What type of bond would yx4bvkb*o 6:o zm 2rjp9ou expect for
(a) the $N_2$ molecule,
(b) the HCl molecule,
(c) Fe atoms in a solid?

Describe how the moleculepi1+j xlp83 o qv ba02rnfm:-s $ \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 moleculel 33 wu-.7zvqga, cr5n1dgtv k*vty*o $ \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 are1aj0fz6jl d k: they?

  Would you expect the molecuc1nwz/hued9n; jj,bxc , g4 c8gzw65ble $ \text{H}_2^+ $ to be stable? If so, where would the single electron spend most of its time?{yes|no}

Explain why the carbon atoma wj+j o*ien-w;i.4zh ($ Z=6 $) usually forms four bonds with hydrogen-like atoms.

If conduction electrons are free to roam about in a medkc; k-bvqr 0v0alr 59tal, why don't they leave vvba5rq;c 0r9k- dl0kthe metal entirely?

Explain why the resistivity of metals increases with temperature whereas mru 7ph60hx y87y, qhmthe resistivity of semiconductors may yu p 7h08,hmqrm6y7xh decrease with increasing temperature.

(Fig. Below) shows a "bridge-typtv99z )z*jhj re" full-wave rectifier. Explain how the current is rectified and how current flows duritzz j)h9jr* v9ng each half cycle.

Compare the resistance of a pn junction diode connected in forward bk06z(uwin xa3* 1 zh xjq+e* wppo2je2ias to its resistance when conn p1zjep*zixakhj w3n0uw*6e+2qo(x 2ected in reverse bias.

Explain how a transistor could be used as a switcu.9egv/85rle ji x9 8h/+nmswwve5 m xh.

What is the main difference benl; pf-zdv ny4lz 6c4 2)vr1skeak8(q p*1 zehtween n-type and p-type semiconductors?

Describe how a pnp transistor can operate as anqn3;c 8/4bxt ct mky4 6-tptpl amplifier.

In a transistor, the base-emitter junction and the base-collector junctionmi,79j*k9kpkk o( -oy e7pf7ieao4 yj are essentially diodes. Are these junctions reverse-bias9 7m ke7k-y79,ekj*ik io4o(fa oppjy ed or forward-biased in the application shown in (Fig. Below)?

A transistor can amplify an electronic s:-gc)99g ahuwo xtus e0alm2b--yx t2 ignal, meaning it can increase the power of an input signal. Where does it getyehlc- s- u)axag2u9t9 x b0tm-o: wg2 the energy to increase the power?

A silicon semiconductor is doped with phosphor ; rn wdxlc+xifl-k(+7 t/x.kvus. Will these atoms be donors or accepto-dlfixk n./+w;(cxl 7rk+txvrs? What type of semiconductor will this be?

  Do diodes and transistors obey Ohm’s law? Explain. {yes|no 5cr:55s:v*:lqfqft kebbt ,o}

  Can a diode be used to amwwrgg1xe* : iugnn;)qpr*7p3 w/p h( uplify a signal? Explain. {yes|no}

  Estimate the binding energyux gni-nj01) .pvkae/ of a KCl molecule by calculating the electrostatic potential energy un n x1epg)v -/kji0.awhen 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 eVuqg+ io*na2d, nby2:r . From the result of Problem 1, estimate the contribution to the binding energy of the repelling electron clouds at the eqn b g,ioda *2n2+yruq:uilibrium distance $ r_0 = 0.28\ \text{nm} $. $PE_{\text{clouds}} =$    $\ \text{eV}$

  Estimate the binding energy of the/bg 7a.h fds ;c:jfot2 $ \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 measureqscq2yw4 /fj*d m g9-ed 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 going from kcal per mole to eV permec2j4s yw/fqqg- d* 9 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 thaw kg96r -1qysit in the text for the states in the formation ofw1ry69ki -s gq 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 quantir w5jjiv4d:,lty $ \frac{\hbar^2}{2I} $ has units of energy.

  The so-called “characteristic rg +0c, .p b*zbfzhtb d)x,q qr.j),aiqotational 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 0 1he8quftn( crotational 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 atg/-;3 0;dx-iswp fru b-ybajx5 crs7 voms 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 molv*7e hk+hzua *ecule given that three successive wavelengths for rotational transitions are 23.1 mm, 11.6 hah +u*v7e* zkmm, and 7.71 mm. $r = $    $\times 10^{-10}\ \text{m}$

  (a) Use the curve of (Fig. -eor g//8 dje(9uisyh Below) to 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 im iwzfr h78wu-jedx 6g. eqw kqt*.)y3 u00sg*n a NaCl crystal is 0.24 nmwry q 3 iug.h-0*jwsdkm7.) 8 uwt0e6f*xzeqg. What is the spacing between two nearest neighbor Na ions? D =    nm

  Common salt, NaCl, hadyuxe*6f21bjy3+5b st7ld ua s a 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 whose density is:ef 8st8jyt406 jrurg-zn9 xl ,q3 -ba sui8kp $ 1.99\ \text{g/cm}^3 $. $s$ =    nm

Explain on the basis of energy bawn;r.j5y zxb (6efng2 nds why the sodium chloride crystal is a good insulator. [Hint: C bfgw6(r nzyjxne2.5 ;onsider the shells of $ \text{Na}^+ $ and $ \text{Cl}^- $ ions.]

  A semiconductor, bombardeb0nb nh)q9.ax84 xynz9o lp.ad with light of slowly increased frequency, begins to conduct when the wavelen n0za.xpy4.bn9xbonha9)8l q gth 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 electronh5pq rci52s 3p 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 conductpk;j8 , rytb-hion bands in germanium is 0.72 eV. What rank8 ry p-,th;jbge 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 jb7z a ob1enti(ffa( v y -q6mzn3(+*q$ 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 th3 ck*,3zg; brr 6bczgh+)yps iat one silicon atom*c+rg ki3,3pbc h6zzgry)b;s 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 radif gc :c*3n9o :2hr oc+nka2adcate if made from a material with an energy gadaagc+3hcn c9 o*22fo:kr: ncp $ E_g = 1.4\ \text{eV} $? $\lambda $ =    $\mu m$

  If an LED emits lightgrtne0hg s) n nz57/p+ 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 curren.vs):g 4hv6sly e98gj2pwvgj t-voltage characteristics are given in (Fig. Below), is connected in series with a baslvg.9js6w 82vvy)h4j g p:gettery and a $ 960-\Omega $ resistor. What battery voltage is needed to produce a 12-mA current? $V_{\text{battery}}$=    V

  Suppose that the diode ofs vzmc-+ 59 bgtgphbvzxw;6 y.d(r (7l (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 functio nlnf(, (ava/(uado6 oifas/3n of 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 the averagewhq+id0 tt6h,1guif k57o9 7rthad:q current inoa5i,i rdh6+h90g:qqw udhft t1tk 77 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 +cens2b8t)hssignificant current only if the forward-bias voltage exceehncs bt)2s+ e8ds 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 (( 2voxig 4rh 4nim*0f- scgjgfull-wave rectifier (Fig. Begc gv0ix-jhr4*gis2( f ( 4mnolow), 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 t fdcc5n7 -f5vv ztv2pq v6ow4egt-0(fhe 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 xo,2 mhbo ks2;(qo5cmd (q -gb49 suio$ \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 iari. 4t q2cvt3 .ttd3is 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 y9-hk gx;4 6agsq( dgenm.
(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 lattice, with ea*h 2+ hjmlrf+ 0p,ocuuch atom connected to six neighbors, ej+mf r+,* uhuc02pho lach 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 rml3 *jx+o7 5/jj kzon1.4 eV. When the moleculeojr75*/j+x zljk3n o m is disassociated, 1.6 eV of energy is released. Draw a potential energy curve for this molecule.

  When EM radiation is incident on diamond, it is fou*ij2n; )biok h xbp6/fnd that light with 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 diamo*i )p2;bokbhxn 6jf i/nd? $E_g$ =    eV

  A TV remote control emits IR light. If the detector on the TV set is nou;za0 s jiydb030wy 8wt to react to visible light, could it make use of silicon as a "wi3su ybid00w 08 ywza;jndow" 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, a qgzteyc+4h,c-b 9n-cssume that the "extra" electron moves in a Bohr orbit about the arsenic ion. For this electron in the ground state, take into accoun --qccct zhn ,g4+eby9t 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 wavelength5/) exgcmbn m11q4nxl s shorter than 1000 nm. For a solar cell ecg5m1xm1n4/)qx ln bto absorb all this, what energy gap ought the material have? $E_g$ =    eV

  For a certain semiconductor, the longest wavelength radiation that cjt6- 6yhjq)zji.q7yzw 1hr3lo py3 3qan be absorbed is 1.92 mm. What is the energy gap inq p73ryothyq.3 z zl6 )yh6ijqj3w1 -j this semiconductor? $E_g$ =    $ \times 10^{-4}\ \text{eV}$

  Green and blue LEDs bec5; ;/ogjq1u2o(ot 9 6nja-c8f sivq 4rvcuqk same available many years after red LEDs were first developed. Approximately what energy gaps would you expect to find in gree r(;g jquvo;jn8 5coo6q2f utk1cq4s-v a/9sin (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. Below). Suppose/w q9sytu+j, v 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?    $\ \text{k}\Omega \leq R_{\text{load}} < \infty$