What type of bond would you expdscxr6,1 voqrml-z; b84l e0g e0h*yject for
(a) the $N_2$ molecule,
(b) the HCl molecule,
(c) Fe atoms in a solid?

Describe how the moleculun/ au8s9,zrayb (vf3 e $ \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 molecul t5o1is--am qkig0x6ye $ \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 theu(pgx*ho4;rk06c tj*9m h cb iy?

  Would you expect the molek .pern7,5vjye*hm h9f* qvp/ cule $ \text{H}_2^+ $ to be stable? If so, where would the single electron spend most of its time?{yes|no}

Explain why the carbon atom y*xzk f0z( h1ce kx5v4($ Z=6 $) usually forms four bonds with hydrogen-like atoms.

If conduction electrons are f 5l3(4( dqdoa a vdu6rax2-cnwree to roam about in a metal, why don't they leave the mxddo46 qcw( lrau-vda235n( aetal entirely?

Explain why the resistivity of metals increask d974 j (6eb*vtz7n3/ yrrab neas;npes with temperature whereas the resistivity of semiconductors may decrr74a j9p3ds*z (6tneb e any;rknbv/7ease with increasing temperature.

(Fig. Below) shows a "bridge-type" full-wave rectifier. Explain how the currj.v.m 49swmfe h50nlz ent is rectified and how current flows during each half cycle. 94 h.50m vzfnj lsw.me

Compare the resistance of a pn junction diode cqac2ex891gl5z n fy;aonnected in forward bias to its resia zfye21 5lg9n;a xcq8stance when connected in reverse bias.

Explain how a transistor could be used as a switcf 1xi1rjw.bd;h.

What is the main difference between n-type and p-type semism( n(e3wk(m3qjn ng7 conductors?

Describe how a pnp transistor can operate as t 0ai4clwe 3r.favn*f 666 rmvan amplifier.

In a transistor, the base-emitter j ti0k8xzr-z-junction and the base-collector junction are essentially diodes. Are these junctionsz 0rjzi -kt-8x reverse-biased or forward-biased in the application shown in (Fig. Below)?

A transistor can amplify an electronic signal, meaning it can in,*l)t0 cf fjjwxg j:bj9ij8uyi* x4g /crease the power of an input signal. Where does it get the j uyw f4tjxc9)j,fix* j/lb8jg:0gi* energy to increase the power?

A silicon semiconductor is doped with phosw.cm*q2 e6x qqphorus. Will these atoms be donors or acceptors? What type of semiconductor will this b c.q qw6e2*xmqe?

  Do diodes and transistors obey Ohm’s law? Explain. {yeso:-jgvadjcm6 + 5+tto|no}

  Can a diode be used to amplifyj8holjh(g.t ; a signal? Explain. {yes|no}

  Estimate the binding energy of a KCl molecule by calculating the electrostatilin 14 w)xq(gdmeo/s:d)sr6nj3a 4kqc potenaik)w 4 eg3)1xl4mq 6: dons/ds (njrqtial 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 ofihfnag(zq +5y e ; og42a* 1*axflt;nh KCl is 4.43 eV. From the result of Problem 1, estimate the contribution to the binding energy of the repelling electron clouds at the equilib*xhflnta q1fi(yeo2g;*;gn54a azh+rium distance $ r_0 = 0.28\ \text{nm} $. $PE_{\text{clouds}} =$    $\ \text{eV}$

  Estimate the binding ene ir/j m8ft4/z1dzx3h irgy of 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 arefmt-y.mgdjtw3e;y h, .:i x)/f, ek yb often measured experimentally in kcal per mole, and then the binding energy in eV per molecule is calculated yef/ywt .,,e fj;k:)id3th.b- gym mxfrom that result. 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 in the formk hurre h+gpbsk 3:on73q9q)/ls+4jbation of theeg/r7++qo kjlss4pb :k3 q 9)u nrhh3b $ \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+j445 mwiz +e3sevp en $ \frac{\hbar^2}{2I} $ has units of energy.

  The so-called “characteristic rotationlwp 0ym 0142nutmu/9dunm 8ao al 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 rotati* 4k7q9quph)ccr2)x ioup h6:etf.aeonal 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 separa9vfsx 5;*qvpq tion 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 the NaCl molecule givenun7;q ndgiq)2r c1/ij that three successive wavelengths for rotationalc qg 7/2idin; ju)1nrq 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 estimate the stiffness constant +gz;9vq 0v6js;v d zep$ 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 neij n(: /8k1lidpu2h:icl4ml rbghbor” Na and Cl ions in a NaCl crystal is 0.24 nm. What is the spacing betweund kjli:1hrp li/(m l: 8bc42en two nearest neighbor Na ions? D =    nm

  Common salt, NaCl, has a density ofl,u0ja.nsx 6 x/s t5kk $ 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 Kslu l ws1adp; ;bee(p*ev1m46em*q ; lCl whose density is $ 1.99\ \text{g/cm}^3 $. $s$ =    nm

Explain on the basis of energy bands why the sodium chl+x+dp( ripid5d2qv )foride crystal is a good insulator. [Hint: Cop)fdq2d vii+r xd(5+ pnsider the shells of $ \text{Na}^+ $ and $ \text{Cl}^- $ ions.]

  A semiconductor, bombarded with light of sc0 l5f.fmh.te3xts4 cv7/ evc lowly increased frequency, begins to condu0/tth.sel3cc.7mx e5 fv fvc4ct when the wavelength of light is 640 nm. Estimate the size of the energy gap $ E_g $. $ E_g $ =    eV

  Calculate the longest-wavelength photon that can cause an electron in silicon nj 8b6j bkm68y($ E_g = 1.14\ \text{eV} $) to jump from the valence band to the conduction band. $\lambda $ =    $\mu m$

  The energy gap between valence * r4 kthcmf+ )ua))w u(x1hgtv9 u2brtand conduction bands in germanium is 0.72 eV. What range of wavelengths can a a(cw4*hb r2 t))u )tg fr+h 1xumv9kutphoton have to excite an electron 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 arw;*1z ulg rui,d/e2hd ndi(w obz*) 2ye $ 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 phosphorus so that one siliwu 9+t hz.5lqicon atoiztq9 l uw5h.+m 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_{\text{doping}}}{N_{\ce{Si}}} = $    $ \times 10^6$

  At what wavelength will an LED radiate if made from a materia5 ml5ll fz;y 9nn0o;yll with an energy gap l 9y5o nlm;zfl; 5l0ny$ E_g = 1.4\ \text{eV} $? $\lambda $ =    $\mu m$

  If an LED emits light of wa bl 2,zy ,/rf d,obqi53,yzhxxvelength $ \lambda = 650\ \text{nm} $, what is the energy gap (in eV) between valence and conduction bands? $e_g$ =    eV

  A silicon diode, whose cu9mn:s6lh2/ oxvj dku 9rrent-voltage characteristics are given in (Fig. Below), is connected in series with s/jl :h6d992mxko vnua 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 of o+f5qs*0 lx5 qan xe;v(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 ofv dpvw 3;n (r*g0iyrz4 current, for $ V > 0 $, for the diode shown in(Fig. Below).

  An ac voltage of 120 V rms is to be rectified. Estimate versv1pycs *+ila0)zz)g y roughly the average current z +ipa1 gs0c) zy*svl)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 forward-bdwgj0jn6 pt6:wvu 8 n-ias voltage exceeds about 0.6 V. Make a rough estimate of the avendp: 0jw-8j6wnutv g 6rage 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 rectifier ( :rx7w2z +ebm2ad;x rqFig. Below), where22w zexxqdb +rm:a;7r $ 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 between tl**ufb9;t0et526 w gljf xkp 5yucu0/saco (jhe base current $ I_B $, the collector current $ I_C $, and the emitter current $ I_E $ (not labeled in the figure).

  Estimate the binding eneo;yk-* yq mti:rgy 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 energy of an atom or molecule is t4lpoz+ z gq(-wf9e d(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, n2t cz:bwd;;ii,cfnq)s9y+1 tffg2 ythe separation distance between ions 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 bound cubic latttn ) pw3 pc,x;/wdb(byice, with each atom connected to,wtdcx)y/p;w nb3pb( six neighbors, each bond 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 activation eneryx(tw:6w * ne7*v+lpgq/kpu ngy of 1.4 eV. When the molecule is disassociated, 1.6 eV of energy is released. Draw a potential energy curve for p+vg w/ 6(7ly nq pnwk*u*:texthis molecule.

  When EM radiation is im,3eykjr k0 1dyjvx uq7w1 ;s4ncident on diamond, it is found that light with wavelengths shorter than 226 nm will cause the diamond to conduct. What is the enqxev jduj1;mr1ky k34w y0s,7ergy gap between the valence band and the conduction band for diamond? $E_g$ =    eV

  A TV remote control emits IR light. If the detector on the TV set is not to rez n. kgl6c7ar3xs1bs( act to visible light, could it make use of silicon a n1 bk.szgsr(6xlc7a 3s 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 silicon semiconductor, assume that the,hxy;l a8 /xwl/kr ks7 "extra" electron moves in a Bohr orbit about the arsenic ion. For this electron in the ground statewasrx/x/lhk7 y8,; l k, 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 than (wxoqh -x f7sqd8+k:s 1 kqqt41qp;kh 1000 nm. For a solar cell to absorb all this,7s -8kfqhqso; hxw4k 1p(qt kxq: +1qd what energy gap ought the material have? $E_g$ =    eV

  For a certain semiconductor, the longest wavelength radiation that can b u/a)9 kl8rv)3-hq xd a(fbrvje absorbed is 1.92 mm. What is ( 8)- /ad9fv hxaur3lbkvj)qrthe energy gap in this semiconductor? $E_g$ =    $ \times 10^{-4}\ \text{eV}$

  Green and blue LEDs became available many ye u,tna3us81 jgxx)/pvars after red LEDs were first developed. Approximately what energy gaps would you expect to find in green (525 nm) and in blue (46g8/jxp tsvun,u xa3)15 nm) LEDs?
the green $E_g$ =    eV
the blue $E_g$ =    eV

  A zener diode voltage regulator is shown in (Fig. Below). Suppose d hcsp9q8 fb(4that $ 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?    $\ \text{k}\Omega \leq R_{\text{load}} < \infty$