What type of bond would you75rs,mk soi 7qu9b7 aju6 v78oxa4m zy expect for
(a) the $N_2$ molecule,
(b) the HCl molecule,
(c) Fe atoms in a solid?

Describe how the molecule(smr 0;szud0ih u)0)l8h4pdejjh qv 9 $ \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 6*0y -zbqlkvh0p;xin e fztb1l +t/ 3w$ \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 fo 4tb , 7dt(;jm;alqq7khv6d hvur categories. What are they?

  Would you expect the ks;oh;j(xcc+ z o;i )tmolecule $ \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 (e krv h1nc5w40$ 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 leave mx/kh2 .yatg2the metal entirely? gh.y /mta2kx2

Explain why the resistivihyvi.npxe5 (u ow8 hkn47w v*)ty of metals increases with temperature whereas the resistivity of semiconductors may decrease with increasn)pku 8v(wo . h7i whye*vn54xing temperature.

(Fig. Below) shows a "d+ cvzdc,) bjmh): q.wbridge-type" full-wave rectifier. Explain how the current is rectified and how current flows during each half c+b,:. qd zchv)jc)dwmycle.

Compare the resistance of a pn junction diode connected in fotymym5)usidmy8hn6 j 4; vuo:ztx 5 ,4rward bias to its resistance when connected in reversxht y, 5) 44ut;mm:8zmov iju5y6synde bias.

Explain how a transistor could be used as a switcrxxa 604ctoal ay6:u5h.

What is the main differ0 to8v8zl zqt/xxrqt024 ehi9ence between n-type and p-type semiconductors?

Describe how a pnp traup7 yte qx,/ cu 9 ycb2tqb+x/tm/:ko7nsistor can operate as an amplifier.

In a transistor, the base-emitter junction and theumuz-zvjw,2 +p 2s:5jams )hyabg.u( base-collector junction are essentially diodes. Are these junctions reverse-biased or forward-biased in the jha:u+g s jsp.5wmv( zua)ub2m-2 zy,application shown in (Fig. Below)?

A transistor can amplify an electronic signal, meaning it canf25etd aj a.a0 increase the power of anaae daj .052ft input signal. Where does it get the energy to increase the power?

A silicon semiconductor is doped with phosphorus. Will these atmil*u ,/ sanm-oms be donors or acceptors? What type of semicondm alus in-m*/,uctor will this be?

  Do diodes and transistors obey Ohm’s law? Explain. {yes|nqv 11cy ;d:lm a28wskno}

  Can a diode be used to amplify a signal? Explainckq2kwk 9m6f; . {yes|no}

  Estimate the binding energy of a-t;yq a*lyn t i;)izp. KCl molecule by calculating the electrostatic potential energy wh *iq-l;y)pitz tnya ;.en 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 energbd awh s2/rfy2*3sk)fy 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 equilrd2sk*b fy /h3 w2)sfaibrium distance $ r_0 = 0.28\ \text{nm} $. $PE_{\text{clouds}} =$    $\ \text{eV}$

  Estimate the binding ener+jt ; jrwe,cj08 a:dgegy 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 26yeh n1h3aedmom p;.l+b8yg ip*5vz 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 per molecule? zyh gynb5e e.+pivmpo2d3 h ;l16m8*aWhat 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 similc/fo1;sn 3 c7 igt7d+7 k(yn ndwd7 rmsii0)zoar to that in the text for the states in the formation nid7sii+77;ronf (t )d/ymk dc03c noz gs7w 1of 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. oi 0f *uowtav-ny fwx62 z;6rjw;ps4 $ \frac{\hbar^2}{2I} $ has units of energy.

  The so-called “characteristic rotational ene2y/9tzg poq zfd(+p(grgy,” $ \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 rotationaly7zt2w 0:uo-n tvx -9bvhdhupz-7t g) 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 separationwqsd4ykk,44 5z7 lmfn 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 molecule given that three succtd nm/2 n*wusx15/tv wessive wavelengthsns m/1 *uvwdn/t wx2t5 for rotational 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 th j 6u o9tc1vaamn/t+m/e 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 crynfv.q5c nzqyvo4 -vm2* ;+rlpstal is 0.24 nm. What is the spacing between t fvnq+n4v;m*cvl5 y-z2o pr.qwo nearest neighbor Na ions? D =    nm

  Common salt, NaCl, has a densityy(m9xu, r3mw9edib e ye 2u:)g 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 densitynnws0o4 dag ot4; 2.sy is $ 1.99\ \text{g/cm}^3 $. $s$ =    nm

Explain on the basis of energy bands why the sodium chloride crystal is a good xg/g r+7xq9bga7 pk/ zce8 l)yinsulator. [Hint: Consider tk7gy/zgxq)pb+ /r 7 gl9aexc8he shells of $ \text{Na}^+ $ and $ \text{Cl}^- $ ions.]

  A semiconductor, bombarded with light of slowly i/h 9joeh8p9ho6d btt 1ncreased frequency, begins to conduct when the wavelength of light is 640 nm. Estimate th 8tdphj69t b h/oe1ho9e size of the energy gap $ E_g $. $ E_g $ =    eV

  Calculate the longest-wavelength photon th7g;b0eo7 o7m zcig*laat 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 l3ywgl2o ph6 7and conduction bands in germanium is 0.72 eV. What range of wavelengths can a photon have to excite an electron from the top of the val 27lhyolg3wp 6ence 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 l )xq6)v sbmr6$ 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 silicone 4f jheo,k+u2 semiconductor is doped with phosphorus so that one silicoo,+je4ufh2k e n 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_{doping}}{N_{Si}} = $    $ \times 10^6$

  At what wavelength will an LED radiate if made from a mater)5qxitrx7 x; jou/pa8ial with an energy gax /u85 pa;i7)xjrx toqp $ E_g = 1.4\ \text{eV} $? $\lambda $ =    $\mu m$

  If an LED emits light) 8ouwoqy7 25z3bbq pbgydh66 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 are given in 2r6ns gcoj;4u(Fig. Below), is connected in serr;nj46 og2sc uies 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 connes 9v svizq90m(fa 0jg1cted 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 le yo2i:i:/vh *dp.z afunction 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 roughly the)7cjqahr nq5wca/+i s0*m p 7b average current in tsmi c b 5chr 07q7/nw+ajpaq)*he 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-b ;iz fm)iz)9bfias voltage exceeds about 0.6 V. Make a rough estimate of the average current in the outpf;)mbz )z f9iiut 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 fulrtgo9 lmf10rtqb13 1cl-wave rectifier (Fig. Below), whert0gtm frr9ob1c l1q31e $ 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 hudrik( tlysc 0/t7ze :z v(-k ,km y1lnh;0:brelationship 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 energf1v7c4u o+bj fy 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 k dha -9(st73qjkuaea :w5p3jsz 97favinetic 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 dis 0uutjm ok)s (hjos d;;6)xul6tance between 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 monoatomic solid with a weakly bound cubic lattice, with each atom cnb4qn 0fv,,tbhj0v b+onnected to six neighbors, each bond having a bind ,vq fbn,nbbvj+0t0h4ing 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 an9 eut gw0lv;e; activation energy of 1.4 eV. When the molecule is disassociated, 1.6 eevu9g;; wlt 0eV of energy is released. Draw a potential energy curve for this molecule.

  When EM radiation is incident on diamond, it is found that light with wavelengzc7q7ky8uc)h0ai)uvb v m1 g +l7nh h5ths shorter than 226 nm will cause the diamond to conduct. What is the energy gap between the valence band and the conduction band for diamouh q+zhy 1)0 c i n5cl7km8)ub7h7agvvnd? $E_g$ =    eV

  A TV remote control emits IR lightqzf uvj (5wurfve07*0. If the detector on the TV set is not to react to visible light, could it make use of silicoqwu0( zvf fru e705*vjn 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 semic,ah e*qjeu : s 1zao.:o,7qaoaonductor, assume that the "extra" electron moves in a Bohr orbit about tqo aoa.ze* 17uq,:,hejs:o a ahe 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 hah9n3wdv7n1 dseg6-g8;wa tyw s wavelengths shorter than 1000 nm. For a solar cell to absorb all this, what energy gap ought thy9v3a18;hn e 7s-dwwtgg wnd6e material have? $E_g$ =    eV

  For a certain semiconductor, the longest wavelength radiation thak.,px p6;x+ itij v2f.ve2lam0c ry)jt can be absorbed is 1.92 2 fyk.6;ave v,ji+)p.tcp 0rm 2iljx xmm. What is the energy gap in this semiconductor? $E_g$ =    $ \times 10^{-4}\ \text{eV}$

  Green and blue LEDs became available many years after red LEDs were first devel: a.*1wef m0r7wtpjbi oped. Approximately what energy gaps would you expect to find in green (525 nm) apjw w.*fr a1e:t i0bm7nd in blue (465 nm) LEDs?
the green $E_g$ =    eV
the blue $E_g$ =    eV

  A zener diode voltage regulator is shown in (Fig8615(fs/wi1hyue ylg4jfib p. 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?    $\ \text{k}\Omega \leq R_{\text{load}} < \infty$