What type of bond would you expe5 ;7dv p,bices f+uxi1ct for
(a) the $N_2$ molecule,
(b) the HCl molecule,
(c) Fe atoms in a solid?

Describe how the molecule pu9hfcdy90w 9 (u3zek wsko8,ws:az- $ \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 moleculeal (9q nenha aqfzv(w.w089i; $ \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 caob+y (geg;1fy p 2x(bk2aw + p*jb;ivbtegories. What are they?

  Would you expect the molecuuvla:l:h6tb/ le $ \text{H}_2^+ $ to be stable? If so, where would the single electron spend most of its time?{yes|no}

Explain why the carbvq ,t:g krm1y9on atom ($ Z=6 $) usually forms four bonds with hydrogen-like atoms.

If conduction electrons are free to roam about in a met5o7 e31amn/bc7ovf b wal, why don't they leave the metal v1 7ecb3ab/fnm 57oowentirely?

Explain why the resistivity of metals in67 :: s eqyw4mur a2yqfiye+g+lcp 4k5creases with temperature whereas the resistivisqiewy+my:2+q u44:6 ep5cylkrg7afty of semiconductors may decrease with increasing temperature.

(Fig. Below) shows a "bridge-type" full-wave rectifier. Explain how tszn;sxz(y1 m//0j1 x8zdsa e the current is rectified and how current fls8 zm /0z ds( txsy/z1ne;1xajows during each half cycle.

Compare the resistance of a pn junction diode conneckz2s ,bk i n+rean,-f/ezfh8 n1d 6s)hted in forward bias to its resistance when connec,bhn- r/fne f6szzk kn)h s2i+,1da e8ted in reverse bias.

Explain how a transistor couk5mmu- 8 h ;-emz:gfheld be used as a switch.

What is the main difference between n-type and p-ty l5;n gazd d:fz / k;-pt+j-ugrw0pye3pe semiconductors?

Describe how a pnp transistor can ;kux m/icwm+n*f - 4kwoperate as an amplifier.

In a transistor, the base-emitter junction and the base-coll,t qq7m/ozvgf 9:h ub8ector junction are essentially diodes. Are these u:fb,hqz7ogv/ q89tm junctions reverse-biased or forward-biased in the application shown in (Fig. Below)?

A transistor can amplify an electronic sr3s;x wgsixlzd j.1k);,d6.j8 z d /madk0h mwignal, meaning it can increase the power of an input signal. Where does it get the energy to increasesr. .;,xk0d3majj z dw lz isk;gh)1xd/m68wd the power?

A silicon semiconductor is doped with phosphorus. Will these atvz m77avy02 f5;. 0watzlrda*+uff sy oms be donors or acceptors? What type of semiconductor will thi a2zzwm0*faayly. 5vvuf7t ;0 7dfr+s s be?

  Do diodes and transistors obey Ohm’s law? Explain. tugz7f +cy(y2j :w-sv{yes|no}

  Can a diode be used to am ,u8vi r4h1mq1j)gwja vs:udxey)a 7;plify a signal? Explain. {yes|no}

  Estimate the binding energy of a KCl molecur:sbxcs:w p/ pt.8m+yzwe+, yle by calculating the electrostatic potential yzs w ,ex: 8 r+.bppms/+tc:wyenergy 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 ons0;,0l fna dcf Problem 1, estimate the contribution to the binding energy of the repelling electron fld; , nsan0c0clouds at the equilibrium distance $ r_0 = 0.28\ \text{nm} $. $PE_{\text{clouds}} =$    $\ \text{eV}$

  Estimate the binding energy of thenbd6:wew8l /q $ \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,)bgzcr(/+i3r v op, 81 lr bgdat7nih mole, and then the binding energy in eV per molecule is calculated from that result. What is the conversion factor in going from kc7z /(l+,81,vgghc r r)tabiinb 3podr al 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 1vnw-cs bii /3(yg8 xjin the text for the states in the formation ofwb/(yiv1x3 g-s c8nji 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 quantity :.lmw /kly ,ea 8/wv3j2t nw0 2pwhidc$ \frac{\hbar^2}{2I} $ has units of energy.

  The so-called “characteristic rot /h.+imb d.dwyational 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.q+uo k;:tk7q svgt. -hrb:q e 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 k.- scvl 21exms3 dgwxch8 4;din 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 o)ex5fkc8a*r ltn58 i,qkxf6 wavelengths for rotational transitions are 23.1 mm, aot65ef )kr8k,q5*x f cnxl8i11.6 mm, and 7.71 mm. $r = $    $\times 10^{-10}\ \text{m}$

  (a) Use the curve of (Fihc p q93u b+ /yaal(z4iclf:xb +b.vq,g. Below) to estimate 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 Ni9x; 2z rsc8vbaCl crystal is 0.24 nm. What is the spacing between two srb2xvi9c;8 znearest neighbor Na ions? D =    nm

  Common salt, NaCl, has a dens+*cd mn mndl1sr6 r9llfkc2 )0ity 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 who t0rtzgaq06t/8- 4xjab1 3oqdpnkw 5d se density is $ 1.99\ \text{g/cm}^3 $. $s$ =    nm

Explain on the basis of energy bands why the sodium 8zecslr,b,27m,fxx n chloride crystal is a good insulator. [Hint: Consider8rsm ec,nxz l2,7fb,x the shells of $ \text{Na}^+ $ and $ \text{Cl}^- $ ions.]

  A semiconductor, bombarded with light of slowly increased frequency, begins to ktqfnxigqub7;: 7vv w,s)4 q3conduct whe37; tg7: i qvfbqsq,vuxk)nw4n the wavelength of light is 640 nm. Estimate the size of the energy gap $ E_g $. $ E_g $ =    eV

  Calculate the longest-wavelength pho3.v :ox c-;sm jft1eqeton 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 5ub 96bl8tmq hgo,d -lgermanium 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 conduction baob5b,6 hmtl - 8uqdgl9nd? $\lambda \leq$    $ \ \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 are 2f*ck:qovxtj 5aq-t- $ 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 semiconductpk s+hbb(;j- hor is doped with phosphorus so that one silicon atom inp+k(hsb -b;hj $ 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 mcmn n;qj 7)ym7h5 zcza8b+ 3nbaterial with an energy gap z ah)bqyjcbnnm7 3z;n8+ cm57$ E_g = 1.4\ \text{eV} $? $\lambda $ =    $\mu m$

  If an LED emits light of wavelengthkidh w))ha;igl /:7wd $ \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 (Fig.vfb6x ycf.n ro *413se Below), is connected inbr x 6 s3y41vfnfo*.ec 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 connected imj dlm:sdpwf h vm5 :/xk3(,k8n 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 curm1bptt/zqoe /2. u8,i)l* qe1ndwyil rent, for $ V > 0 $, for the diode shown in(Fig. Below).

  An ac voltage of 120 V rms is to be rectified. Estimate (9 o 8 n-wyw4p m:qlyp72bqplavery roughly the average current in t nap oqwly2y4 lpb7-:w9p m(q8he 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 tpfi .3 h;vrgx83uri6 only if the forward-bias voltage exceeds about 0.6 V. Make a rough estiif x3 vtihrr63.g8pu; mate 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 by htwn2k+9dm8 e rectified with a full-wave rectifier (Fig. Below),wh d 8t2myk+n9 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 relation.- a e.jhq2 lafr7prc.p)a r4fship 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 ro/hbg(8w-kt 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 translatio:+ ak*q tkbimo5:d-m-f.h c lhnal kinetic 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 separation distance between ions z3ulmht-25 p61ovb fg 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 laty q2:ghch +k58z bt:tltice, with each atom connected to six neighbors, each bond having a binding+ct bz gly:2q8 hk:5ht 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 0 dp -8*y3kxmbyn/tg jeV. When the molecule is disassociated, 1.6 eV of ene/8t *xy3bp- nykgm0dj rgy is released. Draw a potential energy curve for this molecule.

  When EM radiation is incz- ,nompkx3 t(ident 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 tzn-(3pk t,xmohe valence band and the conduction band for diamond? $E_g$ =    eV

  A TV remote control emits I5e-+bl l.yippquu 3: mv+ gxq bt88-jyR light. If the detector on the TV set is not to react to visible light, could it make use of silicon as a "window" with its energ:bppb x u3je8q-8qt5lm.vug-+ + ylyiy 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 doce4une7wl)v a.5/zy t,2zg o vped silicon semiconductor, assume that the "extra" electron moves in a Bohr orbit about the arsenic ion. For this electron in the ground state, take into account the dizv n)oe 754l/ga2uwy. v,tezc electric 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 wavelength9a ewhyy,1rbr ls0*5rs shorter than 1000 nm. For a solar cell to absorb all this, what energy gap ough yehras1*9b,0 rwyl5rt the material have? $E_g$ =    eV

  For a certain semiconductor, the ln25rrir+r zj0ongest wavelength radiation that can be absorbed is 1.92 mm. +r0zrr52ji nrWhat is the energy gap in this semiconductor? $E_g$ =    $ \times 10^{-4}\ \text{eV}$

  Green and blue LEDs became available many years a- /m /nhye vl)otp4cg7fter red LEDs were first developed. Approximately what energy g-ym/)n7 pl tvge o4ch/aps 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 show- uxjlvau (,a(,ta1oyn 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?    $\ \text{k}\Omega \leq R_{\text{load}} < \infty$