If you charge a pocket comb by rubbing it with a ,tmv8d8be rs. silk scarf, how can you determine if the comb is positivelv etbs8r,8m .dy or negatively charged?

Why does a shirt or bl/7n,r 7-go4 to k(ict91hr rhxs 6jljvouse taken from a clothes dryer sometimes cling to your body? rg ,71n6osix-7kotjj4 (h t9lhrcvr/

Explain why fog or rain droplets tend to form around ions or bipu2eaa /ucut k7:1f*z6db 9electrons in the aire2taczf pukaubb *du 176:i 9/.

A positively charged rod is brought close to a neup * sjqnq1fej6ax-* k:tral piece of paper, which it attracts. Draw a diagram showing the separation of charge an*-skq6 fex :napq1j j*d explain why attraction occurs.

Why does a plastic ruler t:t w inete 8.gu 9n1h.hs6+wcjhat has been rubbed with a cloth have the ability to pick up small pieces of paper? Why is this difficult eeu.gc nnt6jw:ih8swh+19t . to do on a humid day?

Contrast the net charge on a conductor to the “free charges”fwk :jkkr/ f/zhttu4gw. 9(k) in the conductor.

Figures 16–7 and 16–8 show how a charged rod placlpsq 0rquvr02h0yq()ed near an uncharged metal object can attract (or repel) electrons. There are a great many electrons in the metal, yet only some of them move as shown. Why not all of themyrs( vl0pq00qhq)r u 2?

When an electroscope is charged, its two leaves repel each othbq5zg06jm ;jq er and remain at an angle. What balances the electric force of repulsion so that the leaves don’t separate further j gq;65z0jbqm?

The form of Coulomb’s laalv85pmlk*u a,(*+-t7 qz9zhtpqty t w is very similar to that for Newton’s law of universal gravitation. Wzmt q v*tp*85hq+ t (a-7kpz,autyll9hat 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 tt6cb4 qf/buznggj ;o+3gbc/sh zy ;/4wo ordin/ bgczf c t ubs3;/h; gznog4q/bj4+y6ary objects. What is the reason in each case? Give an example where we are aware of each one and why.

Is the electric force a conservative force? Why or why 7cn 49frtwh)bqal u;t20l( tb not? (See Chapter 6.)

When a charged ruler attracts small pieces of paper, sometimes a piece s+f2ywofy/enfbh 473 jumps quickls7/ y2fo wbf34yfhn+ ey away after touching the ruler. Explain.

Explain why the test charges we us uly6jlligmuv 8/db;m +u1; 9he when measuring electric fields must be small;m +uyhvj/16 iu; um98llgbld.

When determining an electric field, must we us) xf)n4oms0o) mbfeq+ /mru -ue a positive test charge, or would a negative one do as well? Explafqm uomnx/o4 f+e0s m)r- ))ubin.

Draw the electric field lines surrounding two negative electric charges a d i873f7*gy* gwp(x p:z ylxzcfistancewf*x*ig:( 8 7lyyxz3pg7 cf pz l apart.

Assume that the two op/ r2h rt0u;orcq/l-zcposite 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 — top, bottz rlc/- to/hqrcr;2u 0om, left, or right — is the electric field the strongest? The weakest? Explain.

Consider the electricqgs4 w9a1kfghq;d/- f field at points A, B, and C in Fig. 16–48. First draw an arrow at each point indicating the direction h-k df9gqw;4s 1 fq/agof 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 never cros+7ouh4sogf, el4.) fzg nx6x5mu xn)ss?

Show, using the three rules for field lines given in Section 16–6d t gi/n7kcy-8, that the electric field lines starting or ending on a single point charge must be symmetricallytng-7 ci6yk d/ spaced around the charge.

Given two point charges Q and 2Q, a dist-nsrt/bt-;n oance l apart, is there a point along the straight line that passes thronsbo - -t;tn/rugh 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 positi-tfc-2m vdr3ta; xrkn6wyj- f8 bfp7z *li *.cve test 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 acceleration of the test charge along this line? - tjzt;xw .3f6y28-inl*pm * vcdffck-rb7 arDiscuss.

Sketch the electric field lines for a uniform line of charge whic2j )bupt: ojg mu/(taou*z ve5 q4su*(h is infinitely long. (Hint: Use symmetry.) Is the electric field uniform in strezmo4sp() u qv ut/* *ub: ejjou5(ta2gngth?

If the electric flux through a closed surface is zero, is the electr yd*s2xp c bbt+wo.yz, qedy1yjrx8yd9 : ./+zic field necessarily zero at all po.y98td*o.wy,dc+ 2y+rbb/xp ezxz:y y q j1sdints 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 spherical zs4djn(rv0 wlzz9/1ggaussian surface of radius r. If the sphere is reprjvsn04d (g z9z1/ lwzlaced by a cube of side r, will $\Phi_E$ be larger, smaller, or the same? Explain.

  

  How many electrons m9n*f5q/y ,rmmo v9a dh* 1w3cqema;hcake up a charge of $-30.0\mu C\,?$   $ \times10^{ 14}\, electrons $

  What is the magnitude of the electric force of attraction between ansmr e6(hkn7q s 4g,uk) iron nucleus s(7) neks k4gmr6 uhq,$(q\,=\,+26e)$ and its innermost electron if the distance between them is $ 1.5\times10^{-12 }\,m\,?$    $ \times10^{-3 }N$

  What is the repulsive electricalc 5)pv x/vx1zn force between two protons $ 5.0 \times10^{ -15}\,m$ apart from each other in an atomic nucleus?    N

  What is the magnitude ofsrlajp w/s w))iq5-o7 the force a $+25\,\mu C\,C$ charge exerts on a $+\,3.0\,mC$ charge 35 cm away?    N

  Two charged dust par0x ncps-wuvi9dt:2y gvgd +fu at52v52 g8 d0pticles 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, 7 q60whsj. y24rcwiugand the force on each of them is found to have been tripled. How far apart are they now?gyw0is ru 4qwh62c7j.    cm

  A person scuffing her feet on a wool rug on a dry dhpa5j/-iw8sd 4wk b)(kqkk zs4/t mn8ay accumulates a net charge of 8hsw t) ab(kq-z/m/j 85n 4 4sdpkkiwk$-42\,\mu C\,.$ 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(n9f7do+r mzrs)m8p 9bmly f2 all the electrons in 1.0 kg of $H_2O\,?$    $ \times10^{ 7}\,C$

  Compare the electric force holding the electron in orbit)vmh bn3ojs 8qmd z (bt7 a6ciw:;o4l- $(r\,=\,0.53 \times10^{-10 }\,m)$ 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 arel0:jbe /0 ugz0rg6uvp a fixed distance apart. The sum of their charges is What charge must each have in order to lj0vg6pze/:uu0gb0 r
(a) maximize the electric force between them,
(b) minimize it?

  Particles of charge 3flfytl4k4xmudi l-fiin) ju,,8qvj4 f 2l 4)$+75$,$+48$ 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 9rrwebg0:o z9i0b/jf 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 pddxw/xw +h,a, laced at each corner of a square 0.100 m on a side. Determdhw+wd,x, / xaine the magnitude and direction of the force on each charge.
$F_4$ =   $ \times10^{ 7}\,N$
$\theta$ =    $^{\circ}$

  Repeat Problem 14 for the case, vwfj8cl +a+qx js.y1 when two of the positive charges, on opposite corners, are replaced by negative charges of1 wvyjxj+ +af,l.8qsc the same magnitude (Fig. 16–51).
$F_4$ =   $ \times10^{ 7}\,N$
$\theta$ =    $^{\circ}$

  At each corner of a square of side l there are poz7.7rc malvx 76ao7s lint charges of magnitude Q, 2Q, 3Q, and 4Q (Fig. 16–52). Determine th677a xvalm o77cslr z.e 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* oarlu0 fmy7-rb lje14qi;x3b0q0qf triangle of side 1.20 m (Fig. 16–53). The chargesiboyqql-j x*bu0e 31r fr 70qlma4;0f 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 /xpfv3 dwmpwk 6u++y(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 sphere)1kauuvc 0mvt+ c, abgrx2- e5s 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 uncharged plastic ball-jfvoo* (x-r ojd .6a8 okxt2f to an identical ball 12 cm away. The force of attraction is then 17 mN. How many electrons were transx dj o-ov tx(j8*6or a.o-2kffferred from one ball to the other?    $ \times10^{ 12}$ electrons

  What are the magnitude and direction of the electric force on an elmh4rtxq yn(723 mh/ i fgt2gb fik()/aectron in a unq t74f/gfb) 2(h/a k2 imty( mi3nhxrgiform 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 experie j:/rvm e(rl5qbpuyiwm)1 x54 p,j7 1wbc jfy-nces an electric force ofexjymj (,4wpwcv- 55j mqrpbf/ )y :7rl1ui1 b $ 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 ex-)4tcw mh6 r iz0arar-erted 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: s 0tz1 wywy0o/d7o8nx w to3uru:hl))l glt2.0 cm directly above an isola/wyhlwu ):xt2yt:0n37ztr80 ow llgsdo)ou 1 ted $33.0 \times10^{ -6}\,C$ charge?    $ \times10^{6 }\,N/C$ ----待选择----updown 

  What is the magnitude of the acceleration experienced by an el m :,vt4mi:phfectron in an electric f4hp,:tmv :imf ield 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 directk7p; dxc:b3m6 hzp ;1upw4ir eion of the electric field at a point midway bet41; xi 6pz p:7kum db3;prchewween 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 eldyv/7h 97kg)p1 ctxk /qx 7yplectric 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 sctv1o8r9u k e9y1q,h bpace where a proton $(m= 1.67\times10^{ -27}\,kg) $experiences an acceleration of 1 million “g’s”? $\approx$    N/C（Round it to one decimal place.）

  An electron is released from rest in a uniform electric field and accelerates to9,ynpe5rm,g sydg1 v- the north,vmgnyrd5 g,9- es yp1 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 charges isp .m-u:pdonv c:;q2g; e56jpl.d qelo $745\,N/C\,,$ and the distance between the charges is 16.0 cm. What is the magnitude of the charge on each?    $ \times10^{-10 }\,C$

  Calculate the electric field at the center of a square 52.5 cm on w go2u0+f8l sia side if one corner is 8 s go0w2ufil+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 cucnq )/g 6cmgd zpm340hae f+; ff(2oyorner of a square 1.00 m on a side if the other three corners are occupied byq6gc /y2fz ;u+apofef0dghc)4mmn (3 $ 2.25\times10^{-6 }\,C$ charges.    $ \times10^{4 }\,N/C$   $^{\circ}\,$ from the x-direction.

Determine the direction and magnitudev4iovcb 7f8 y9 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 your answer in terms of Q, x, a, f79o8v 4cyivb 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 electrid.vwv)musm4-kbxlw3 5.cn z( c field $\vec{E}$ at the origin 0 in Fig. 16–56 due to the two charges at A and B. (b) Repeat, but let the charge at B be reversed in sign.

  Use Coulomb’s law to determine the magnitude and direction of the:;tt;la w2s8;+mae c) gwfac j pk0*ba electric field at points A and B in Fi)8jp* tfaw+e :k;ca;t;lm basc20 agwg. 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 poin yut*192u-2 pjotbxmo t 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 thevhk gm-ucih(2.: xlgbq,)1lv7jq z1z point P shown in Fig. 16–59. The two charges are separated by a distance of 2a. Point P is on the perpendicular bisectorvl1(b: )uzz jk, g7gx-h2v1i q hmql.c of the line joining the charges, a distance x from the midpoint between them. Express your answers in terms of Q, x, a, and k.

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

  An electron moving to the right at 1.0% the speed of ef23agjim upu,w.0b+ light enters a uniform electric field pefa+gb20uw m3 . j,upiarallel 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 box 28.0 cm on dnmp-q46rl( pa 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 ele0jnnfb. bu5)b ctric field of magnitude0u5nnj bb)fb. $ 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 objfglfav 7v7q7 au*ql/ g 7u.-vzects, $O_1$ 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 pla*wj su2ck -ur a 7(:krv08zsaaced 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 between two square metal plates h/ m r3qm10s0 n9jg.llwue8seis 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 oppo/.n01rls3 gl98h 0mu jeqewsmsite)? Neglect edge effects.    $ \times10^{-9 }\,C$

  The field just outside a 3.50-cm-radius metal ball is52pa++l/ hnicyyl5ic $ 2.75\times10^{2}\,N/C$ and points toward the ball. What charge resides on the ball?    $ \times10^{-11 }\,C$

  A solid metal sphere z,c-isvz m3rh2p + jsc wc4h49of radius 3.00 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 thi b )b2n e;lb*24 .wuymkajme.kn spherical conducting shell. (See Fig. 16–33.) What is the electric field E as a function of r (a) for r less than the inner radius of the shell, (b) inside the shell, and (c) beyond the shell? (d) Does the shell affect the fie)b.e2b*j bme.42lukky m; anw ld due to Q alone? Does the charge Q affect the shell?

  The two strands of the helix-shaped DNA molecule are held together by electrb kq34w, o9raxostatic forces as shown in Fig. 16–44. Assume that the net average charge (due to electron sharing) indicated on H and N atoms is 0.2e and on the indicated C and4,qwkob9 ra 3x 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 electrr bc*h-0ljfje 92c. ldons be if the electric force between them is equal to the weight of either at the Earth’s surfaf-e9 jljrdch* 0.lbc2ce?    m

  A 3.0-g copper penny n8r fgt)jnujd8b+lq1 1z-d.r 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 t 7sm7xdnh3y* lhere is an electric field surrounding the Earth. Its magnitude is about sxy*l 37hnm 7d$150\,N/C$ 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 exper mx3xu9usc1 vc+jwds ;0 d(zx2ienced by an electron near the surfacss xuuv jxzxc9;d(c+ mw32d01e 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 the airpncr9jy5v+(pj5v w-szu4 2 xr. If the downward-dircvunp 5r9 2 vs jwjxyz+-(5p4rected electric 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 gru3*+o) yu 5tscexvtc 8oup and the HN group shown in Fig. 16–62. The C )euoc8u tc*3yv+x t5s 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, 63fs4:gigz.+crfy wp the electron revolves in a circular orbit around the . w +6z4ycpgisgff3r: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, rather than gravity, werj 7d p ru5yj0q ;;+dkdpx*jux7e 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 orbdk70du7 ;*jrq+5xj pypx d ;juit? 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 spee+ tdz (kzak;k1)s b,gxd $v_0\,=\, 21.5\times10^{6}\,m/s$ 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 zlw1u8*gx3h i$Q_1\,=\, 2.5\times10^{-5}\,C$. 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 ijbzx*rp4z 0 0gnsulating plastic and suspended vertically from ap4z 00gx*b jrzn 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 “leaves” si8 4pr w7eo */*dfvwh 5of9ogthat are 78-cm-long wires with tiny 24-g spheres at the ends. When chargewv5ohp8 o 7*is4 f*wr/of9egd d, 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 a+av :d4 x /1iek0p*0pfppdzywu2 x9kund generate a spark if the electric field exceeds abouty p1:ak*d fp2zeud4k90vxw0iu+xpp/ $ 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:q8maxit 1 g 7rk-x/a)lek-dc 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 tho7; nsa-7:hn:ls5drtg(i t xle 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)eq jv0ws, ord5zv8v4 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 wzjv)sv8qv, eo5d4 0rvery far away. What is the net force now acting on sphere A? (c) Sphere C next makes contact with sphere A and is then moved far away. What is the force on sphere A in this third case?

Given the two charges shown in Fig. 16–68, at what position(s) x is the electricg 89 pt5pldkm hdy8v)( field zero? Is the field zero at any other pvk8d)5p(y8d9pg m htl oints, 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 charge ;atj5uei2 g;q$8.0\,\mu C$ 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?