What type of bond would you expect fodn msmcyii78.q 3)y)o r
(a) the $N_2$ molecule,
(b) the HCl molecule,
(c) Fe atoms in a solid?

Describe how the molecu)s8da,rje,i vle $ \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 molecule4 byc,gn+m* 8qkyy /bk $ \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 catelg x( ufi/-hf+o m;z;2snkis 6gories. What are they?

  Would you expect the moleculen ;sqf82eq1m bepvg7 0 $ \text{H}_2^+ $ to be stable? If so, where would the single electron spend most of its time?{yes|no}

Explain why the carbon atomth3c.ms,/o8d0* x y cwh vjuf(5 cu7viy0,oag ($ Z=6 $) usually forms four bonds with hydrogen-like atoms.

If conduction electrons are free to roam about in a mk; 7v nd1ip1jtetal, why don't they leave the metal entirely?pk1td j1n7 ;vi

Explain why the resistivity of metals inc k u.hk2pts2r*reases with temperature whereas the resistivity p2rk.*uk ths2of semiconductors may decrease with increasing temperature.

(Fig. Below) shows a "bridge-type" full-wave rectifier. Explain gi +x utlqzf rk2z4y5q(mxyd8.-yt1:how the current is rectified and how current flows lgxy yqdy qtztm-z rk+.2 1ix(8u5f4 :during each half cycle.

Compare the resistance of a pn junction diode connected in fygb4 qadhnu3/9 9f,qiorward bias to its resi, 4ibqudqa gny9h/9f3stance when connected in reverse bias.

Explain how a transistor could be used as a s gg 5)e8wf-fiqwitch.

What is the main difhd4c(nq . uwj0ference between n-type and p-type semiconductors?

Describe how a pnp transistor can operate as anbi+n 1g,jj ,bgh *sqg: amplifier.

In a transistor, the base-emitter junctio ka8,pg0m4 qr6uxhf(en and the base-collector junction are essentially diodes. Are these junctions reverse-biased or forward-biased in the application sho qx 0e8 g6mh(kur4,pfawn in (Fig. Below)?

A transistor can amplify a872xf e;zwf.yot e*d ,oldf.dn electronic signal, meaning it can increase the power of an input signal. Where does ;dwddo zf82.e7et .xlff *y, oit get the energy to increase the power?

A silicon semiconductor is doped with phdc,ycoq(x,+k h.y3np osphorus. Will these atoms be donors or acceptors? What type of semicondxc,d q,yo. ynpk(+h3 cuctor will this be?

  Do diodes and transistors obey Ohm’s law? E djk 45+9m ,;nyysogkyxplain. {yes|no}

  Can a diode be used to amplify a esv8o9 j5p6dy ue6p 5jsignal? Explain. {yes|no}

  Estimate the binding energy of a KCl molecule by calculating thsp.1- ht,dk4i il6nl xe electrostatic potential energy whenn4,it1kld 6h-ip s x.l 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 KClo,-lxy / x.aw:qev5ih is 4.43 eV. From the result of Problem 1, estimate the contribution to the binding energxl :x ye-a,qvh/ wo.5iy 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 hl6z2n 4c7 ml o*hhy9lthe $ \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 kcal per mole, and then +;y fev4h(ztzq2/lff 1n n .:q p6cyysthe bindin/v.1yz: +4n(q 2f psqyez ;6nlyfhtfcg 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 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 the text for the statud3jb rgr tpq;44+:kmze rd+, es in the formation ofrd4 ur;m dzq:,+bper gj k3t+4 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 quantitl5*h)kas:3t o7fayzn2ugd / jy $ \frac{\hbar^2}{2I} $ has units of energy.

  The so-called “characteristic rotational e26xh0o : uzqqrnergy,” $ \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 chaipzu; )ir ,g;t )ju(mgracteristic 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 c-nv,n .s7loz$ \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 givs2m os,ec 1p*ten that three successive wavelengths for rotational transitions are 23.1 mm, 11.6 mm, and 7,1s2cmse p*to.71 mm. $r = $    $\times 10^{-10}\ \text{m}$

  (a) Use the curve of (Fig. Below) to estimad.+cqe 5 o3n n4xu+irqhovw*u-p s8rx )+iu(zte the 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 n/b jr,eua3*(bd( foqteighbor” Na and Cl ions in a NaCl crystal is 0.24 nm. What is the spacing between j/et(br*3fo ub,(qad two nearest neighbor Na ions? D =    nm

  Common salt, NaCl, has a density;39 t n.shvth 85,yczx; flvro 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 densityx-6pst2s ws+3 le-idf*g2 jcqax 6d2lrw1q n: is $ 1.99\ \text{g/cm}^3 $. $s$ =    nm

Explain on the basis of energy bands why the sodium chloride crystal is a good ;j(+i2edmc akinca;+midj ke2( sulator. [Hint: Consider the shells of $ \text{Na}^+ $ and $ \text{Cl}^- $ ions.]

  A semiconductor, bombarded with light of slowly increased frequency, begins t .vblgibt8( c yb4ahfjx(n/f k2d 536ho conduct fi2. 6xny4 bdg h k/bthc l5vj38b(f(awhen the wavelength of light is 640 nm. Estimate the size of the energy gap $ E_g $. $ E_g $ =    eV

  Calculate the longest-wavelength photon that can cause an electron in siliconcul/+kdqk) 4i tf,em1 ($ 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 cxti q3:*ka-u 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 into the tx3-ick u q*a: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 aremff v*a ,goc6: $ 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 sewgzp 7jw::8s wet v,r2miconductor is doped with phosphorus so that one silicon atom inws, :e28:7tjp vwr wzg $ 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 4.hxxw 2-b hm:*rummhLED radiate if made from a material with an energy ga wm r:hmu.2b4xh *xhm-p $ E_g = 1.4\ \text{eV} $? $\lambda $ =    $\mu m$

  If an LED emits light of wavelenem 1/llo a9z/*dll :gzgth $ \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 (F3f7u5uink 3 bvbbq 3w2ig. Below),ni wvuu3k2b7b5bf33 q 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. Bel5x/f(ys eh: 2qd .mntaow) 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 *ax2n m.z)if6q pm:;/ mr6 xzb5imdvo $ V > 0 $, for the diode shown in(Fig. Below).

  An ac voltage of 120 V rms is to be rectified. Estimate very roucanw o2 k22exlc/x0/h ghly the average current in the output res02new 2c/ l2okahc/x xistor $ 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 for,ooj4 lz 8;hfhxk j94rward-bias voltage exceeds about 0.6 V. Make a rough estimate of thor844 j oj 9lx;,hfhzke 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 with2gv te qd3xgq)z)6s0 n a full-wave rectifier (Fig. Bel ev0 s)tnqdx3zg2qg 6)ow), 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 relationsh)ccof3) a asza)4fwn1ip 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 energy of,1dra*+b+eftj- nn gi 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 ab k- s6wcc b9miljdi2m4mjq;7* om6v v)out $ 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 distanceldj 0xr*,v7lq46 xkhf 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 cubicdf2z4nuu.rn onc*1ab/ f4 l)a lattice, with each atom connected to six neighbors, each bond havin d4c/2 1nf) u4zbn*urlan .aofg 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 isuo02pwzsjo4e1 s6 wn. found to have an activation energy of 1.4 eV. When the molecule is disassociated, 1.6 eV of energy is released. Draw a potential enero.sjoew40 up6 z1wns 2gy curve for this molecule.

  When EM radiation is r,g )2mqqjscwfb lzxg/ ,.z a+15:ase incident on diamond, it is found that light with wavelengths shorter than 226 nm will cause the diamond to conduct. What is the energy gf smzj.exz) a+g 2ql/rc, qsw g:,ab51ap between the valence band and the conduction band for diamond? $E_g$ =    eV

  A TV remote control emits IR light. If the vpsx4p m.-bphr.7c bq )vtk30 detector on the TV set is not to react to visible light,rqps.k)- vp3xm vhb 0p4c b7t. could it make 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 doped silfazo2ehe x qv hllc8r742l 8*+icon semiconductor, assume that the "extra" electron moves in a Bohr orbit about the arsenic ion. For thiqfe2+2vo 8hz8 cerl*ahxl7l4 s 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 has wavelengths shorter than 1:ouidk +6r e:y/ovby j i) 39h);puids000 nm. For a solar cell to absorb all this, what energy g;+)3udo bvu9p y yr :ek)jdiios6/ih: ap ought the material have? $E_g$ =    eV

  For a certain semiconductor, the longest wavelengthha*ww,o* seoy 5+ 7dad radiation that can be absorbed is 1.92 mm. What is the energ 5hoy 7dw a+d*saw*e,oy gap in this semiconductor? $E_g$ =    $ \times 10^{-4}\ \text{eV}$

  Green and blue LEDs became 6 iw5/pataa0kavailable many years after red LEDs were first developed. Approximately what ener5awat/pk 0ia 6gy gaps would you expect to find 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 g6ws p;;b:b mfin (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?    $\ \text{k}\Omega \leq R_{\text{load}} < \infty$