What type of bond would you expect -qm orsax*) f, hy2g7c 5r9qdmfor
(a) the $N_2$ molecule,
(b) the HCl molecule,
(c) Fe atoms in a solid?

Describe how the molhi/h,g e vecz4/en 7o2ecule $ \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 molecul5 :cd*w8cpcwq37ki5t 6ghwu pe $ \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. What are ok z7if ,ccl)ew;f,q;y+rrgml gd);6 they?

  Would you expect the molecu+n* )y;p-5ambkh 9aif9obhsa le $ \text{H}_2^+ $ to be stable? If so, where would the single electron spend most of its time?{yes|no}

Explain why the carbkhxy6: ar,.eza6ys2gon atom ($ Z=6 $) usually forms four bonds with hydrogen-like atoms.

If conduction electrons a,h gulih:k -t0re free to roam about in a metal, why don't they leave the meuki,h g0thl :-tal entirely?

Explain why the resisk0+ajgr 0thcc z9) l+vtivity of metals increases with temperature whereas the resistivity of semiconductors may decrease w 9a k+cv0z +tr0ghc)jlith increasing temperature.

(Fig. Below) shows a "bridge-type" full-wave rectifier. Explk7kbg-ok, 98tpn3 cydf v.jf/si 10xn ain how the current is rectified and how current f vp3 xky /jcof9gbk-.d7,n0sft8n1i klows during each half cycle.

Compare the resistance of a pn junction diode connected in forward biash kh/ ;f3rzab* to its resistance when connected ia;krfh zb *3/hn reverse bias.

Explain how a transistor could be used as asok 1* pz /.pfs -kvu8jlt,u6t switch.

What is the main difference between n-typif: z/*jj)x qvg26 efae and p-type semiconductors?

Describe how a pnp transistor can operate as an amplifier. s z+gt.+ez41wgdz e,u

In a transistor, the base-emitter junction and the base- qgl2 ,3b:(fu2*r9erf; oztsu cre7oqcollector junction are essentially diodes. Are these junctions reverse-biased or forward-biased in the application shown in (Frger2st*eu; :uq7zo rb(2 9clo f3f,qig. Below)?

A transistor can amplify an electronic si b 62 - /8bolmk3q36eqrubfalsgnal, meaning it can increase the power of an input signall6q lm 3uqo/bef8ka2r3 s6bb-. Where does it get the energy to increase the power?

A silicon semiconductor is doped wi )-kbepix*:o h8hr+zi th phosphorus. Will these atoms be donors or acceptors? What type ofhe x8i)r+h: -pk*iozb semiconductor will this be?

  Do diodes and transistors obey Ohm’s law? Explaqr,fb* 5 zem v(2s01mmn xanq;in. {yes|no}

  Can a diode be used to amplify a signal? 0vli k:tug8 lcm65 l8 i0hmmb(Explain. {yes|no}

  Estimate the binding energy of a KCl m o66ww/n4x.icw 7utcs olecule by calculating the electrostatic potential energy when th6wccww 67un4xits o/. e $ \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.w s/ 0d t7d6rb43r9 kop*qawegmjp/l; From the result of Problem 1, estimate the contribution to the binding energy of the repelling electron clouds at the equilibrium distance jge4pwr /bw6tqr09o3;/dma*7d kpsl $ r_0 = 0.28\ \text{nm} $. $PE_{\text{clouds}} =$    $\ \text{eV}$

  Estimate the binding energy of 7mn hm9v ;cmv/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 ofjbw1my x * +g1ccljioey r6is,(f3+m8 1zrt 0tten measured experimentally in kcal per mole, and then the binding energy ir8* i6mrj t 1+iy(b3z+c1eylfsc wog ,0 jtx1mn 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 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 t, w1ozpm) h6 9l20fype.rhkfto that in the text for the states in the formation of thw zflko0,pr) p1f e. 2h9tmhy6e $ \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;mekd6x:yo 75w9prx h ty $ \frac{\hbar^2}{2I} $ has units of energy.

  The so-called “characterf (;(wj ea2 p8o8hm,u ed+ g:wv4fxwzuistic 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 characterirzt b,4vw7qt * n d / +gdmp;n.e(gvro5op8f7estic 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 ajb3zb/gw(uiwrvud 8 :+a ew53toms 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 thatn +js+ju+b nlxv h-t3; three successive wavelengths for rotational transitions are 23.1 mm, 11.6 mm, and 7.71 mm. nsuj ;-+ jvnxth3++l b $r = $    $\times 10^{-10}\ \text{m}$

  (a) Use the curve of (Fig. Below) to 55k:ngaq.n 6h7ygue x 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 a7-u *qrawtseowv h9.2 nd Cl ions in a NaCl crystal is 0.24 nm. What is the spacing between two nearest neighbor N.vw w*e 7 -at92rqushoa ions? D =    nm

  Common salt, NaCl, has ;q if*7 qfypytvy 89k8a 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 densi u1+z74. *sumyqnrhhfty is $ 1.99\ \text{g/cm}^3 $. $s$ =    nm

Explain on the basis of energy bands why the sodium chloride crystal is a ( +t gmgtd, -h5+hqmxfgood insulator. [Hint: Consider the shellf dmmx-g( ,5tg+thh +qs of $ \text{Na}^+ $ and $ \text{Cl}^- $ ions.]

  A semiconductor, bombarded with light of sh8-( g:fl3,acsqili elowly increased frequency, begins to conduct,cfi3(alheq s:-gl8i when the wavelength of light is 640 nm. Estimate the size of the energy gap $ E_g $. $ E_g $ =    eV

  Calculate the longest-wavelength photon that can cause an ele bd9i tt17b0ri0ocwu9ctron 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 condu 2njki zv) pefl djf)49+u2k2nction bands in germanium is 0.72 eV. What range of wavelengths can a photon have to excite an electron from t 2)vfu 4ilfn9dnjpe zjk +2k2)he 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 areipe d4t)ma0v2j)j 8fw $ 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 dopo;-n ak5sn xoy-s4l9 med with phosphorus so that one silicon a9 n5-;akloxosn4-ysmtom 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 an LED radiate if made from a material with an en +ceg r7q 3kr*6(lbtykergy gapk6r qgkt( b*el3c 7+ry $ E_g = 1.4\ \text{eV} $? $\lambda $ =    $\mu m$

  If an LED emits light of wavelength8- i aod6r.hhclim0k)z ld f)( a14els $ \lambda = 650\ \text{nm} $, what is the energy gap (in eV) between valence and conduction bands? $e_g$ =    eV

  A silicon diode, whose current-m*c ry9*vzq ; 7i 3ph)ugmwg+uvoltage characteristics are given in (Fig. Below), im9*mhqgc+yupr3; i *v) uzgw7s 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 connected in series to a 4gyox s nfg;yps:0tg+ri8o9 :)hot5g$ 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 fub5tsg h;kev jr2b03;x 9xfh5jnction of current, for $ V > 0 $, for the diode shown in(Fig. Below).

  An ac voltage of 120 V rms is to be rectified. Esti 3eus )mp(bbeg y7(e(tmate very roughly the average current in the output resistse(p)b (t 7gu3eym(be or $ 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-bias voltage u,2dcx,irql*dnu5vbz: l2 e3v8i o, iexceeds about 0.6 V. Make a ro2u 32v5eux drd,q*iz ,ni i,l cbv8ol:ugh 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 o1wq 21-l zc t4h5ddufto be rectified with a full-wave rectifier (Fig. Below), w1t15d -z uoh4qwdl2 cfhere $ 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 betu iaw87m(i/bxh/ah 88mjfe g/ween the base current $ I_B $, the collector current $ I_C $, and the emitter current $ I_E $ (not labeled in the figure).

  Estimate the binding en8,xji5)6 fp( i hpzfavergy 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 jo7f(g,h la,v zm2e,9hks:nu7 g9mw xenergy 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 KF9q: vnhw4 fb5vuxb6 ;s, the separation distance between 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 solid with a weakly bound cubic 5)qk5 3smvaqilattice, with each atom connected to six neighbors, e5 miv)aqqsk3 5ach 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 energy of 1.4 eV. When thy -*qgzzp ;o,je molecule is disassocia;g -* pz,yzoqjted, 1.6 eV of energy is released. Draw a potential energy curve for this molecule.

  When EM radiation is incident on diamono9 p,ho4:m2 j: 2llsndcl qi/hd, it is found that light with wavelengths shorter than 226 nm will cause the diamond l o9sjh2:2 cmloi q4 ,nl/ph:dto conduct. What is the energy gap between the valence band and the conduction band for diamond? $E_g$ =    eV

  A TV remote control emits Iwg(m 9tghfn0dn5( 5f v(pe2kh may( v-R light. If the detector on the TV set is not to react to visible lighte(9ah5 ygn2nv mhm -(5kdfpw (fg(t0 v, 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 semicondu ol0 w vxcd3x7zr)r)r(ctor, assume that the "extra" electron moves in a Bohr orbit about the arsenic ion. For this elecvr0r xxd)w( 7lcor z3)tron 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 wavelengths m otisz q*(72gshorter than 1000 nm. For a solar cell to absorb all this, what energy gap ought the material hav2izqt ms*g7 o(e? $E_g$ =    eV

  For a certain semiconductor, the longest wavelength radiation that can be absonb yrtqp2k8i;, 6zwyt k nt3.4rbed is 1.92 mm. What is the energy g;t t.4nyn,bi6w kzqrp3tk82y ap in this semiconductor? $E_g$ =    $ \times 10^{-4}\ \text{eV}$

  Green and blue LEDs became available many years after red LEDs wen+q9++e8b0 n-nb in dghq+ t)auxhb; ure first developed. Approximately what energy gaps would you expect to find in ahbn+ u 9tiq0nh-gbx)q++nu8ned b+;green (525 nm) and in blue (465 nm) LEDs?
the green $E_g$ =    eV
the blue $E_g$ =    eV

  A zener diode voltage repdpr+m 7; v6migulator is shown 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?    $\ \text{k}\Omega \leq R_{\text{load}} < \infty$