What type of bond would you expect fs5 fiv 4ip;hk:2a: basor
(a) the $N_2$ molecule,
(b) the HCl molecule,
(c) Fe atoms in a solid?

Describe how the molecule gpj+1k c,jz9cqad g);$ \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 molecule0a 9)qwwt;+ 8qfvo vhw $ \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 qnhqy0 gagakw-105d5g; c su+they?

  Would you expect the molecule31ra aj h/2sgoa/v9rfle6lx/t , e*is $ \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 jvh4dcyt4-9v ($ Z=6 $) usually forms four bonds with hydrogen-like atoms.

If conduction electrons are free to rou.:+nq/l gqofam about in a metal, why don't they leave the:ql/qng o.uf+ metal entirely?

Explain why the resistivity of metals increases with temperature whereas thzlw;n z 7fpgg(yw9 71he resist(py1ggl;wf h97 7z wznivity of semiconductors may decrease with increasing temperature.

(Fig. Below) shows a "7xolr67ig*x9 -7 jo zt5wmjxr j-ao4uy5d tn:bridge-type" full-wave rectifier. Explain how the current is rectified and how current flowsj5 x t7z 7wj6o 9uo4:gm5ydlxtn *x7ra ji-r-o during each half cycle.

Compare the resistance of a pn junction diode connected in 9bctgp1:+w5 aai 9jpk forward bias to its resistance wg1 ak: 5jtaip+bp9 9cwhen connected in reverse bias.

Explain how a transimqb ),wdvtuiq8g c2z+o f 7*4vstor could be used as a switch.

What is the main differenqsk: 7syc+p 1gce between n-type and p-type semiconductors?

Describe how a pnp trantf8g( z3 ze9desistor can operate as an amplifier.

In a transistor, the base-emitter junction and the base-collector junctehmvg-8yn4 a(lsklxm e p0)87ion are essentially diodes. Are these junctions reverse-biased or forward-biased in the application shown in (Fig. Belo074ns v)- lxhy8ame m(el8gkpw)?

A transistor can amplify an electronic siggm s 4d,+*l ,3amyesoznal, meaning it can increase the power of an input signg+ms3,y*s, mo4 ale zdal. Where does it get the energy to increase the power?

A silicon semiconductor is doped with phosphonz7eil;ssz. z)52v j ,z/hulxrus. Will these atoms be donors or acceptors?vs2h zexilzu 7 zs;j l/)5n.,z What type of semiconductor will this be?

  Do diodes and transistors obey Ohm’s lawj5e q s2:*3f4yyomye l? Explain. {yes|no}

  Can a diode be used to amplify a signal? Explain. nc5 /hsk1l*vb {yes|no}

  Estimate the binding n e3(aqft60ama vx qs*: u ,d9h:m2oiv-syjh/energy of a KCl molecule by calculating the electrostatic potentia d3q-y9 /xq,shnvv(u6f e 0 ha:*ms2aijmt:o al 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 KCl is 4.43 cxvn/tovkq 3f.),af + eV. From the result of Problem 1, estimate the contribution to the binding energy of the repelling efv . nk vqoa3,/c+xf)tlectron clouds at the equilibrium distance $ r_0 = 0.28\ \text{nm} $. $PE_{\text{clouds}} =$    $\ \text{eV}$

  Estimate the binding energy of w3v*npnj, d. o7 web:qthe $ \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 1s 7f2 :vja-zwdyc wjm6t8artso 6 ,7lper mole, and then the binding energy in eV per molecule is calculated from that result. What is the conversion factor in going from kcal peovm,rt 7l8y-wcj1 26saz s wd7 tf:6jar 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 rhi r7 ww g.mk3m ;q)yxd*,7yaformation of) wyq3.rgkh,w a7d m*y7 imxr; 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 quantity/g(vhgws28 gx $ \frac{\hbar^2}{2I} $ has units of energy.

  The so-called “characteristic rotational energy,”b+ m -p5yvk5r)5chevc $ \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 rotatiq z8+ 7vp oozgpz0dq,ugcj0k( ;p )e1wonal 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 in the 0j/sk;pdeezo+6 ao;gc7i j m0$ \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 b,v+vn eb) qz+three successive wavelengths for rotational transitions are 23.1 mm, 11.6 mm, and bz) evn v+q,+b7.71 mm. $r = $    $\times 10^{-10}\ \text{m}$

  (a) Use the curve of (Fig. Below) ; u)qtd u1*zwdto 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 iob6 d+s58 i 1(macp h+mjbtc0zons in a NaCl crystal is 0.24 nm. What is the spacing between two neap 56 cs(+0zdmibbom8t +c 1ahjrest neighbor Na ions? D =    nm

  Common salt, NaCl, hab0lnrnt rn;.;h,a8dynmp 6v;j i)5 u gs a 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 densuxm6l 5229 twnc8 puho8t3hciity is $ 1.99\ \text{g/cm}^3 $. $s$ =    nm

Explain on the basis of energy bands why the sodium chloride crystal is a good f fdxprh7dr,yi,rdti62g 89+insulator. [Hint: Consider the shells otyfr8fr,2dh p +gr ix6i,d9d7f $ \text{Na}^+ $ and $ \text{Cl}^- $ ions.]

  A semiconductor, bombarded with light of slowl,4piftj :g*m zy increased frequency, begins to conduct when the wavelength of light is 640 nm. Estimate the size of the enerf i,4 j:zmp*tggy gap $ E_g $. $ E_g $ =    eV

  Calculate the longest-wavelength photon thatto/s*rby (b)v ;gfj 89i ktzk.1 hp:wh 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 bands in germjm 79u ;c+u 2cbbgm2axanium is 0.72 eV. What range of wavelengths can a photon have to exci22j cm;9c gm7xbba u+ute 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(0z.8)3f(,hiixi p;qyrz bqhkfqfc 2 $ 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 r qat wq..lx(ru:0 iv 0e-n49owi(quj one silicon atom ioe qnri9. wjwx 4t(au0 (:. qqv0l-urin $ 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 s,m hs k/-opkl g9 7dlv,daf(6if made from a material with an energy galk9(asg h,ls-d6d,kmvf p/7 op $ E_g = 1.4\ \text{eV} $? $\lambda $ =    $\mu m$

  If an LED emits light of wavele+t2,z y *xfeiangth $ \lambda = 650\ \text{nm} $, what is the energy gap (in eV) between valence and conduction bands? $e_g$ =    eV

  A silicon diode, whose cuxh3y ygu5go)a-p4r k. rrent-voltage characteristics are given in (Fig. Below), is conney) -u3 gkp.oa yxh4g5rcted 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 connectedvw07bxflm8x 2)xv ry: 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 cukbmaky8j17u6 w0spk( rrent, for $ V > 0 $, for the diode shown in(Fig. Below).

  An ac voltage of 120 V rms is to be rectified. Es2t uu+ .rvi10lcpqs1stimate very roughly the average current in the outpqp 01svu+s 1.lru2 ctiut 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 forward-bias voltageehfj zg,z0:p 7 exceeds abouf ,:z0p j7hezgt 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 voltdr /*os*4y/udv wvg7 jage is to be rectified with a full-wave rectifier (Fig. Below), w gv r74/wu yvd*soj*d/here $ 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 u/ q./9tg1bxh)/b k3byyl vva5z wqq6base current $ I_B $, the collector current $ I_C $, and the emitter current $ I_E $ (not labeled in the figure).

  Estimate the binding energy*p*:a ljn8 d 4hzfjt6vz.:kzx 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 s4qd7p 0qbya5molecule 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.lh3xz5j a80fbur24s r k3ioa627 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 eaca.vwqcv y9hjn,3f9r jt** 1 vrh atom connected to six neighbors, each bo,ayn vrvjcf9*.*13r w 9h vjtqnd 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 -2avjo :wzj1-jwd 4wzhave an activation energy of 1.4 eV. When the molecule is disassociated, 1.6 eV of energy is re-vd a jj4ow1:ww j-2zzleased. Draw a potential energy curve for this molecule.

  When EM radiation is incident on diamond, it is found that light wio/t+2gcxy5hpc-o 7v d th wavelengths shorter than 226 nm will cause the diamond to conduct. What is the energy gap between the valence band and the conduction bandt-7ox5/2cvp+ ohcydg for diamond? $E_g$ =    eV

  A TV remote control emits IR light. If the detector on t s2x om o-g mqa8f6,65pvqt-boa,u,z che TV set is not to react to visible light, could it makcszb-q, 5op,62u gvaxm6f q,a-8tmooe 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 semiconductor, as-:oh 70go hy7zudnif 6sume that the "extra" electron move-d nui7o f6yhg7h0o:z s 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*t4* xzqu/diy nm. For a solar cell to absorb all this, what energy gap ought the mater4xtyd**u q/ ziial have? $E_g$ =    eV

  For a certain semiconductor, the longest wavelength radiatio4edtrygz-5 j wz 6by,4n that can be absorbed is 1.92 mm. What is thegj4y6w- yertd4z z5b, energy gap in this semiconductor? $E_g$ =    $ \times 10^{-4}\ \text{eV}$

  Green and blue LEDs became aval ,e2ou2f1nk7sf au 4ailable many years after red LEDs were first developed. Approximately what energy gaps would you expefusoe7la24a,u 2 1 knfct 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 shown in (Fig. Belowi0 k:sq 0odnudzz9olbgc) )xm;* w.e*). 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?    $\ \text{k}\Omega \leq R_{\text{load}} < \infty$