What type of bond would you expect vt(2 6fkd7 n;jiw/wcsfor
(a) the $N_2$ molecule,
(b) the HCl molecule,
(c) Fe atoms in a solid?

Describe how the molecule 5xkt.sy-kq/ fw;w7 h z$ \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(p;sxye)h1r dcg 4/xu $ \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 categh 7(odbx01 ntcories. What are they?

  Would you expect the molecq,k2)53pd xkomppa guy ;q43e ule $ \text{H}_2^+ $ to be stable? If so, where would the single electron spend most of its time?{yes|no}

Explain why the carbon at9zi* xudd)j 6vom ($ Z=6 $) usually forms four bonds with hydrogen-like atoms.

If conduction electrons are free to roam about in a met 89 pno*bdjxq7al, why don't they leave the nb9qjp 87 xod*metal entirely?

Explain why the resistivity of metals increases with temperature whes+ b(aa1 fd,.trp ycx49qvl8rreas the resistivity of semiconductors may decrease w(y +v14lxqar pt8df ar9.sbc,ith increasing temperature.

(Fig. Below) shows a "bridge-type" full-fmrd1w55v5 wrg0.ujbvrf l 6l dr)64hwave rectifier. Explain how the current is rectified and how current flows55 )f rd646hjr fubmw1ldg .5l rrvvw0 during each half cycle.

Compare the resistance of a pn junction diode connectpt8 d 1u ib/00db ff9jjlycj3/ed in forward bias to its resistance when connected in reverse bic108bj9 /ffu ybdp0dlji/j t3 as.

Explain how a transistor could bd o-us, .wmjs*e used as a switch.

What is the main differ .vlgs 18the, (p xcwlw/(r;8 bykjng0ence between n-type and p-type semiconductors?

Describe how a pnp transistor wz olq wnpef 25)5co1g9 p8ec)can operate as an amplifier.

In a transistor, the base-emitter juwsg h.equ748 qnction and the base-collector junction are essentially diodes. Are these junctions reverse-biased or forward-biased in the application shown in (Fig. Bel7q.su8 ew4 gqhow)?

A transistor can amplify an electronic signal, meaning it can increase the to3qz-0ip ,oei j.quxn)v7;w power of an input signal. Weiq- 70o . 3tn)ijovxw,puzq;here does it get the energy to increase the power?

A silicon semiconductor is doped with phosphorus. Will t5ee(guuyfoa ta j8ch8rz. z.l83h q,8hese atoms be donors or acceptors? What type of semiconductor will this 58 tey ogf(lh.cq,h 8aruu.8ae8 zzj3 be?

  Do diodes and transistors obey Ohm’s la) *x 34ik2ba+p yn c5rnocsc3kw? Explain. {yes|no}

  Can a diode be used to amplify a yyhsh*ik;xk xq67+5rsignal? Explain. {yes|no}

  Estimate the binding energy of a KCl molecule by calculatint,5 z fygqh)i5g the electrostatic p ,ziytqf5h) g5otential 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 energy of KCl is 4.43 eV. From the result nrt (mf w.:xfelz-p20of Problem 1, estimate the contribution tr z- .xpml :0fe2(twnfo 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 eneu kaxr0kv5i; 6rgy 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 inuf 4dyzatv*86 kcal per mole, and then the binding enet684uyva* zf drgy 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 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 tn ccc 6iqh 3,v1lf0q,uo that in the text for the states in the formation of thcil,c6q0n,1 v f3cuqhe $ \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 quantit00p 7 fo k7r;2 e6 dwmvzk*q:ssysntb4y $ \frac{\hbar^2}{2I} $ has units of energy.

  The so-called “characteristic rotational enew.*n (o r*xwoergy,” $ \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 energi; y3:r bru.3sf ua hr dxf47,39h (fpmhrud0ly, $ \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 in the(9.0oln9dgr pc9izxk $ \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 successib;.v +o-ig,r avd 9)5dobxfzv-jl 2ka ve wavelengths for rotational trajv 9lo5iz-a g, 2db .bx)r fa-vodk+v;nsitions 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 therh o96t w2;lbxn4 bs0t 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 pdpy gcbkhs63vqu,k4h k).:7“nearest neighbor” Na and Cl ions in a NaCl crystal is 0.24 nm. What is the spacing between two nearest neighbor Na ions?4v3c :k pq)bpdh. hyk7s6ug,k D =    nm

  Common salt, NaCl, has ad xkzb4y *xml)pw/2jvjw )oov:; +z 9 vcd;(ks 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 densi8zviza8ci7s,v4 j ,- wmrn8c pty is $ 1.99\ \text{g/cm}^3 $. $s$ =    nm

Explain on the basis of u.o8+ n:c tyfienergy bands why the sodium chloride crystal is a good insulator. [Hint: Consider the shells oi+t8:u .fyo ncf $ \text{Na}^+ $ and $ \text{Cl}^- $ ions.]

  A semiconductor, bombarded with light of slowly increnrthj91h i oge )h8+f,ased frequency, begins to conduct when the wavelength of light is 640 nm. Estfh,rh 8hge tj)o+in 19imate the size of the energy gap $ E_g $. $ E_g $ =    eV

  Calculate the longest-wavelength zv9vyku)4q9w z3.lr dtoeox:k2 ,1j aphoton 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 germaniumb (xej k+ 3v:y8zm tw1 kj1zk5jnac,+c is 0.72 eV. What range of wavelengths can a photon have to excite an electron from the top of the valencjbz k 1yjnj,k1w8x z m(avekc53c+t:+ 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 ar-q,s6/72ftaiquf a uu 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 semiconductz 72z x+sz9sqc.yl4n kor is doped with phosphorus so that one silicon atomyzz29kzc4s x n7.s ql+ 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 y j09 2(*bvtnwfs ny0.o ovsmv7im9n1an LED radiate if made from a material with an energy gap70syj* v0v fnm9tyi(v2 mon wo1n. bs9 $ E_g = 1.4\ \text{eV} $? $\lambda $ =    $\mu m$

  If an LED emits light of wavelenu/x(ks hz.8g. s9s se2fsex oeu)b0y 5gth $ \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 character8zz 0dbktu8 (vistics are given in (Fig. Below),(ubtdv 0k8zz8 is connected in series 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. Beloc3zc4czw:2n wr iq7scfn4ane ,k 7: yi*5hzo*w) 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 ast cqvvox6tzb3g79 f)k1fv y+( a function of current, for $ V > 0 $, for the diode shown in(Fig. Below).

  An ac voltage of 120 V rms is to be recti2d ,,b5axgo ipkg*l vbnw6lz o3j*o* ;fied. Estimate very roughly the average current in the output resgwnopj* 3zbo ,abkv;2*,l d*6gx5lio istor $ 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 if7n ei/xm;h9v a the forward-bias voltage exceeds about 0.6 V. Make a rough estimate of the average currn/i xmv7;9ahe ent 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 w h9hrw7 z(c-tn-pa2im4g,m*/gwg uhis to be rectified with a full-wave rectifier (Fig. Below), where r- /-w iw h(7,wg hagnhmmp9*2utcg4z$ 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 between the base n/wde9 zpf,z 1current $ I_B $, the collector current $ I_C $, and the emitter current $ I_E $ (not labeled in the figure).

  Estimate the binding enf5iyh1.f1cv m ergy 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 a0-fb 8q1fgjwt-z d)b i57epson 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, tc3fv (;jfx1c/th+znspy g35 z he separation 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 bn91 lg bn5/j3ojv4vd with a weakly bound cubic lattice, with each atom connectb 3 dnln j4/oj5v19gvbed 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 an activation energy of 1.4 eV. When thf2xcb9 l4:fuw+wez g (e molecule is disassociated, 1.6 eV of energy is released. Draw a potential energy curve for this m:( gl x9c+4f2uwwbefzolecule.

  When EM radiation is incident on diamond, it is found that light with wavelengthub1s(w. bne -2i*heisfe.lh . s shorter than 226 nm will cause the diamond to conduct. What is the energy gap between the valence band and the conduction band for disuh1neb. .f.ieh ( *b2wli-seamond? $E_g$ =    eV

  A TV remote control emits IR light. If the detector on the TV set is/ju-d1z7dar u v 2rd/v not to react to visible light, could it make use o-uj71dazvrvd/ dr /u2f 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 ato )5yp 2 aud)35zowbpm.ysy 21i fjr(uzm in a doped silicon semiconductor, assume that the "extra" electron moves in a Bohr orbit about the arsenic ion. For this electron in the ground state, take inf zy5 o2djuyawz2.br)p ( yp3 i5mus)1to 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 radiationo5jvfg(st0;41ilp4 k y x : i7ael2ajn has wavelengths shorter than 1000 nm. For a solar cell to absorb ial;tpv1 2io4sn(jgj0 e:4 afk5 y x7lall this, what energy gap ought the material have? $E_g$ =    eV

  For a certain semiconductor, the longest wavelength radiation that can be absoq bn(-k;wulk;/.qya lrbed is 1.92 mm. What is the energy gk(-q qu/ak;nly. ;blwap in this semiconductor? $E_g$ =    $ \times 10^{-4}\ \text{eV}$

  Green and blue LEDs became available many years after red L0as+1rbsp,2t(b ifwa65 cx vtEDs were first developed. Approximately what energy gaps would you expect to find in green (525 nm)a 5vw01c tp(6bs s fiabr,t2+x and in blue (465 nm) LEDs?
the green $E_g$ =    eV
the blue $E_g$ =    eV

  A zener diode voltage regulator is 3oidvg93u nm, bqq r89shown 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?    $\ \text{k}\Omega \leq R_{\text{load}} < \infty$