If you charge a pocket comb by rubbing it with a silk scarf95f z7dz4vzu/ drkkn*)dnh 7o, how can you determine if the comb is positivelz f)zn/vrz45kn 9*dh7u7k odd y or negatively charged?

Why does a shirt or blouse taken from a clothes dryer sometimhcm cgpjhi/ l6cp4j64ohw;/7p s 9hg6es cling to your bodyh 6jplc4p9hg6cw/hs6/ojm; 7g hc 4 ip?

Explain why fog or rain droplets tend to form around ions or elect/)h qrp7 mkfh8yd38 ksvkb1w (rons in the airkhkbk( qrhy/ 8)8f dws vm137p.

A positively chargedj 39svou74fwd rod is brought close to a neutral piece of paper, which it attracts. Draw a diagram showing the separation of charge and expwou734vjfd 9s lain why attraction occurs.

Why does a plastic ruler that has been rubbed with a cloth have the ability to yic 1og7v:g*rx ,mx7 xpick up small pieces of paper? Why is this difficu7 gx:rix yxgc*vmo,7 1lt to do on a humid day?

Contrast the net charge on ac-/+ 1)vzzoyac4r uyb conductor to the “free charges” in the conductor.

Figures 16–7 and 16–8 show hni5 1 //b-k;adtbpx efbm;i h(ow a charged rod placed near an uncharged metal object can attract (or repel) electrons. There are a gh;tei mb;1kf5- /a(pib xn/b dreat many electrons in the metal, yet only some of them move as shown. Why not all of them?

When an electroscope is charged, its two leaves repeloryf9yvv v6,x- 6da ;j each other and remain at an angle. What balan6vvrjy ;xd 6-, 9ayfovces 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 law of universaw 7e0o sarij 3mwim*y5-ip03 il gravitation. What are the differences between these two laws? Compare also gravitational mass and elj0i7p3s mw03riai wi-5 *yoemectric charge.

We are not normally aware of the gravitational 1-b0(dyri 3w6ixvv pz or electric force between two ordinary objects. What is the reason in each case? Give an example where we are aware of each one ab-yvp1r (306 vzi diwxnd why.

Is the electric force a conservative force? Why or wh gfu .9d,nnu:d9yf1 fmy not? (See Chapter 6.)

When a charged ruler attracts small pieces of pa* dqa2r +edot+per, sometimes a piece jumps quickly away after +tre * q2doad+touching the ruler. Explain.

Explain why the test charges we use wk0bc12rittt4)jy kq7 dkg,y; hen measuring electric fields must be smalldt;,tbc k041kikyg)2 y7j r tq.

When determining an electric field, must we use a positive test ali d6*w)) vzdcharge, or would a negative 6))li *adwdv zone do as well? Explain.

Draw the electric field lines surrounding two negative electricsh;;mw6l 0ouj charges a distance lh0 omluj;6sw ; apart.

Assume that the two opposite charges in Fig. 16–31a are 12.0 cm apart. Concn7gvnd2u /s.+pln2m sider 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 the strongest? The weakest? Exnd+m2ugsn /2nl p7v.cplain.

Consider the electric field at points A, B, and C in F 9hmv:bf8 e-h-, ye9vik1tjji ig. 16–48. First draw an arrow at each point indicating the direction of the net force that a positive test charge w1i 9ek:e-hfb,yv mi jv9 jth-8ould experience if placed at that point, then list the points in order of decreasing field strength (strongest first).

Why can electric fielw+ef mc36fy i5d lines never cross?

Show, using the three rules for field lines given in louh4c3 uod i*s)9zee +x r/a7Section 16–8, that the electric field lines starting or ending on a single point charge must be symmetrically spaced around tha)e 3r 74o hzu i*ecxuls+/do9e charge.

Given two point charges Q and 2Q, a distance l apart, is there a pojf zsi dsi.54m*xo54zf+mc. tint along the straight line that passes through them where E=0 when their signs are (a) opposite, (b) the z4ms i5.o+ 4mj5*s .dzt icffxsame? If yes, state roughly where this point will be.

Consider a small positive test charge located on any he:dp ree qogi60:jq/1y.1e electric field line at some point, such as point P in Fig. 16–31a. Is the direction of the veloc1i:hyr e1eqpde qe 0jo6g.:y/ ity and/or acceleration of the test charge along this line? Discuss.

Sketch the electric field lines for a uniform line of charge3nyz 6 ))p61 ouhdo go9)uji)kol+jkn which is infinitely long. (Hint: Use symmetry.) Is the electric field uniform iioy)n )nd)j oj 3lu16 ukpo)ok+g6h z9n strength?

If the electric flux through a closed surface is zero, is the electric 3z6qky,h k0xc field necessarily zero at all points on the surface? Explain. Whaxq36zkc , yhk0t about the converse: If $\vec{E}\,=\,0$ at all points on the surface is the flux through the surface zero?

A point charge is surrounded by a spherical gaussian surface of radius rjepg/ ti 8(pz2. If the sphere is(/ziep jt82 pg replaced by a cube of side r, will $\Phi_E$ be larger, smaller, or the same? Explain.

  

  How many electrons make up db)nifdq n vah/65/q5y(;.ctvf5rc s a charge of $-30.0\mu C\,?$   $ \times10^{ 14}\, electrons $

  What is the magnitude of the electric force of attraction between amq,g/a2a p2z yn iron nucleus g, /amyap22zq$(q\,=\,+26e)$ and its innermost electron if the distance between them is $ 1.5\times10^{-12 }\,m\,?$    $ \times10^{-3 }N$

  What is the repulsivelynpz6 k0;-4pind )zj electrical force between two protons $ 5.0 \times10^{ -15}\,m$ apart from each other in an atomic nucleus?    N

  What is the magnitude ofwa +o* k n/na32y.jill the force a $+25\,\mu C\,C$ charge exerts on a $+\,3.0\,mC$ charge 35 cm away?    N

  Two charged dust particles exert a forcqd 1o(w)yn)ice 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, andm24 +;v,ci2rib7f c ny p4lzeh the force on each of them is found to have been tripled. How far apart are e h+bp4742 mryincif;z2clv ,they now?    cm

  A person scuffing her feet on a wool rugwook: h*qer m*b 8pn70 on a dry day accumulates a net charge of:bhow7* * m ron0p8keq $-42\,\mu C\,.$ 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 electjirbfz;aisk 0w7;( xj1 .q ac3rons in 1.0 kg of $H_2O\,?$    $ \times10^{ 7}\,C$

  Compare the electric force holding the elj7np2dj8+d mm ectron 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 chargrcn lt+l0 s*7fes is Whatl t+7c fr*sn0l charge must each have in order to
(a) maximize the electric force between them,
(b) minimize it?

  Particles of charge v .rs46 t ;7vw61/ub0fphg1 ybfs xxcf$+75$,$+48$ 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 equal charqu 0 cg7tji69ige, $+11.0\,\mu C\,$ 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 0.100 m on a side. Dbqe0/uy4cx:15 avo/ty q q *utetermine the magnitude and direction of the force on eu*yqq/ye 1vxo/ ctb:t4a 05qu ach charge.
$F_4$ =   $ \times10^{ 7}\,N$
$\theta$ =    $^{\circ}$

  Repeat Problem 14 for the case when two of the po bi4x 3b*on(wositive charges, on opposite corne*xiw(bb3no 4 ors, are replaced by negative charges of the same magnitude (Fig. 16–51).
$F_4$ =   $ \times10^{ 7}\,N$
$\theta$ =    $^{\circ}$

  At each corner of a square of side l th v8,ckf qcla9ekw;k6t*wd /hwnmw 552 ere are point charges of magnitude Q, 2Q, 3Q, and 4Q (Fig. 16–52). Detert*wfkc/82 v ;59wwwh,cln5k kd6qe ammine 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 equilab x1n7 nbno(9hteral triangle of side 1.20 m (Fig. 16–53). The chargesonn19 bx(7hnb 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 tof)uhg/q ,dv 4ttal 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 6+va 7u+jgzrtr0yf 5xm(vse7spheres have a total charge of $90.0\,\mu C\,.$
(a) When placed 1.06 m apart, the force each exerts on the other is 12.0 N and is repulsive. What is the charge on each?    $ \times10^{ -6}\,C$$\;\;\;\;$    $ \times10^{ -6}\,C$
(b) What if the force were attractive?    $ \times10^{ -6}\,C$$\;\;\;\;$    $ \times10^{ -6}\,C$

  A charge Q is transferred from an initially k,uee0u 5c .reuncharged plastic ball to an identical ball 12 cm awa,. ecu0euk5ery. 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 electroneuaufw2// kqli5j j53 in a uniualfj3 5 5jquie2/w/ kform electric 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,pik cb+7xy:g o67 .mzd and it experiences an electric fok gymdoxc7.:7z i +b6prce 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 exertov p ns* 3o6zhx,m)4jped 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 cm19so 4z*qeh:5i1 npw +cjt*iem 9kfz w directly above an iso5:if+nhti94j *9wsqepoc m zz*wek11lated $33.0 \times10^{ -6}\,C$ charge?    $ \times10^{6 }\,N/C$ ----待选择----updown 

  What is the magnitude of the acceleration experienced by an electro h9+.)3n inrmy:xlf den in an electric field of 3d.n )rfhe9+ymlx: ni $750\,N/C\,?$ 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 a - qbs*/yv w xkbbc2i:cfy22l4nd direction of the electric field at a point midway betwex:bsqvfwb4k2c*lb iyc22 y/ -en 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 r gsfe2qytpz9w097z (/ nq iyw g2ri5+charges, $+Q$ and $-3Q$ which are a distance l apart.

  What is the electric field strength at a u4i .)f04wq1hry hdnp5 lg-axpoint 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 fr 5b ixf9qt+e4bom rest in a uniform electric field and accelerates to the north b ebt4xi9 fq5+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 opposite poinng+9;fj ls3 5ci5q02m arzcaxt 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 taa5.)pmih p+ k-3rz chhe center of a square 52.5 cm on a side if one corner is occupied by+a chzmkr3 a)ph5.i-p 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 square 1(liic3lo7wd04s k.n t7 opv5a.00 m on a side if the other three corners are occupinivo 37ot l l5k4a0w(d7i csp.ed 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 5 bxa8wib7yu4lbk4dz5lo .s 45szxj) at the point P in Fig. 16–54. The ch 4.54ylzbl i5bas54)wouxj 8szxb7 dk arges 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 electric field) pmqoo+v q*cmg ,k:.u $\vec{E}$ 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 electriuwee-tl7vu7, c field at points A and B in tv7w7e ,eu- ulFig. 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 z,e(:kgl8h5n o f4s gkfh5;ox 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 pointlsqni.q;v:(l:k s .u.qn:uhx P shown in Fig. 16–59. Tuql.iq( ::n.xs l.:;snq hvu khe 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 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 t v*;4juk pebe;7a x9ubo the right at 1.0% the speed of light enters a uniform electric field parallel to its di jx4v u7*eka;beu 9;pbrection of motion. If the electron 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 fromq ewm;vr /4u7n 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 isqcd*t /kuc9 x8 placed in a uniform electric field of magnitude dq/*9 utcckx8$ 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 objectihpev +y9yqb cn8jj.z1:hz(w+ 0h:ils, $O_1$ 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 uniformt5y5 trsab,y5s yba;b3 qc5n 8 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 T4w)2xqvca s 1mhe plates are 1.0 m on a side and are separated by 3.0 cm. Whaw12vasx )qc 4mt is the charge on each plate (assume equal and opposite)? Neglect edge effects.    $ \times10^{-9 }\,C$

  The field just outside a 3.50-c-4*0zusgc / f 5lhx)ydsxo8tfm-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 carriesk 3l+r,a2xm9 gh q:xck a total charge of $-3.5\mu C$ What is the magnitude of the electric field at a distance from the sphere’s center of
(a) 0.15 m,   
(b) 2.90 m,   
(c) 3.10 m,    N/C
(d) 6.00 m?    N/C
(e) How would the answers differ if the sphere were a thin shell?

A point charge Q rests at the center of an uncharged thin spheri;p 4q+b ,ruyhycal conducting shell. (See Fig. 16–33.) What is the electric f 4q ;+uyrp,byhield 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 due to Q alone? Does the charge Q affect the shell?

  The two strands of the helix-shaped DNA moleav6 5lyhd b8uxg4c78 a82bhrgcule are held together by electrostatic forces as shown in Fig. 16–44. Ass8bgh4 6cd2hba5r y8xuga l78 vume 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 electrons be if the electric force1q;,ji zh1qhy uf 0oa7 between them is equal to the weight of either at the Earth’s surface jh;uhyq,0 1 zoqai1f7?    m

  A 3.0-g copper penny h+ moe6 .xe)tlb boll5-h-2 brpas 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 6wp mtt0pneevfc98,xs ;o f) gi5e0u(electric field surrounding the Earth. Its mupf fn9)5 ct ,ot6v0e;s8i(wmeegp0 xagnitude 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 acy jmxdo(5i90uceleration experienced by an electron near the surface of the Earth?doix(9j5 0ym u    $ \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 0.0182g:fzy) os v7yi55ply mm remains stationary in the air. If the downward-directed elec7 )v f gly5yiyo:s25zptric 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 between the CO group and the HN group shown inrcnp9j xw8g8c:s9yd) Fig. 16–62. The89 wdxyc)sc9n j gpr:8 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 ts8r q* 07rhybpv pzj6+he hydrogen atom, the electron revolves in a circular orbit around the protrj 8z*sqh0yr+v pbp 67on 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 electrica 1bmyhxj3+b: i; za3/s; lnripl attraction, rather than gravity, were responsible for holding the Moon in orbit around the Earth. If equal and op ;yziisbhb:3jp1 /nl+3 xa ;mrposite 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 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 spew ye/ vcla,k,;ed $v_0\,=\, 21.5\times10^{6}\,m/s$ 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 char4cu2( yv.bnmz ge $Q_1\,=\, 2.5\times10^{-5}\,C$. 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 in0xeh(8s6o f +pb tlsk2sulating plastic and suspended vertically from anhsx0l26ko8 p +(btsfe ideal 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 mq6 0.dj, imhg1jfpfn 7x;v)pis made with “leaves” that are 78-cm-long wires with tiny 24-g spheres at the ends. When chxin 1gmvj ,hfp j7q0p)m ;.f6darged, 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 electr-a0xbo)qrkv)mffb (h;* ius-ic field exceeds aboutu vfr (x;0sf ab*obqm))- kh-i $ 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 char9 kk)pa+e z )m( l;glmwc4za(ziob6w3 ge $+0.340\,\mu C$, 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 thfk4: .rb,,, 84dputkgfs9p r5tm xhys e 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 5tknur:k o8-bconducting spheres A and B are a distance R apart; each carries th8 5:rtukk o-nbe same charge Q. (a) What is the force sphere B exerts on sphere A? (b) An identical sphere with zero charge, sphere C, makes contact with sphere B and is then moved very far away. What is the net force now acting on sphere A? (c) Sphere C next makes contact with sphere A and is then moved far away. What is the force on sphere A in this third case?

Given the two charges shown in Fig. 16–68, at what posihn),nvap-/ qduu1 qd* tion(s) x is the electric field zero? Is the fieq /qadp*v)-1 hun u,ndld 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 of c,mzobl o-. bw*nj,.i6 r rmr9mharge $8.0\,\mu C$ 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?