What type of bond would you/8t bo;bital eca+) )11pztal expect for
(a) the $N_2$ molecule,
(b) the HCl molecule,
(c) Fe atoms in a solid?

Describe how the mol8hl cs4j m:o+aecule $ \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 :zx 0a7t8r3++yflf 5 ayaxl z2ygr0ta $ \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 dia: 5wer0zgu; 7ncfv1 uvided into four categories. What are they?

  Would you expect the molr+ cgrdtmy/l(10m k) p hngg+ pw(0-ovwoj+u/ecule $ \text{H}_2^+ $ to be stable? If so, where would the single electron spend most of its time?{yes|no}

Explain why the carbon atom (3n/g 5vhf omn:q857*aix :nx p( m ndxgs,1uto$ Z=6 $) usually forms four bonds with hydrogen-like atoms.

If conduction electrons are free to roi*ldg(6rr g0tmivr8a ;ovb9r7; u.fr am about in a metal, why don't they leave the metal entirely? *ol8;7(tf06a rgdgb vrirvrri9 . um;

Explain why the resistivity of metals increases with temperature whereas the9sf)g9tej ,fnxsp,+u resistivity of s, xps9f+9se ),u gjtnfemiconductors may decrease with increasing temperature.

(Fig. Below) shows a "bridge-type" full-wave rectifier. Explain how the c:e3lnv 5k dghntblj7 /+51 edeurrent is bte/ lnej1g dn7:d e55hk+v3lrectified and how current flows during each half cycle.

Compare the resistance of a pn junction diode connected in forward v3hp+h*v n y)-ancx:au-o5wh bias to its resistance when connected in reverse biasa3v+n c u-anv-*hpxy) 5hhw:o.

Explain how a transistor could be uct9d;v z12hc qcz*c qpp x0(6ssed as a switch.

What is the main difference between n-type anjk3p v n;sz3m(xat /of3y60gs d p-type semiconductors?

Describe how a pnp transistor can operate as an aeonb(c: :8clm mplifier.

In a transistor, the base-emitter junction and the base-collector junction arev -efzv pq 311b+qc/rn essentially diqpnzv3+ q1-vrf/1ce bodes. Are these junctions reverse-biased or forward-biased in the application shown in (Fig. Below)?

A transistor can amplify an elecqy40ycv2i9 rctronic signal, meaning it can increase the power of an input signal. Where does it get the energy to incyvi02c r94y qcrease the power?

A silicon semiconductor is doped with phosphorus. Will these 5 t425auwmjik:5 dxoc atoms be donors or acceptors?4uka52mx5j iwtc :od5 What type of semiconductor will this be?

  Do diodes and transistors obey O p,lrm)bi*in/hm’s law? Explain. {yes|no}

  Can a diode be used to amplify;u4f8b kk1rm0 jn7v gsx46rcb a signal? Explain. {yes|no}

  Estimate the binding energy of a KCl molecule by calculating the electrostat ; or1(pys ,w5x2dakqhic potential energy wxq ds5rho( w2kp;1a,yhen 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 4.9fiihl ,si5.rf5 ipvw h/5*qe(9imlb 43 eV. From the result of Problem 1, estimate the contribution to the binding energy of the repelling electron cloudsis ri*5hivi9i.lw mfh55bf e,p9q/ (l at the equilibrium distance $ r_0 = 0.28\ \text{nm} $. $PE_{\text{clouds}} =$    $\ \text{eV}$

  Estimate the binding energy of the6p jl:tmr;t,amcg :mdxd8b s4ki h 220 $ \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 -o,hqujolu0cbr - e; *:z/xgqcc u -1aoften measured experimentally in kcal per mole, and then the binding energy in eV per molecule is calculu*b-zl1/gc 0-o :c q ujoh;r a-exquc,ated 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 imfq oqmy,1 ((r0 1)ex srplsc7n the text for the states in the formation of txe(ps o1r(fc0l qrmm)y7q s,1he $ \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 quanti).r vuhqil .-crjw ++oty $ \frac{\hbar^2}{2I} $ has units of energy.

  The so-called “characteristic rotati n.zha4sl5 se:f+z 5pgonal 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 characterist0fcmwk( r6,e gic 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 separaar 4hw-o 7kq-ltion 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(yz165jpiv6vly :9lr ru)tz t molecule given that three successive wavelengths for rotational transitions are 23.1 mm, 11.6 mm, an(i)1zup:6 ltt9 v lrjvy6z5 yrd 7.71 mm. $r = $    $\times 10^{-10}\ \text{m}$

  (a) Use the curve of (Fig. Below) to estimate the stiffb c 8u)t: yfndt(qz2-efi *h)cf++ikc ness 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 ne),,yquab/,l/mc oy-yjjp lz .ighbor” Na and Cl ions in a NaCl crystal is 0.24 nm. What is the spacing between two nearest neighbor Na )yobqyp ./,yclmz aj/-u, j,l ions? D =    nm

  Common salt, NaCl, has l ocy 8pi :;.8+vhvllwa 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 r (nwsw/en.lcfc.m+ 9amg (d)is $ 1.99\ \text{g/cm}^3 $. $s$ =    nm

Explain on the basis of energy bands why the sw ,iyx4hu/pqci* mny g-ki8 6;odium chloride crystal is a good insulator. [Hinkcu4ni6w-qx8*,y im p y/gh;it: Consider the shells of $ \text{Na}^+ $ and $ \text{Cl}^- $ ions.]

  A semiconductor, bombarded with li 3(alofx3no .mckf 7n)ght of slowly increased frequency, begins to conduct when the wavekofl o(7)xafc nn.33mlength of light is 640 nm. Estimate the size of the energy gap $ E_g $. $ E_g $ =    eV

  Calculate the longestd(i4 b6s8hcmi1 b bv-x-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 conduch)95(gex q.wq kkblw8gncy gq,9hb+ 0tion 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 conductionngqeq y,qg +xkgk5 w(l98. bc)0whhb9 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 arev wk:4b /prhfw+/zj,k $ 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 sem .r6.4vm/() hgcssbvhv kcc6hs zk a,(iconductor is doped with phosphorus so that one silicon ask.hzav/s s,.chmv)v (b 4 c crkh(66gtom 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_{\text{doping}}}{N_{\ce{Si}}} = $    $ \times 10^6$

  At what wavelength will an LED radiate if made from a material with an energj -ise/in32;-,v r),o eairpevulrn 6y gai23vio e-pea) l-i,j n e /;n,vrsrr6up $ E_g = 1.4\ \text{eV} $? $\lambda $ =    $\mu m$

  If an LED emits light of+h8nq kl (5f;tz3o uq5b myot: 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 giv8iqo/d1wqu,g 4/ crs; ycyd/t e j-kd7en in (Fig. Below), is connected17q qrg -iyksyw; ue //o4/d, cjdt8dc 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 connected in series t:w jqq7y0.j tzo 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 functiif2qrs bq-.9z /z0eg5 x)khgu ayx4 j8on of current, for $ V > 0 $, for the diode shown in(Fig. Below).

  An ac voltage of 120 V rms is t,h6le5 ftm;qx o be rectified. Estimate very roughly the average curre,e;hq 65 xflmtnt in 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-b q)ljt-x febw2b3 ,4muias voltage exceeds abolm)x3-fu2 ,jqw te4b but 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 tp;a;o7mi:c xpo be rectified with a full-wave rectifier (Fig. Be p;mxi co:pa7;low), 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 relationship between the qc1y93r3, pb fz t3:ktrf0pvw base current $ I_B $, the collector current $ I_C $, and the emitter current $ I_E $ (not labeled in the figure).

  Estimate the binding ew8maxsi7 ;avcixq6,6nergy 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 kinetisrbn6 yd0wx)(+bj:ej c 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 io4yp:/ dajn8mp2:y cy xns 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 lattice, with nll zp+(hb-zyv0 w1.c each atom connectnyvzl. 0-h(lb 1zwpc +ed 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 activatir2:r w6a gvy;th;vurq ep 5p::on energy of 1.4 eV. When the molecule is disassociated, 1.6 eV of energy is released. Draw6r tyqvg5; u; :a:wr hr2vep:p a potential energy curve for this molecule.

  When EM radiation is inna418rvkx kdoz5 o.a4m,q y*ycident 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 the valence band and the conduction band for diamond? xqa8k ov4a yk,my* 5do4zn r1.$E_g$ =    eV

  A TV remote control emit3kg1 vi;le bm8k)jty thh7-k9s IR 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 ljkkeg-h 7 tmkvy i18h3);9tbits 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, ass 69e6xqvcjjz(y2(mz. ris. ( jze,oadom;6dp ume that the "extrz6 xq9 pjj 6j(me,merdvyooda6z.2s; ( (.zica" electron moves in a Bohr orbit about the arsenic ion. For this 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+-2fl mrczho,aov(* m wavelengths shorter than 1000 nm. For a solar cell to absorb allm,h-af(2czomr+v * lo this, what energy gap ought the material have? $E_g$ =    eV

  For a certain semiconductor, the longest wavelkx*;vwp/nha: v: 5dtu ength radiation that can be absorbed is :*w/v ptdu5xvn:k;ha 1.92 mm. What is the energy gap in this semiconductor? $E_g$ =    $ \times 10^{-4}\ \text{eV}$

  Green and blue LEDs became available many years after red LEDs were firsrv.a9j6u +vhit developed. Approximately what ei6a .rhvvju +9nergy 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 in (Fig. Below). Suppose thakiyx,z2ost:2fqmm hu)*p s z :7l1/g it $ 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?    $\ \text{k}\Omega \leq R_{\text{load}} < \infty$