What type of bond would fy/p2e -h2v6h s:i ijmyou expect for
(a) the $N_2$ molecule,
(b) the HCl molecule,
(c) Fe atoms in a solid?

Describe how the molec y. /cxpuwrwy)rc99q ;ule $ \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 molecul4q/khsu4jv: 2;opv hm e $ \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 categoazzm swc,0 ab/;wj5 8kries. What are they?

  Would you expect the 0l n .m;2z1tw/3 bn3 ccv v ch.ypx9e6qfdhzc(molecule $ \text{H}_2^+ $ to be stable? If so, where would the single electron spend most of its time?{yes|no}

Explain why the carbodu2 wk34g8ujyn atom ($ Z=6 $) usually forms four bonds with hydrogen-like atoms.

If conduction electrons are free to roam about i se )waqnb7iwotcp7-/ qa:.9bn a metal, why don't they leave the me beqp -7a:nqo9wbcais/ 7wt) .tal entirely?

Explain why the resistivity of metals increases with temperature whi9z+k hzziy6; ereas the resistivity ofi9zhzyz+ ; i6k semiconductors may decrease with increasing temperature.

(Fig. Below) shows a "bridge-type" full-wave rectifier. Explain how the cr-tkbcjan zy*j8 p91 sc9 +a2iurrent is rectified and how current flows during each half cycle92r1a j9 n +ck-pjazs ci*byt8.

Compare the resistance of a pn junction diode connected 2i:cr u9xzd (din forward bias to its resistance wherd:c dz i9u(2xn connected in reverse bias.

Explain how a transistor could be used as3s55ktr:hs,e4 zr iyh,(xz ws a switch.

What is the main difference between n-type and p-type semiconductors1+um1+9 f ccw+lchias ?

Describe how a pnp transistor can0qnh hg yeab:h;7o45q operate as an amplifier.

In a transistor, the base-emitter junction and the base-collectm7yt8( +sl2q.k ma6vgn1 y yx +ixod(ror junction are essentimyxxgt+( y6ansm2 qoy +r dv(i1l8.7k ally diodes. Are these junctions reverse-biased or forward-biased in the application shown in (Fig. Below)?

A transistor can amplify an electronic signal, meaning ) )0hqpjy5 q)t6rodohit can increase the power of an input signal. Where does it phj6drh 5qy0 ))o)oqt get the energy to increase the power?

A silicon semiconductor is doped with phosphorus. Will these atomsce 2q.az8 yg7z3s klr0 be donors or acceptors? What typek2q.zge8lcrz 037ays of semiconductor will this be?

  Do diodes and transistors obey Ohm’s lawx 7idz.;yho5qilk 3w 6? Explain. {yes|no}

  Can a diode be used to amplify a signal96 srf hy,lshac(w;a:? Explain. {yes|no}

  Estimate the bindingl,z5,x 6+aufmi elqf. energy of a KCl molecule by calculating the electrostatic potential energy,, 5el.lu izfmaf+6 xq 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 ou0uk ;/+kj5e 9 )vkcb+pei quff KCl is 4.43 eV. From the result of Problem 1, estimate the contribution to the binding energy of the reie +0 b)k+f/u5qek;c9kjuupvpelling electron clouds at the equilibrium distance $ r_0 = 0.28\ \text{nm} $. $PE_{\text{clouds}} =$    $\ \text{eV}$

  Estimate the binding ax9 c5tg ,.gufenergy 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 xjr3qq i2ngny8ry.+ 4per mole, and then the binding energy in eV per molecul+ryig ynq.q43j8n2x r e 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 similjpffi46:j r*far to that in the text for the states in the formation of if* 6jrf4:pjf 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 quantity dhyzkh+ ,d :g7j6b,qa$ \frac{\hbar^2}{2I} $ has units of energy.

  The so-called “character xfb1v/,0sm1kb 6mc,u) zxadw: b tjb1istic 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 characteristic rota+* u zc 61nhl5e)htrp2 gr1rhwtional 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 atoms yq2uo emt:9:ain 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 suc(k isnbz w8.517j b csjnt *i*b9lv,. (sopncycessive wavelengths for rotational transitionwbnck jo.7bi8 *nvc*5i, s s(tz(py bnj1s9.ls are 23.1 mm, 11.6 mm, and 7.71 mm. $r = $    $\times 10^{-10}\ \text{m}$

  (a) Use the curve of bste:6dv(*hxps ia8ot) ak :c h)8yj1 (Fig. 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 in a NaCl cr 7fmx-(txur z8ystal is 0.24 nm. What is the spacing between two nearest nu8x7 xmfz (t-reighbor Na ions? D =    nm

  Common salt, NaCl, has a density of4r0.0o2 hq e4s bf6z: krmungc $ 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 foonh4g;q lf p0(tx : ltp:wun21r KCl whose density is $ 1.99\ \text{g/cm}^3 $. $s$ =    nm

Explain on the basis of energy b.un:b1g(+wdvk -k;vvfupg ( iands why the sodium chloride crystal is a good insulator. [Hint: Consider g: kg1v.(uwkvv+; bif-du np(the shells of $ \text{Na}^+ $ and $ \text{Cl}^- $ ions.]

  A semiconductor, bombarded with light of slowl3; f xlsl;mif8kdij/3 y increased frequency, begins to conduct when the wavelength of light is 640 nm. Estimate the sizfkli; i ;s3f/ld3 8jxme of the energy gap $ E_g $. $ E_g $ =    eV

  Calculate the longest-wavelength photon 23sofy- 6omzfwb8u2c0)kr gd 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 bands in germanium is 0urm. xkz/cc v bogie:f9k1( (a3j,.f u.72 eV. What range of wavelengths can a photon have to excite an electron from the top of the valence band into the conduction band3ru9u. g/z :c,v(1kk b mf(j xaef.coi? $\lambda \leq$    $ \ \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 abd(:w;vd /pv $ 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 onep m. u 1a njofoe,::ovfd 3h/m0dww0y;6lm a-y silicon atom in ,w0m/ unev:fmojy6: 0o.adyplw f adh1 ;3- om$ 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 radia8j y0l:l zaqtp7ank3q (uum2)te if made from a material with an energy gap 8t mlkn:3)lj(7q yau0p qzu2a$ E_g = 1.4\ \text{eV} $? $\lambda $ =    $\mu m$

  If an LED emits light ofcby) oq6r.0id+ 7yzc u 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 characteristicso gtl7..j+nmg are given in (Fig. Below), is connected in series with a battery ajl7t.mn+g .o gnd a $ 960-\Omega $ resistor. What battery voltage is needed to produce a 12-mA current? $V_{\text{battery}}$=    V

  Suppose that the diode of (Figu8:byyy +5i i1zs ied(. 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 function of currentze 3y-gnc nk4), for $ V > 0 $, for the diode shown in(Fig. Below).

  An ac voltage of 120 V rms is to be rectified. Estimat(v- 5s 9gfwq(+xp se)igqupoecm t2*4e very roughly the average current in the output )sqoqv4spigu(et* -gp 59mfew x +c2(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 signiv;o(ad9o3 ekdficant current only if the forward-bias voltage exceeds about 0.6 V. Make a rough estimate of ov(3kodae 9 d;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 full-wave rectifiq6gfbue /xagk; /)qp )er (Fig. Below)kg)6/ ga xbqq uf/;ep), 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 t5p gw;s rn:h;between the base current $ I_B $, the collector current $ I_C $, and the emitter current $ I_E $ (not labeled in the figure).

  Estimate the binding0: cfq ,3bkd)qe;ea sj energy 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 atoq, 3,fazlwm(a m 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 0.27 jv*s8eapfqo6av: hml 6c58y5 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 l):s -.6jlst:v jxd tblattice, with each atom connected to six neighbors, each bond having a binding tl-j vd :xsj6:.tbs)lenergy 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 activation8(k5 z+azq(i -acn dlg energy of 1.4 eV. When the molecule is disassociated, 1.6 eV of energy is released. Draw a potential energzkq(-gzid( c+n5la 8ay curve for this molecule.

  When EM radiation is incident on diamond, it is found that lighab1 1ant sn58no me 6bwv/k.7ht with wavelengths shorter than 226 nm will cause the diamond to condusa b76hmv b8 knn1ne 15t.oaw/ct. 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 not todnbsu -p+h xa,d /hz6d-62p ja react to visible light, could it make use o u-,2/hsdjnpb+d6dx- p ahz6af 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 dm-jby:zg 0sm +f4gw0 uq2v0p mjg tu)7oped silicon semiconductor, assume that the "extra" electron moves in a Bqgj+0z7tvugj:0g- )w pm mms02f y 4buohr orbit 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 wavelengths shorter than 1 wt06oac5j 3e-uqsi) l000 nm. For a solar cell to abseo0lt csu3i5aq)jw6 - orb all this, what energy gap ought the material have? $E_g$ =    eV

  For a certain semicond1vrf xza:86tntu/ k0wuctor, the longest wavelength radiation that can be absorbed is 1.92 mm. What is the enek t8arw/nu6f t x1vz:0rgy gap in this semiconductor? $E_g$ =    $ \times 10^{-4}\ \text{eV}$

  Green and blue LEDs became available many years after red LEDs were firb5doq4ol7*5dtp+i+ge j3muj, hlqm 6 st developed. Approximately what energy gapelqdj h3 l4 o 5*5d+, mgi+qtp76jobums would you expect to find in green (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). S6/atnmq;t el8 0ue fg9u8 7bkjuppose 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?    $\ \text{k}\Omega \leq R_{\text{load}} < \infty$