What type of bond would you expect6 ak0i2d;xujv da y67y for
(a) the $N_2$ molecule,
(b) the HCl molecule,
(c) Fe atoms in a solid?

Describe how the molecct;ep y8xby0+ule $ \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 -j7kle h:vps( $ \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 in0 5tyce i 5o1b +dzjyhzrdegs)w4-r5-o )j/svto four categories. What are they?

  Would you expect the molk:+1x 4pq(zjm fauv/bk a9w,vs. +htcecule $ \text{H}_2^+ $ to be stable? If so, where would the single electron spend most of its time?{yes|no}

Explain why the carbonde 6v4uqd 6hwz5 r*;9fvud-ip atom ($ Z=6 $) usually forms four bonds with hydrogen-like atoms.

If conduction electrons are free to roa (svau0zfeenc34ot 19q 7mi1on0( im lm about in a metal, why don't they leave the metal entileqo1mc( 70fmu tv9 s(4o1nz e 3ai0nirely?

Explain why the resistivity of metals 72 a*o qzsnu)us3 xq89g;qzdfincreases with temperature whereas the resistivity of semiconductors may zqs z q7n*) 92xud3 uq8s;ogafdecrease with increasing temperature.

(Fig. Below) shows a "bridge-type" full-wave rectifier. Explain how the curr4 l: bmt;ha7eient is rectified and how current flows during each hl74;a bmt:ei half cycle.

Compare the resistanc iky0-eap0* k8jpu ik)19 zugze of a pn junction diode connected in forward bias to its resistance when co 1z -*uz98jp)ak 0eg0ipiukk ynnected in reverse bias.

Explain how a transistfwk/*k4fm0k vk5015/ yfqqd e a(p bjvor could be used as a switch.

What is the main difference between n-type and p-type semiconductors?1djbkp fyqcs9k .7,0p

Describe how a pnp transisv ewsb 47o+rge5 9xlr 9i )pndzw7rj-*tor can operate as an amplifier.

In a transistor, the base-emitter junction and the base-collector junctio85 wrybvr;c w(n are essentially diodes. Are these junctions reverse-biased or forward-biased in the application shown in (Fig. Below)? 5yvw r8;cwrb (

A transistor can amplify an electronic signal, meaning it can increase the pponx *v,n1 -llower of an input signal. Where does it get the energy to increasx,n-llpov 1* ne the power?

A silicon semiconductor is doped with phosphorus. Wil:6 s s,vjs0efymk ):kfl these atoms be donors or 0 sfvskke,my)sf:j6: acceptors? What type of semiconductor will this be?

  Do diodes and transistors obey Ohm’s law? y8 3 nbs:puv8qExplain. {yes|no}

  Can a diode be used to-ba)r1hq 4sm b amplify a signal? Explain. {yes|no}

  Estimate the binding energy of a KCl molecule by calculat/*hco;;-q3,pw tdw8b qerzzr- p/y moing the electrostatic potential energy when the c;-;ythorw z8d//q,zo bpe3p*wrm q-$ \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 4.43hk tq(awf8uv14 z 5+tg eV. From the result of Problem 1, estimate the contribution to the binding energy of the repelling electron ta8z1( h5tkw4fqu g+vclouds at the equilibrium distance $ r_0 = 0.28\ \text{nm} $. $PE_{\text{clouds}} =$    $\ \text{eV}$

  Estimate the binding e8lenesg, re hvh0re51e3 4qzkr,b -qp4+.l xenergy 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 perpyvz.h q kk57+k ogt,1 mole, and then the binding energy in eV per molecule is calcgkz. o thpv1kkq y5+,7ulated 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 in the text for the states in the formation77 ooxw i 4f;y. ufy(flz5p1eb yxpf15o47(uow be.fyif zl7; of 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 quantittof-lu0cl romrrn( 7 b,74y6oy $ \frac{\hbar^2}{2I} $ has units of energy.

  The so-called “characteristic rot(g8 8 rbt9orrzational 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 characterwi5ynh; 1; x-*stnfpb/nvu2 bistic 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 i6. k eyrb7az 79no.brdn 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 lengthldxeo,wwd-6/9ax zjdt *(rf6 for the NaCl molecule given that three successive wavelengths for rotational tro6 z(ddxfdlw* ,a- w9r 6jte/xansitions 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 constant+wq5vlfc 9t*c ,.aooz $ 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 “nearuci;0sno;ki o:bj- r 5est neighbor” Na and Cl ions in a NaCl crystal is 0.24 nm. What is the spacing between two nearest uo:i-;bkj i;0nro c5s neighbor Na ions? D =    nm

  Common salt, NaCl, has a dens0;n xa414dc da bbcpw/ity 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 densitygke5es t5 j)0m8too*m -u,wfw is $ 1.99\ \text{g/cm}^3 $. $s$ =    nm

Explain on the basis of energy bands why the sodium chloride crystal is xc)alx lq-)s k )2jdv(cl4 x.sa good insulator. [Hi)kcs2-cjxl l)vxa q)(s l4x .dnt: Consider the shells of $ \text{Na}^+ $ and $ \text{Cl}^- $ ions.]

  A semiconductor, bombarded with light of slowly increased freque vmq: omvux dfg9zm5)q4gw5:*ncy, begins to conduct when the wavelength of light is 640 nm. Estimate the size of the energy gap z:4mgfqwd5g 9*x oumq v): v5m$ E_g $. $ E_g $ =    eV

  Calculate the longest-wavelength photon that can cause an electron in silicon 3uo :v(haq0nr j4,vvo($ 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 5 .vtwct-uu0kconduction bands in germanium is 0.72 eV. What range of wavelengths can a photon have to excite an electron from the top ofv-0tu tuk wc5. 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 ar tdx,wmmha /h/o29/0 rb)bg jje $ 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 phosphorus so that one silico- pnj7cy8, mekn aykp-c7e mj,n8 tom 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 axf. ;/fy / hkkcn.egq-0:+kyt ie0aqm material with an energy gap .eyg kfq0a/h+;:im/xk 0efcy t.-kqn $ E_g = 1.4\ \text{eV} $? $\lambda $ =    $\mu m$

  If an LED emits lighgu q(* (vbzka8)8gud gt of wavelength $ \lambda = 650\ \text{nm} $, what is the energy gap (in eV) between valence and conduction bands? $e_g$ =    eV

  A silicon diode, whoe s*ppk*,t t3ose current-voltage characteristics are given in (Fig. Below), is connected in series with a battery andke*,st *o3 tpp 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 conn zryl) x41j.xvected 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 as a function of current, forxz04 qyp7 po.vjexqd f+2-7 qu $ V > 0 $, for the diode shown in(Fig. Below).

  An ac voltage of 120 V rms is to be rectified. Es)a buu/on+ctjsr9 .4s timate very roughly the average current in the output resia/ brn9jo4) s.+utuc sstor $ 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-bivue 9r* 3utmzqckz-2gu9hl5 * as voltage exceeds about 0.6 V. Make a rough estimat*zqrt 2u -l*mek9v9h5 u 3zgcue 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 rectified with a full-w rc*k3xpj;du 1ave rectifier (Fig. Below), wrx;1j p u3k*dchere $ 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 t0jit lstb);3hykrw3 82kac ;ihe base current $ I_B $, the collector current $ I_C $, and the emitter current $ I_E $ (not labeled in the figure).

  Estimate the binding energy o7 r.g6fe) +gtkc.fx(g yv(yhf2nnq9 qf 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 energnk -, dcewn3l*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.svs229vo zirv7xgt36(r f w )2tbo2z e27 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 m/+k3.+w, ywwwmibyr cubic lattice, with each atom connected to six neighbors, each bond having a binding energy of wm. r+y+wymikb,w /3w $ 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 ha5 d3 )(.2 ve ln2ffmnsda89gmejb ldh)ve an activation energy of 1.4 eV. When the molecule is disassociated, 1.6 eV of energy is released. Draw a potentialm(b22d 5lvhl)f fd sgem39a e8)dnjn . energy curve for this molecule.

  When EM radiation is incident j/+f wg.gzu7 mb)erkb,dcl ;od6f0f2 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 cong.do72/ rcm flzjf0b;w,b)dg u efk+ 6duction band for diamond? $E_g$ =    eV

  A TV remote control emits IR light. If the detector on the TV esdim2,;- jhgset is not to react to visible;,g m hdjie-s2 light, 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 h-3ihf9 k xr7latom in a doped silicon semiconductor, assume that the "extra" electron moves in a Bohr orbit abo7kh h-9 il3rxfut 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 wavelengths shorter thando,cw r. x.y0n 1000 nm. For a solar cell to absorb all thiynxd.c.0 wr ,os, what energy gap ought the material have? $E_g$ =    eV

  For a certain semiconductor, the longest wavelength radiation tbyqba nrt*s(bro ,(- inzhq9; 3 yj8(what can be absorbed is 1.92 mm. What is the energy gap 9qq*ry((ra-3 zn yh(wb ;jtb, n bi8osin this semiconductor? $E_g$ =    $ \times 10^{-4}\ \text{eV}$

  Green and blue LEDs became available many years afte(n9kfv 7ve/fj x fj+-yr red LEDs were first developed. Approximately what energy gaps would you expect to find in green (525 ny(jf+/vv-7xnf9 fek jm) 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)c) kv ,*p4(lkoessps *. 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?    $\ \text{k}\Omega \leq R_{\text{load}} < \infty$