What type of bond would you expe:qt jq*b;nxa1 ct for
(a) the $N_2$ molecule,
(b) the HCl molecule,
(c) Fe atoms in a solid?

Describe how the molecubuij7-8d0y pmx)p 7svle $ \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 - iyljw 1ei3 fds50lmo26oqo( $ \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.-(l i7djm6bzel e;cg g.l( xa1 What are they?

  Would you expect the mox2:ukyivvn( )sq q :s ,dcw91plecule $ \text{H}_2^+ $ to be stable? If so, where would the single electron spend most of its time?{yes|no}

Explain why the carbon applfdt84)/3dtb0-r g bkca0h tom ($ Z=6 $) usually forms four bonds with hydrogen-like atoms.

If conduction electrons are free to roam about in a metal, why don'tja0vc )ih0a:auo da:w g3sn9 6 they leave the metal entirelu:oav3g: 9 j0s icaah)6dnwa0y?

Explain why the resistivity of metals increases with temperature w;zh4;t5bnw/hdhpqdq ,03bh.i /otcghereas the resistivity of semi4 d5bh wq0 /oh;3cpz.q /bhntd;,tihg conductors may decrease with increasing temperature.

(Fig. Below) shows a "bridge-type" full-wave recti jblc4)xp5+mifier. Explain how the current is rectified and how currentxilcj )45p mb+ flows during each half cycle.

Compare the resistance of a pn junctiha pg -6,yal3h,yp j4von diode connected in forward bias to its resistance when connecgylhhv3 ,,46 pp-a jyated in reverse bias.

Explain how a transistor could be used as (u:pu6hdebz qwb+//4ft8 psba switch.

What is the main difference becpr8iahrs r 1h2+73 yjtween n-type and p-type semiconductors?

Describe how a pnp transistor can operate ft tjqnf)y 4*5as an amplifier.

In a transistor, the base-emitter junction and the base-collecto j tjh jiim6n-w7:2i6sr junction are essentially diodh 2imjjis:-66 ti j7nwes. Are these junctions reverse-biased or forward-biased in the application shown in (Fig. Below)?

A transistor can amplify an electronic signal, meaning it canwhq ia iqvst 2k+5*+q45fc;uk increase the power of an input signal. Where does it get the energy to increase thh wi5u 25q+*ti qqavkf+k4 s;ce power?

A silicon semiconductor is doped with phosphorus. Will these atoms be2tnbriz o6s363p f,.oksy0ir donors or accep,boi0r 32fzkysn . spr oi36t6tors? What type of semiconductor will this be?

  Do diodes and transistors obey Ohm’s law? Explain. {yn+ 7zx6z efsb)es|no}

  Can a diode be used to amplify a signal? Explain. {yes|nte 1 o7lkb pj6nfq ;:m.r)ft7no}

  Estimate the binding energy of a KCl molecule by calculating the electrostat:utxf(;+ dn6kq1i vg :uur:xj ic potentialuvx(j ;6:+fn1 :kd: q ugixrtu 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 4.43 eV. From the result of Prot4a4p)uop1b4 l;vu qq blem 1, estimate the contribution to the binding energy of the repelling electron claq l4vob1uq ;p4p4)t uouds at the equilibrium distance $ r_0 = 0.28\ \text{nm} $. $PE_{\text{clouds}} =$    $\ \text{eV}$

  Estimate the binding energy of the zjq(3u/4e/ oxklpx n zv. 8vq8u8/qkm$ \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 experimentallyrjim 4jrhl330 in kcal per mole, and then the binding energy in eV per molecule is calculated from that result. What is the conversion factor in going from kcal p4 hij mj3lrr03er 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 ne9t*vc2f 3*kq h j9gkin the text for the states in the formation ohe9 jf9*ktvkn3 cg *2qf 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 quantityotbve 0 /orx: * 8n,( dy.8hrz1gihkxt $ \frac{\hbar^2}{2I} $ has units of energy.

  The so-called “characteristic rotational e/v aemamt40wox :pm,;nergy,” $ \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 character 0 ;ggjmtunpqb 4*5ja:istic 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 ooxa /5 vrkmv75+vly8cf 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 thatw;fa 7qy y.g2l p7 y9i-yefnk+ three successive wavelengths for rotational transitions are 2 al9n 7i e;p2.f-y7ykwqy+yfg3.1 mm, 11.6 mm, and 7.71 mm. $r = $    $\times 10^{-10}\ \text{m}$

  (a) Use the curve of (Fig. Below) tqcu6o. iwu8:kg r p/s1o 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 anbyu r)sf/z ismh0x ko he06537d Cl ions in a NaCl crystal is 0.24 nm. What isfukh6oy0 si0e) bxzsh5 /r73 m the spacing between two nearest neighbor Na ions? D =    nm

  Common salt, NaCl, has a density ofst4 vgp(z36mj* g ef4h $ 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 o( pv kex:e,:8xreyj ,density is $ 1.99\ \text{g/cm}^3 $. $s$ =    nm

Explain on the basis of energy bands why the sodium chloride crystalbn3u+jhwzf.,ach c 3. is a good insulator. [Hint: Cuj+ whb3a h,.3.nccz fonsider the shells of $ \text{Na}^+ $ and $ \text{Cl}^- $ ions.]

  A semiconductor, bombarded with l32 +4i1qwccf yr,is hcight of slowly increased frequency, begins to conduct when the wavelength of li ywr fh q4ic31c2+ic,sght is 640 nm. Estimate the size of the energy gap $ E_g $. $ E_g $ =    eV

  Calculate the longest-wavelengthgl y7 q(:0cx*e5m pfnm photon 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 7ro9 e1*o pmrrvalence and conduction bands in germanium is 0.72 eV. What range of wavelengths can a photon have to excite an electrorp7rm9*1r o oen 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 ar7zxfyeyl ppi7i )z t77-x*j +akj;ai2e $ 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 bj 0ca ikljn2qt;;/y-semiconductor is doped with phosphorus so that one silicon atomj t;aqi;0cb-ylj2k/n 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 made from a material wit6 y9 e9lghuoya-,e c, fk9b2zth an energy gaeya,, 99h6tz klo2c9egfuy- bp $ E_g = 1.4\ \text{eV} $? $\lambda $ =    $\mu m$

  If an LED emits light of w w9:m:okg439 tlmcmm havelength $ \lambda = 650\ \text{nm} $, what is the energy gap (in eV) between valence and conduction bands? $e_g$ =    eV

  A silicon diode, who. h 6i3q49tbxlurw(hr qo o,8pse current-voltage characteristics are given in (Fig. Below), is connected in seri(op4 i8l,rot36.9ruhh qxbwq es 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 connec0 (;d:ht9z9 d r/z kgs3ajxlzkted 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 resistanc .x.fwu:p tfr)-b:ws fe as a function of current, for $ V > 0 $, for the diode shown in(Fig. Below).

  An ac voltage of 120 V rms is to be rectified.1 )j pzzhrqh/;jpg u;t7j*m8x Estimate very roughly the average current in the output resistjrhzj/gjzt u81xpm;h;q) p *7 or $ 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 38kvrw n6z *-khezgb)w j1nq,exceez1re -3*bjk,vwnn q k86wg)h zds about 0.6 V. Make a rough estimate 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 rec 0z ,cnm1tycj,tifier (Fig. Bel0nc j1y,mtc z,ow), 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 tyebklcs01z xq+, /5ybase current $ I_B $, the collector current $ I_C $, and the emitter current $ I_E $ (not labeled in the figure).

  Estimate the binding ehxj (upi.t unk(6*x y-nergy 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 kiltwx nd g1;xx:9 /uu8 -wt;zndnetic 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 io1;,lc5(bj:sk vsx a soeyur(1ns 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 lat)r wv;pv+wo x(6tmm5stice, with each atom connected to six neighbors, each +) v;mw 5rxs(o6w vmtpbond 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*wgyx ;ju* aagq *l2o( the molecule is disassociated, 1.6 eV of energy is relo *2laj*g ygq*(a;ux weased. Draw a potential energy curve for this molecule.

  When EM radiation is incident on diamond, it is found that light wi+2b(b79fu;ds wg piiev9 (br tth wavelengths shorter than 226 nm will cause the diamond to conduct. What is the energy gap between the valence bs9i2+be(trbv dp( 9 7ugibw;fand 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 g;q w9(3zg wqwv67iid w 91e *w-fpgdbto react to visible light, could it make use of silicon as a "window" with its zb9p6dg-w ; *(ef1 q9 gig73wwiwdqvwenergy 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 a8 b3 e1wy ny0hpcx-fn; doped silicon semiconductor, assume that the "extra" electron01 xwpyh-nfy bc83e ;n moves in a Bohr orbit about the arsenic 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 radiaty*-8 rbom dn*y .jpzykw-*8ition has wavelengths shorter than 1000 nm. For a solar cell to absorb al8- o**wd ytip k-m.*brn8yzyj l this, what energy gap ought the material have? $E_g$ =    eV

  For a certain semiconductor, the longest wavelength radiatio8z0 zp ra+ein.n that can be absorbed is 1.92 mm. What is the energy gap in this semiconductor? +0 .ze8 ipaznr $E_g$ =    $ \times 10^{-4}\ \text{eV}$

  Green and blue LEDs became availey/6drsq76 n)z x wk-fable many years after red LEDs were first developed. Approximately what energy gaps would you expect to q6dsryzx- 6nwe f/7k) 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 regulato+s eu.e4rb* lloscu8fp k 38.yr is 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?    $\ \text{k}\Omega \leq R_{\text{load}} < \infty$