What type of bond would you expect fv,h9e(z ot+ bwor
(a) the $N_2$ molecule,
(b) the HCl molecule,
(c) Fe atoms in a solid?

Describe how the moletz7j dz 7v9mh:cule $ \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 pv7,x1 tcv lfe0b4cssb0x24 b $ \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 they?ve+h*iuj(, g1cykg- b

  Would you expect the mol*kg9dqncb(k h.hzdj8gkik 7+o; wu:.ecule $ \text{H}_2^+ $ to be stable? If so, where would the single electron spend most of its time?{yes|no}

Explain why the carbon atom y;6uksd3+ klge8fja-sn 52 w5opr8h m($ Z=6 $) usually forms four bonds with hydrogen-like atoms.

If conduction electrons are free to , k .lx(x.z(sf6s ,ty;pnx pndroam about in a metal, why don't they leave thez,nfpp.ln(; 6sx,xt(kx y d. s metal entirely?

Explain why the resistivitf0l gf0pikl1w 6g+n q1y of metals increases with temperature whereas the resistivity of semiconduq0ig+1ll 160kgnwf pfctors may decrease with increasing temperature.

(Fig. Below) shows a "bridge-type" full-wave rectifier. Expl,92ykzld+ytb jpf6 5; ; cgoetain how the current is rectified and how curren +td;kcj,;pft5gb o 29e lyyz6t flows during each half cycle.

Compare the resistance of a pn junction diode connected in forward bias*7bqfe0e6k k c to its resistance whce7bkfk60 q *een connected in reverse bias.

Explain how a transistor could be used as a switc5if5n g0 /wssxh.

What is the main difference between n-type and p6xq (bc)y8diqoe e (,u9nlfb/-type semiconductors?

Describe how a pnp transistor can operate as an am89/st +v qk o+mpa6xtcplifier.

In a transistor, the babzf:ht d,y q0wcxs60;se-emitter junction and the base-collector junction are esse , xztw yb0s6fd0ch:q;ntially diodes. Are these junctions reverse-biased or forward-biased in the application shown in (Fig. Below)?

A transistor can amplify aktvn kxl3zw m(c91cl+**l g)xn electronic signal, meaning it can increase the power of an input signal. Where does it getc+(zxwgllktm n9c ) *xl*1 v3k the energy to increase the power?

A silicon semiconductor is doped with phosphorus. Will th :l,q hg8ws cp qpgs70;db.d,uese atoms be donors or acceptors? What type of semiconduct.q,d;7,sgq s0:ucdgp l8wbhpor will this be?

  Do diodes and transistors obey Ohm’s law? Explain. {yex6:cz96e1fdz a kgo+es|no}

  Can a diode be used to amplify a signal? Explain. {yes|no}igx7b:dk 2h f:

  Estimate the binding energy of a KCl2v8xh(tykpk.0 u y.ajlolj4- molecule by calculating the electrostatic potential energy whe8koyj .j4uklph02xta .l -y(v n 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 e*e7wzbp sslv0pe(3ll6jxq :h:f 2 :fgnergy of KCl is 4.43 eV. From the result of Problem 1, estimate the contribution to the binding energy of th0l q7p6x*:sj(fws :le23eb zgfvl:phe repelling electron clouds at the equilibrium distance $ r_0 = 0.28\ \text{nm} $. $PE_{\text{clouds}} =$    $\ \text{eV}$

  Estimate the binding energy of thequh l ncgd4- w+t7,os. $ \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 experimentall aq9i )quj0pn7s*un8 yy in kcal per mole, and then the binding energy in eV per jpq87* u qnu9ai0nsy) 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 to that in the text for the stateu z p-4.3ssumjgs5 (krx0emt-s in the formation of th-pugx rjem0m -s u.kstsz34( 5e $ \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 quantity pbb z*(bb9o9qb b2,+e nswxe* $ \frac{\hbar^2}{2I} $ has units of energy.

  The so-called “characteristic rotationrvp jm;rw3u4 ;al 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 characteris4+ibddt/v n.sffa4x/ tic 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 separat5htv ) :sbhdwyn2 f14xion 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 length for the NaCl molecule given that three successdz0eh)8cm5e*n lx5fb0v (epgive wavelength)f ( emhd czpe5ln50ex*08 bgvs for rotational transitions are 23.1 mm, 11.6 mm, and 7.71 mm. $r = $    $\times 10^{-10}\ \text{m}$

  (a) Use the curve of (Fig. unaibb ;do,6*+ ht+ .x jiii1yBelow) to 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 and Cl ions in a -k4mxmm/ rsie+e6 w h9d3i;xjNaCl crystal is 0.24 nm. What is t96md4+ w /xjimim khxrs;e- 3ehe spacing between two nearest neighbor Na ions? D =    nm

  Common salt, NaCl, has a density ovb 9) boidj8(jf $ 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 density is y9 gso t(e lmh/*pz0x- i5 rgf/;wp0 vi,ti/xo$ 1.99\ \text{g/cm}^3 $. $s$ =    nm

Explain on the basis of energy bands why the sodium chlorid q/suecj9ppf)6 tspnt:6w.x2e crystal is a good insulator. [Hint: Consider tpfctpnuqs9p6t.x2:s) /we 6 j he shells of $ \text{Na}^+ $ and $ \text{Cl}^- $ ions.]

  A semiconductor, bombarded with light of slowly increased j6 ;e*q.mklvs frequency, begins to conduct when the wavelength of light is 640 nm. Estimate the size of the energke l6mqv .;js*y gap $ E_g $. $ E_g $ =    eV

  Calculate the longest-wavelength qb4 h,yls9b:c 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 betwee4qbe /ve (t7csn valence and conduction bands in germanium is 0.72 eV. What range of wave7 (esqc4et/bv lengths can a photon have to excite 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 luw-9dc o3 )xq$ 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 thd/2;v uohvq ( +)v/ml-chuhq zat one silicon a) zdqvu v+uq/h2vh;(o/h-cl mtom 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 radiate if made from a material k7iod0d f* leqrt(+,twith an energy gap *( 0q+kio,fl7d tedrt$ E_g = 1.4\ \text{eV} $? $\lambda $ =    $\mu m$

  If an LED emits light of w vl-l 7 .epw j),,1gcewp3j )vmmmfg7bavelength $ \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 characterw7l// 3hy yhx)p:ufbz6a1hr i istics are given in (Fig. Below), is connected in series with a battyrb7apy iu3 /h/6l)hf h1zw :xery 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.d3 m-clxk,o u, Below) is connected 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 funbnhid sy) zmn-7*r6a3 ction of current, for $ V > 0 $, for the diode shown in(Fig. Below).

  An ac voltage of 120 V)el lp0)aa2g)llfn z 3agb7+u rms is to be rectified. Estimate very roughly the average current in the output rebn+)0ul3falga7 gllp)2 ) aezsistor $ 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 currp2 4d+oatx ,r)obq2 1jku.gkdl9rwh 1 ent only if the forward-bias voltage exceeds about 0.6 V. Make a rough kgr.9or,+q u 2dp1dwahk 4b 21jotx) lestimate 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 ful4cqa3y. ik 2lfl-wave rectifier (Fig. Below), where qiack43l f.y2$ 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 1 kyeci9kfra/ 8g4re. 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 q16bzzh cz**a$ \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 kinetik;t0y5by 6 pfac energy 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 u ;ex vof s*v 2)y+z)f2lueju7about 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 withc +xhbs16 o)nk a weakly bound cubic lattice, with each atom connectehxos+ bc) k6n1d to six neighbors, 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 activ :ekk sq1l6 rf2cg3gx6ation energy of 1.4 eV. When the molecule is disassociated, 1.6 eV of energy is released. Draw a potential energy cur3grk6k :s lgfq 612xceve for this molecule.

  When EM radiation is incident on diamond, it is found tha kxvqvbms *7unn*04r5t light with wavelengths shorter than 226 nm will cause the diamond to conduct. What is the energy gap between the valence band and tkq*xsb 0u 7vn5*r nm4vhe conduction band for diamond? $E_g$ =    eV

  A TV remote control emits IR light. If the dqbm*e8l d7c g gs/ed2(etector on the TV set is not to react to visg*g87 c/dlbsmd q( 2eeible 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 atom igu0+::kke wir5liw /u a:9ckf0- wcq kn a doped silicon semiconductor, assume that the "extra" elect -i:u w kc9fr 0kgkw5ul: +k:/aciwe0qron moves in a Bohr orbit about 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 than 1000 nm. For a solar c4w o97vpz oqh2e1cxk(ell to absorb all w7k4xvo9 h1pz(c o 2eqthis, what energy gap ought the material have? $E_g$ =    eV

  For a certain semiconductor, the longest wavelength radiation9g0ej41 4az ta. -j8fq vzi qhx2l8wiamtc:*w that can be absorbed is 1.92 mm. What is the energy gap in this semiconductor? jai wq.at-201h i:ja 8lxm4t 9qcwz8zgf e4v* $E_g$ =    $ \times 10^{-4}\ \text{eV}$

  Green and blue LEDs became available many years after red Livlu 0jw.l)qfw n3.xg91vk)wEDs were first develo)un. fiv 9lwj0)x3w1 qwgkv .lped. Approximately what energy gaps would 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 is s98 *qy.tzk fezhown 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?    $\ \text{k}\Omega \leq R_{\text{load}} < \infty$