What type of bond would yos+67ur.nmphwq dfg uv9;t l 1:u expect for
(a) the $N_2$ molecule,
(b) the HCl molecule,
(c) Fe atoms in a solid?

Describe how the mole7aap a wou11b4cule $ \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 moleculehl0m2 /amqdecay x- 3- $ \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 th g -y6-l9gsi3u qltqp1ey?

  Would you expect the molecule xy.hn4hg c, -enu( j(q$ \text{H}_2^+ $ to be stable? If so, where would the single electron spend most of its time?{yes|no}

Explain why the carb dv fj*msqkgz841/2tz g+1 fvyon atom ($ Z=6 $) usually forms four bonds with hydrogen-like atoms.

If conduction electrons are free to roam about in a metal6(m f/fr q;3cjai )jdm, why don't they leave the metalm jd6/)3rmjc q f(fa;i entirely?

Explain why the resistivity of metals increases with temperature cs b6xqlp -rx6px-63 h1wt9* bz :jlfwwhereas the resistivity of semiconductors may decrease with increasing temperatpr9 w-6bw 6lcps 6f q:lj *1bx3zhtxx-ure.

(Fig. Below) shows a "bridge-type" full-wh-1(mb; ub qskave rectifier. Explain how the current is rectified and how current flows kbu 1h;bq(-ms during each half cycle.

Compare the resistan7xn-:8yy gpyuui c 4uc;m(qd ;ce of a pn junction diode connected in forward bias to its resistance when connectcnp;m i yx ;gc( uy8u4:-dy7qued in reverse bias.

Explain how a transisto6 iw)dguu,1hi r could be used as a switch.

What is the main difference betw7,yo5 h w*72iqpnkrr8 gq*p0b)lkd / vczlg8o een n-type and p-type semiconductors?

Describe how a pnp transian6; cdov0fq ( uukrzns v5;zp6,3rm, stor can operate as an amplifier.

In a transistor, the base-emitter juncti piid(hh)b(x5on and the base-collector junction are essentially diodes. Are these junctions reverse-biased or forward-biased in the application )dip b(( h5xhishown in (Fig. Below)?

A transistor can amplify an electronic signal, meaning it can incby+u dv/ pqxq0 s2d.x/oo s+*grease the power of an input signal. Where does itxxyoq*sqdps o2.+//g vbu+0 d get the energy to increase the power?

A silicon semiconductor is doped with phosphorus. Will these /av21 z 0swrclatoms be donors or accrzl /s21awv 0ceptors? What type of semiconductor will this be?

  Do diodes and transiade.qmw-8 g/qstors obey Ohm’s law? Explain. {yes|no}

  Can a diode be used to amplifys) zky.zinvv wja 3:,(s5gs3h a signal? Explain. {yes|no}

  Estimate the binding energy ;c upgt wq mog9o:3:t0of a KCl molecule by calculating the electrostatic potential egt:w3: u0qp ;omt9 cgonergy 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 enezv0p4t qrp/d.rgy 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 equilibriu0dvqpt z/p4r. m distance $ r_0 = 0.28\ \text{nm} $. $PE_{\text{clouds}} =$    $\ \text{eV}$

  Estimate the binding energy oqs.6zs pv.f)26 ipzzx-u,vvc f 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 oftrbgg3p83i bm8 en measured experimentally in kcal per mole, and then the binding energy in eV per molecule is calculated from that result. What is the conversion factor in 3b3ig8mgp8br 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 ma;ae yfkf i3bd5zfh5em.6 *t+w 3.pothat in the text for the states in the formation om5 .;pzyeekiw *3o bd+5fm 3ff6.aathf 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 quantity kr i6 36rna6v hp,)sqv$ \frac{\hbar^2}{2I} $ has units of energy.

  The so-called “characteristis :.rv+ cn)bwwc 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 charactf e,)3qz n2a8mpenl.m04s x cxeristic rotational 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 of H ato m,emgeh im; v;q0 ,.dbck ojkxq4peka1u38)1ms 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 th*adbpm*gs; n/at three successive wavelengths for rotational transitions are 23.1 mm, 11.6 mm, andd*bsp ngma* ;/ 7.71 mm. $r = $    $\times 10^{-10}\ \text{m}$

  (a) Use the curve of (Fig. Below) tvr9uy, n t5:*+jl -i 8c:co go.uitixqo 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 “nearest neighbor” Na and Cl ions in a Npntrl-m4g+; h aCl crystal is 0.24 nm. What is the spacing between two nearest neighbor Na l mr-h+ 4tpgn;ions? D =    nm

  Common salt, NaCl, has a density of-eew/i(w .i7dpjtmg2-u s k h; $ 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 dm/ndc4q zl, ;density is $ 1.99\ \text{g/cm}^3 $. $s$ =    nm

Explain on the basis of energy bands why the sod6x0:d/rhzqe k2d)hykium chloride crystal is a good insulator. [Hint: Conside2dhzxk6y0)h: q/edkrr the shells of $ \text{Na}^+ $ and $ \text{Cl}^- $ ions.]

  A semiconductor, bombarded with light of slowly it 5q 3s .dxgi8c4)wum m;z)hzzncreased frequency, begins to conduct when the wavelength of light is 640 nm. Estimate the size of the energy4 )5szm.w)x3 qm 8zu;hitcdg z gap $ E_g $. $ E_g $ =    eV

  Calculate the longest-wavelength p hu44z 0xt,; s/xajjxtdj tk84hoton that can cause an electron 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 and conduch8gso+i ivg2 z6r y6y9tion bands in germanium is 0.72 eV. What range of wavelenr sg ohv2 +yi9i86zyg6gths 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 o; x6yogi)rzzn tv0 kk.d;3,iae (uy )$ 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 sem/)hu;b,tff6 u szs gqh )4ls.miconductor is doped with phosphorus so that one silicon atom tf/qbs,h4 )sm.zf6 h)usl;gu 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 radiate if p gct54zyp,vd+g24zv made from a material with an energy gap v+c p,4 d 45vtg2zzypg$ E_g = 1.4\ \text{eV} $? $\lambda $ =    $\mu m$

  If an LED emits light jr )zx2jom)8, gk-i4op-20 ajjoikbz of wavelength $ \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 characteris03w7opt shek: . artokd) o ;+f3,uvvgtics are given in (Fig. Below), is connectd3wh t+)p.g0s: ;toov,7k ufokevra3 ed 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 of (Fig. Below) is connected in series to 7 bb+i7qmfn4l*hus . zc8 *pfja $ 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 jv*39v b. vu yv3wpm+fof current, for $ V > 0 $, for the diode shown in(Fig. Below).

  An ac voltage of 120 V rms is to be rectified. Estimate very roughly)p22pasby4ly9bi o z. the average current in the osap4lbzb2y 2o). y 9piutput 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 s; kpmec +yw2oan sy.5/ignificant current only if the forward-bias voltage exceeds about 0.6 V. Make a rough estimate of the average current in the output resistonkyw;sye2c +5/ amo p.r $ 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 volta gpygs1xj33n c8hp7 c-ge is to be rectified with a full-wave rectifier (Fig. Bep7ggh-cp1y8j 3snx 3 clow), 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 equatioh2 cmrel(,c9zdst q. 1n 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 ene a eebii .3z..mq-d*nqrgy 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 c 3yvl :;tk8 6t xpo2rnjzxu**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 , 6dz;gy2bnbfnm.
(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 cubiykafuj + s.)3vc lattice, with each atom connected tos)kj .3a yfvu+ 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 energy of 1.4 eV. When thc4jh - pn d,rb t.8gu2c1n/oqye molecule is disassoci-g .hcrtuoj8bn n ,pq1d4/yc2ated, 1.6 eV of energy is released. Draw a potential energy curve for this molecule.

  When EM radiation is incident on diamond, it is found that light withk42scm,jzy7q h,wy f l:4wv2 k wavelengths shorter than 226 nm will cause the diamond to conduct. What is the energy gap between the valence band and the conduction band for diwzym72y vjc,h4 wf 42,ks:lkqamond? $E_g$ =    eV

  A TV remote control emits IR light.f 6s/sxt5d c3v If the detector on the TV set is not to react to visible light, could it make use of silicon as a "window" with its energy gapf /v5tcdx36ss $ 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 ab(b09 gheug a hsu5*: ft)5pssilicon semiconductor, assume that the "extra" electron moves in a Bohr orbit about the arsenic ion. For this electron in the g usfh9u5aht 0*beg)asg(p5b :round 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 1000 nm. For a solar / o2nord -m(+iqfb8xv cell to absorb all this, what energy gap ought ther2 nxiqf-ovdb(o/8+m material have? $E_g$ =    eV

  For a certain semiconuqa+4ekp.)d g ductor, the longest wavelength radiation that can be absorbed is 1.92 mm. What is the energy gap in this semiconducpa+gk )ud q.4etor? $E_g$ =    $ \times 10^{-4}\ \text{eV}$

  Green and blue LEDs became available many years after red LEDs wefnh w.)4cd h-qre first developed. Approximately what energy gaps would you expect to find in green (525 nm) and in blued)4fwh -nhc .q (465 nm) LEDs?
the green $E_g$ =    eV
the blue $E_g$ =    eV

  A zener diode voltage regulator is shown c5.qdb dph.nip/r, zy9 / ,pviin (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?    $\ \text{k}\Omega \leq R_{\text{load}} < \infty$