What type of bond would you expe.-b(mynu b mb/b7v2cjf 0 csd5ct for
(a) the $N_2$ molecule,
(b) the HCl molecule,
(c) Fe atoms in a solid?

Describe how the mol p+me ta)0iv5 8bmo9noecule $ \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 hxut6b- j3a xvpj9b- 7$ \text{H}_3 $ is not stable, the ion $ \text{H}_3^+ $ is. Explain, using the Pauli exclusion principle.

The energy of a molecule canima4ez)eyb nq p,.)+/vasss. be divided into four categories. What are they?

  Would you expect theerbi(7uo2 ny v.nupr)-:vwn( 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 ato;7i *xsc 4bzqgm ($ Z=6 $) usually forms four bonds with hydrogen-like atoms.

If conduction electrons are free to roam aboutao(h( f *r,qxa 1q;qct in a metal, why don't they leave the metal entirely?*f1t;q,xroa (h cqq a(

Explain why the resistivity of metals increases with te2; t0ifj h fc 2ba) w5+ryjzz 2v;b,xwc(ugd+fmperature whereas the resistivity of semiconductors may decrease with increasing tempeba fy 2+ fit+2;zf5;(x,jjh0wucz w brcd2)vgrature.

(Fig. Below) shows a "bridge-type" full-wav )uqa(6uw17p ryf, iqre rectifier. Explain how the current is rectifi)w (p,1uqa7qyrif ru6 ed and how current flows during each half cycle.

Compare the resistance of a pn junction diode c7oepxe6hp 3 q /;sdur1onnected in forward bias to its resistance when connected in reverse bia3;h/61 xoeq 7 rpusepds.

Explain how a transistor couldkh ufsgh))x7s8rm, a f4:h +cm be used as a switch.

What is the main differi8l t/hhrr+ y4ence between n-type and p-type semiconductors?

Describe how a pnp transistor can opv5ugz9sa c;) berate as an amplifier.

In a transistor, the base-emitter junction and the base-collector junction are efbqmor 9u.d791arzj kyw79v(6( eryoxj 4,vyssentially diodes. Are these junctions reverse-biased or forward-biased in the application shf x9u7rr y(.z m9o rvyj7o9k v,wdea41b6q(y jown in (Fig. Below)?

A transistor can amplify an electronic signaat;.v ejm tg4,,3tbc1 t6uu 15o; qf1cmuppxfl, meaning it can increase the power of an input signab e.jmmp 1gpo,c46 ,tut;tvqa1fcxu3u5; tf1l. Where does it get the energy to increase the power?

A silicon semiconductor is dopedfsdhd4iv iv;4, 67m *iw yrwp,cj)6ch with phosphorus. Will these atoms be donors or acceptors? What type of semmvvw,d r *fs4y6h)wd4h;ij,p i7 ci6ciconductor will this be?

  Do diodes and transistors obey Ohwjjzv*xf*9b +hk -lx9 m’s law? Explain. {yes|no}

  Can a diode be used to amplify a signal? Explain. {a+2 t:gcgv84zw*i nhxyes|no}

  Estimate the binding ener1td)r u bur8ou/yn2yh suvqv4 e0;41mgy of a KCl molecule by calculating the electrostatic potential enervb)uo1sd8 ;yruth412vnum4/r0yu qe gy 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 of KCl isb4d d1bd h0lv1 4.43 eV. From the result of Problem 1, estimate the contribution to the bih41b 1l v0bdddnding energy of the repelling electron clouds at the equilibrium distance $ r_0 = 0.28\ \text{nm} $. $PE_{\text{clouds}} =$    $\ \text{eV}$

  Estimate the binding evc6z y;) 5wgqbn9-ej0gz al4gnergy 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 k 8o4z3yj.ptcoften measured experimentally in 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? What is the binding e8j4ytczp3o . knergy 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 fozk4/// nc vhtbeh .*gjrmation of t* vzbe.n4/ghtkc/j h/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 quantity -n*fuv*xta.b x f4ws; $ \frac{\hbar^2}{2I} $ has units of energy.

  The so-called “characteristic rotatx2evt.*bx gvm;s v8b3ional 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 characteristicne+of o, wt81 2kjhp m*ezv;e/6j q6xnpc8xg4 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 aton:y5m 7 mg-ttv 0t 7abxdx)ei*ms 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 g jbv(6ezwiv 49mxu+ 8xiven that three successive wavelengths for rotational transitions are 23.1 mm, 11.6 mm, and 7.71 mm 4uw98iv 6x+bmve(xz j. $r = $    $\times 10^{-10}\ \text{m}$

  (a) Use the curve of (Fig. Below) to estimate t2ax5u11elpz uemw5.4/eykz d he 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 /sc ftfkse0 9)*cwtg:NaCl crystal is 0.24 nm. What is the spacing between two ncet)t/ 0ss f:gcwk*f 9earest neighbor Na ions? D =    nm

  Common salt, NaCl, has a density ov 3.ue7umnpy e7yp:g21k0g3r icf m4jf $ 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.wgkeq,tpy)/s 2(jq6 c.eq h7jknp 6x density is $ 1.99\ \text{g/cm}^3 $. $s$ =    nm

Explain on the basis of energy bands why the sodium chloride cry10wjmge k,+wb stal is a good insulw1wmkj,e0+ bgator. [Hint: Consider the shells of $ \text{Na}^+ $ and $ \text{Cl}^- $ ions.]

  A semiconductor, bombarded with light of sl) 6e z/h(kv)j:weygnyowly increased frequency, begins to conduct when the wavelength of light is 640 nm. Estimate the size o) :jv)zwn eyy(/e kgh6f the energy gap $ E_g $. $ E_g $ =    eV

  Calculate the longest-wavelength photon that can cause an electron in silico(bfp,*x90bvzw-jutxfn m) ftl* l- 0dn ($ 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 conductitcop 4yjoc. z-cwk39:1fjk, qon bands in germanium is 0.72 eV. What range of wavelengths can a photon have to excite an electron from the top of the valence band fcjkko:w 9,t3c 4zqj-c1y o.p 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 ql/8r9 1h9gtpib9n-hb/h bfr$ 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 dop08fdhmzg. u8x* t9q1zhsf( yded with phosphorus so that one silicon a.(0 tqyzmu fd1*hhdsx g8z f89tom 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_{\text{doping}}}{N_{\ce{Si}}} = $    $ \times 10^6$

  At what wavelength will an LED radq9upnh es4 i*+iate if made from a material with an energy gans*u e4iphq9 +p $ E_g = 1.4\ \text{eV} $? $\lambda $ =    $\mu m$

  If an LED emits light t6qlyb 6 kr/1*wvz9zq8eh(avof 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 (Fig. Below)d+m-kxgpiti99 m6chb- (sme;, is connected in series with a battery and6+xmih dst;gpmm 9 i-9k-(ebc a $ 960-\Omega $ resistor. What battery voltage is needed to produce a 12-mA current? $V_{\text{battery}}$=    V

  Suppose that the diode of (Fi4kmdmajc ro/ n)0 i9nc:n4w5kg. 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 current, for *+k +vmxhimr2f7zw 2j$ V > 0 $, for the diode shown in(Fig. Below).

  An ac voltage of 1208/5 ux )l*9yrpykcqvs V rms is to be rectified. Estimate very roughly the average current in the output resistoqyc)8vyru*p sx lk95 /r $ 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 forwa7m ) : o-gmw*a3 zth:k)cl8dsdimjru ;rd-bias voltage exceeds about 0.6 V. Make a rough estimate of the average current in the output dcm : i7 j*u;-ahw8rl zgts) dm3)km:oresistor $ 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 r /jl /qzhin8c:ectified with a full-wave rectifier (Fig. Below/i:lh nj/z8cq ), 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 relationsl x;cb -kvjp;mn351xchip 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 energ k+wed15mgnms(ui *;zy 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 il8ea; r i 9owj+r*cjwnx2lj5u;ob, m,s 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 distan a;,h,v w2agtkce 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 athl gubgn n at0oj5n: )7/v0mi0om connected to six neighbors, each bond having a binding enehg0j:7oui/ntm vnbl)g0 0an5 rgy 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 activation energy o .h4 (exkfu8xaf 1.4 eV. When the molecule is disassociated, 1.6 eV of energy is released. ua84 ehkx(f.xDraw a potential energy curve for this molecule.

  When EM radiation is incip+rzwq f:c/-r2xp, d kdent on diamond, it is found that light with wavelengths shorter tha2/w,r -+ rcpz:qkfdxp n 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 not to reac-li)1wx+xymy)uq +zdt to visible light, could it make use of silicon as a "window" with i+m iy1 lq-w))yzu+xdx ts 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 semicondubsxglc 82 z t9jyk ,x;d8wzch4w0rcyjb8n+52ctor, assume that the "extra" electron moves in a Bohr orbit about the arsenic ion. For this electron in the ground state, take inx+9c88hky b42 sgdbrn jzw8lxc5 jz,2ty0cw; to 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 thanuo:2 5ily5+0 z tfc paktkxf3; 1000 nm. For a solar cell to absorb all this, whau;tz2 kk+l atp05oi5f fy:3c xt energy gap ought the material have? $E_g$ =    eV

  For a certain semiconductor, the longest wavelengc.jswm0sy a ppc0q,6 l*en8 5uth radiation that can be absorbed is 1.92 mm. What is the energy gap in this semico c,q*cy sejwsu060.n5p lp8a mnductor? $E_g$ =    $ \times 10^{-4}\ \text{eV}$

  Green and blue LEDs became av r8tq6x4fbzj 9ailable 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) LEDs? 6jqt8 fxrz9b4
the green $E_g$ =    eV
the blue $E_g$ =    eV

  A zener diode voltage regulator is shown in (Fig. Bspffv-9wx a 5am8aj9.elow). 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?    $\ \text{k}\Omega \leq R_{\text{load}} < \infty$