What type of bond would you exp8*juzl86 xpw .jcv hm)ect for
(a) the $N_2$ molecule,
(b) the HCl molecule,
(c) Fe atoms in a solid?

Describe how the molecule wtprz;6r s(,p9p1l7 z2oitzg $ \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 a 57(as tay ijk+otw94xmmqjps:q+3 6+myp6 g$ \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 /fed qf)3dy;fr re7*h;jcmd: four categories. What are they?

  Would you expect thequh8lgkh7 6 (f molecule $ \text{H}_2^+ $ to be stable? If so, where would the single electron spend most of its time?{yes|no}

Explain why the carbon atkd 33qew4funyx 3 vx92om ($ Z=6 $) usually forms four bonds with hydrogen-like atoms.

If conduction electrons are free to roam about int,. z4t*a .zi,swc htri *8pbv a metal, why don't they leave the metal entirely?t,zc ibr.s *8v4aht ,wi .pzt*

Explain why the resistivity of metals increases with temperature wher/vj 5j3d4shv)m f tw;oeas the resistivity of semiconductors mayw;/sv4h tf j5vmd3oj ) decrease with increasing temperature.

(Fig. Below) shows a "bridge-type" full-wave rectifier. Expa3syvd06o mi(lain how the current is rectified and how currents0 (y 6iao3mvd flows during each half cycle.

Compare the resistance of a pn junction diode connected in forward biaaofdbm0l 4bl/0:a :e gs to its resistance when connected in revers0gllo :4 da:a 0mefb/be bias.

Explain how a transistor could be oeq05 z(w0m. 9cs ;hwgwpjxv-used as a switch.

What is the main differej;sftl(fw c r*l8xj-- nce between n-type and p-type semiconductors?

Describe how a pnp transistor can op3chmxq 6l rty-z44 b*jerate as an amplifier.

In a transistor, the base-emitter junction and the base-collector juiiorgt-i8q/-p * ho 7inction are essentially diodes. Are these juii-q/r o7-8* toi gpihnctions reverse-biased or forward-biased in the application shown in (Fig. Below)?

A transistor can amplify an electroueyj fi c 2,uh8qf;p1/ lolg//nic signal, meaning it can increase the power of g /l//c2pui1ufeq; o 8jf ,lyhan input signal. Where does it get the energy to increase the power?

A silicon semiconductor is doped with phosphoru5k m8y cx2vtz8s. Will these atoms be donors or acceptors? What t88 5yczv2kmx type of semiconductor will this be?

  Do diodes and transistors obey Ohm’s law? Explain. w6nmqlpz:m n5 pna i0:)3oin ){yes|no}

  Can a diode be used to ammr,y hgk6fo jbauu;5qc )o*3/plify a signal? Explain. {yes|no}

  Estimate the binding energy of a KCl molecule by calculatu bz bpumm-d nwr5(jo)go5./sf75h(fing the electrostatic p7jdow)f5f5mmu5 z((obr/hg u.n sp b-otential 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 x,yqhw* 0k.j:thlti 2l;zro7i0mcu( energy of KCl is 4.43 eV. From the result of Problem 1, estimate the contribution to the binding energy of the repelling electron clouds at th07h*0,k hqomx;lw :l(iit 2.jcyut zre equilibrium distance $ r_0 = 0.28\ \text{nm} $. $PE_{\text{clouds}} =$    $\ \text{eV}$

  Estimate the binding energdk,t cp j.e(*u os 7jm63cxc/qy 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 4j9q wlotlb uv-x:p,2per mole, and then the binding energy in eV per molecule is calculated fr92ll-ptjwvx b, q:o 4uom 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 to that in the text for the states in the forma (uva wle2qrbj x6t/j6t)ui-2tion of tqj )r6-xj et 2uult26wabi(v /he $ \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 quantitc h 2wgj:yu( egw2*p/fy $ \frac{\hbar^2}{2I} $ has units of energy.

  The so-called “characteristic rotational energdc)r.p.ja zr4 y,” $ \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 rotatiouauo:eo s5rzgw/uf4 -rmj* 4 :nal 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 separatihz,i1b*gh 4,yxa qdwglb/d ( ,on of 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 moleculeietm ggit 3s qvb2 9d ,+:k(xu+)(hsws given that three successive wavelengths for rotational transitions are 23.1 mm, 11.6 mm,h:xtmi9s2t sied)gqwub( +v+(k,g3 s and 7.71 mm. $r = $    $\times 10^{-10}\ \text{m}$

  (a) Use the curve of (Fig. Below) to estimate thl ip 0k92ye*nuczc926 qlay t2i+ u4mne 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 anvg l5iu9r(8zoo5z) ka jg,/3 u,iwcspd Cl ions in a NaCl crystal is 0.24 nm. What is the spacing between two nearest 5z(lugk 83aji/soc5)w z9i ,uv, rpogneighbor Na ions? D =    nm

  Common salt, NaCl, has x07tenh 3/ glja 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 i:)8vd7 3g//i .9le,qfoiqycuuogkf qs $ 1.99\ \text{g/cm}^3 $. $s$ =    nm

Explain on the basis of enwp )0mwt :.jpu kpt 9;qcq2hm1ergy bands why the sodium chloride crystal is a good insulator. [Hint: Consider the shelmpu9; w) 0 t2k.q:p th1cpqwmjls of $ \text{Na}^+ $ and $ \text{Cl}^- $ ions.]

  A semiconductor, bombar16 k -mfdowdd hv8*.ihded with light of slowly increased frequency, begins to conduct when the wavelength of light is 640 nm. Estimate the sizh.8of ddhkd* i-6w v1me of the energy gap $ E_g $. $ E_g $ =    eV

  Calculate the longest-wavelength photon that can csr0oscty g:+f- 60 yskzwb(d9 ause 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 valenlb y,hk/q- g2b;5uqhq ce and conduction bands in germanium is 0.72 eV. What range of wavelengths can a photon have to excite an electron from th;k byqhhq/b5-2, qul ge 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 5; dq:opf re-t3 id)5n5z o;co bvt4oj$ 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 wi vs 2 xwy0+lkm:yz1(tuks3wi r85t8 zath phosphorus so that one silicon atozrktx(lku1 y83ys+ vz0atm5 w s:8w2im 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 with an energbor y ;gy 02c64ybue-xfc2c t5y gay b-g 4;0xo26ftrcc bey 2yc5up $ E_g = 1.4\ \text{eV} $? $\lambda $ =    $\mu m$

  If an LED emits ligh unfor1v6agi)ge n/1nrl1 f 5,t 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 current-voltage characteristics aohp:, xz)b nt 6j)w+uchs h46kre given in (Fig. Below), is conne4j:,nwpk6sbhxhh) zt u 6)+co cted 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 conv2r; c+bpte fup2i98qio+e v+nected 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 functionfa.9:r y+6 r9e +fj h xqrn+*fiownwt9 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 roughly2ibjk/.mz.e 8 ov/rmg w-u*wh the average /* o-zimew kvj.h r.wg8bu/ m2current in 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 significant current only ig cazx o4/j0o9f the forward-bias voltage exceeds about 0.6 V. Make j o/gxc4oa0z9 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 rs t; .wdd c(3.fkx(yp mvp.)axectified with a full-wave rectifier (Fig. Below), where .pmkdfv;x..d)w((xt3 y pa sc$ 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 oee34 p n;yr;rytv43v base current $ I_B $, the collector current $ I_C $, and the emitter current $ I_E $ (not labeled in the figure).

  Estimate the binding energahgio f8 -)rb2y 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 cu9fyd.b ,x/i 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 about 0.z7l(ntn,9cr)e dehl 927 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 solidg5umor;i )v x5 with a weakly bound cubic lattice, with each atom connected to six neighbors, each bond having a binding energy ;5u xro im5g)vof $ 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 acm( +ijx gr/6eltivation energy of 1.4 eV. When the molecule is disassociated, 1.6 eV of energy is released. Draw a potential energy curve for thi j+lx6r( im/egs molecule.

  When EM radiation is incident on diamond, it 2mesk(v1lrp 7is found that light with wavelengths shorml svke p71r2(ter 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 light. If the detector on the TV set is no v+7.hdk5sukrox: ;pqt to react to :h;dp.q 7u oxv+kks5r visible light, could it make use of silicon as a "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 semiconductord tfop(s9;5 g hp.8o.7fcksno, 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 diele .nk7ocf. ospdt8 (9f5g sh;poctric 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 than 1000 ner,dh u,5ui+xm. For a solar cell to absorb all this, what energy gap ought, eruh5+d,u xi the material have? $E_g$ =    eV

  For a certain semiconductor, the longest wavnw s6s 5fdjt42xz(z:ajq-t p )elength radiation that can be absorbed is 1.92 mm. What is the energ2at-snztzp (f d:6 4xqj5jsw )y gap in this semiconductor? $E_g$ =    $ \times 10^{-4}\ \text{eV}$

  Green and blue LEDs became availablef. t,cept+c0goz ec3 )0iw+bp many years after red LEDs were first developed. Approximately what energy gaps would you expect to find in green (525 n3 0b oezp+)0 ,pc.ecf+ttw icgm) and in blue (465 nm) LEDs?
the green $E_g$ =    eV
the blue $E_g$ =    eV

  A zener diode voltage regulator is shown in (Fizo/a4fvxz 3 c)g. 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?    $\ \text{k}\Omega \leq R_{\text{load}} < \infty$