If you charge a pocket comb by rubbing it with a silkks26i .: sjbcb scarf, how can you determine if the cob.6cs:kbi2s j mb is positively or negatively charged?

Why does a shirt or blouse taken from a clothes dryer sometimes cling to your .kqyf4yi covgoh99c 0 p 03(gebody?yk 4c ye(cgi 0h 9oo0v9.3fgqp

Explain why fog or rain droplets tend to fopa ;ge 4sx-wx-rm around ions or electrons in the air.e;-swpxgax 4-

A positively charged rod is brolqqsqmvn,cf-(o 1/ r4 5ucrt3py ;z;q ught close to a neutral piece of paper, which it attracts. Draw a diagram showing the separation of charge and expl,q (z;s4ccr-y of q/3q 1mlr5; qupnvtain why attraction occurs.

Why does a plastic ruler that has been rubbed with a rvu4f 8d yj2-vcloth have the ability to pick up smav r u8y2jfd4-vll pieces of paper? Why is this difficult to do on a humid day?

Contrast the net charge on a conductor to the “free charges” in the conducfeztf 9 0shdj gl)fd+0 xj0;7stor.

Figures 16–7 and 16–8 show howt*8w(h7utqx t on zi k-u5+ep- a charged rod placed near an uncharged metal object can attract (or ik+xqz5 w7pent*-o(t-u u8t hrepel) electrons. There are a great 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 repel ea-g7z.sco06rl9l log+r )g a mvch other and remain at an angle. What balances the electric force of repulsion so that the leaves don’t separamor 7arlvo +6glgg09z) s-.c lte further?

The form of Coulomb’s law is very similar to that for Newton’s l bb63mahqb7v)itd h5me r9+7 caw of universal gravitatioda t m7 qi)cb957me+rv3bh 6bhn. What are the differences between these two laws? Compare also gravitational mass and electric charge.

We are not normally aware of the gravitational or electric force between ynfp z3)axf si 3;+a:z*y6nu atwo ordinary objects. What is the reason iz fnaxy )a+z u 6na*si;:f3p3yn each case? Give an example where we are aware of each one and why.

Is the electric force a conservative force? Why or why not? (See Chapt(2e0pp dwqu8k :*k xater 6.)

When a charged ruler attracts smallwd:56ljlx+z ) tz ux; uk8/vfq pieces of paper, sometimes a piece jumps quickj/vwq+x l) ld;8zk:65z txuufly away after touching the ruler. Explain.

Explain why the test charges we use when measuring electric field) vkn, hux nfgx./b4e7s must be smalln kv nf,x/4u .ghe)7xb.

When determining an eld. z*-ak4:eohy g hbx/ectric field, must we use a positive test charge, or would a negative one do as well? Explainh:y-zoxa.g/ek b d *h4.

Draw the electric field lines surrou/aoh r5(it 6/uxcy/gjnding two negative electric charges a distance ru/i/h(xcg y6aot/ 5j l apart.

Assume that the two opposite charges in Fig. 16–31a are 12.0 cm apart. Cbzkka q+:p2scq;*7 *,hxc sg lonsider 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 weakeshaqkxcbqk;*g 7 :ps ls2c* ,z+t? Explain.

Consider the electric field at points A, B, : qs6 jaadtx;r1zi 6(zand C in Fig. 16–48. First draw an arrow at each point iad66sx: jqa;1( rzi ztndicating the direction of the net force that a positive test charge would experience if placed at that point, then list the points in order of decreasing field strength (strongest first).

Why can electric field lines neu0zl0t8gw n hyi s576+qh/zry ver cross?

Show, using the three rules for field lines given in Section 16–8, eew ppm,8 4vg4that the electric field lines starting or endinpw,mp484g ee vg on a single point charge must be symmetrically spaced around the charge.

Given two point chargriepa m57hj6vbq /oc,h/pd4,es Q and 2Q, a distance 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 bhq/a 4,,ijr5vh7 epdcom6 p/where this point will be.

Consider a small positive test charge located 10cyr dkn*wt4wxk7nnc:0c jz 42 p6kron 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 :2xpr4cwj0nwk*n 6 c1yk4k7tnzd r 0c test charge along this line? Discuss.

Sketch the electric field lines for a(56k r 6 uvqf,jdq5b9lkhb/tv uniform line of charge which is infinitely long. (Hint: Use symmetry.) Is the electritrkdhqj bq6b 965l/,vkf vu5(c field uniform in strength?

If the electric flux through a closed surface is5t ;c*ogh d;o(di ly 5+hhbf,x zero, is the electric field necessarily zero at all points +o,(i5h l*c h do x;fgdthb5;yon 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) y )v;kjz+jdkk-v8gzh6uh4 o a spherical gaussian surface of radius r. If the sphere is replaced 4gj; kdvj hz6 y)k+ov)uhk-8z by a cube of side r, will $\Phi_E$ be larger, smaller, or the same? Explain.

  

  How many electrons make up a charge ofv td:;zw.u2 r: +erm6 zl bd/xsuw60wc $-30.0\mu C\,?$   $ \times10^{ 14}\, electrons $

  What is the magnitude of the electric force of attraction between an iron nucleuqnu)sqf 6ns 6e/ 4u;jas n6; fsjseuan6)4 uqq/$(q\,=\,+26e)$ and its innermost electron if the distance between them is $ 1.5\times10^{-12 }\,m\,?$    $ \times10^{-3 }N$

  What is the repulsive electr5b b iko: lmk u50a14gq2lsb 0)bof+aau :fxr.ical force between two protons $ 5.0 \times10^{ -15}\,m$ apart from each other in an atomic nucleus?    N

  What is the magnitude59t /+ jobok9bxr0twp of the force a $+25\,\mu C\,C$ charge exerts on a $+\,3.0\,mC$ charge 35 cm away?    N

  Two charged dust particles exert ah 0p )f1;(zt+bi0im ufm)pugg 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 1nb d3:a f3gylsvf4t3the force on each of them is found to have been tripled. How far apart areld a:s3tvyf b f4g331n they now?    cm

  A person scuffing her feet on a wool rug on zkw .xtm2kx8d 2wqw 1g5*fp r2a dry day accumulates a net charge ofmkd1x2rt z. qfgw2*5p kw x2w8 $-42\,\mu C\,.$ How many excess electrons does she get,    $ \times10^{14 }\,electrons$
by how much does her mass increase?    $ \times10^{-16 }kg$

  What is the total charge of all the electrons in 1.0 yvq6y:y1 2ak qkg of $H_2O\,?$    $ \times10^{ 7}\,C$

  Compare the electric force hol4xn9f tbb-u4 dwk e5n5ding the electron 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 l:8fdt,0 5h d/iuqb kwof their charges is What cha wd0dt: /h5 ki8,fqulbrge must each have in order to
(a) maximize the electric force between them,
(b) minimize it?

  Particles of charge xh96js j; jgcj8- zmw) tvyf/6g9/xae $+75$,$+48$ 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 chartj14*zag3u -)5gatn19/laif sdkjte ge, $+11.0\,\mu C\,$ 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 ofu:yx /doegh8r 1a,ya)j ys)pj3+(tfa a square 0.100 m on a side. Determine the )uj8h3 g/a +ds)ay o:ej p rytyf1,(xamagnitude and direction of the force on each charge.
$F_4$ =   $ \times10^{ 7}\,N$
$\theta$ =    $^{\circ}$

  Repeat Problem 14 for the case when two of the positive charges, on k(0x ts0a , u*de1aszbopposite corners, are replaced by negative charges of the same magni0(, 1xksb*e0u tadza stude (Fig. 16–51).
$F_4$ =   $ \times10^{ 7}\,N$
$\theta$ =    $^{\circ}$

  At each corner of a squah;-hy/kkd; +ymf/qn vre 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 k;mvy/n- +/dkh h;qfy(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 z*qno m2n *ybwjf;8nksuv) 6:an equilateral triangle of side 1.20 m (Fig. 16–53). The charges a;k* 6njymovs2un * b): fw8znqre $+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 a8n6x-lctiba2 total 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 have a totu56m ri8tb)4nvjdh .x al 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 uncharged plastic t) rq*qeu18 xuball to an identical ball 12 cm away. The force of attraction is then 17 mN. How many electrons were transferred from one ball to the otheru* x)1eq qr8tu?    $ \times10^{ 12}$ electrons

  What are the magnitude and direction of the electric force on an electron in 0 ag0v( gwq5x,uv5mb za unig5z 0 agmb(w,5v0quxvform 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, and it experr;a + 1 (g : -uxlbdxxgl9.qczg0cgca/iences an electric forc-ggxz x+la cdcl. 9/qgcxb1r(:ga u;0e 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 exertew1bgi(/*yaj-uz rqu : d 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 fiel gnh+ l4t2 ;j/gxhknj 7jl .o8jpaa2:gd 20.0 cm directly above an isolan gxptnj2k; : a8lj4.ggh2a jl 7j/oh+ted $33.0 \times10^{ -6}\,C$ charge?    $ \times10^{6 }\,N/C$ ----待选择----updown 

  What is the magnitude of the acceleration experisz r;t rh/q7 app448mienced by an electron in an electric fie4pq8rt7 s ; z4ami/hrpld 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 pointml9xs-oe4z5w-9sr dm-z b fw, midway betwzlw- f5mxew-zssr ,99dbm4o- een 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 abtvb:ri y.i:y-out two point charges, $+Q$ and $-3Q$ which are a distance l apart.

  What is the electric field strength at a point6i 57vx2-rv c m0ngygapk4ut : 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)0 ad4 bs wd*ua;zewv8 vo.a5h from rest in a uniform electric field and accelerates to the north at aado a b szw5u)0 eva4h;w8vd.* 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 midwop r u fzd:g5kuyvn84 1c/l)-uay between two equal 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 ondh5jf5;07 lyckv m 5wg:l: 1ljs* kcin a side if one cor jlf:c:s l7k;c lgi1 0wndjkyh5v* 55mner 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 fieldt3 jpx1ut +p+ zd*ql.s at one corner of a square 1.00 m on a side if the other three corners are occupied by 1 ds.u3qltj x+ t+pp*z$ 2.25\times10^{-6 }\,C$ charges.    $ \times10^{4 }\,N/C$   $^{\circ}\,$ from the x-direction.

Determine the direction andop)j9 8,u9n a cokgdmi,g6u/crtg.q 8 magnitude of the electric field at the point P in Fig. 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,u986uc t.d rcaonkqpg/o, 9ji mgg )8 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 elucu blhc:)7m0g+20e.lim xaxectric 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 determhk-mo g8bh7s/x6 use ,ine the magnitude and direction of the electric field agbo sx8/ ,m hshu-ke67t points A and B in Fig. 16–57 due to the two positive charges $(Q\,=\,7.0\mu C\,)$ shown. Are your results consistent with Fig. 16–31b?
$E_A$ =    $ \times10^{6 }\,N/C$
$\theta_A$ =    $^{\circ}\,$
$E_B$ =    $ \times10^{7 }\,N/C$
$\theta_B$ =    $^{\circ}\,$
(16-51)
(16-31b)

  You are given two unknown point chargesdt2.gl+ bzqh5 zsz a7w9t x,e91 yqfi ez58y2b, $Q_1$ 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 at7suiop 7fyc /ovv85 6mii2z5j 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 teu57v/6i5moj z cvfioiy78s 2 prms of Q, x, a, and k.

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

  An electron moving to the right at 1.0% the speed of light enters a uniform elecx0o 2h i5egxcex*xy- 1ec2gxxi5x1 -y*eo0hxtric field parallel to its direction 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 from a cubical bo yq+-nz ynzi)w ) j6c-c1hih-mx 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 electric field of 0. ys3uy (;6pfpbjt bdmagnitudejyydb.(f0 s3;up 6 tpb $ 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 objects2l*kev)xyk ,jpjv 0dz m+q/t8, $O_1$ 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 unifor;q4 ylq-fw lp6*/g wffm 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 bett5n sk*eq+4 9ml*i jopween two square metal plates is The plates are 1.0 m on a sideoq4+*j *i tm nsp5elk9 and are separated by 3.0 cm. What is the charge on each plate (assume equal and opposite)? Neglect edge effects.    $ \times10^{-9 }\,C$

  The field just outsi,rsil9 j7c,6,g iwrd: *q plgqde a 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 total charge obs. dc 7s+ lfg;er+olwm7dl8maca/c8 .v1:q kf $-3.5\mu C$ 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 conducting s;.haou6ctu0n 0m8vhy ; qyf/ ax4cp* shell. (See Fig. 16–33.) What is the electric field E as a function of r no *;h/ t0a.8cq hfpyca6yu;u4 0vmsx(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 DN mv*iq068znr xm8da: nA molecule are held together by electrostatic forces as shown in Fig. 16–44. Assume that tnn68vx8di 0m:rqm z*ahe 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 electronkc7wf0 :ze s //aaxp3ss be if the electric force between them is equal to the ew 3z /0:cspsx7/a kafweight of either at the Earth’s surface?    m

  A 3.0-g copper penny x 6a)qvyl7pj7 has 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 o v2wsw ku9/y.m*mn;wan electric field surrounding the Earth. Its magnitude is awm m*/;wou kns2yw 9v.bout $150\,N/C$ 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 electrn/bsp7zk . d.wic field of what is the acceleration experienced by anp 7..dzbkn w/s electron 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 0.018 mm remains stationary in th3 n)lgx(st yq(g6 brb6bw+nswbi ,x0n.6 hqt2e air. If the downward-directed electric fiel6sb rwtql6nt(g+ ) . (nwxgix6bb30hb q yn2s,d 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 grou .ezfmk ;f55mc ol0ka.p shown in Fig. 16–62. The C and O have chargl a.m5f;cof0.z5k emkes $\pm0.40e$, 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,()hby1q mbx2nwd c,m revolves in a circular orbit around the proton with a y1q,)mbb,c2(nwm h dxspeed 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 attdas;*7skw/+z ;vl /mo mc8avxraction, rather than gravity, were responsible for holding the Moon in orbit around the Earth. If equal and opposite charges Q were placed on the Earth and the Moon, what should be the value of Q to maintain the present orbit? Use theazvw+/aov; sdl 7xk /8s*mm;cse 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 s) :tuhvh,)w6q.yiked $v_0\,=\, 21.5\times10^{6}\,m/s$ 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 charssc* zl 16;y-kgl3l udge $Q_1\,=\, 2.5\times10^{-5}\,C$. 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 plast7h*0f.w g -nn fbkm1tuic and suspended vertically from ann0hknbm wf*f- 17.gut 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 withsu a ow-6+jwy+ “leaves” that are 78-cm-long wires with tiny 24-g spheres at the ends. When charged, nearly all the chaousaw++w 6j y-rge 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 exceeds a*-lmrf k37c wmbout cmf -3r*mkwl7$ 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, hy()9yk.lg ik9q 8g zland net charge $+0.340\,\mu C$, hangs at rest at the end of an insulating string above a large sheet of charge. The horizontal sheet of uniform charge creates a uniform vertical electric field in the vicinity of the point charge. The tension in the string is measured to be 5.67 N. Calculate the magnitude and direction of the electric field due to the sheet of charge (Fig. 16–67).    $ \times10^{7 }\,N/C$  ----待选择----updown 

  What is the total charge of all the electrons in a 15-kg bar of alzi) r 7rti5g-luminum?    $ \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 conduc r.l,/fssvj1 .v9nlrt ting spheres A and B are a distance R apart; each carries the same charge Q. (al 1v.r/t9 jrvfl,ns s.) 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. 16–6d/)1tdq abzsg5ny:0k8, at what position(s) x is the electric field zero? Is the field zero at any othe51z k d0tbagnqs/:d)yr 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 :*s2n:,twq h0e fcann point 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?