What type of bond would you expect for *v rr z89x*6v-;tma yzn;pmph
(a) the $N_2$ molecule,
(b) the HCl molecule,
(c) Fe atoms in a solid?

Describe how the molec)sgxcpo05w,oxx4 iid3 p/zoybe; ,h9 ule $ \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 b+a 4feo2zw6sc 8sq(s$ \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 are tik i;+ 5(xhv.qoisdq( hey?

  Would you expect the m n+ sticzfwe7 dkj2;j ye4)vbr6h88v0 olecule $ \text{H}_2^+ $ to be stable? If so, where would the single electron spend most of its time?{yes|no}

Explain why the carbong5fy azja-r(6 xvhaj*7 2mxcd;2x1 xy atom ($ Z=6 $) usually forms four bonds with hydrogen-like atoms.

If conduction electrons are free to roam about in aal+hs*z78a6j 8rldym metal, why don't they leave the metal entiryah jlam +6lsz7*r 88dely?

Explain why the resistivitj;,ce3pzy xvf9te:ust p4*,f y of metals increases with temperature whereas the resistivity of semiconductors may decrease with increasin zf je;txf39*u,4p y:,pscvetg temperature.

(Fig. Below) shows a "bridge-type" full-wave rectifieko k),rt(c/-)l nnak :w3x-)rzejq gdr. Explain how the current is rectified and how currenj-o,/gkka ed) nk c3) -xrwtz)qlr(:nt flows during each half cycle.

Compare the resistance of a pn jslbnx8e-p8 x82 b8iwaxb o98dunction diode connected in forward bias to its resistance when connected in re 2 ib x wab98onb8p88xd-sx8elverse bias.

Explain how a transistor co xktr:mxmaym1 0gs87/ uld be used as a switch.

What is the main difference betwe(kf8 eieh391.zpm2dica)w ca a--ql w en n-type and p-type semiconductors?

Describe how a pnp transistobg) c :(kmgkm)r can operate as an amplifier.

In a transistor, the base-emitter junction and 0)u4nwnyw-d q the base-collector junction are essentially diodes. Are these junctions reverse-biased ny-nqdw )u0w4 or forward-biased in the application shown in (Fig. Below)?

A transistor can amplify an electronic signal, p2pf-xlv( c6fbks 0r,z .rc3m6gd9hxmeaning it can increase the power of an input signal. Where does it get the l gx ,3z2f0xhkp. 9cvrm(cfd-r6b 6psenergy to increase the power?

A silicon semiconductor is doped with pho93 p m):jun5nre8x xhwsphorus. Will these atoms be donors or acceptors? W x3e :nnjwhx 5p9r8um)hat type of semiconductor will this be?

  Do diodes and transistors obey Ohm’s lh9u2yno 2o1 a3 f(ffu 0k3za 3n lahis5)0daoaaw? Explain. {yes|no}

  Can a diode be used to amplify a sigp))kg6 g p5kvvnal? Explain. {yes|no}

  Estimate the binding energy of a KCl molecule by calculating the electrostaticnc v7xx-jtcq)0/i55 ddo6ujk poten -5odnikt/dx)u c670vjjx cq 5tial 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 is 4.43c l.gamu4( a2mg) 5lqf eV. From the result of Problem 1, estimate the contribution to the binding energy of the repelling electrl)2m l 4 .magq5uca(gfon clouds at the equilibrium distance $ r_0 = 0.28\ \text{nm} $. $PE_{\text{clouds}} =$    $\ \text{eV}$

  Estimate the binding energy of thcd,*nes13l n he $ \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,jec* pt.mj q). and then the binding energy in eV per molecule is calculated from that result. W)emj*p.jqc. t hat 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 in- qpq/g:lq0dcxns(70k bygh 8cn0a2r the formation of the bq d2:g-qy7 cq0ks nrnx / c008pl(hag$ \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 quantity e2-iq9yw t fww2xte3) $ \frac{\hbar^2}{2I} $ has units of energy.

  The so-called “characteristic * sg/ceth61wycvk86e 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 rqs27ct p- 2 .bv,zs-sz exqc(pyf61trotational 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 separation o 2tpz q:0ludgmc+/r uiykxl s//xji5 456gtq0f 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 the NaCl molecule given that thr g: k2elz gq;cox;(d3x (rz/vzee successive wavelk:v d zoqg;zl/g((z3 2cex;xrengths for rotational transitions are 23.1 mm, 11.6 mm, and 7.71 mm. $r = $    $\times 10^{-10}\ \text{m}$

  (a) Use the curve of (Fig. Below) to estimsa0g89:pewh sate the stiffness 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 neighbor”nman 3wnxxz:09d. 9ib Na and Cl ions in a NaCl crystal is 0.24 nm. What is the spacing xd wn.mai3x0z: 99nbnbetween two nearest neighbor Na ions? D =    nm

  Common salt, NaCl, has a dq cy99h1t hd8fifo9u:c5.th gensity of $ 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 KCwd4h bjmzi5vhq 2k0 e5xut)((l whose density is $ 1.99\ \text{g/cm}^3 $. $s$ =    nm

Explain on the basis of energy bands why the sodium ch4z)j(- wcrfr gloride crystal is a good insulator. [Hint: Consider tgrf (rcw4z-j) he shells of $ \text{Na}^+ $ and $ \text{Cl}^- $ ions.]

  A semiconductor, bombarded wisqb -:9 :q1m t1 ;w:pkdfpiatfth light of slowly increased frequency, begins to conduct when the wavelength of light is 640 nm. Ei1::k 1 fbf9tq:md;q wpp- satstimate the size of the energy gap $ E_g $. $ E_g $ =    eV

  Calculate the longest-wavelength photon that can cause an electron in+jlc ya z:w69 aw.jr9x2 k9jsp 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 and condriutjwjtzf0 *40 9hy):nehmn 6 ) 7cjkxlic8,uction bands in germanium is 0.72 eV. What range of wavelengths can a photon have to excite an electron from the top of the valence band into the conduction btn9njh u,y7cjl6 timz4jkexc 00f*wi:))8 rh and? $\lambda \leq$    $ \ \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 are n 1ds4a.emk,g $ 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 semiconductorq d7hzyfd f r/1m0v1t7 is doped with phosphorus so that one silicon atom in v y1t0dfdfm7rqh7/1z$ 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_{\text{doping}}}{N_{\ce{Si}}} = $    $ \times 10^6$

  At what wavelength will an LED radiate if made from a material with an energy gamga dvm 19qz5tw-fy4n(67e xyp mx(e4y1 zmwa nd6yg-q5v97ft $ E_g = 1.4\ \text{eV} $? $\lambda $ =    $\mu m$

  If an LED emits light of wnd 9v: fi ol7d(qsws.1 adcyvy0-:k 5favelength $ \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 characteristics are given in (Ft- -,su8o dupye9:ztv ig. Below), is connected in series with a battery and vd es-8t-uo,9 ty p:uza $ 960-\Omega $ resistor. What battery voltage is needed to produce a 12-mA current? $V_{\text{battery}}$=    V

  Suppose that the diode of (Fig. Below) is connected in ;vxid4finq)k irie j +8uk-8to/2/b yseries 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 func m o4og4 zxccgo he6 :x9o5a:3zbp6/wqtion of current, for $ V > 0 $, for the diode shown in(Fig. Below).

  An ac voltage of 120 V rms is to be rectd;u/ )f4 rgwtki-b4 ksified. Estimate very roughly the average curr;dkr ugsk4w /ft)4 -bient in the output 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 current only if the for-p)c70ur opta kl26 gwward-bias voltage exceeds about 0.6 V. Make a rough p2r)aw -oguc70p6k ltestimate of the 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 voltage is to be rectified with a full-wave rectifa, xe8pl ur273qz q rqn*.b*opier (Fig. Belo7rpnq2q,a8. *pleq3 *ouzx brw), 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 equatio (ee9q7i* yty/ wnc-jhn for the relationship between the base current $ I_B $, the collector current $ I_C $, and the emitter current $ I_E $ (not labeled in the figure).

  Estimate the binding energy of the juo z;l-6ekdkd2ds;my r/v :5 $ \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 kineticb5abq-/ pqy 8p energy 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 ions is about 0.27 nmh+l3 x8t 8hgt0btpd8a.
(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 bound cubic lald 8 ydpp(4)iecvee ),ttice, with each atom connected to six neighbors, each bond having a p4lyc d)8 eve d,i)(epbinding 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 activation energ. ili o7enq.fs::lyc;y of 1.4 eV. When the molecule is disassociated, 1.6 eV of ener: flc;iq7eo s.yin:l. gy is released. Draw a potential energy curve for this molecule.

  When EM radiation is incident on diamond, it is found that light wic)(omkdbh;ep 3nc (jxm:6c 9wth wavelengths shorter than 226 nm will cause the diamond to conduct. What ) bd 6kenjx9(m3( co: h;pccmwis the energy gap between the valence band and the conduction band for diamond? $E_g$ =    eV

  A TV remote control emits rof;vy5uqip 11*1 rch IR light. If the detector on the TV set is not to react to*;v 1iu1rqhyropc 15f visible light, could it make 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 sila zf*:vy*ex1b icon semiconductor, assume that the "extra" electron moves in a Bohr orbit about the arsenic ion. For this electron in the ground state, take infbv :z* aexy1*to 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 +rgk(f*yj6j.t4 eka wshorter than 1000 nm. For a solar cell to absorb64 fr kk*eagjty.wj(+ all this, what energy gap ought the material have? $E_g$ =    eV

  For a certain semiconductor, the longest wacb p/tg / kg:xsbivrv(8 (fd:*velength radiation that can be absorbed is 1.92 mm. What is the energy gap in this semicondr:fbbv( t*s8ki c//pg(gx:dvuctor? $E_g$ =    $ \times 10^{-4}\ \text{eV}$

  Green and blue LEDs became available many years after r*jr4;g08xoaj w3 s( tfbq1ubged LEDs were first developed. Approx b *1arfj bwtjsqo( 43x8ug;0gimately 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 shown in (Fig. Barwr d+ ;w0m9 1azkvz8elow). 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?    $\ \text{k}\Omega \leq R_{\text{load}} < \infty$