What type of bond would r j kj,5 rivje)a+hjcs(qr 2.,you expect for
(a) the $N_2$ molecule,
(b) the HCl molecule,
(c) Fe atoms in a solid?

Describe how the moleculetu bkbft *ijx*xd2jz 03v6-v 5 $ \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 moleculp7-b 6.n dty1xnc2+bsk- gouye $ \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 categories. s )ptai 1gr0r;(.u j 8gv)akvwWhat are they?

  Would you expect the mole5yo1b ,*jo czc t:a-ojcule $ \text{H}_2^+ $ to be stable? If so, where would the single electron spend most of its time?{yes|no}

Explain why the carbon atom56 xaoii w5g-qx 6p0dez:en6t ($ Z=6 $) usually forms four bonds with hydrogen-like atoms.

If conduction electrons5rd6z+k9j8m j 5agmg n are free to roam about in a metal, why don't they leave the met5m+6akjgn 5gr 8 9dzjmal entirely?

Explain why the resis gbx;is/* -pfupsv -s4tivity of metals increases with temperature whereas the resistivity of semiconductors may decrease with xf/pb4-v-usi* sgps ;increasing temperature.

(Fig. Below) shows a "bridge-type" full-wave rectifier. Explain how the currenqcx(i:clxf:m la)t,e p2 e3b :t is rectified and how current f baf)ee:,mix qc(:2 l:c x3tlplows during each half cycle.

Compare the resistance00jv/ *bxig fw of a pn junction diode connected in forward bias to its resistance when conw0g 0/vjxfi*b nected in reverse bias.

Explain how a transistor could baad o1 p20las-e used as a switch.

What is the main diffe* h3p9anmrq4rrence between n-type and p-type semiconductors?

Describe how a pnp to;bn3 n z.8/wvkucdyfb 11q,zransistor can operate as an amplifier.

In a transistor, the base-d:2 w -tknky(vm-0qaz emitter junction and the base-collector junction are e0mwnkk (:tv-d2 z -qayssentially diodes. Are these junctions reverse-biased or forward-biased in the application shown in (Fig. Below)?

A transistor can amplify an electronic signal, mean4orscgt4m4 1jf. wju;dqbi -8ing it can increase the power of an input signal. Where does it get the energy to increase the powuwfj 4rs-qoibg m1cj8.4t 4d;er?

A silicon semiconductor is dopg4v(f /ramq/*s noq5kfwei. +ed with phosphorus. Will these atoms be donors or acceptors? What type +f 5s/ qwf/gqoe(im * arkvn4.of semiconductor will this be?

  Do diodes and transistors obey Ohm’s law? Explain.(09ebygnv2;eqix: e m {yes|no}

  Can a diode be used to amplify a signx0 jjd4tq/vd4 b,-javsh)b10uu sq6bal? Explain. {yes|no}

  Estimate the binding energy 3s /.yy5 fm0-t2 ifuy* snifxyof a KCl molecule by calculating the electrostatic poten ./i yi yx0-ff3yt n5y*fssm2utial energy 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 KClq(k9b kwu6 sc0.;gkna is 4.43 eV. From the result of Problem 1, estimate the contribution to ;.qkbn 69kku(c 0wasgthe 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 enerq qb :1cpf-)bgd ,)vewgy 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 kcal per pwf (m/3(q8lw h 9tetzmole, and then the binding energy in eV per molecule is calculated from that result. What is the conversion factor in going fromqte8f( t(/l mpz hw9w3 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 k+vstf8z 4ggq8 c n-u+ w;b;b0w7 xlzgtext for the states in the formation of tb c0 k4zn wu+t7 gq-;+;l xg88bwfvgzshe $ \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 quantity22vc,we;ot m m $ \frac{\hbar^2}{2I} $ has units of energy.

  The so-called “characteristic rotational g5ufu/w f l;3buh(xv )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;rb(zbyq2j+ kxh*7r o 3wz;vo 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 sepa7 imrmq,tx./uczg6 e7 tq;hz1ration 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 leng8k 1 v5zwc-in 44njmw-iyx)kjth for the NaCl molecule given that three successive wavelengths for - wk4wny1j 5i8vzn x)mkcj4-irotational 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 stiffness c19icv8v /cqi7y hczdi :c6i s0ue// aponstant $ 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 aqj)p 6pswk5i irz j4+6nd Cl ions in a NaCl crystal is 0.24 nm. What is the spacing betweenp4 zk )6w+ qs6rp5iijj two nearest neighbor Na ions? D =    nm

  Common salt, NaCl, has a d qs(x;dcp) orjlc9h7 2ensity 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::fthf-1 wukfn z 1yqaw3.u +use density is $ 1.99\ \text{g/cm}^3 $. $s$ =    nm

Explain on the basis of energ gwdqvpz:fm 8id3 ; t8ncq)r/+y bands why the sodium chloride crystal is a good insulator. [Hint: Consider the wcdzq; v8td+ fp8 nm)r/3g:qishells of $ \text{Na}^+ $ and $ \text{Cl}^- $ ions.]

  A semiconductor, bombarded wbqnq 3q32o d3uhv5gb5ith light of slowly increased frequency, begins to conduct when the wavelength of light is 640 nm. Estimate the size of the energy ub53 qdno32 q5h v3qgbgap $ E_g $. $ E_g $ =    eV

  Calculate the longest-wavelength photon that can cause an electron in sic:mlu3ytn )mdwkb0g5y(s0 s 2licon ($ 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 is 0.72 eV. m+0 /syb.b xjxfvk;y2What range of wavelengths can a photon have to excitmvx. fbk+ jbs/y;y2 0xe an electron from the top of the valence 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 y l;0c b/1.vhzv b)xtd$ 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)1g*v3ez9hu-tvcuxfk)+6z ( u ku f lpiconductor is doped with phosphorus so that one silicoe ulv c-kgufz *phx f1( )vzk6)9uu+3tn atom 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 ad7g,klouf -7j;nk )u f:g 4j 1co5tabradiate if made from a material with an energy gap bngl5 -k;7fjaf,7tu) : duj4ogco1ak$ E_g = 1.4\ \text{eV} $? $\lambda $ =    $\mu m$

  If an LED emits light of wavelengtqsn. df 8yjn5u odh7(:h $ \lambda = 650\ \text{nm} $, what is the energy gap (in eV) between valence and conduction bands? $e_g$ =    eV

  A silicon diode, whose curreqc pe+0npu +)fnt-voltage characteristics are given in (Fig. Below), is connected i+ q+cpup0)nfe n 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 seriu 2 h:,n3sr8osir ose,es 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 cur3hb5(wn 4byopl j-vp3+6m glrrent, for $ V > 0 $, for the diode shown in(Fig. Below).

  An ac voltage of 120 V rms is to be rectifi frmcz* o9jl xan61)l0ed. Estimate very roughly the average current in the output resisto)no lz19m lxf0aj c*6rr $ 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 on1af+ ,eb f1/lilxmi ,wly if the forward-bias voltage exceeds abllfaw be/mxi+f11 ,,iout 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 rewlgdw:05m52xx7cu q 2d *z mjhctified with a full-wave rectifier (Fig. Be w* :75hmjmxud2w0q2 dc5xglzlow), 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 rela9 op)+xx4xct so )nw0u4k0prz tionship 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 ofmi *e6 zlr-7(;krkcez j:fcyt1l8. tv 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 energoqh6u4 p v)-m11ysfhk y 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 is about 0.27+9myu ok( fb/w 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 latx3o*5hdr,*. czg-s zjggi*fe tice, with each atom connected to six neighbors, each bond having a biije* .g5 hc*-, *rsfg dzozgx3nding 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 eV. When dui2 ,lr98dq zao8h+v/s b 6t)pgq8ybthe molecule is disassociated, 1.6 eV of energy is released. Dra /8zq6d8 2hi,v9lstyrq 8b ob dp)uag+w a potential energy curve for this molecule.

  When EM radiation is incidelqmb* q(.r.z ent on diamond, it is found that light with wavelengths shorter than 226 nm will cause the r .(zbe*mq lq.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 the TV set oh:gs66 mjp6p is not to react to visible light, could it make use of silicon as a "window" 6spmjh 6g6op: 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 i ik1 (vozmo*0a doped silicon semiconductor, assume that the "extra" electron moves in a Bohr orbit about the arsenic ion. For this electron in the ground si1 io oz*mkv0(tate, 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.va is*wrd0u kx (;c2q nm. For a solar cell to absorb all this, what qr(wxa2si0cvk *d.u ;energy gap ought the material have? $E_g$ =    eV

  For a certain semiconductoxfi/y g7cq 9h z-wye1(r, the longest wavelength radiation that can be absorbed is 1.92 mm. What is the energy gap 1/icy(qzx-y 7f w egh9in this semiconductor? $E_g$ =    $ \times 10^{-4}\ \text{eV}$

  Green and blue LEDs became available many ye 5+wk+ ,-ou5v jgyxiprars after red LEDs were first developed. Approximately what energy gaps would you expect to find in green (525 nm) and in blue (465 no u wv5jkigy-xrp5,++m) LEDs?
the green $E_g$ =    eV
the blue $E_g$ =    eV

  A zener diode voltage regulator is shown i7ny+ +2+7s b5vya jk;t t(6cxodkhcte n (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?    $\ \text{k}\Omega \leq R_{\text{load}} < \infty$