What type of bond would you expet +b u)bm ;.-yqs1hqkpct for
(a) the $N_2$ molecule,
(b) the HCl molecule,
(c) Fe atoms in a solid?

Describe how the moleculfsg ;pu;8;wfs 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 moleculea.(b 2hf xdjn: $ \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 dal5x(ff:g 42of5 c2xrktom 7zmbe.0k ivided into four categories. What are they?

  Would you expect the mol,3hs *nv1w6vcg s/ mvoeh,q3u ecule $ \text{H}_2^+ $ to be stable? If so, where would the single electron spend most of its time?{yes|no}

Explain why the carb h28zre 7fa9nbwt 8wfao uv8/*on atom ($ Z=6 $) usually forms four bonds with hydrogen-like atoms.

If conduction electrons are free to roam about in a mpux hmxq+s)24 )b x u8u:btejg )cx6nj(yv9d6etal, why don't they leave the metal enctx)qeu ))u6 24s86u g vjnb(xpx :9x+j hymbdtirely?

Explain why the resistivity of metals increases widgd-zgmchz 18s5f; -bth temperature whereas the resistivity of semiconductors may decreas8m;z-ch sg-zf d51dbg e with increasing temperature.

(Fig. Below) shows a ou -mquh)5 : om)r)evq"bridge-type" full-wave rectifier. Explain how the current is rectified and how current flows during each halm)q):uh r5 )o-eqou vmf cycle.

Compare the resistance of a x0(byz uh3pq3pn junction diode connected in forward bias to its resistance when connected in reverse0 px( zyb3qh3u bias.

Explain how a transistor could be lpu(fju+e a; 5used as a switch.

What is the main difference between n-typlc( gwg9j30m bbxwp d5 0b:l)a+3dhvxe and p-type semiconductors?

Describe how a pnp transistor can operate as an sr)c lev3-7 vpamplifier.

In a transistor, the base-emittq /22dy9 4njuzkt2lxcer junction and the base-collector junction are essn2 qzlyk/dx2t9u cj24entially diodes. Are these junctions reverse-biased or forward-biased in the application shown in (Fig. Below)?

A transistor can amplify an electronlbp+p*ld .pq 8j4h 0c/vsc /dnic signal, meaning it can increase the power of an input signal+8ds./d vp ql/4h0plpjcnc* b. Where does it get the energy to increase the power?

A silicon semiconductor is doped with phosphorus. Will these atomm,wz9o8nsk )ip(mlf* qkjhd 0zx7s+,s be donors or accepto(0kqo9iz, m 8*7f zklds+mwn s)pxj,hrs? What type of semiconductor will this be?

  Do diodes and transist7 *c;boi6o-nj9gns egors obey Ohm’s law? Explain. {yes|no}

  Can a diode be used to a( a; b)*m)uc do(,ml tdigu1l()bhpin mplify a signal? Explain. {yes|no}

  Estimate the binding energy of a KCl molecule by calculating the ele4r spt sa;rq e1 afvju98e(6ndk1f6;h ctrostatic poterrf shdv 64 6t s1n1u8(qpe9ejf;;kaa ntial 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 eh/i4c2 jv cy4unergy of 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 equilibrium distan 2vuc44/i cyhjce $ r_0 = 0.28\ \text{nm} $. $PE_{\text{clouds}} =$    $\ \text{eV}$

  Estimate the binding enzfc/a7 8oie2ngjih. 57 iomw(h mrb6 :ergy 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 are often measured experiment,/5mr(z vmmuoally in kcal per mole, and then the binding ene5u (orm/zm ,vmrgy in eV per molecule is calculated from 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 state) q0;d.bgpg b qipu-:vs in the formation of th-v)bpq gg;u0. qi dpb:e $ \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 quantixd8sdvihnl )9 f*f+ d(ty $ \frac{\hbar^2}{2I} $ has units of energy.

  The so-called “characteristic rotationa3sl df,a ;w wi8pn1vf/l 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 rotational enen*/rm4o9tpg ht-l)zuxw bwym,h/2 v7rgy, $ \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 separatinr6dom a72n;h)dxei 1 on 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 taei*vc 5s;loatep 1 ms3:5v 5yhe NaCl molecule given that three successive wavelengths for rotational transitions are 23.1 mm, 1a1 5lea y:p5s*io3;vsv tce m51.6 mm, and 7.71 mm. $r = $    $\times 10^{-10}\ \text{m}$

  (a) Use the curve of (Fig. Below) tb3b u umh9jb)f3 3ujz0o estimate 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 “nearekpjf0rqge7a*f.m(mb )8zu0k st neighbor” Na and Cl ions in a NaCl crystal is 0.24 nm. What is the spacing between two nearest neighbor Na ions? D k.) jugk70ae(mfb8q*mrzf 0 p=    nm

  Common salt, NaCl, has *+qd go;l7f rfa density 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 KCl whovaq5hk jr+ - +6h) ex2ncz7qxvse density is $ 1.99\ \text{g/cm}^3 $. $s$ =    nm

Explain on the basis of energy bands why the sodium chloride cryst6fthq s; i7l- )ryar+zuwc h-ge, k3p6al is a good insulator. [Hint: Considerr l;cq-iguhfw rsay66 h -7, +e)3ztkp the shells of $ \text{Na}^+ $ and $ \text{Cl}^- $ ions.]

  A semiconductor, bombarded with light of slowly increased frequ7/rn 4j2aofb cency, begins to conduct when the wavelength of light isfn br c4/7a2oj 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 a bg*9 df0jx:by/5d ct(jrwb1silicon ($ E_g = 1.14\ \text{eV} $) to jump from the valence band to the conduction band. $\lambda $ =    $\mu m$

  The energy gap between valence and6t(i 0kq cj1ud conduction bands in germanium is 0.72 eV. What1dj ukt0(i6q c range of wavelengths can a photon 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 are jjlt97wbx0*l $ 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 semzg5* i0 i 1tin+7.efot3 hgc(cc.jkrhiconductor is doped with phosphorus so that one siliconer1n 7jc g5 .tkz(hoiitg icc3.0h*+f atom 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 wi6 lzolrli-)(f ll an LED radiate if made from a material with an energy gapi-l olr zl(6)f $ E_g = 1.4\ \text{eV} $? $\lambda $ =    $\mu m$

  If an LED emits light af7po1oq5s8bpmf q:rqk7 ssx 6q/3a 0of wavelength $ \lambda = 650\ \text{nm} $, what is the energy gap (in eV) between valence and conduction bands? $e_g$ =    eV

  A silicon diode, whose curws35 bol)zbd/kho)ta 8q5 gy( rent-voltage characteristics are given in (Fig. Below), is connected in series with b g5s(ho3twydo 8) zkaqb)l5 /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 of (F8g kotxucz+f3, a46p /pqq12n1dk b jtig. 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 aslk95 ly-*nldu a function of current, for $ V > 0 $, for the diode shown in(Fig. Below).

  An ac voltage of 120 V rms is cb0ybc*/re5 mto be rectified. Estimate very roughly the average current in the output re0c/r5mbb*cy esistor $ 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-bias voltage excet:thqi ij,bx0 d*o: 8reds about 0.6 V. Make a rough estimate of the average current in the output resji*:tq:xit h 8ob0 ,rdistor $ 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 wibum h.60wb 9s+f7z vx +;qpmx5ra(ehfth a full-wave rectifier (Fig. Belowa6sm+rx7vhf(w;90 bxpeq mu.bz+f5h ), 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 between the base curr dz,mk4 x0g76igjj 6rlent $ I_B $, the collector current $ I_C $, and the emitter current $ I_E $ (not labeled in the figure).

  Estimate the binding energy of the2. , fagvc0yhg $ \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 eneh h sthbj 2-z17nvg2,vy-xs9brgy 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 nm e)ay bs)wr--o *:zsz.fvj8kasx /mp *.
(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 cub 6 ir)tv3qy+cdh mt/g/ 8;ceiyic lattice, with each atom connected to s+r3ci 6imyc; / vt)dgt8/yhqeix 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 energy oib73(2c2ll umiv e8jqf 1.4 eV. When the molecule is disassociated, 1.6 eV of 2m3li7ue 8qi2 v(clbj energy is released. Draw a potential energy curve for this molecule.

  When EM radiation is incident on diamond, it is found that oow,,yz3 cklpfpwot xl+ (v 2c7 54bz0light with wavelengths shorter than 226 nm will caus otpl +27wbvx 04zof(,cwzkylco3p 5,e the diamond to conduct. What is the energy gap between the valence band and the conduction band for diamond? $E_g$ =    eV

  A TV remote control emits IR lig3t-)enj7fioltqsw j 5t0rk9q 9kgw5 8 ht. If the detector on the TV set is not to react to visible light, could it make use of silicon as a "window" withw5qttjtnj7ols) k9q ierk85 -w930fg 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* ,z5tnbegya5 that the "extra" electron moves in a Bohr orbit about the arsenic iot5ney ,*azgb5n. 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 than 2ey,gwnw/wupf/ j; c 21000 nm. For a solar cell to absor;ewgn2u/j,/cw 2p fwy b all this, what energy gap ought the material have? $E_g$ =    eV

  For a certain semiconductor, the lop t*-lstw ,;uf, ii5xxngest wavelength radiation that can be absorbed is 1.92 mm. What is p- lu xfitwx,,5; i*stthe energy gap in this semiconductor? $E_g$ =    $ \times 10^{-4}\ \text{eV}$

  Green and blue LEDs became available many years afev(v3d6 yh(*4cs*n eslmw 0 gzter red LEDs were first developed. Approximately what energy gaps would you expect to find in green (525 nm) and in blue (465 nm) LEDs?0ylc ge*z3v6 (4s wv ens*(mhd
the green $E_g$ =    eV
the blue $E_g$ =    eV

  A zener diode voltage regulator is shfo9p o on.y /)y/qio564wjcmkown 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?    $\ \text{k}\Omega \leq R_{\text{load}} < \infty$