What type of bond would you expectxe8ou9 ss9a, f6bm ss6+n-n ei for
(a) the $N_2$ molecule,
(b) the HCl molecule,
(c) Fe atoms in a solid?

Describe how the mol9wx a0ixtczm lo/*v 9+ecule $ \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 gs0(p+o*6hwe vok r* bz8zw5u$ \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 foul6xct9 lmi 9y.r categories. What are they?

  Would you expect the molecule4 (v dpecz qpjoqqk:72z2k(u , $ \text{H}_2^+ $ to be stable? If so, where would the single electron spend most of its time?{yes|no}

Explain why the carbo+ dbkg*tm( kd.n atom ($ Z=6 $) usually forms four bonds with hydrogen-like atoms.

If conduction electrons are free to roam abg5rzz59 dvrk d o))tc1out in a metal, why don't they leave the metal ent5)r d9 cgr5zotk1vz) direly?

Explain why the resistivity of metals increases with tempe*8b53pf:j9uuivqi i + *nql jorature whereas the resistivity of semiconductors may decrease with incrp:ijbloq qui+ ij5n8 f*v9u3*easing temperature.

(Fig. Below) shows a "bridge-type" full-wave rectifier. Explain h5 cw,rcid8;dr ow the current is rectified and how current flows durinc8wr ir5;cd, dg each half cycle.

Compare the resistance of a pn junction diode conn 35u/diw qku7rected in forward bias to its resistance wikw q53u /7druhen connected in reverse bias.

Explain how a transistor could be used+v w8nv kq xc4 0zsgk i71yda4,(ft4hg as a switch.

What is the main difference between n-type and p-typ)0 v :jhc:td8bh6h2sjbsxzg8e semiconductors?

Describe how a pnp transistor can operate as an ampnld w2;vqc3j7 lifier.

In a transistor, the base-emitter j-jv/ **pvocspunction and the base-collector junction are essentially diodes. Are these junctions reverse-biased c j-*ppv*s/voor forward-biased in the application shown in (Fig. Below)?

A transistor can amplify an electronic signal, meaning it can inc ./pq xuh12h;xgwhgc2rease the power of an inwpc1q2gg u x/h;hh2 x.put signal. Where does it get the energy to increase the power?

A silicon semiconductor is doped with phosphorus. Will these atoms be donors or9wv*7wrewe0o-3 soe4- toe njas+ *dd acceptors? What type of semiconductor will this b+rojweatse4 n e*s7-woved 93d0* -ow e?

  Do diodes and transistors obey Ohm’s law? Explain. {ytuz*k/l:ng:wjrjz 7( - nl6cn es|no}

  Can a diode be used to amplify a signal? Expl3b vgu9 +b w0+cdcmlb1ain. {yes|no}

  Estimate the bindingdx,po- wn9 7-4a ua8g:c htexy energy of a KCl molecule by calculating the electrostatic potential energy whex9 : e7-x 8 oatch-yud4np,gwan 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 K)--2 kb 6vop s1fiypboCl is 4.43 eV. From the result of Problem 1, estimate th6-po v)byfi s-p k1b2oe 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 energy48 z zhe 9hs1ec8oxzm5 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 in kcp4,h/epa 8n 5zddz1uw al 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 bindinu,p 4ddhpze8/ 5wa z1ng 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 states in the formatpo5ng6* peh)xion of the)pngxp5*6h o e $ \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 quantityy-g/iazp9 k)nzp 2ln5 $ \frac{\hbar^2}{2I} $ has units of energy.

  The so-called “characteristich-7azwiwe /s 5 rotational 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 eneh avt,o.ac) pn6t.cw :kezm;,:u6tg ergy, $ \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 separa9 mfd2vezu75 dtion 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 give001zydo0kyk1aj n-q g9kgb.g n that three successive wavelengths for rotatik1qkdyjn0g0bg 9ozag .0 y-k 1onal 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 estima,du ,eg*)rpp:f p p4 5wu4pp-vpe(q+el+ztw ote 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 neighbor” Na and Cl ions in a NaCl crystal is 0.24 q-ctr wha9 0 4ma8mp/vnm. What is the spacing betweewar/a 0tp9m hm -8vc4qn two nearest neighbor Na ions? D =    nm

  Common salt, NaCl, has d- bkn tpv:42ra 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 density i)-l:v9i6m v 0dulu 7ejroi2 w+mte er:s $ 1.99\ \text{g/cm}^3 $. $s$ =    nm

Explain on the basis of energy bp6iztn v46l(0b5 llwo) -skpqands why the sodium chloride crystal is a good insulator. [Hint: Consider the sh5 pl)isqv z6w4t6-0pn okl(lbells of $ \text{Na}^+ $ and $ \text{Cl}^- $ ions.]

  A semiconductor, bomcm;t* n-fp.x 1k+gejzq6 )b wrbarded with light of slowly increased frequency, begins to conduct when the wavelength of light is 640 nm. Estimate the size of the energ p +f1jk;xm*r)c.we-b tqzn6gy gap $ E_g $. $ E_g $ =    eV

  Calculate the longest-wavelength photon that can cause an ele l-zg-1qr: gzectron 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 germanwr aly:sl1 4iso f/fxc*4gya7x 6cl,/ium 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 con6s, g:7c4soriwa yl f1x x//4ylfcla*duction 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 arium( .xm3hbxe .r;n7)r ikwe5e $ 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 3k c7tahdo ( :tap.b6kthat one silicon atom o(7kt3.t b6cdakpah: 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; 5otn2 cvy6vq an LED radiate if made from a material with an energy ga 2yqcot;nvv56p $ E_g = 1.4\ \text{eV} $? $\lambda $ =    $\mu m$

  If an LED emits lighdbmdh q9 a5m8uqd- ji j2c9a-.yk4x*at of 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 bx9k u o7f(k4egiven in (Fig. Below), is u 7ok (xbke4f9connected 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. Below) is conni/6lyqv yaw0ew (gz* u0s8m 0wected 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 f/b6 scw.i58u t)qipzssa:q o8unction of current, for $ V > 0 $, for the diode shown in(Fig. Below).

  An ac voltage of 120 V rms is to be rectified. Estimate very roughly thd;e)xyota:7yxs2 p h 7e average current in :xy7ps2h)ox;t e a7 ydthe 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 s.nglensu34k g,h8q 9t- sq a-eignificant current only if the forward-bias voltage exceeds u 4hlne s qtn-sgg9-eq,a8k3.about 0.6 V. 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 re m37mo t)ll 3fn gvv. ia*h5.lccfji.)ctifier (Fig. Below), cm)) l.i5avco7.f3f h jlim*. t3lnvgwhere $ 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 hgo5m8;h7lzg 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 ener, yi11fq2inov gy 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 -t(pb+rxhv- sor 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 separation distance between ions is about 0.27 nm. z4) uqp4j7 l5c4fjydk
(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,pw9(m*tkvmup , q g ,wemm87iice, with each atom connected to six neighbors, each bond having a binding energy8 mpmek(ugtq7 *w , 9,wimp,vm 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 vucioxptbaydw,rx 96)5n c nk7;3m)8of 1.4 eV. When the mole 7t)ib ruvc w9y 8,xoa56mnxpn d3)ck;cule is disassociated, 1.6 eV of energy is released. Draw a potential energy curve for this molecule.

  When EM radiation is incident on diamond,7.jxyl(ncgd*mhr*r (-7pi yk sfx6 7w it is found that light with wavelengths shorter than 226 nm wills7dxy .lf7*y7ixkhwmrj *-c (n pg (r6 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 kxfws24wf bh. * 5 04itoyvh3ethe TV set is not to react to visible light,sofkwei h0bw tf.y44 32 xvh*5 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 silicon semiconductor, assume that the "extlyo m8 wn8zcb(*. b)(huaq 7mara" electron moves in a Bohr orbit about the arsenic ion. For this electron in the ground c8bym7hwa(*lo)a 8m.bz(un q 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 1000 nm. Fo+af pgo34/dmbr a solar cell to absorb all this, what energy gap oubap/3+o4 df gmght the material have? $E_g$ =    eV

  For a certain semiconductor, the longest wavelength radiation that can be a js(;-zlgqeomefu9 2a ;j,)pf bsorbed is 1.92 mm. What is the enezemqlfepu aj)s-(2f; ,;9ojg rgy gap in this semiconductor? $E_g$ =    $ \times 10^{-4}\ \text{eV}$

  Green and blue LEDs bz76.e tz1rcrfx; 9)rkfgcz/ became available many years after red LEDs were first developed. Approximately what energy gaps would you expect to find incefr r9).bkc/z71r ;zgt z 6xf 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.c( zaq *,/ zmr. nx*dm7maefc $ 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?    $\ \text{k}\Omega \leq R_{\text{load}} < \infty$