What type of bond would you expect( l1n4hqm3a :wi-r zxl for
(a) the $N_2$ molecule,
(b) the HCl molecule,
(c) Fe atoms in a solid?

Describe how the moleculehdel-/2o4 u( gp:lnx bz tj:(x $ \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 4:qvi uum5.ks $ \text{H}_3 $ is not stable, the ion $ \text{H}_3^+ $ is. Explain, using the Pauli exclusion principle.

The energy of a molecusli(7g2qzv 7qq 2h /b.uo3kgf le can be divided into four categories. What are they?

  Would you expect the molecu6ph51 ft/ rxrhi,e:rxq 1u8lqle $ \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)sti4l ci ,, c.e5tcum ($ Z=6 $) usually forms four bonds with hydrogen-like atoms.

If conduction electrons are free to roam about in a metal, why tim.y/kabm3ja 33 ik 6don't they leave ybkmi3 a3/imt6jk.3 athe metal entirely?

Explain why the resistivity of metals increases with temperaturej h,eo.xr7mm 1 whereas the resistivity of semiconductors may decrease with increasi7 oe.hj 1mxmr,ng temperature.

(Fig. Below) shows a "bridge-type" ful7)o 1k(6yii;7 rrjfqmg-ozs5r .bry ll-wave rectifier. Explain how the current is rectified and how c1r.rz(gr;o-b7l)k5f j qisi6 rym oy7 urrent flows during each half cycle.

Compare the resistance of a pn junction diode connected in forward b9ydh261k b9n;/ avltcg5dlq1(r ov csias to its resistanh;lqd51glt 1cak99 vs/ (dbyncvr62 oce when connected in reverse bias.

Explain how a transistor coulttc2h uytl fe): 0i6)xd be used as a switch.

What is the main difference between n-type and pjh jswx0zlrs;m a+;4mzf8l/5-type semiconductors?

Describe how a pnp transistor can operate as an amplifiezijgt(j/ 85m ,9jrgtd -qj 5 4,t4 dfdp-msevar.

In a transistor, the base-emitter juncvk 1;cn 9v,jlction and the base-collector junction are essentially diodes. kj;1cl v9,cnvAre these junctions reverse-biased or forward-biased in the application shown in (Fig. Below)?

A transistor can amplify an elhkbdi /0a0t6a ectronic signal, meaning it can increase the power of an input signal. Where doe da0k 6a0bi/ths it get the energy to increase the power?

A silicon semiconductor is doped with phosphorus. Will these atoms be donorq e.h85ffhsozfqxx 9j1*0wm 98rgo :qs or acceptors? What type of se *fs 0fj.zq fx5 hg:1qhw8o 9qrmx8o9emiconductor will this be?

  Do diodes and transistors obey Ohm’s law?zcnmj pdd8u 02p9wa24bn.c xy/lk39b Explain. {yes|no}

  Can a diode be used to amplify a signal? Explain. {yes|q wn-m x(k lpocp01s(c(1ly (cno}

  Estimate the binding energy of a KCl molecule by calculating the electrostaxtn/;(kbqg .q8y hd;xo:n lz+tic potentiak: 8.n/ ;q og( dxhztnxybl+;ql 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 rkeep,oq ljz*8:/a /95h1q6diltd po a esult of Problem 1, estimate the contribution to the binding energy of the repelling electron clouds at the equilibrium distance ai5t1p/oje*lq hd6p: /oz 9,ke8qdla $ r_0 = 0.28\ \text{nm} $. $PE_{\text{clouds}} =$    $\ \text{eV}$

  Estimate the binding energdx *+mwg6l) m76se)y:fxvyl z y 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 measure ,xzsp;jw/9m te-r;o nd experimentally in kcal per mole, and then the binding energy in eV peozx n;pwrje;-,/9mt sr 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 tf rvp3s:;soj mcw6+ 1no that in the text for the states in the formation of sc3:r+wsfjpo v;1nm 6 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 quanti5fz2f0g8gen la i v,(dty $ \frac{\hbar^2}{2I} $ has units of energy.

  The so-called “characteristic rox* p qro0f1*gxy4d j4xtational 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 energy, ) oc7g) xoanf8$ \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* 6msa)i)kch-x fl1 dt 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 that three successive wav/4j iu gw+f/ncelengths for rotational transitions are 23.1 mm, 11uc+/ijn/g w4f .6 mm, and 7.71 mm. $r = $    $\times 10^{-10}\ \text{m}$

  (a) Use the curve of (Fig. Below) to estimate the st /64g9poysk/j hdd. zkmd/n)ciffness 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 neigj-b9 .03l)pi- ohuyflzr;q o phbor” Na and Cl ions in a NaCl crystal is 0.24 nm. What is the spacing between two nearest ne -iol3f 0 jo)z9r. l-u;ppbqhyighbor Na ions? D =    nm

  Common salt, NaCl, has a density*ou w ocs7n;z: 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 7gx/p p2dy3cj KCl whose density is $ 1.99\ \text{g/cm}^3 $. $s$ =    nm

Explain on the basis of energy bands why th3kptadkp;h( :nl2t *i e sodium chloride crystal is a good insulator. [Hint: Consider the :kk h t*pp(itd;3a 2lnshells of $ \text{Na}^+ $ and $ \text{Cl}^- $ ions.]

  A semiconductor, bombarded with light .,mu9dc8*8, pqotqpp3 e reibof slowly increased frequency, begins to conduct when the wavelength of light is 640 nm. Estimate the size of the en8edi c*u rqpp9,pq8et3b m., oergy gap $ E_g $. $ E_g $ =    eV

  Calculate the longest-wavelength photon that can cause an electrgt0 z6/w i6hw-q- yunqy h(s2egr g+0mon 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 conduxg(plt3hre+ k bg3,lebv2 +be t 882ufction bands in germanium is 0.72 eV. What range of wavelengths can +8glu txvpb2e+ e3b2(83 ,eht bfgrlka 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:d e8:qqbsi lh jc-+-6ak4jpr $ 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 sembiz3n c9247kii j y(sa-cg zg2iconductor is doped with phosphorus so that one silicon atois kciz27jn39c z2ayggi-b4 (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_{doping}}{N_{Si}} = $    $ \times 10^6$

  At what wavelength will an LED radiate if bt36 k q)cdkj7made from a material with an energy gap kdt37 6kq)bj c$ E_g = 1.4\ \text{eV} $? $\lambda $ =    $\mu m$

  If an LED emits light of wavelengtqd -u5 l/xt-uwb0mmna)io3hs ** )qhfh $ \lambda = 650\ \text{nm} $, what is the energy gap (in eV) between valence and conduction bands? $e_g$ =    eV

  A silicon diode, whose curren4 7-s6)l0 mcinmg euent-voltage characteristics are given in (Fig. Below), is connected s7)lun gn0mm i-6e4ec 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 p aya aex25:jzg dbi/9*2*ev pa $ 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(0 fqfrqyh9s+)h6.q v6k qbf d function 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 fj,l5 b5a+ni groughly the average current in the +jinlf,55g baoutput 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 only1gme 3wx7wm4a if the forward-bias voltage exceeds about 0.6 V. Make a rough estimate of the average current in thg34ew 71mamxwe 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 rectifiet8 r p sd3u(z)yp4wjkhfe2,6i r (Fig. Below), whezpph,w2rfie) 64jd s3u (kyt8re $ 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 currentx9.l*vg ;agf is+bfu ,:w+n ko $ I_B $, the collector current $ I_C $, and the emitter current $ I_E $ (not labeled in the figure).

  Estimate the binding e71kawa;z0 u5-jb5po;p hw xmtq -mxk1 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 h5; hc ;8+gmms55oz:ms uqbqakinetic 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 ionspc24ug/0 ir ng 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 w.6 i;hw1 ,hppao*ard/a; dfufith a weakly bound cubic lattice, with each atom connected to six neighbors, each bond havi*ou;h p/.fi1a;pr,aa w6 ddfhng 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 6 ,9r3gkhxyr;9 z ddfythe molecule is disassociated, 1.69,yry 6hxrkz d9f;g3d 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 with gf,*ftvk3d rwf-2h h 1wavelengths shorter than 226 nm will cause the diamond to conduct. What is the energy gap between the valence band and tf*vw h3dfg-2h,1kt rfhe conduction band for diamond? $E_g$ =    eV

  A TV remote control emits IR light. If the detect3e79 vck1p)iecqfd*+upk ;r ior on the TV set is not to react to visible light, could it make use of silicon as a pvqr*)+c;ii1fep kekdu7 c93 "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 semicon9pl 1z sryl)6a uo3okn12 jhoq4w.w l+ductor, assume that the "extra" electron moves in a Bohr orbit about the arsenic ion. For this electron in the ground state, take into account the dielectr9u yjo6+k. z1ls a r142o hopwwlqn3l)ic 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 tha)xl - evtwu3mnnfio;c*; 1 my+n 1000 nm. For a solar cell to absorb all this, what energy gap ought tlxm)fn v-u;tym3*woi ;1nc + ehe material have? $E_g$ =    eV

  For a certain semiconductor, the longest wavelength rad9 zc6+dg,mk w+vfxem- iation that can be absorbed is 1.92 mm. What is the enerv edckxmm6-gz+w, 9f+ gy gap in this semiconductor? $E_g$ =    $ \times 10^{-4}\ \text{eV}$

  Green and blue LEDs became available ma z(elm 5zwt4w2ny years after red LEDs were first developed. Approximately what energy gaps would you expect to find in grwl 4zwmzet52( een (525 nm) and in blue (465 nm) LEDs?
the green $E_g$ =    eV
the blue $E_g$ =    eV

  A zener diode voltage regulator iszkj:n z0s cj;:3 i-onf 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?    $\ \text{k}\Omega \leq R_{\text{load}} < \infty$