What type of bond would you e65m:mc;2 yry06mxn ypmt 4y nbxpect for
(a) the $N_2$ molecule,
(b) the HCl molecule,
(c) Fe atoms in a solid?

Describe how the molecudx2fbrrbmdg3w d8di+x;*cwkx3 l;4 ( le $ \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 qye;38h izx)) g :2 qw-2gjcr,pjzpftis9i 7c$ \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 dividedet xz .ni4f5t,q*5b vx into four categories. What are they?

  Would you expect the molecule gy+dov 4hk5h: +-w5sy.z by utg* f6dl$ \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 (qca 5 fg/4p r7erq1m3x$ Z=6 $) usually forms four bonds with hydrogen-like atoms.

If conduction electrons are free to roam about in a metal, why don't they r w34 5omd4dwb* f)mvfleave the m*)fdwbvm 4wfd3r mo54etal entirely?

Explain why the resistivity of metals increases with temperature wherns0 e aswi;aujg0 n:qk0 0f17leas the resistivity of semiconductors may decrease with i1wagjeskf 0 nas00uq0 nl:7;increasing temperature.

(Fig. Below) shows a "bridge-type" full-wave rdz f/:2b wq85r ,h y)1vvswipaoz2gj9ectifier. Explain how the current is rectified and how current flows during each ha:z y2wh89isb zvp5 ad)ov rg/, 1wfqj2lf cycle.

Compare the resistance of a pn junction diode connected imw1ly p. 4(wjjt.3jown forward bias to its resistance when connectt34powjj w.wm 1.y j(led in reverse bias.

Explain how a transistor could be used as a switc a0 ,*jcra2d6kwm,hz)pe3hol 2g9 l.b r entv7h.

What is the main difference beyx6 xq5 ckv mlzuc: (28c)jac*tween n-type and p-type semiconductors?

Describe how a pnp transistor can operate as an amplgqyof)+c:r j(ifier.

In a transistor, the base-emitter junction and the base-collector jun ps-n;y5+iud mction are essentially diodes. Are thius;n dy pm5-+ese junctions reverse-biased or forward-biased in the application shown in (Fig. Below)?

A transistor can amplify an electronic signal,6ftt. t *4;bh fctznn0 meaning it can increase the power of an input signal. Where does it get the energy to increase thft *c4 tnzn 6.t0t;fhbe power?

A silicon semiconductor is doped with phosphorus. Will these atoms be dok/0 2nwbt1qjn nors or acceptors? What type of semiconductor will th0 bnj2nwqkt 1/is be?

  Do diodes and transistors obey Ohm’s law? Expl19 s xvx8r5ldaz*k x .ctlg1sat 7/1tfain. {yes|no}

  Can a diode be used to amplify a signal?q: 7lnfm:z hl(s3ifz y5e)hw+ Explain. {yes|no}

  Estimate the binding e 5pm7hpl i)4hvnergy of a KCl molecule by calculating the electrostatic potehhpv)7pi54l mntial 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 energyx d, . t7xgkur0jsf*4z 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 the equilibrium disfgz*0k xd r,.4u7 xstjtance $ r_0 = 0.28\ \text{nm} $. $PE_{\text{clouds}} =$    $\ \text{eV}$

  Estimate the binding energy16 a q-q-kpk6x w1qelx 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 per mole, anfe b* zc:rdrwdy / .6ad4b80tvd then the binding energy in eV per molecule is calculated from that res.zweyfd6v 4/ rdrca* 0b d8t:bult. 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 *gmf/w px:h *z-d;sg ufor the states in the formation of hpdfmgw;u :sg**zx- / 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/m+tx)j0 ke/q aur ui+3ce d-y3od2k :4dqc dm $ \frac{\hbar^2}{2I} $ has units of energy.

  The so-called “characterisls:l75e,m b hjtic 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 cha**x , klxrexf-racteristic 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 atoms e zyry y-fg;*,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 tvkfig4m3 0kc 7befy-7 he NaCl molecule given that three successive wavelengths for rotational transitions are 23.1 mm, 11.6 mm, and 7.71 cf0gy7vk4be- k 7mf3i mm. $r = $    $\times 10^{-10}\ \text{m}$

  (a) Use the curve of (Fidplg w3 *0xfimrx; z988fr5(:ycntyz g. 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 neig40rkzr*z1gux+r x8 cagz4h 4lhbor” Na and Cl ions in a NaCl crystal is 0.24 nm. What is the spacing between two nearest neighbor N4 cxzrug*4z4x g k+ rzrh1l0a8a ions? D =    nm

  Common salt, NaCl, has9gc4 9+uthb-wupsm k* a 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 is (5iz: 8dicssll (gdt)$ 1.99\ \text{g/cm}^3 $. $s$ =    nm

Explain on the basis of energy bands why the sc:rn*mcwg-iy;f 94r*ovffj ;odium chloride crystal is a good insulator. [Hint: Con9*:-m4;j*f ocrfrvg;iwcfn ysider the shells of $ \text{Na}^+ $ and $ \text{Cl}^- $ ions.]

  A semiconductor, bombarded with light of slowly increas vs2.*z;j oh6wd/ plvled frequency, begins to conduct when the wavelength of o/vpl .ldj w s6h2;vz*light is 640 nm. Estimate the size of the energy gap $ E_g $. $ E_g $ =    eV

  Calculate the longest-wavelengthlr n j6ix.:n0r 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 andnosa z4c3 *(m4p.cy eo conduction bands in germanium is 0.72 eV. What range of wavelengths can a photon have to excite an el sc4 opc3zn*4e.y(oam ectron 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 arnz( w6vg3eyh *e $ 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 semicondeu(h0*hag7 zuuctor is doped with phosphorus so that one silicon aea(7 u* guhzh0tom 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 energycr 7 jngay)cdq n8, * oekv(0dc33d,zw16rltt gap*tdrw nk7o6g8 a1lr3dc qcc,yj(ten,)3 zv 0d $ E_g = 1.4\ \text{eV} $? $\lambda $ =    $\mu m$

  If an LED emits light of wb cq8y8219dys6y ly bwavelength $ \lambda = 650\ \text{nm} $, what is the energy gap (in eV) between valence and conduction bands? $e_g$ =    eV

  A silicon diode, whose current-volt4hhgs ohtjen6()2 /odage characteristics are given in (Fig. Below), is connected in series with a battes4ejh th6ho2) (godn/ry 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 (F)6uhplpsm z8sd00w5h ig. 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 cuuf/1c: vh5l/ckre0s trrent, for $ V > 0 $, for the diode shown in(Fig. Below).

  An ac voltage of 120 V rms is to be rectifie.kjd1fn yx3g-h )y. 3ur8kuj yd. Estimate very roughly the average current in thegy 8ry)u djkfj.y -h31u3nxk. 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 si5ybm*dlwan 4f . kp3 ,hoves06gnificant current only if the forward-bias voltage exceeds about 0.6 V. Make a rough estimate of the aver lwa,4edkf50hps omn3*ybv6 . age 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 bedul d(h.bp+l3 rectified with a full-wave rectifier (Fig. Belb(+lp .dhl3udow), 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 /w*wq fvuw j4*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 energfq9l ; r0f12gyv wk.a8zkxyx:y 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*8vz8z jd 4s aw-5ng4lu)omu u kinetic 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 about 0.2 56xihcn uylt d)wnb99wyt)2d*j, hd27 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, wt+ 1;rwiffyykvda sq*.53 eye3t8 tuuh+ ,(rx ith each atom connece5ye fvuuy t3.rs di, 8xkf1++tqahw*(;try 3ted to six neighbors, each bond having 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 anxyc ic*vna t327k l-.u activation energy of 1.4 eV. When the molecule is disasy-v lx3tkc7naic u*.2 sociated, 1.6 eV of energy is released. Draw a potential energy curve for this molecule.

  When EM radiation is 4tgi4znhj* v8 incident on diamond, it is found that light with wavelengths shorter than 226 nm will cause the diamond to conduct. What is the energy gap between the valence bandv gn* 44jit8zh and the conduction band for diamond? $E_g$ =    eV

  A TV remote control emits 31xh ng gb)vb+vd4te4IR light. If the detector on the TV set is not to react to visibdehgn1 bv4b)x +gv3 4tle 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 semiconductor, an 7a9u7 3+yafw 3bmxokssume that the "extra" electron moves in a Bohr orbit about the arsenic ion. For this electronof9 u +y7 axbk33wm7an 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 radiatiovbt 3gsvl7)mo l3f;v/n has wavelengths shorter than 1000 nm. For a solar cell to absorb all this, whasgvmv;l 3v3olbt/)f 7 t energy gap ought the material have? $E_g$ =    eV

  For a certain semiconductor, the longest wavelength radiation that can be abmcgh-zk/rdwfw; (w5dam 3f2)4:cvb v sorbed mwd-g;f2 zd r/:w m4hc5wf kcvabv)(3is 1.92 mm. What is the energy gap in this semiconductor? $E_g$ =    $ \times 10^{-4}\ \text{eV}$

  Green and blue LEDs became availabllxhbxk0;pwo 7 8,(talbtmd.c 9a;9kue many years after red LEDs were first developed. Approximately what energy gop;a t;xabkx(cl,0h 87kl 9d9. ubmwtaps 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 show)l0 lie)q f m34hxouw2n 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?    $\ \text{k}\Omega \leq R_{\text{load}} < \infty$