What type of bond would you expect for x bis;jahhny35v 6qi,+e*-:pt3jh e5xc0po u
(a) the $N_2$ molecule,
(b) the HCl molecule,
(c) Fe atoms in a solid?

Describe how the molec/a0b hi;bjy m/8ycg69bso c q.f /f1nzule $ \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*plbgql l*kh* 9 ,hk p6g*pco27di,0qwigt (f $ \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 arevp9wl2)pt1 gs they?

  Would you expect the mol c+e8a9ndrpa .ecule $ \text{H}_2^+ $ to be stable? If so, where would the single electron spend most of its time?{yes|no}

Explain why the carbo28 ok4)p ( jzsqliqp2jws: ag4n atom ($ Z=6 $) usually forms four bonds with hydrogen-like atoms.

If conduction electrons are free to roam about in a metalqh z8;(ubusytg 4l xw +4-;vfj, why don't they leave the metal entirely4jyf+qtgx 4;w -z( ub8 lush;v?

Explain why the resistivity of metals incrv4bb +8 boev jzl;7b8l vm/zy01h +2snl uf:rfeases with temperature whereas the resistivity of semiconductors may decreasvn r01 mf 7olvuyfb8:e+bbzs l ;+4zbl/8v2jh e with increasing temperature.

(Fig. Below) shows a "bridge-vs9 fh 0nq.8motype" full-wave rectifier. Explain how the current is rectified and how current flows during ea09.qhn8 smfov ch half cycle.

Compare the resistance of a pn ju1 9lqvwdm z2q;nction diode connected in forward bias to its resistance whq zdq ;w9mvl12en connected in reverse bias.

Explain how a transistor could m07 f2x 3ta2;rat dapcbe used as a switch.

What is the main difference between:yd.9/57olqc y8z e (1wkyivs+gxwqr n-type and p-type semiconductors?

Describe how a pnp transistor can operate as 1pw/ ejd,nn u8hp+rfiaao9fe4 u-)x1an amplifier.

In a transistor, the base-emitter junction and thejb0 1ger;io .y base-collector junction are essentially diodesjib. 0gy re1;o. Are these junctions reverse-biased or forward-biased in the application shown in (Fig. Below)?

A transistor can amplify an electronic signal, meanig7,.5tk2qx /4 wkl) yawcjubyz ;n;fy ng it can increase the power of an input signal. Where does it get tzg/),abk wflkqy5. yxtn42 cu7 yw ;;jhe energy to increase the power?

A silicon semiconductor is doped witl: :xbu:2py/ h,i mrk w.m/dloh phosphorus. Will these atoms be donors or accepho rm y:2x/p.u wikml:b,d/:l tors? What type of semiconductor will this be?

  Do diodes and transistors obey Ohzeb(oj0b 0u 6ym’s law? Explain. {yes|no}

  Can a diode be used to amplif2n4c+ct oal.i38 zdd0d) aw dry a signal? Explain. {yes|no}

  Estimate the binding energy of a KCl molecule by calculating thr()e( e: f-o3fqfga yep7q d-ce electrostatic potential energy whendepr7:fq 3 (-c -g(yoeqae) ff 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 isvdxdq. 6iu7n0tue ;9r 4.43 eV. From the result of Problem 1, estimate the contribud qr0ix7u n.vue6;t d9tion to the 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 energy -b v.vf4qm:dbu-i1qs 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 experimentallye - ,0pde xekzji;(lzd(qh+m5 in kcal per mole, and then the binding energy in eV per molecule is calculated from that result. What is the conversion factor in going from kcal per mole to eV per molecule? dk(, +mx;( 5jzd0 lqehzeipe-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 textv u-o;bh5,dhy for the states in the formation of b,hdh 5yu -ov;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 quanti4:tr e(fv rz0 .p j)ul3zj*fmlty $ \frac{\hbar^2}{2I} $ has units of energy.

  The so-called “characteristic rotationcn mdh7*2/ stdal 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 rotational energy, 2u og,hat3602niq spf$ \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 in n4hnc x8s n4tszr/12 hthe $ \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 giv,p c+0xvi3j3bx( dv mdwa)ad8-hzx0 ien that three successive wavelengths for rotational trw jcvia0bdx+-mx8z)( d ,phidv033x aansitions 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 consi oicpa9( wy1+tant $ 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 “a1mtwx, lm:rk.:d f8h nearest neighbor” Na and Cl ions in a NaCl crystal is 0.24 nm. What is the spacing between two nearest neighbor N8:1h: tmdf.l,wxmk a ra ions? D =    nm

  Common salt, NaCl, has tr zt daj4a*562fa+b ta 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 for0lfpxy:xh/43mdofzq)y.w0npq ,;g 3f bkn.c KCl whose density is $ 1.99\ \text{g/cm}^3 $. $s$ =    nm

Explain on the basis z(tct.- qw(k w:d*mu8j ke2vmss 1z/aof energy bands why the sodium chloride crystal is a good insulator. [Hint: Consider the shells ofad2j z-swme1kvtm cs kzw (.qt*8 :(/u $ \text{Na}^+ $ and $ \text{Cl}^- $ ions.]

  A semiconductor, bombarded with light of slowly increased r :4l0u ynzmxb.v+ g4nhiih/. frequency, begins to conduct when the wavhnli04./ ivn gy.r bhxm 4:u+zelength of light is 640 nm. Estimate the size of the energy gap $ E_g $. $ E_g $ =    eV

  Calculate the longest+1o mmjk, *r6aa jr8kv-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 bandq u9 y+12qmxdjx hh*5ds in germanium is 0.72 eV. What range of wavelengths can a photon have to excite an2x1 x* m9duh qdj+qyh5 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 v6z tnhaer4kvu:lb9h3 (b;) b$ 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 semiconductvd** ; yhl9b8jvef0w qor is doped with phosphorus so that one silicon atom in ed9l w yq8*f0 *vhbjv;$ 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 mat1tju+( 3jpulf(hw) fterial with an energy gap (uj)uh lf1(w3pt f+jt$ E_g = 1.4\ \text{eV} $? $\lambda $ =    $\mu m$

  If an LED emits light o;:f vb:2kdmoof 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 given in (F- :(q ipelh p*; i5nkf8r;gcxo(/lqw pig. Below), is connected in series with a battery andlpf:k -pq/ (x ;pqg 5ncwhrilie8(;o * 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 and -gf cpmg;48 9x7bli $ 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 functionygy)pugfnzhgku fs 96akz7e: :6 3 8b: of current, for $ V > 0 $, for the diode shown in(Fig. Below).

  An ac voltage of 120 V rms is to be rectified. Estimatedb578jvgpq9 di uma7)5kkxz2 very roughly the average current in g7)k5xjia5vq 8bp 7 m2dukz9dthe 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 forwadd +c1/ neb+s.irb9 ferd-bias voltage exceeds about 0.6 V. Make a rough estimate of the average currentfr /e1+e9sdb d+b in.c 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 rectifi4-jg -ukif 8lted with a full-wave rectifier (Fig. Below), whf4ul jtk g8-i-ere $ 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 base zu dd xa+q:31b sae/p1current $ I_B $, the collector current $ I_C $, and the emitter current $ I_E $ (not labeled in the figure).

  Estimate the binding enere-sul(b*c2 ,xbjhri6k /wgw :gy 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 energy of an atom or molecule is abammay5mvp-l:o7f:tc 1ah7fr71 w5lnf, wm/ oout $ 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 be0z/qamzju5f; f6 7rrxtween 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 lattice, with each c(4hb9bixceo:hdr7 *-y zq9a atom connected to six neib9yxcq:(b7o-caeih*9 4h rd zghbors, 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 tod 7iqio:jsc b:*ur+j1 have an activation energy of 1.4 eV. When the molecule is disassociated, 1.6 eV of energy is released. Draw a id:*b1+i ucoqs7:jr jpotential energy curve for this molecule.

  When EM radiation is incident on diamond, it is found that light with wav-j i0h:pnhl pjdg/s r//(;qia elengths shorter than 226 nm will cause the diamond to conduct. What is the energy gap between the valence band and the conduction band for pdjgl:/q snji(;h/r-h/0a pidiamond? $E_g$ =    eV

  A TV remote control emits IR light. If the detector on the TV setf,*sc m :0kb6h nl(rf aa2x8hh is not to react to visible light, could it make use of silicon as a "window" with its energy fk2s mh6lhanc,08 bhax*r(f: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 atpj8gpse -b)r753ibr f om in a doped silicon semiconductor, assume that the "extra" electron moves in a Bohr orbit about the arsenic ion. For this electron in the ground state, take in83 e-rb pgbjris5)7 pfto 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 radiatio:/q7nelx1 furn has wavelengths shorter than 1000 nm. For a solar cel u:efx17 /nqlrl to absorb all this, what energy gap ought the material have? $E_g$ =    eV

  For a certain semiconductor, the longesl +yrk4rx*yrxgd) x 65t wavelength radiation that can be absorbed is xkydr4*xr 6l)+5rx yg 1.92 mm. What is the energy gap in this semiconductor? $E_g$ =    $ \times 10^{-4}\ \text{eV}$

  Green and blue LEDs became9y3f y0qjim r1 available many years after red LEDs were first developed. Approximately what energy gaps wo9r3f1 ym iyqj0uld 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 isy 0ft y5y:*f*cr mdph) 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?    $\ \text{k}\Omega \leq R_{\text{load}} < \infty$