g spheres at the ends. When charged, nearly all the charge resides on the spheres. If ;wfq-qqdy rbt.+;u k. 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 exc2 2xhdl (x5roieeds aboutxlhoidx(22 r 5 $ 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 char hno)fy9.j,v kge $+0.340\,\mu C$, 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 og;f)3gtc, 5fze yk u-vf all the electrons 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 distance R apart; rk1t6 9 0h0n6jgv:fu( emd mkeeach 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 A0 v1k tr fm 9(e6mknhduj6e0:g? (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 el*8) j,o(zim2dnfc58kheh cnaectric field zero? Isef c ,a5 onk*dhznj(2mci8 h8) 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 oc)ewgagjfd 8 (:(pe z+f 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?