What type of bond would you expe w8xim e 5e;*z+7qkud 0gstdy*ct for
(a) the $N_2$ molecule,
(b) the HCl molecule,
(c) Fe atoms in a solid?

Describe how the molecul6ovo mk1n7f; e il,udr )7zfd3e $ \text{CaCl}_2 $ could be formed.

  Does the $ \text{H}_2 $ molecule have a permanent dipole moment? Does $ \text{O}_2 $? Does $ \text{H}_2\text{O} $? Explain.

Although the molecule -z0sqmj ki (4y$ \text{H}_3 $ is not stable, the ion $ \text{H}_3^+ $ is. Explain, using the Pauli exclusion principle.

The energy of a molecule can be divided into four categories. What arzqd . )+u7yyh8ciuk w-e they?

  Would you expect the moleculeca4tl:d 2aqg7 $ \text{H}_2^+ $ to be stable? If so, where would the single electron spend most of its time?{yes|no}

Explain why the carb8,gs 5(v e,vsyv ib8/cxknt6xon atom ($ Z=6 $) usually forms four bonds with hydrogen-like atoms.

If conduction electrons are free to roam about in a metal, why don't they l;u+3;y45jx vedt i bzro m/ ,rsyx17rweave the metal entvxew u+j;3xt4rm ,i;r 7z1y5b/ yrosdirely?

Explain why the resistivity of metals increases6 skuf)dpn /blp e /(n:2h5dmimp6rxe iqj9;3 with temperature whereas the resistivity of semiconductors may decrease with increasing temperature9 ne xdqmudp3m6e5:lf/ ki/ bi2jp(6p;) nrs h.

(Fig. Below) shows a "bridge-type" full-wave rectifier. Explain )w8/j nj8ex+ djs.*eoqlzq h ,how the current is rectified a. )*wdq/+xo8jhjnl,z e sj8 qend how current flows during each half cycle.

Compare the resistance of a pn junction diodx,d; *s occhh2;x/bnde connected in forward bias to its resistance w* ;bhx2ncdhx s /d,c;ohen connected in reverse bias.

Explain how a transistogod:p0t0k ee,sk 22fnr could be used as a switch.

What is the main difference between n-type and p-type semiconductor) f qjx:ajqc*6s?

Describe how a pnp transistor can operate as an amplifierqt *s:: nd98dx,g4 -saiq .q,ethiva m.

In a transistor, the base-emitte 5i8ppew+ eu6br junction and the base-collector junction are essentially diodes. Are these junctions reverse-biased or forward-biased in the application shown in (Fig. Below)?peu5w +ib6 8pe

A transistor can amp u1oq7cq q.jl *zrmm( ;9ida2klify an electronic signal, meaning it can increase the power of an input signal. Where does it get the energ q(k z aocmq*m7rq j.l91;2iduy to increase the power?

A silicon semiconductor is doped with phosphorus. Will t lv))z(jiwc/uvri1gd4g25ax hese atoms be donors or acceptors? What type of semiconductor will this b)ii1 25c4vxgjlz wd vu/ r)g(ae?

  Do diodes and transistors owyvmq-yh+qdx (i1(0pu0,2 h g7pbp l abey Ohm’s law? Explain. {yes|no}

  Can a diode be used to amplify a signal? Explain. {y( mxwn01* /h4yrmhyg des|no}

  Estimate the binding energy r- pr6 wz:am8tof a KCl molecule by calculating the electrostatic po rp-:6 rta8zmwtential energy when the $ \text{K}^+ $ and $ \text{Cl}^- $ ions are at their stable separation of 0.28 nm. Assume each has a charge of magnitude $ 1.0e $. Binding energy =    eV

  The measured binding energy of KCl or(l8p/f7 g /jv)0df8/hovpwd4wkim is 4.43 eV. From the result of Problem 1, estimate the contribution to the binding energy o/0iov(gddh4 p fomvwl)//jp 8r78kw ff the repelling electron clouds at the equilibrium distance $ r_0 = 0.28\ \text{nm} $. $PE_{\text{clouds}} =$    $\ \text{eV}$

  Estimate the binding energy 21v -vbl mw8zkof the $ \text{H}_2 $ molecule, assuming the two H nuclei are 0.074 nm apart and the two electrons spend 33% of their time midway between them. Binding energy =    eV

  Binding energies are often measured experimentally in kcal per mole, and thenqy/fsf5h2+d a(k ,vn cy)d ;nr the binding energy in eV per molecule is calculated from that resultd,kchqnsry +5fd; ()a/ n2y vf. What is the conversion factor in going from kcal per mole to eV per molecule? What is the binding energy of $ \text{KCl} (= 4.43\ \text{eV}) $ in kcal per mole?
We convert the units =    $\text{eV/molecule}$
For KCl we have =    $kcal/mol$

(a) Apply reasoning similar to that in the text for the states kql)d mudu-17in the formation ofu17mldk- )dq u the $ \text{H}_2 $ molecule to show why the molecule $ \text{He}_2 $ is not formed.
(b) Explain why the $ \text{He}_2^+ $ molecular ion could form. (Experiment shows it has a binding energy of 3.1 eV at )

Show that the quantibqop f /oy4pb 0o(3cc+ty $ \frac{\hbar^2}{2I} $ has units of energy.

  The so-called “characte lr0rc oqq,5q8(oe9 wkristic rotational energy,” $ \frac{\hbar^2}{2I} $ for $ \text{N}_2 $ is $ 2.48 \times 10^{-4}\ \text{eV} $. Calculate the $ \text{N}_2 $ bond length. $r = $    $ \times 10^{-10}\ \text{m}$

  (a) Calculate the characteristic rotationalofs t: ;6 :qdx2bbn4rt energy, $ \frac{\hbar^2}{2I} $ for the $ \text{O}_2 $ molecule whose bond length is 0.121 nm. $\frac{\hbar^2}{2I} =$    $ \times 10^{-4}\ \text{eV}$
(b) What are the energy and wavelength of photons emitted in a $ L=2 $ to $ L=1 $ transition? $\lambda $ =    mm

  The equilibrium sepafl)+ p )o4ga3lh c2chqration of H atoms in the $ \text{H}_2 $ molecule is 0.074 nm (Fig. Below). Calculate the energies and wavelengths of photons for the rotational transitions
(a) $ L=1 $ to $ L=0 $, $hf $ $=$    $ \times 10^{-2}\ \text{eV}$$\;\;\;\;$$\lambda $ =    mm
(b) $ L=2 $ to $ L=1 $, $hf $ $=$    $ \times 10^{-2}\ \text{eV}$$\;\;\;\;$$\lambda $ =    mm
(c) $ L=3 $ to $ L=2 $. $hf $ $=$    $ \times 10^{-2}\ \text{eV}$$\;\;\;\;$$\lambda $ =    mm

  Calculate the bond length for t:buv ep4d5 fk/j(z jy9he NaCl molecule given that three successive wavelengths for rotational transitions are 23.1 mm, /e94b uyf:jk5djp z(v11.6 mm, and 7.71 mm. $r = $    $\times 10^{-10}\ \text{m}$

  (a) Use the curve of (Fig. Below) to estimate the v/mpvt pf m 8l;-+omi0stiffness constant $ k $ for the $ \text{H}_2 $ molecule. (Recall that $ PE = \frac{1}{2}kx^2 $) k =    N/m
(b) Then estimate the fundamental wavelength for vibrational transitions using the classical formula (Chapter 11), but use only the mass of an H atom (because both H atoms move).$\lambda$ =    $\mu m$

  The spacing between “nearest nei0ts+l ftpj h:p xiebm3pp/lslci z *w. -,490wghbor” Na and Cl ions in a NaCl crystal is 0.24 nm. What is the spacing bet0sme4 iblpf+/ pcppsz3j,0l9: *w ih-lt.xw tween two nearest neighbor Na ions? D =    nm

  Common salt, NaCl, has a density of -+lone,9hu;n:tt cx oezrw7 o5z;t4h $ 2.165\ \text{g/cm}^3 $. The molecular weight of NaCl is 58.44. Estimate the distance between nearest neighbor Na and Cl ions. [Hint: Each ion can be considered to have one "cube" or "cell" of side $ s $ (our unknown) extending out from it.] $s$ =    nm

  Repeat Problem 13 for KCl whose de0b g-vup-hf*x/l+hrg nsity is $ 1.99\ \text{g/cm}^3 $. $s$ =    nm

Explain on the basis of ener5 8 9mznv njlw)9gi kx,u,ck+bgy bands why the sodium chloride crystal is a good insulator.mikbu c9n5 nl + ,9v8wk,)zjgx [Hint: Consider the shells of $ \text{Na}^+ $ and $ \text{Cl}^- $ ions.]

  A semiconductor, bombarded with light of slowly increased frequ d+ oex:alh3+yency, begins to conduct when the wavelength of light is 640 nm. +: de oxy3l+haEstimate the size of the energy gap $ E_g $. $ E_g $ =    eV

  Calculate the longest-wavelength photon that can cause an ele.zrq b7q/lfq7 6lwh2s/ /r fbfctron in silicon ($ E_g = 1.14\ \text{eV} $) to jump from the valence band to the conduction band. $\lambda $ =    $\mu m$

  The energy gap between valence bk c;nq5 7j*lqxfleya: (5f b)and conduction bands in germanium is 0.72 eV. What range of wavelengths can a photon have to excite an e(xfl knbfqa7)bj c ly; *5:e5qlectron from the top of the valence band into the conduction band? $\lambda \leq$    $ \ \mu\text{m}$

  The energy gap $ E_g $ in germanium is 0.72 eV. When used as a photon detector, roughly how many electrons can be made to jump from the valence to the conduction band by the passage of a 760-keV photon that loses all its energy in this fashion? N =    $ \times 10^6$

We saw that there aregh/21s sw*i/yej6 ma0.xdhj o $ 2N $ possible electron states in the 3s band of Na, where $ N $ is the total number of atoms. How many possible electron states are there in the
(a) 2s band,
(b) 2p band,
(c) 3p band?
(d) State a general formula for the total number of possible states in any given electron band.

  Suppose that a silicon semiconductor is doped with phos 2uel3 ,sf2q+hmo j+piphorus so that one silicon atomu++hfmieo2p2 ,l3qs j in $ 10^6 $ is replaced by a phosphorus atom. Assuming that the "extra" electron in every phosphorus atom is donated to the conduction band, by what factor is the density of conduction electrons increased? The density of silicon is $ 2330\ \text{kg/m}^3 $, and the density of conduction electrons in pure silicon is about $ 10^{16}\ \text{m}^{-3} $ at room temperature. $\frac{N_{doping}}{N_{Si}} = $    $ \times 10^6$

  At what wavelength will an LED radiatbmemm,1v9 m3xpkp mm,lrs/dd 5vmaf,u866 b0 e if made from a material with an energy gap 9k, rmdm3m1msm b,f 6u, x8dvamb5v m e60lp/p$ E_g = 1.4\ \text{eV} $? $\lambda $ =    $\mu m$

  If an LED emits light of wac7 rqy 3rl*m o8*vep pqtp9u46velength $ \lambda = 650\ \text{nm} $, what is the energy gap (in eV) between valence and conduction bands? $e_g$ =    eV

  A silicon diode, whose current-voltage characterist xj-bal; qsro;6ri3* )jba)zzics are given in (Fig. Below), is co ba;36bs-) jq)rjz*xail; rzonnected in series with a battery and a $ 960-\Omega $ resistor. What battery voltage is needed to produce a 12-mA current? $V_{\text{battery}}$=    V

  Suppose that the diode ot c)0wkb0cz ;pf (Fig. Below) is connected in series to a $ 100-\Omega $ resistor and a 2.0-V battery. What current flows in the circuit? [Hint: Draw a line on (Fig. Below) representing the current in the resistor as a function of the voltage across the diode. The intersection of this line with the characteristic curve will give the answer.]    mA

Sketch the resistance as a function of currenzck 3piea, xfonx xf*t/40.*et, for $ V > 0 $, for the diode shown in(Fig. Below).

  An ac voltage of 120 V rms is tjj)i+8kt5ld to be rectified. Estimate very roughly the average current in the outj lktti+j)58dput resistor $ R $ ($ 25\ \text{k}\Omega $) for
(a) a half-wave rectifier(Fig. Below a), $I_{av}$ =    mA
(b) a full-wave rectifier (Fig. Below b) without capacitor.$I_{av}$ =    mA

a

b

  A silicon diode passes significant curg 8lwxzd e fvq/7 f4-.1zpgv4trent only if the forward-bias voltage exceeds about 0.6 V. Make a rough estimate of tvl zffqzpt8-/g4wd. 1v4 e7gx he average current in the output resistor $ R $ of
(a) a half-wave rectifier (Fig. Below a),$I _{av}$ =    mA
(b) a full-wave rectifier (Fig. Below b) without a capacitor. Assume that $ R = 150\ \Omega $ in each case and that the ac voltage is 12.0 V rms in each case. $I _{av}$ =    mA
a
b

  A 120-V rms 60-Hz vo lry qm,u/ 5d+zy93yhbltage is to be rectified with a full-wave rectifier (Fig. Below,9zymu+/5lyb drh3y q ), where $ R = 21\ \text{k}\Omega $ and $ C = 25\ \mu\text{F} $.
(a) Make a rough estimate of the average current. $I_{av}$ =    mA(smooth)
(b) What happens if $ C = 0.10\ \mu\text{F} $?$I_{av}$ =    mA (rippled)

From !num!2%, write an equation for the relationship betwee6yph :usx e;y:n the base current $ I_B $, the collector current $ I_C $, and the emitter current $ I_E $ (not labeled in the figure).

  Estimate the binding energyc 5gcmqj)5y s98)cpo 7v;i 2b2t hnnzr of the $ \text{H}_2 $ molecule by calculating the difference in kinetic energy of the electrons between when they are in separate atoms and when they are in the molecule, using the uncertainty principle. Take $ \Delta x $ for the electrons in the separated atoms to be the radius of the first Bohr orbit, 0.053 nm, and for the molecule take $ \Delta x $ to be the separation of the nuclei, 0.074 nm. [Hint: Let $ p \approx \Delta p \approx \hbar/\Delta x $]    eV

  The average translational kinetic enbvopo,,f s+t0 bim h 2p6;m7jjergy of an atom or molecule is about $ KE = \frac{3}{2}kT $ (Eq. 13-8), where $ k = 1.38 \times 10^{-23}\ \text{J/K} $ is Boltzmann's constant. At what temperature $ T $ will $ KE $ be on the order of the bond energy (and hence the bond likely to be broken by thermal motion) for
(a) a covalent bond of binding energy 4.5 eV (say $ \text{H}_2 $), $T =$    $ \times 10^4\ \text{K}$
(b) a "weak" hydrogen bond of binding energy 0.15 eV? $T = $    $ \times 10^3\ \text{K}$

  In the ionic salt KF, the separation distance between ion 6i,oycivo,jmv co.du s2f(9ni i4*k 2s is about 0.27 nm.
(a) Estimate the electrostatic potential energy between the ions assuming them to be point charges (magnitude $ 1e $). PE =    eV
(b) It is known that F releases 4.07 eV of energy when it "grabs" an electron, and 4.34 eV is required to ionize K. Find the binding energy of KF relative to free K and F atoms, neglecting the energy of repulsion. Binding energy =   eV

  Consider a monoatomic solid with a weakly boun4;gzg jx plf)u wrw 2+n-t68ynd cubic lattice, with each atom connected to six neighbors, each bon8l4pgxtf)2yj u r nng;- w+w6zd having a binding energy of $ 3.9 \times 10^{-3}\ \text{eV} $. When this solid melts, its latent heat of fusion goes directly into breaking the bonds between the atoms. Estimate the latent heat of fusion for this solid, in $ \text{J/kg} $. [Hint: Show that in a simple cubic lattice (Fig. Below), there are three times as many bonds as there are atoms, when the number of atoms is large.]$L_{\text{fusion}} =$    $\times 10^4\ \text{J/kg}$

  For $ \text{O}_2 $ with a bond length of 0.121 nm, what is the moment of inertia about the center of mass? I =    $\times 10^{-46}\ \text{kg·m}^2$

A diatomic molecule is found to have an activm msjhx,e;pa3b 78if7 ation energy of 1.4 eV. When the molecule is disassociated, 1.6 eV of energy is released. Draw a potential energy curve for this mm m8;fh37p, jbaesx7i olecule.

  When EM radiation is incident on diamond, it is found that light with wav4n rrl6gzk6l )elengths shorter than 226 nm will cause the diamond to conduct. What is the ene46grl6 )lnr zkrgy gap between the valence band and the conduction band for diamond? $E_g$ =    eV

  A TV remote control emits IR light. Ifdy6 j 4;d)iu4bdaq1mc the detector on the TV set is not to react to visible light, could it makemq jyc4ua);d1d4 6i bd use of silicon as a "window" with its energy gap $ E_g = 1.14\ \text{eV} $? $\lambda $ =    $\mu m$
What is the shortest-wavelength light that can strike silicon without causing electrons to jump from the valence band to the conduction band?

  For an arsenic donor atom in a doped silicomm,pxeq,zl,we qem, 2sxy9p lno.6kt1yz -5 8n semiconductor, assume that the "extra" electron moves in a Bohr orbit about the x ,em,wmo1 qe6,lsx.2- pp8ylqmn,k t9y 5ezzarsenic ion. For this electron in the ground state, take into account the dielectric constant $ K = 12 $ of the Si lattice (which represents the weakening of the Coulomb force due to all the other atoms or ions in the lattice), and estimate
(a) the binding energy, E =    eV
(b) the orbit radius for this extra electron. r =    nm

  Most of the Sun's radiation has wavelengths shorter than0jh*wes+ 0)cl )qlzyz20 sry l 1000 nm. For a solar cell to absorb all this, what energy gap ought the material have? ew0hl0q 0 +yjy2)zcs l*szrl)$E_g$ =    eV

  For a certain semiconductor, the longest wavelength radiation tha (n)m .xiso)73 ,yb*gjuk mstwt can be absorbed is 1.92 mm. What is the energy gap in this semic, )mmy. uto*( xssnw7bg3k)ijonductor? $E_g$ =    $ \times 10^{-4}\ \text{eV}$

  Green and blue LEDs became available many yeark5xj;7glqgud2 /4 dcys after red LEDs were first developed. Approxuglkxygj7cq2/;4 5d d imately what energy gaps would you expect to find in green (525 nm) and in blue (465 nm) LEDs?
the green $E_g$ =    eV
the blue $E_g$ =    eV

  A zener diode voltage regulator is -yivjv0*/ogr shown in (Fig. Below). Suppose that $ R = 1.80\ \text{k}\Omega $ and that the diode breaks down at a reverse voltage of 130 V. (The current increases rapidly at this point, as shown on the far left of Fig. 29-28 at a voltage of $ -12\ \text{V} $ on that diagram.) The diode is rated at a maximum current of 120 mA.
(a) If $ R_{\text{load}} = 15.0\ \text{k}\Omega $, over what range of supply voltages will the circuit maintain the output voltage at 130 V?   $\ \text{V} \leq V \leq $    $\ \text{V}$
(b) If the supply voltage is 200 V, over what range of load resistance will the voltage be regulated?    $\ \text{k}\Omega \leq R_{\text{load}} < \infty$