If you charge a pocket comb by z2a9z*q.d bb vrubbing it with a silk scarf, how can you determine if the *av 29. bdzzbqcomb is positively or negatively charged?

Why does a shirt or blouse taken from a clothes dryer sometimep*hdj+p/ .7hc hzd :gos cling to your boh/*dhppzgdo7 ch.j: +dy?

Explain why fog or rain droplets ten6z4 w1 /lxq15zct waqwd to form around ions or electrons in the air.tzwa5 qxq 1c/z1l 4w6w

A positively charged rod is brought close to a neutral ptrw4z 1z 1-ujmiece of paper, which it attracts. Draw a diag-tmzzjru41 w 1ram showing the separation of charge and explain why attraction occurs.

Why does a plastic ruler that has be5ik; e dl7k 0rnyq7el-en rubbed with a cloth have the ability to pick up smallkl q e57;d-n0ke7ryil pieces of paper? Why is this difficult to do on a humid day?

Contrast the net charge on a conductor to 21k*c lijl3ic the “free charges” in the conductor.

Figures 16–7 and 16–8 show how a charged rod placed near an uda);* vbe jdw26csd4 pncharged metal object can attract (or repel) electrons. There are a great many electrons in the metal, yet only some of thadwv* 6 ;)42jdcpsde bem move as shown. Why not all of them?

When an electroscope is charged, its two leaves repel each othp i8 zfxk)6s/i6gsl( rer and remain at an angle. What balances the electric zsixs/ki(f l86p) 6rg force of repulsion so that the leaves don’t separate further?

The form of Coulomb’s law is very similar to thatfx966a zca-yjej m4w( for Newton’s law of universal gravitation. What a4-6( 9wcz xje m6fyjaare the differences between these two laws? Compare also gravitational mass and electric charge.

We are not normally aware of the graux5:-hn x;sf y;xg;ox t nr*6;sppxr4vitational or electric force between two ordinary objects. What is the reason in each case? Give an example where we are aware o;xo ;y-nxfx;pxurpr6n * hsx:4s 5;tgf each one and why.

Is the electric force a conservative force? Why or why r2ps n)iym5l(uncz:4t ar: x1not? (See Chapter 6.)

When a charged ruler attracts small piec-7h 7. tmnufdaes of paper, sometimes a piece jumps quickly away after touchinh7tm - d7an.fug the ruler. Explain.

Explain why the test charges we use when measurincs;i up7wp20wx1p+apvy k a 6:g electric fields must be smalli1p7xvakuw2py+p cwa ;6s0:p.

When determining an electric field, must we use a positive test chargtu hx(v:hn/ z+e, or would a negative one do ast:vn(hhu +/zx well? Explain.

Draw the electric field lines surrounding two negative electric ch,nwhe4tov w,ys1dtr+ t)n ( v)arges a distance l ap1+,( sdtr 4hwtoe)y, n)wntvvart.

Assume that the two opposite charges in Fig. 16–31a are 12.0 cm apart. Cons,wdont(gm 4; yf5k:r dider 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?,rd;okt( ywg :f 4dn5m The weakest? Explain.

Consider the electric field at points A, B, and C ixrcfrkli1 7q;+avh+ ;n 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 thk+;ifhl 1vx+7 qr ;carat point, then list the points in order of decreasing field strength (strongest first).

Why can electric field lines never cronpt 3om xl5+5gss?

Show, using the three rules for field lines given in Section 16–8, that th /4/gqq pmupl5+zjhb4u6k /rqe electric field lines starting or ending on a single point char qhuk4q//rl5+ q6um pj b4z/gpge must be symmetrically spaced around the charge.

Given two point charges Q and 2Q,k5wmnp 5/r7*jlze n4i a distance l apart, is there a point along the straight line that pakimz5wr/45lj* pnn 7esses through them where E=0 when their signs are (a) opposite, (b) the same? If yes, state roughly where this point will be.

Consider a small positive tqnje yg 16sr35 o.jhh-est charge 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 acj6 -h rojs3 h.51ngqeyceleration of the test charge along this line? Discuss.

Sketch the electric field lines for a unifo3 l lutyrx*+h+rm line of charge which is infinitely long. (Hint: Use symmetry.) Is the electric field uniform inl+3hl y t+ru*x strength?

If the electric flux through a closed surf(j+ hwptj9 r ba;u; pebs;y *c9wd8jk9ace is zero, is the electric field necessarily zero at all poih*uj9 t;9brwacdjj9p+ 8yws b;pek;(nts 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 surrounded by a sphericaxoq7:pl oxu0x0 lbr2 7l gaussian surface of radius r. If the sphere is replaced by a cube of sq ru7lx :x72l0poxob 0ide r, will $\Phi_E$ be larger, smaller, or the same? Explain.

  

  How many electrons make up a chargeaarc -+h.gzw 7 jrvl,8 of $-30.0\mu C\,?$   $ \times10^{ 14}\, electrons $

  What is the magnitude of the electric force of attraction be ti.obu70g e.6zb3t js s7.9ny;bt uqrtween an iron nucleuszt7i;0n6.qbtg 3ybrsu..s o buje79 t $(q\,=\,+26e)$ 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 ,g ykmls)n x41protons $ 5.0 \times10^{ -15}\,m$ apart from each other in an atomic nucleus?    N

  What is the magnitude of3hhb3g x3 x4z9ji*qg t the force a $+25\,\mu C\,C$ charge exerts on a $+\,3.0\,mC$ charge 35 cm away?    N

  Two charged dust particles av3kw. c 2 z5lt0hbhu9h:zi,a 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 cm apart. They are moved, and the force on eac 8m-3t etf 4b5t8dtok1c * z-pfbxjt/nh of them is found to have been tripled. How-b- 1n tpf8 5tcm3/t oztekd4b8jtf x* far apart are they now?    cm

  A person scuffing her feet on a wool rug on a dry day accumulates a net c8 k /k;e6yn(bf ngwo)aharge of /n8k w6 k fo;g()eanyb$-42\,\mu C\,.$ 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 oxf758 wp kzf(cf all the electrons in 1.0 kg of $H_2O\,?$    $ \times10^{ 7}\,C$

  Compare the electric force holding the e2xx2 2j bb4agshm ;nn9lectron 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 a0 u od/i osm9rt8+szl.wqr8d4 re a fixed distance apart. The sum of their charges is What charg8wti.dqordl 0+s4 r8 9zs m/oue must each have in order to
(a) maximize the electric force between them,
(b) minimize it?

  Particles of charge 1mp+8)eynxq2wn4- kvyta b ( p$+75$,$+48$ 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 equ*,j fro, rhcw*3*ioacal 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 pbcep;jvo5k*o3yko 8lfyz 1) )laced at each corner of a square 0.100 m on a side. Determine the magnitude)yokf vobzcp51l; j8o 3 k*y)e and direction of the force on each charge.
$F_4$ =   $ \times10^{ 7}\,N$
$\theta$ =    $^{\circ}$

  Repeat Problem 14 for the case qv4m.p5zc owdh6x-): bfm. ghwhen two of the positive charges, on opposite corners, are replaced by negative charges of .p:zf. 5bdm c6g4xh-m vo)whq the same magnitude (Fig. 16–51).
$F_4$ =   $ \times10^{ 7}\,N$
$\theta$ =    $^{\circ}$

  At each corner of a squajouwnk- 9 io47re of side l there are point charges of magnitude Q, 2Q, 3Q, and 4Q (Fig. 16–52). Determine the force on (a) the charge 2Q, and (b) the charge 3Q, o4 9 7onjiuwk-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 ofjd;kzr3o8v q( r7rk-4 j 5dpqw side w qd4pqr 5j3vkrz (7ko;dr8-j1.20 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 tota/kve hf 26oqj/8 q*8(w kkihnyl charge of $560\,\mu C\,.$ When placed 1.10 m apart, the force each exerts on the other is 22.8 N and is repulsive. What is the charge on each?
q = $ 5.54\times10^{a }\,C$ a =  ,
$ 5.54\times10^{b }\,C $ b =   
Q-q = $ 5.54\times10^{a }\,C$ a =  ,
$ 5.54\times10^{b }\,C$ b =   

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

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

  Two small nonconducting spheres havey r2 vk;/ubi9e 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 un8.b0mn u06 tio-f be/zghekx5 charged plastic ball to an identical ball 12 ck.6b0h8un / og ie5 xf-0tezbmm away. 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 gs25e)gpa.xebl ,mms :vj3qr0e)1k o and direction of the electric force on an electron in a uniform electric field oerapv:x ,s2bs1) 5o0 eek qg3m. l)gmjf strength $2360\,N/C$ that points due east?
   $ \times10^{ -16}\,N$
 ----待选择----westeast 

  A proton is released in8 q6x60e zb/aj)orluz a uniform electric field, and it experiences an electric forcee6 ojax zr8 z6)lqb0/u 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 er6ejg ih0 )vg7xerted 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 andk*c)tj n6ch ncd-ii6 ) direction of the electric field 20.0 cm directly above anc-))ih6t ndj *k6 nicc isolated $33.0 \times10^{ -6}\,C$ charge?    $ \times10^{6 }\,N/C$ ----待选择----updown 

  What is the magnitude of the accarfd/o *gvr:3 vhmg)px )k26heleration experienced by an electron in an electric) g)a vorhdv k2r:hm3x6f/g*p 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 direction of the electric field at a arh, v8-c ari(z1-jpr point midway between az,j ap 8r(1 hir-va-rc $-8.0\,\mu C\,$ 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 electrijg o,+9/d3 s cxauxq1ic field lines about two point charges, $+Q$ and $-3Q$ which are a distance l apart.

  What is the electric field strength at a point in vn4of;rx/ . vnfqng:o nt17z01uwb t( 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 i.b+xc q8dkh we-6) p)e f1qwpjn a uniform electric field and accelerates to t8e+6d)k q w1phc)-p wexqjfb .he north at a rate of $115\,m/s^2\,.$ What are the magnitude and direction of the electric field?    $ \times10^{-10 }\,N/C$ ----待选择----northsouth 

  The electric field midway between two equal but opposite point cha iu,+:m s acmmz4o 0de6hax1v0rges 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 onn p779mer yex2 a side if one corney7er7pm9xn 2er 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 ofzznaj(m(ev h .k: -,zy a square 1.00 m on a side if the other t eaz: mnyz,-h((jkvz.hree 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 Fio 3up 3twoz*x6g. 16–54. The charges are separated by a distance 2a, and point P is a distance x from the midpoint between the two charges. Express your answer in terms of Q, x, a, anou zotpx*33 w6d 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 electdf1 c42do0 sz7hp 4ytqric 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 magnithk l5ich6pc, -ude and direction of the electric field at points A and B in Fig. 16–57 due to the two positive charg6ilkhp h,c5-ces $(Q\,=\,7.0\mu C\,)$ 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 unknowipn /(ze.lpdz*wfpcbhs9 7 66n 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 thhlz5svh n a1tuzh s*8 sz.6(o9e 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 answers in terms ofzzsn 5*6ho v819t lhz.s(sa uh 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 speedhao/rn 4) ujz8b 4iwv, of light enters a uniform electric field parallel to its direction of motion. If the electron is to be brought to rest in the spihu,br/ 4 8ovzw j4)naace 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 flux81mch ,lewx5 d from 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 uniform e kluea xu 5ie4b3g**q3lectric field of magnitude lx3eu 3ea54q uki*gb *$ 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 obje:9ohd flzbq+g yg w/de9oo.6 /n7 p7vhcts, $O_1$ 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 uniform field :rn8yhubi.,wt vze 62 $ 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 3i w6a4dnry v;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 ;w ian3vy4dr 6(assume equal and opposite)? Neglect edge effects.    $ \times10^{-9 }\,C$

  The field just outside a 3.50o8/w:f6m 3vbkvvuk q4-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 3.057ik-1s umd*g2ez5d xysza e50 m carries 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 spherical .yqsqm .qx dk.o*:n)t9bqq )rconducting shell. (See Fig. 16–33.) What is the electric field E as a function of r (a) for r less than the inner radius of the shell, (b) inside the shell, and (c) beyond the shell? (d) Does the shell affect the field due tk 9dqton .m)qq rs.:*.qb) xyqo Q alone? Does the charge Q affect the shell?

  The two strands of the helix-shaped DNA molecule are held together by el 2ddzlp2i.*1ygg+ zg eectrostatic 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 indicated12zy+glp z *egid g.d2 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 between them is equaxh9f gmk x8*1fh(.xsml to th*sghm( x.x1 8 9mfxfhke weight of either at the Earth’s surface?    m

  A 3.0-g copper penny has a positive crigd5zvl:6 p 5harge of $38\mu C$. What fraction of its electrons has it lost?    $ \times10^{-10 }\,$

  A proton $(m\,=\,1.67 \times10^{-27}\,kg)$ is suspended at rest in a uniform electric field $\vec{E}$. Take into account gravity at the Earth’s surface, and determine $\vec{E}$.    $ \times10^{-7 }\,N/C$  ----待选择----updown 

  Measurements indicate that there is an electric field surrounding the Earth. ;9qwz:ouf/3nv x9 jm: xzt1gr Its magni91;3v t/wzn9mouf:xg qx zjr:tude 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 exh u/+8thgiux 0perienced by an e/t8 h u0giux+hlectron 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 radius 0p o 7 rf,n0p c(2),sv;drkhedu;wx z*t.018 mm remains stationary in the air. If the downward-directed electric field of 7r 0xd(2 u e;t* hk,;srn)cpzvofpw,dthe Earth is $150\,N/C$ how many excess electron charges must the water droplet have?    $ \times10^{ 6}$ electrons

  Estimate the net force between the COzqa7w(dpw 6hk 8q bn/6 group and the HN group shown in Fig. 16–62. Theh qa pznwk7q6(86d/wb 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 el dz95 zveo.ds*ectron revolves in a circular orbit around the proton wzzvsdd5e 9o.* ith 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-e8 (6 1jeujydsvr; sc, were responsible for holding the Moon in orbit around the Earth. If equal and opposite charges Q were placed on the Earth and the Moon, what should be the value of Q to maintain the present orbit? Use these data: ma 1jdc( essvje8y-;r6 uss 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 gc.m(qa7+1d q nbtz/iz3tptgx* jw.1 $v_0\,=\, 21.5\times10^{6}\,m/s$ 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 charge/kbv5g-e.r4xd 0o*jqtp k:g* 4 zcaup $Q_1\,=\, 2.5\times10^{-5}\,C$. 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 c6na3 p2rgfh2 insulating plastic and suspended vertically fromhg36apr2 fnc2 an 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 is made with “lklgpxop 2 g: 16u0zsg5eaves” that are 78-cm-long wires with tiny 24-g spheres at the ends. When charged, nearly all the charge resides on0zl g1xp o5kusg62gp: 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 sbr dr:/3xp fv8park if the electric field exceeds aboutr8/v3fx:d bpr $ 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 0z865n* sx +2hbkkqaov3+ mcbd.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 b;k kdncpd*0k wch:* ulj2)y *oar 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 anybdo l9 vkbk :ql8;c98d B are a distance R apart; each carries the same charge Q. (a) What is the force sphere B exerts on sphere A? (b) An identical sphere with zero charge, sphere C, makes contact with sphere B and is then moved very far away. What is the net force now acting on sphere A? (c) Sphere C next b kqd98 ;9vlo8kc by:lmakes contact with sphere A and is then moved far away. What is the force on sphere A in this third case?

Given the two chargess16j2oef l55u ;vku e t)phjd: shown in Fig. 16–68, at what position(s) x is the electric field zero? Is the field zero at any other points, not on the x axisje6d5luj h:ktv su e;f1p2 )5o?

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, eaw a b2btach*4 t/)1tm(c awq4ach 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?