What type of bond would you expect forbnppf3no+l 3b qd4i 57rj+6rz
(a) the $N_2$ molecule,
(b) the HCl molecule,
(c) Fe atoms in a solid?

Describe how the molecu8nde -u*+8c cn bso b)hqri6+wle $ \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 moleculvf4 ovscz+xce 0plx,sw)0ubfkr (05 2e $ \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 categori (grzr30qtdm z86xs (ies. What are they?

  Would you expect the molecu srh7h bjy l vdd1z4)o/u:)n7ole $ \text{H}_2^+ $ to be stable? If so, where would the single electron spend most of its time?{yes|no}

Explain why the carbon at c1)3kwea+sn kom ($ Z=6 $) usually forms four bonds with hydrogen-like atoms.

If conduction electrons are free to roam about in a metal, why don't q1kt,h9 i-ai l,yzdt+3dgps.h w v a+2they leave t l t.hpz3 ,+1 hii,y2dk-9gwvt d+aqashe metal entirely?

Explain why the resistivity of metals increas94g-ai1vz lpx fi0fj3es with temperature whereas the resistivity of semiconductors may dec0f4jiv z9f1gap- 3 lxirease with increasing temperature.

(Fig. Below) shows a "bridgq;mq )c 4n3gkvk m.sc3e-type" full-wave rectifier. Explain how the current is rectified and how current flmk.m) kqsc v3; qng4c3ows during each half cycle.

Compare the resistance of a pn junction diode connected in forward bx60usg t72p u a3;pldkias to its resistance when connected in reverse0g 2s3puu dlk;6x7pt a bias.

Explain how a transistor could be used as a y89uiy 3a()pvmc glyw: 82oifswitch.

What is the main difqjtfj:7dd q)f8q2pzd* i,hp/ference between n-type and p-type semiconductors?

Describe how a pnp traqmz+p* c 7prp5kkoqqx6rria/ ;t8j4 + nsistor can operate as an amplifier.

In a transistor, the base-emitterzfvwojtd c oi71yy/+0lls :/+ junction and the base-collector junction are essentially diodes. Are these junctions reverse-biased or forward-bia +1/zocs:jfowyl0 +v dt/iy 7lsed in the application shown in (Fig. Below)?

A transistor can amplify an electronic signal, meadq eb/7xka f 5is2h92cning it can increase the power of an input signal. Wher7/ is2e9cfab5x dk2hq e does it get the energy to increase the power?

A silicon semiconductor is doped with phosphorus. Will these atoms z5rd+kedcv)7 be donors or acceptors? What t+75vk edz drc)ype of semiconductor will this be?

  Do diodes and transistors obey Ohm’s law? Explain. {yic8pg0baa +s o 17lj5ly.,eav+ qme7 ues|no}

  Can a diode be used to amplify a signal? Explfptcv9t)y+kx) f0 jg3ain. {yes|no}

  Estimate the binding energy of a KCl molecule by calculating th1acaet 5os,nh z8.1b te electrostatic potential enee a 1htason8bz,t.1 c5rgy 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 +ssw/sw -0:dg shczy9result of Problem 1, estimate the contribution to the binding energy of the repelling electron clouds at the equilibrium:0sh+-/ yss swd9cgwz distance $ r_0 = 0.28\ \text{nm} $. $PE_{\text{clouds}} =$    $\ \text{eV}$

  Estimate the binding ener .lsk)yihx n25lzz 2t9gy 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 i8 -h1nvg bf k3s-hh6lan kcal per mole, and then the binding energy in eV per molecule is calculated from nf-g3 v1kh6lashh8b - 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 simila8l x ,b8we(l(l 9imoowr to that in the text for the states in the formation elwil (l,8xmb(9oo8 w of 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 quantity9lgab*xg yf99d 1 vq(y $ \frac{\hbar^2}{2I} $ has units of energy.

  The so-called “characteristic rotational energy,(gj q,) 6scy.7tuhcwi 1 sn-cz” $ \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 characteristihaqg c,1jemrn)v 9zwz,i5p--:j r9t bc 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 in the wp :c,jj5,o(;dehc *b+gd kkx $ \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 NaC apu7pzw;017-e .bmqiy7v pchl molecule given that three successive wavez -y aiwp7.h0 p7 qvecub7;p1mlengths 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 the stifxjj+zz*psx-/d 8n h( edflp6 *fness 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 i7ier.m.zdm j+a(q31g* m rgd “nearest neighbor” Na and Cl ions in a NaCl crystal is 0.24 nm. What is the spacing between two nggr.mdq d7+.imj( ie1a m3*r zearest neighbor Na ions? D =    nm

  Common salt, NaCl, has a den5to )ggykv6g f+-8sq(n o3nuq sity 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 densitydxvdg(q6-mblc6/ao 4 q8m 2jm is $ 1.99\ \text{g/cm}^3 $. $s$ =    nm

Explain on the basis of energy bands why the sodium chloride crystal is a goofg 6 m v./v0anmtb);dfd insulator. [Hint: Consider the shelvn)fm g;.d/m t 6b0afvls of $ \text{Na}^+ $ and $ \text{Cl}^- $ ions.]

  A semiconductor, bombarded with light of slowly increased frequency, begins ;gjf.u h jhu2q2lp8rtt5*t x- to conduu2f- 2hgx.qt8pj rlt 5u; htj*ct when the wavelength of light is 640 nm. Estimate the size of the energy gap $ E_g $. $ E_g $ =    eV

  Calculate the longes hi0m7i5 wx.u 0qxx6qyt-wavelength 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 conduction bands in germanium is 0.72 eV. Whap* f/hrckss 4i:q6 h+ft range of wavelengths can a photon have to excite an electron from the top of the valence band into the condfs/ :+6k chpisrq4 f*huction 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 arebrt:cwc gerw6s)2q1 -om8 xp - $ 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 phospd1bvf d *br, 1fu1xy1;nt, ewyhorus so that one silicon arv1ff ndy,e1*yb1 1,dtu bxw; tom 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 energy 92xu2pld 5d z 2abc1jn2cuz4ugap22n4zau 2ljc 9xd2ucpb 15dz u $ E_g = 1.4\ \text{eV} $? $\lambda $ =    $\mu m$

  If an LED emits light of wavelen jp2no:/ q*f8g-gvh: r /epgohgth $ \lambda = 650\ \text{nm} $, what is the energy gap (in eV) between valence and conduction bands? $e_g$ =    eV

  A silicon diode, whosedt(f b .(lp2fh current-voltage characteristics are given in (Fig. Below), is connected in series with a battery andt(2 . (lbhpffd 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. Belowpqi(pkm- d7cc .-za 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 as a function of current, for t vh,gx 87pb/k$ V > 0 $, for the diode shown in(Fig. Below).

  An ac voltage of 120 V rms is t 0s /pnwn(r/gho be rectified. Estimate very roughly the average current i//gw(npr s nh0n the 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-bi8 gzaah*ruf 12rw7ffm3xcl* )as voltage exceeds about 0.6 V. Make a rough estifxu 32ah* zrar*mf 7fcg1l)w8mate 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 rectifihc,/ocw(sy; 5q7vz0fa( s h uued with a full-wave rectifier (Fig. Below), w ( ,zhcwy(;u/ f5qvousc0has 7here $ 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 eqst6wbl h8.c bj u3gh7r/:3ff*.iw q evuation for the 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 energmi1znyg7ahw7r ;wi2( 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 kinetic energy of an atom or molecule is a1 w9t4p ou)dgqm0i*h dbout $ 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 0.27 ni. di-(r4jjufm.
(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 cz, ++ s*- 3u asm+jg7wdzxtltkonnected to six neighbors, each bond havingak-ltz x 7 +z,td+sm+sg w*j3u 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 hxr+t/rs5jl.1ezog7 t; aeka, ave an activation energy of 1.4 eV. When the molecule is disassociated, 1.6 rsaex/ 1;5l+,oka .etztrg7 jeV of energy is released. Draw a potential energy curve for this molecule.

  When EM radiation is incident on diamond, it /j,7rhhujg ywx12 ) mqis found that light with wavelengths shorter than 226 nm will cause the diamond to conduct. What is the energy gap between the vamwu,xjr j7h/hgy )q2 1lence band and the conduction band for diamond? $E_g$ =    eV

  A TV remote control emi0 atz*v/+k2tl/cz1 s3jaw cf rts IR light. If the detector on the TV set is not to react to visible light, could it ma+* ck a/1zl2jwstar /3 c0tfvzke 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 do e:v.6uw a)nicped silicon semiconductor, assume that the "extra" electron moves in a Bohr orbit about the arsenic ion. For this electron in the ground )n.wv6u ei:ac 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 wavelengths shorter than b 0( j9wksi7g(lhc3 5wk5+t mcm/iwti1000 nm. For a solar cell to absorb all this/j kti+(gw li mw9m(5w 5t7csk3chib0, what energy gap ought the material have? $E_g$ =    eV

  For a certain semiconductor, the lonj mhdpc344s q)vm r3z3gest wavelength radiation that can be absorbed is 1.92 mm. What is the energy gap in this sem d3)z rch 4sv4jp33qmmiconductor? $E_g$ =    $ \times 10^{-4}\ \text{eV}$

  Green and blue LEDs became available many years after red LEDs were fqjpiu8*xqa-t9xx -c7 i)( mlmirst developed. Approximately what energy gaps would you expect to findc7-uxt)-q 8xmp mijqi9 a(x*l 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 shown in (Fig. Below). Suppose that jk+0u j2hw8hw $ 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?    $\ \text{k}\Omega \leq R_{\text{load}} < \infty$