What type of bond would you expect for jtu)st5kko9 i91 dypj. *ig7s
(a) the $N_2$ molecule,
(b) the HCl molecule,
(c) Fe atoms in a solid?

Describe how the molel 1bu1 04jx;tkobah,ccule $ \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 moleculoav6pa9qow2s5y, ; qie $ \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 divided6ybl l/wv m;3w into four categories. What are they?

  Would you expect the fw;(jo g5drt(k8 c 1lumolecule $ \text{H}_2^+ $ to be stable? If so, where would the single electron spend most of its time?{yes|no}

Explain why the carbon ao( hzw2: 8dt umpg1(hxm ffu4qvk)gv;+ wy4,htom ($ Z=6 $) usually forms four bonds with hydrogen-like atoms.

If conduction electrons are free to roam about in a metal,sfrwo n9 -1fk6 why don't they leave thefsw6o f -n9r1k metal entirely?

Explain why the resistivity ofr8 h j(k.t3a uf9 8i4mnosm;ko metals increases with temperature whereas the resistivity of sekm t8si4 ;orhjn8mf.(u 9 3aokmiconductors may decrease with increasing temperature.

(Fig. Below) shows a "bridge-type" full-wave recoi;5a 3rrp;rvtifier. Explain how the current is rectified and how current flows durr;oap5 3;irv ring each half cycle.

Compare the resistance of a pn junction dioc6 x: )1jt* kyo5cloorh;d fq+de connected in forward bias to its resistance when connected in reversecr1: o6;djo th5 kq*lfyocx+) bias.

Explain how a transistor could be used as a swijwder;h9b 8sibl e/c;h *g +2rtch.

What is the main difference between3dz )jip;pgxlfs ++1 e n-type and p-type semiconductors?

Describe how a pnp transistor can operate as an4zv-5od0(s bhuj,f /)q3 k p)iy6c pf1bwnf en amplifier.

In a transistor, the base-emitter junction and the base-collew0fuz0nuqbio qy 6i hmn:73,+jfjd,/ctor junction are essentially diodes. Are these junctions reverse-biased or forward-biased in the apbfi yfq/6nzj h3:n, 7jw,m+iq0u d0 ouplication shown in (Fig. Below)?

A transistor can amplify an elecwyv n b6((fdm,e z8dh.85tm6hqzjno- tronic signal, meaning it can increase the power of a8wjny d nzbz-ve,((q .hf oht 5d8mm66n input signal. Where does it get the energy to increase the power?

A silicon semiconductor is doped with phxo m 10,dk1iokv(:3cia bvv.o osphorus. Will these atoms be donors or acceptors? What type of semiconductor will thm1iovo aki(o,:vb ckdxv10.3 is be?

  Do diodes and transistors obey Ohm’s law? Explai+ qbu2ne;l 4.pphe1kin. {yes|no}

  Can a diode be used to amplify a sivnojv)y*zw7 ;: a 8r.oqw uu:vgnal? Explain. {yes|no}

  Estimate the binding energy of a KCl molecule by calculating the electrostatz2/og3y91 sh rkou+k37rb fqpic potential energy when 3o/fgqz bh 7skpr39 1kr+y2uo 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 Kmhri b3pp93 q(Cl is 4.43 eV. From the result of Problem 1, estimate the contribution to the binding energy of the repelling electron clouds at the equilibrium 3(b3 p i9mqrphdistance $ r_0 = 0.28\ \text{nm} $. $PE_{\text{clouds}} =$    $\ \text{eV}$

  Estimate the binding 6qyqz4xz7cppn,75f kenergy 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 experimentally in kcal pb r9f:c(xu. c/3oyibo er mole, and then the binding energy in eV per molecule is calculated from that result. What is the convy9buc. bo3fo/r(x: i cersion 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 to that in the text; wrmnam/q2+i for the states in the formation 2ni r;a/qmm+ wof 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 quantitxdy)/ n p0n kwp5)ohc9y $ \frac{\hbar^2}{2I} $ has units of energy.

  The so-called “characteristic rotational enero/ gtilg25 jt,my/.mm gy,” $ \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 en5s sz+.b,+ vf nhrrd(zergy, $ \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 atomsm,u d gkh:3g)rsy*2 mo 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 lengibz1 2:dl5 *ldx4idk vc a7j5zth for the NaCl molecule given that three successive wavelengths for rotational2 4x5jcdz7 k:zlv al5*ibid1d transitions are 23.1 mm, 11.6 mm, and 7.71 mm. $r = $    $\times 10^{-10}\ \text{m}$

  (a) Use the curve of (Fig. Below) to estimate thenczdk5x.fz y41. 7bmy 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 “ndmz ttfq/+3jyi r*h81earest neighbor” Na and Cl ions in a NaCl crystal is 0.24 nm. What is+my 1t/rhjtidf* 3 8zq the spacing between two nearest neighbor Na ions? D =    nm

  Common salt, NaCl, has a den(m yc fkq6jvn109f pj(sity 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 nqq87ewhdz9t-z *zw, $ 1.99\ \text{g/cm}^3 $. $s$ =    nm

Explain on the basis of energy bands why the sodium chloride crystg(di8 i:*g4 7ev( ebp8veke hkal is a good insul ib vk*7 kg(ievphe8e:4ed8g(ator. [Hint: Consider the shells of $ \text{Na}^+ $ and $ \text{Cl}^- $ ions.]

  A semiconductor, bombardu9ixguq2-cf v 3 fpkw9,g5hp3 ed with light of slowly increased frequency, begins to conduct when qvuf, 9fcu 3hi2p5 xw-3gp9 kgthe wavelength 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 electron in silicon onbqw) kj6 zq0qp4, z)augg -i507xdg ($ 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 bands in ge,yl g06thxq *t: ,fxjnrmanium is 0.72 eV. What range of wavelengths can a photon have to excite an electron from the top of the valence band i f6h,0qtn x*j:,xygtlnto 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 arebclpms 4;c;ap*(7f qh $ 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 phosphoru5 a)srzh abi-1s so that one silicon at )ahrza-5sib1 om 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 m nn5dlbc8r3xu il( ;5yade from a material with an energy gap cd(55rn;ilbx ly8n3u $ E_g = 1.4\ \text{eV} $? $\lambda $ =    $\mu m$

  If an LED emits light o(ivuizfbwnf ;l9mz*a( ) - y(if 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 characteristics areneago t8+i5/m+8 hqsl given in (Fig. Below), 8n8e+og+ /lhsam5tiq is connected 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 connectedc nsmalrsa8*4 z+u ;v, 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 function of curri-dmm78xfemg w- zfo1kzv)6 byk4 1l8ent, for $ V > 0 $, for the diode shown in(Fig. Below).

  An ac voltage of 120 4xpy*ojh-1 iy V rms is to be rectified. Estimate very roughly the average current in the 1* ojyi-hy4px 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 significant current only if the forward-biask j ,s3ie/3 (pktlsa+d voltage exceeds about 0.6 V. Make a rough estimate of the average current in the ouekjsatl(+ 3 , s/pd3iktput 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 iq;/mz;(pk y6ygxf g;be rectified with a full-wave rectifier (Fig. Below)z/;ypqgi f mygk;;6(x , 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 b f;5r-dr 1he+luvamj7 etween the base current $ I_B $, the collector current $ I_C $, and the emitter current $ I_E $ (not labeled in the figure).

  Estimate the binding eneso;.zu)t :*s7pb /dejum2v uvrgy 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 energy of an atom or molecule isonu50+xr* v lutslk6rt, 6;cq 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 b:im;ku 962ewig. aw y.i+pgeuetween ions 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 monoatomih;uih1/ka d; uc solid with a weakly bound cubic lattice, with each atom connected to six neighbors, each bond having a binding energy of h1;uiaku /hd ;$ 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 hav( h1 4bh4rfi5l2 nvweae an activation energy of 1.4 eV. When the molecule is disassociated, 1.6 eV of energy is released. Draw a potential energy curve for this mvl45h ih b(4fa2we1 rnolecule.

  When EM radiation is in* wzkvapw0tu29ig;v1 cident on diamond, it is found that light with wavelengths shorter than 226 nm will cause the diamond to conduct. What is the enkitza vw2;w1*0 u9vpg ergy gap between the valence band and the conduction band for diamond? $E_g$ =    eV

  A TV remote control emits IR light. If the detector on t/w.e83bij. +8sdlo 6t:n1 jxytrrja ehe TV set is not to react to visible light, could it make use of silicon as a "window"nr./jae3j+w 1 r:b 6idyxt otj.e8s8l 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, assume - pfgkn*o;0kf2v a4uxthat the "extra" electron moves in a Bohr o pog0;a*xfk 2fu4 nk-vrbit 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 radiation has wavelengtmhof: u e/s)liq:.x, rhs shorter than 1000 nm. For a solar cell to absorb all this, what e: /r:quls.i xhmf, o)energy gap ought the material have? $E_g$ =    eV

  For a certain semiconductor, the longeu4nxvek:e-by66 fn -ftoefc53k07y w/ fr ye.st wavelength radiation that can be absorbed is 1.92 mm. What is the energy gap in this semiconducto3ry- 054u t/y- o7fnxwcy.k :be66 feffnev ker? $E_g$ =    $ \times 10^{-4}\ \text{eV}$

  Green and blue LEDs became availr5edwih v4u) )able many years after red LEDs were first developed. Approximately what energy gaps would you expect to find in green (525 nm) and in blue (465 nm) LED5wud)ih e)r 4vs?
the green $E_g$ =    eV
the blue $E_g$ =    eV

  A zener diode voltage regulator is shown )/8c5oj q ebonin (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?    $\ \text{k}\Omega \leq R_{\text{load}} < \infty$