What type of bond would you expecteq s/g2m.c n)x for
(a) the $N_2$ molecule,
(b) the HCl molecule,
(c) Fe atoms in a solid?

Describe how the molecuv gf.k 752tk,jmly1jax38hx dle $ \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 moleculea6)z(el m roh+ $ \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 intoua0o 7iz0: hgq four categories. What are they?

  Would you expect the moleculebo,24q4h lrxkf d k:0q $ \text{H}_2^+ $ to be stable? If so, where would the single electron spend most of its time?{yes|no}

Explain why the carbon atomimgm 2o :)bus g 1vis/-b3ru1sk/a h+p ($ Z=6 $) usually forms four bonds with hydrogen-like atoms.

If conduction electrons are free to roam aboutj dg6gxlfqm; 4/+ z1 cwzjo1-g in a metal, why don't they leave the metal engjcdmj -1g;x/q1zo+6 fg l 4wztirely?

Explain why the resistivity of metals incr l*s.)c vsd, dxa*6rcueases with temperature whereas the resistivity of semiconductorsxrulv cd6*c ,)d*. ssa may decrease with increasing temperature.

(Fig. Below) shows a "bridge-type" uo9upaee5 ubx pj*c1s-8w7 i 4full-wave rectifier. Explain how the current is rectified anucb9 u1i7 x awuee45*o8pps-jd how current flows during each half cycle.

Compare the resistance of a pn junction diode connected in forward dto,fk+.v.hkv4 t q3gxg/-fe bias to its resistance w/qfe- . t,o4vh+v3dxgfk g.tk hen connected in reverse bias.

Explain how a transistor could be used a(, w;lhiyna b 64x u:ie1y;qmvs a switch.

What is the main difference between n-type and 5v*y zm8ps pch( ks/i/pak:f(/qa nc3p-type semiconductors?

Describe how a pnp transistor 8v)l4: hf7a eiaxnw p be-.uj-s k.fs39k8zbu can operate as an amplifier.

In a transistor, the base-emitter jut 73yfd7kqo/76oy3jbn n/ ayunction and the base-collector junction are essentially diodes. Are these junctions reverse-biased or forward-biased in the application shown7t3ak3 /yoj7bf67uy n y/q dno in (Fig. Below)?

A transistor can amplify an electronic signal, meani h3) 2fci tvt7k82tctwng it can increase the power of an input signal. Where does it get the energy to increase the povfcc82t h237wt)itkt wer?

A silicon semiconductor is doped with phosphorus. Wilyfy/ijwyi 4:q pq/:j*l these atoms be donors or acceptors? Why qf*/qjiy j:i4/p:wyat type of semiconductor will this be?

  Do diodes and transistors obey Ohm’s law? Explain. {yes|no}ta/ i1 bbgo7mok/ 2e+ssvw-.v

  Can a diode be used to amplify a signal? Explain. {ye1zkwk70s-wjbt wey)+1 a edsup5s v 8/s|no}

  Estimate the binding energy of a KCl molecule l wz999r:nynud3 g t2vby calculating the electrostatic potential energy when then3ltu 992nyrw vz d:9g $ \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/t*9 8b8 oqb;tzwlxuo eV. From the result of Problem 1, estimate the contribution to the binding energy of q8wo ux lt;*to/zb b89the repelling electron clouds at the equilibrium distance $ r_0 = 0.28\ \text{nm} $. $PE_{\text{clouds}} =$    $\ \text{eV}$

  Estimate the binding energy of thw wf/c tgmh4e8;yfw57e $ \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 ls vlelc7gs *v6 -0k 5g/tiiy0then the binding energy in eV per molecule is calculated from t5lls-6 c ylgv7 i 0/ige*tskv0hat 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 oah uit2:(*hkto that in the text for the states in the formation of tku:(*a2 ihoh 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 quantitypn4 /c/xqitlx 0 ev69a $ \frac{\hbar^2}{2I} $ has units of energy.

  The so-called “characteristic rotational energlr3dl3)l+ki a; t c(oxjkji4ey7 k*c 7y,” $ \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 characteristicsf 3 dr aax;-7jih.wh7 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 ifg1- a)f4 j * v(btdqizm+n dtnz37i)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 given that three successive wav0:t)hidwnj 3v*4:x-x )m(od kishf xvelengths for rotxv 3)kv ddf4 )*:m ohxwith-ixs:(n0jational 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 stiif87jd8v u s.cffness 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 npzd 3e3.xkx k16vr 0rwb5noq 8eighbor” Na and Cl ions in a NaCl crystal is 0.24 nm. What is the spacing between two neareo53p.dbrnxver01 3z kkwx6 q8st neighbor Na ions? D =    nm

  Common salt, NaCl, has a density oj 5t /l:rrfj-o(gol w6f $ 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 w4ixfne0 :iz p01(cfgo6y 1zkdensity is $ 1.99\ \text{g/cm}^3 $. $s$ =    nm

Explain on the basis of energy bands why the sodium chloride crystal is a good b a-x p.**v/;tn:w esalyi4 9atp r7jlinsulator. [Hint: Consi*4x avt.atpne *wi-lp s/7y:b j9l;rader the shells of $ \text{Na}^+ $ and $ \text{Cl}^- $ ions.]

  A semiconductor, bombarded with light of slowly increased frequency, begins0 s 4rmgi y;d8vn znutbe2i-3; to conduct when the wavelength of light is 640 nm. Estimate r;0ndnyi 4v-28t mzugb e3si;the size of the energy gap $ E_g $. $ E_g $ =    eV

  Calculate the longeszswikhl.j j18/ya,:b t-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 isf-.18jnhcv1l kh ,rbj 0.72 eV. What range of wavelengths can a photon have to excite an electron from the top of the valencv, h r-18kljfbj n1ch.e band into the 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 are h4xv5s11ehx0 x6jeyw $ 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 phczo 2ycjw(3s ,h8)xh gosphorus so that one silicon atom inxo3csh2c8wh)z( ,jy g $ 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 2r -o1m/a4x,pe 1yc +p8sevjcuf : jasmade from a material with an energy gao1 yps2easp, j u/r: jc1+mcv8-a4fxep $ E_g = 1.4\ \text{eV} $? $\lambda $ =    $\mu m$

  If an LED emits light of wavelen.*r3ao9 i nuiogth $ \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. Belomcah1 s55kafyy2f q3 )w), is 5k )fs1aqah5m2yfc3 y 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. Below) is connectedc:*9*kjjt :w7bkcz ih1u3d yg 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 aseh 48ha-qlj 7/mw9c3 w.jzk iz a function of current, for $ V > 0 $, for the diode shown in(Fig. Below).

  An ac voltage of 120 V rms is to be rectified. Estima :h th:g5mam .gc*+be8ezo(at te very roughly the average current inm.mb+ez *og8 c ea:h5ahgtt:( 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 onl*qoo b3+) p :rsklhprcnt47 b-y if the forward-bias voltage exceeds about 0.6 V. Make a rough estimate of the average currp:)s hqctk7lro rb*3n4b o+- pent 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 ro trgn*r4,c )gectified with a full-wave rectifier (Fig. Below), where gn4c g)*or t,r$ 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 sotx9;; mp49necan2 9tgyg5a 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 the 2 lrrm;2cxq/bfvf+v 2$ \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-d+bg.rxh ;0aqx,jgojh7,e(m )al wm 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 )sono//z)u e dbetween 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 solimd9i36nlfb;i d with a weakly bound cubic lattice, with each atom connected to six neighi6ifd9l3m b; nbors, 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 activation energ0j qm)u: i8gayy of 1.4 eV. When the molecule is disassociated, 1.6 eV of energy is released. Draw imu ) a:jyq80ga potential energy curve for this molecule.

  When EM radiation is incidentti3db8gm+c6w 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 conductio+8miwbd6 3gct n band for diamond? $E_g$ =    eV

  A TV remote control emits IR light. If the d5ypjp0h3t ;w)q pk0qf z/jj i(etector on the TV set is not to react to visible light, could it make use of silicon /i5jkq;j)(fqp0z 0 3j tpyp whas 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 semi: zksup,vjoj o1697 ;n voz nv8:ycms8conductor, assume that the "extra" electron moves in a Bohr orbit about the arsenic ion. For this electron in the ground state, take i9ojv8sz8 6:7m,nuj nc :k ;svyovo1z pnto 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:dchrp 4c53l an::;p hw j9jrr than 1000 nm. For a solar cell to absorb all this, what energy gadwh r:rcn;arj:9lc35j hp4 : pp ought the material have? $E_g$ =    eV

  For a certain semiconductor, the longespy2kc/s-z.bqdp d) e8t wavelength radiation that can be absorbed is 1.92 mm. What is the energbke qs)./zy2pp8d-c dy gap in this semiconductor? $E_g$ =    $ \times 10^{-4}\ \text{eV}$

  Green and blue LEDs became available many years after red LEDs were first deniz :iwz: 7+ktbs : ecp2jbpv4 3w.i kpyv0u*5veloped. Approximately what energy gaps would you expect to find in green (525 nm) andb.iv+ z34pbiu k2: *5 iwptp ec7zsj:0nkv: yw in blue (465 nm) LEDs?
the green $E_g$ =    eV
the blue $E_g$ =    eV

  A zener diode voltage regulator is shown in (Fh8: bnuejty8/ ig. 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?    $\ \text{k}\Omega \leq R_{\text{load}} < \infty$