What type of bond would you expvb)zfyo0)5*6/h m jhxq 5td orect for
(a) the $N_2$ molecule,
(b) the HCl molecule,
(c) Fe atoms in a solid?

Describe how the molecule .nkfk+i8o2cuoe8 u6 hb :muu*$ \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 moleculeqc8w, wde 0 z*zm.m0ku $ \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 dievk3w yhi5 txi/t220*da uji6 vided into four categories. What are they?

  Would you expect the mo8a a-5yv*8e9n5-m kz o1pc helm2rjiolecule $ \text{H}_2^+ $ to be stable? If so, where would the single electron spend most of its time?{yes|no}

Explain why the carbo xmz mq4qtu2 ek(kwmv9l; /8q*n atom ($ Z=6 $) usually forms four bonds with hydrogen-like atoms.

If conduction electrons are free to roam about in a metahyflc, o1 ;*igl, why don't they leave the metal en *y,o1hc fgli;tirely?

Explain why the resistivity of mex8 k,xd2jxi ixm,0mt60 ir fh0*uxk2l skap4)tals increases with temperature whereas the resistivity of semiconductors may decrease withx4m ,r)liafi 2s08x u60txkxk, x p*k02jhdim increasing temperature.

(Fig. Below) shows a "bri3ugc+ xv7kl 73 abw,rddge-type" full-wave rectifier. Explain how the current is rectified and how current flows during each half cyclv 77rg3cd+k3lbx uw,a e.

Compare the resistance of a pn ju)*t*r/gxa 6u4hyyljn nction diode connected in forward bias to its resistance when connected in reversegya*y/u )j4*r 6xht ln bias.

Explain how a transistor could be used as amq0)y)fpz2( x+ xwlo+ ih(cfufm6od gbk;u.3 switch.

What is the main difference between n-type and p-type semicox -yob;6jnslxw8 nv)7s m1 h1cnductors?

Describe how a pnp transistor ckjdqag :s/.s (d 9bev0an operate as an amplifier.

In a transistor, the base-emitter junction and the base-collector junction arew,r+z,3t *p/z sa0e kp+xsayu essentially diodes. Are these junctions reverse-biased or,tpks*+wz z 0xaus,p3 e ray/+ forward-biased in the application shown in (Fig. Below)?

A transistor can amplify an electronic signal, meaning it c.r7b r:rq;p4+k*xts4l yxhksan increase the power of an input signal. Where does it get the energy x*+hxkrqypt.4b :slrrs47 ;k to increase the power?

A silicon semiconductor is doped with phosphorus. Will i m9bc:c2q4rr these atoms be donors or acceptors? 9 icqr:b42crm What type of semiconductor will this be?

  Do diodes and transisli1b ki*8tm* qtors obey Ohm’s law? Explain. {yes|no}

  Can a diode be used to amplifnx*)7q*do*ike7g;v btbj;fxx q 5cd1 y a signal? Explain. {yes|no}

  Estimate the binding energy of a KC xtpv/)5;wxq9glc fc2 l molecule by calculating the electrostatic potential f5xgvw9pt/cclxq2 ); 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 jt7 z2r7djwm/ 4.43 eV. From the result of Problem 1, estwjz7/72dmr jtimate the contribution to the binding energy of the repelling electron clouds at the equilibrium distance $ r_0 = 0.28\ \text{nm} $. $PE_{\text{clouds}} =$    $\ \text{eV}$

  Estimate the binding17+f aw*qtr sq energy 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 experimeau:x7n+wmp7z;m 3v fkntally 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;u zpka nm:7x mvw73+f 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 u 9c(kf,h0k ovstates in the formation of09(kuh ,kc fov 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 quantit4lf1h9vfl0 b.fq wf;v y $ \frac{\hbar^2}{2I} $ has units of energy.

  The so-called “characteristiw 9vpoias3 ( 9a*6wmonc 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 characterie1hzcvt 7/)4r srvlifvs7e+ 1 stic 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 atoyr .ooo t6t2*cms 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 gi :2 r el*fny-tg1 -oyls:esg,xven that three successive wavelengths for rotational transitions are 23.1 mm, 11.6 mm, and 7.ge1: lytox esgl:-2*yrns-,f71 mm. $r = $    $\times 10^{-10}\ \text{m}$

  (a) Use the curve of (Fig. Below) to estimate t37 cxpg4kr*:tjz sbk6 he 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 N)h mom)cw9q 8faCl crystal is 0.24 nm. What is the spacim))owf 8c qh9mng between two nearest neighbor Na ions? D =    nm

  Common salt, NaCl, has a density ou+0 6 -wwy- od14crzdq elbuupf5f- ;xf $ 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 )cvlf6xa5je) density is $ 1.99\ \text{g/cm}^3 $. $s$ =    nm

Explain on the basis of energy bands why the sk)wrx/ g le jnemnz)ysz .38yl09w u9.hb,sx8odium chloride crystal is a good insulator. [Hint: Consis 8 x h . yzys zlnnr9,)gx/lwju)0wb.8k9mee3der the shells of $ \text{Na}^+ $ and $ \text{Cl}^- $ ions.]

  A semiconductor, bombarded with light of slowly dmkp8kp exf,i 39vp79increased frequency, begins to conduct when the wavelength of light is 640 nm. Estimate the size of the energy gafpkx7k8 3 pi9edv, pm9p $ E_g $. $ E_g $ =    eV

  Calculate the longest-tm yg97k au1 sh88h;aukt*x u7wavelength 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 valence and conduction ban o3v 9ts6r9y-ai r v+kck6qdt0ds in germanium is 0.72 eV. What range of wavelengths can a photon haveaik t +3kv6ovys d 96r9rcq-0t 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 are7:cmkvxq0nk ixwk 2 .l3u 0 +mid4hdf+ $ 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 that ojl ,hi vw;jtr()me.7nne silicon r;7 vn)ih tw,(ej.mlj 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 will an LED rad( /b -qzq 4cqg3104gznjmuk e/vs(dqbiate if made from a material with an energy gancqzuqs /d/mv(gq1b0 gbk443 qz-j e(p $ E_g = 1.4\ \text{eV} $? $\lambda $ =    $\mu m$

  If an LED emits light of wavelength 7hevw1 t 3u oozgij10/-:umqn $ \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 characteristics are given in (F-) 9zjbr (to- yne(ckeig. Below), is conneeyeo b(tn(-j-r )z9ckcted 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 +ri: n1m8i tl1g7okcc (d xy4xui4 cn4series 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 function of currx ,x zt /u.s/(rsl k)-tdhf3hwent, for $ V > 0 $, for the diode shown in(Fig. Below).

  An ac voltage of 120 V rms is to be rectified. Estimate veyd -s6 cn-ef0ary roughly the average current in the ous-f -da0ne6c ytput 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 only if the forwajyw+b 9m/1ppp rd-bias voltage exceeds about 0.6 V. Make a rough estim9 bp+wy/p1mjp ate 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 c8fn0- vnlk+hc y2e.nto be rectified with a full-wave rectifier (Fig. Below), where l-h.c eyvfn2nn+8 ck0$ 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 e yjn:,3g+ adnpl 8sv:gquation 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 energy of. l ms-kkk .y(ql:awa- :f/lrtk+jr;v 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 /6txgg9 ro e84w0yo(qmqcqv3u-z gd6kinetic 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 abouta9/-k d yqzlvg34k0y 5hyhb /s 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 lattice, with each atomerqp k:k5 me41 connected to six neighbors, each bond having a bin4pmqk e:5re1 kding 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. Whif j7 akz18 l::iri2ipen the molecule is disassociated, 1.6 eV of energy is released. Draw a potential energy curve fra18i 2f :zljiiki:7por this molecule.

  When EM radiation is incident on diamond, it is found y1ewgz 96oazm/v q+*jthat light with wavelengths short zv+ wa jyzgme6*o91/qer than 226 nm will cause 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/kguc tz bs1wn+xo 9xi5t1:k7 light. 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 e9skk5n1g w7 :+o1uztbtx ic/xnergy 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 4lea 84kyf, bj6c;listhat the "extra" electron moves in a Bohr orbit about the arsenic ion. For this electr e;6j 8al,4bilcky f4son 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 e2e c62nwqln1 wavelengths shorter than 1000 nm. For a solar cell to absorb a2cnl6 en 1q2ewll this, what energy gap ought the material have? $E_g$ =    eV

  For a certain semiconductodf3p ju0l 2o8b7nbv6t r, the longest wavelength radiation that can be absorbed is 1.92 mm. What is the energy gap in this semicond7 lbd 6fv n08uj32obtpuctor? $E_g$ =    $ \times 10^{-4}\ \text{eV}$

  Green and blue LEDs became available many years after red LEDs c 4d(wg-kwp0 xwere first developed. Approximately what energy gaps would you expect to find in green (525 nm) and in blue (465 nm) LEDs? wd-kwx0(p4cg
the green $E_g$ =    eV
the blue $E_g$ =    eV

  A zener diode voltage regulator is shown in (Fveyj9 n;e3e z:o4lgj. ig. 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?    $\ \text{k}\Omega \leq R_{\text{load}} < \infty$