What type of bond would you expg t6h uj2glvl1+)(bmsect for
(a) the $N_2$ molecule,
(b) the HCl molecule,
(c) Fe atoms in a solid?

Describe how the molecd0r* cswzi/h2d25 5 rz g;kzwdule $ \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 yq+x*t4wi2skm; 67gacdh94g wtxrh6 $ \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 categories. What are th ch4+p * *vcfhg -pdfizs3,/ehey?

  Would you expect the tbp, b*c3-qlxn of k/,yu2p;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 atob2gawne+ ;r5ksv g;,im ($ Z=6 $) usually forms four bonds with hydrogen-like atoms.

If conduction electrons are free to roam about in a metal, why don't t,*b5ttv( zadvhey leave the metalv abv*,d(ztt5 entirely?

Explain why the resistivity of metals increasef zm*i2bm u6g9j) aifw oqm -l0p0v8;ms with temperature whereas the resistivity of semiconductors may de )pjmv;2mqz i ibwgf-fl*096o aum8 m0crease with increasing temperature.

(Fig. Below) shows a "bridge-g yn -.fy/hex3n2mnlq0 k6xw) type" full-wave rectifier. Explain how the current is rectified and how currele 0/xmnq 2g6hyxn. )w-y3fknnt flows during each half cycle.

Compare the resistance of am1ufd ea3.,* 4ybl(vdupux3 e pn junction diode connected in forward bias to its resistance when connected in . 3 ydfd(3*pvbxlau 1 ,emeuu4reverse bias.

Explain how a transistor could be used as a sg(o j2rrb/oki1;az h9witch.

What is the main difference between n-type and p-typeoy(/niz, bl(b72plfwku(xd :i * ydl* semiconductors?

Describe how a pnp transistor can operate as an nhz tt6o3y x5(amplifier.

In a transistor, the base-emittex*k.uv 8 vjff5r junction and the base-collector junction are essentially diodes. Are these junctions reverse-biased or for *5xk 8f.jvvufward-biased in the application shown in (Fig. Below)?

A transistor can ampj8bdag/(8uxj2ds(t2a wv y*q lify an electronic signal, meaning it can increase the power of an input signal. Where does it get the energy to iata*j 8u 2w x2dqg((j8vbs/dy ncrease the power?

A silicon semiconductor is doped with phosphorus. Will t/kk e:9xc /hrbhese atoms be donors or acceptors? What type of semiconduct kx he//r:b9ckor will this be?

  Do diodes and transistors obey Ohm’s law? Explain. {cg c j+rh6lq:.yes|no}

  Can a diode be used to aqu30c7k362)aume teht3 pvv lmplify a signal? Explain. {yes|no}

  Estimate the binding energy of a KCl molecule by calculating the electrostatlxc /-6p xytg )t,3offic potential energy when t fyotpxfc/-l,t 6) x3ghe $ \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 energ,c5nm fi lrw5 o2t+szfnzr6 (71 dw.hdy of KCl is 4.43 eV. From the result of Problem 1, estimadnc l,f2h67 5(rsirt.1zo dzwm5w nf+ te the contribution to the binding energy of the repelling electron clouds at the equilibrium distance $ r_0 = 0.28\ \text{nm} $. $PE_{\text{clouds}} =$    $\ \text{eV}$

  Estimate the binding energy of ta3s/ wqgh+:ez he $ \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 experimentallyfhzlxl63f:d x l4p-* 3v)imfc 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 isi:3lh lcd v*x3lxf -pz 4f)m6f 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 tg5azr honre.:p8.2 l*m od4vthe text for the states in the formation of the5agm: . honlpo*2dr4tv8r e.z $ \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 quantitox9knuh +5l r6y $ \frac{\hbar^2}{2I} $ has units of energy.

  The so-called “characteristic rot:sr m4)pwbs 1 -w8.nkif8 yxniational 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 rotational jz2u4 2+l-.dvg0yz ) fcwtpky. t(vveenergy, $ \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 separatib7 l, jxm9 5jpe jb0pk)(f2wpkq1tk8kon 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 successive wacna 1p5es3 / zhi:llz5velengths for rotational transitions are 23.1 mm, 11.zlhc p3z 5a:elnis 15/6 mm, and 7.71 mm. $r = $    $\times 10^{-10}\ \text{m}$

  (a) Use the curve of (Fig. Below) to estimate the stiffness constqh4xxe) 42nck- mngw+uch)j .ant $ 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” N4oga ;mj s*2jla and Cl ions in a NaCl crystal is 0.24 nm. What is the spacing between two nea*42ogjlsj ;m arest neighbor Na ions? D =    nm

  Common salt, NaCl, has a density of ;4qy7mfpgw;gofhr *g52 qc) d$ 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.izy sl ss-5 hq;t*qh3 is $ 1.99\ \text{g/cm}^3 $. $s$ =    nm

Explain on the basis of energy bands why the so,-v.wpvvc wnt 9u(emsx75nj9 *px jt0dium chloride crystal is a good insulator. [Hint: Consider .5tpn,jtwu v (mwnv*je 0px9c xs9v-7the shells of $ \text{Na}^+ $ and $ \text{Cl}^- $ ions.]

  A semiconductor, bombarded with light of slowly increaskuxunjo */- m2:x :dqoed frequency, begins to conduct when the wavelength of light is 640 nm. Estimatux * 2:mjukndq/ox-o:e the size of the energy gap $ E_g $. $ E_g $ =    eV

  Calculate the longest-* wsi7lf*m2c7 jp/zlhwavelength 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 and conductiono ci/pck5 oi5( bands in germanium is 0.72 eV. What range of wavelengths can a photon have to excite an electron from the top of the valencpio/ci5 5cok( e 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 arq :93bgm ahdw(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 semiconductor is doped with phosphorus so that one clsfwvy wb4rz1 qj3y,2/q55b ss6qb2siliconyb21,sw4s bc5q6bqvr3yz js w25f/l q 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_{\text{doping}}}{N_{\ce{Si}}} = $    $ \times 10^6$

  At what wavelength will an LED radiate ifx(f;o)9na c,r 4btwcc made from a material with an energy gapacrwtc o9f; 4b(nxc,) $ E_g = 1.4\ \text{eV} $? $\lambda $ =    $\mu m$

  If an LED emits light of wav mf)rai+4l pz(elength $ \lambda = 650\ \text{nm} $, what is the energy gap (in eV) between valence and conduction bands? $e_g$ =    eV

  A silicon diode, whose curr7t lbi 9idr8aok3 n-qb vx1(4zent-voltage characteristics are given in (Fig. Below), is connected in series wi7dqobx3a(l4 1 bk-nt98irzv i th 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 connected in serijzp2jk+2dh t1n4an( 4kdz4 mmes 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, fo t*hzwb5g)l/ (x p(ywjr $ V > 0 $, for the diode shown in(Fig. Below).

  An ac voltage of 120 V rm iie47qq0dds8 4xd9z vs is to be rectified. Estimate very roughly the average current in the output resisto9is4i 4edq08qzd xd7vr $ 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)0ahtgsbr; feg:h: ia:-pa f,aad/0 g significant current only if the forward-bias voltage exceeds about 0.6 V. h0bgte:r)/ idafsaa a; pagf-0g ,:h:Make 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 rectified with a full-wave rectifieq/k +bhgwt70os60 y xgr (Fig. Below), whh+g w g/07kbsx6o0ytq ere $ 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 betweeg:a 0xm:s* ww(caa5vqn the base current $ I_B $, the collector current $ I_C $, and the emitter current $ I_E $ (not labeled in the figure).

  Estimate the binding zj wow1r* ;1snenergy 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 kinetf;si.p53fw lg ic 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 sv;u mue .jnr0srxze l3)6b)1heparation distance 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 latt+*t( ts) e8yssxz:2z:nh tmbtice, with each atom connected to six neighbors, each bond having a tz+m(nx 82byts)t* zs ::sth ebinding 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 an activation energfc-kig* /sklmndc 5df3qf06 qd17 jv 0y of 1.4 eV. When the molecule is disassociated, 1.6 eV of energy is released.ki dv07-0n mg5k6 c*l3ff/ 1jcqqfsdd Draw a potential energy curve for this molecule.

  When EM radiation is inxi8gw*;x2ec q cident 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 cx*gi2q;e8 w xband and the conduction band for diamond? $E_g$ =    eV

  A TV remote control emits IR light. If the detector on the TVg6.+e;/zyz4 odg c ksg set is not to react to visible light, could it make use of silicon as a "window" with its eg4 6zsk .e+go d/;czygnergy 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 do kb/hi7haf.u; n4c x)hhqfji8k )5:pa ped silicon semiconductor, assume that the "extra" electron moves in a Bohr orbit about the arsenic ion. For this elekbhcuhix)hki a f/f: p4)a7 h.5n;j8 qctron 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 wavelengt2x a -w:kddag3hs shorter than 1000 nm. For a solar cell to absorb all this, dgxa-dk32 a: wwhat energy gap ought the material have? $E_g$ =    eV

  For a certain semiconductor, the lon3)cq,yxcyx 8 7ynna5m gest wavelength radiation that can be absorbed is 1.92 mm. What is the energy gap in this xm qny3ay785cx,y)n csemiconductor? $E_g$ =    $ \times 10^{-4}\ \text{eV}$

  Green and blue LEDs became available many years after red LEDs weria :pq m.e)zc2o rk-b.e first developed. Approximately what energy gaps would you expect to find ineb-a)zrck.2iom: pq . 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). Suppose that gd*eruto61nvcq)h,b9 vn g4, $ 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?    $\ \text{k}\Omega \leq R_{\text{load}} < \infty$