What type of bond would you y2km33) w r7fp7v irsw5y4gxf/yv- o nexpect for
(a) the $N_2$ molecule,
(b) the HCl molecule,
(c) Fe atoms in a solid?

Describe how the molecule8u bccm .d:6,:zddgcc $ \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 5 ;ve/oxn;bmawy m7x*t i67jf(,rfq p $ \text{H}_3 $ is not stable, the ion $ \text{H}_3^+ $ is. Explain, using the Pauli exclusion principle.

The energy of a molecule co+xxab 7 1c+uman be divided into four categories. What are they?

  Would you expect the dmsy3 ) lnx; m4h4nj(yfd nk9*molecule $ \text{H}_2^+ $ to be stable? If so, where would the single electron spend most of its time?{yes|no}

Explain why the carb0)8v xs4naj c-/e lhtkon atom ($ Z=6 $) usually forms four bonds with hydrogen-like atoms.

If conduction electrons are free to roam about in a metal, why do7 42trp ttv4asho.q0dkq bg): j( ok7zn't they leave )(v o2r70a q.: t74 tksj go4btqpkhdzthe metal entirely?

Explain why the resistivity of metals increases with temperature whe3nxpw + (d:ndsreas the resistivity of semiconducwn3+x:s dnd (ptors may decrease with increasing temperature.

(Fig. Below) shows a "bridge-type" full-wave rectifier. Explain how b8-z0x 8kqvguh xm/p.the current is rectified and how current flows during e /.k-08h8u zqvm bgxxpach half cycle.

Compare the resistancevdg 53lj-hb.se ks8+e of a pn junction diode connected in forward bias to its resistance when3 v8b-+.l eseskg5 djh connected in reverse bias.

Explain how a transistor could be use btn,u7ib3 nf1d as a switch.

What is the main difference between j,x:4p6atvgoqir lu m87xk5a/yq08t n-type and p-type semiconductors?

Describe how a pnp transistor can oz4qyo8 ;f y:y ozg21irperate as an amplifier.

In a transistor, the base-ax3j i6sq/y-m emitter junction and the base-collector junction are essentially diodes. Are these junctions reverj6y qisa -3m/xse-biased or forward-biased in the application shown in (Fig. Below)?

A transistor can amplify an electronic signal, meaning it can increase the powep).s;iz dfm44 xs;ddcr;. ;)f4i sdcdzdpsxm4 of an input signal. Where does it get the energy to increase the power?

A silicon semiconductor is 0r:0 qtf-amlp doped with phosphorus. Will these atoms be donors or acceptors? What type of semiconducto-l:0amp qrf0 tr will this be?

  Do diodes and transisdsg7,cyr kkx)6 n9o-ntors obey Ohm’s law? Explain. {yes|no}

  Can a diode be used to amplify a signal? E bo;*26)o0 ahonaoecpd lb (w*xplain. {yes|no}

  Estimate the binding energy of a KCl molecule by calcz +;vwtfr /yy(ulating the electrostatic potentiayf z rywv+(/;tl 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 eV. From the result of7 j98nb ay 5ve-tlx9c(ccyp(w Problem 1, estimate the contribution to the binding energy of the repelling electron clouds at thp-yw5nj bax 899 eyt vc(7(lcce equilibrium distance $ r_0 = 0.28\ \text{nm} $. $PE_{\text{clouds}} =$    $\ \text{eV}$

  Estimate the binding ruj2zl )j)go :o :k5bmenergy 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 per mole, and then tscm 31te 9;fm)r ma k4+sy5aezhe binding energy in eV per molecule is calculated from that result. What is the conversion factor in going from kcal per mole totk m54esefczs)r+ am3 91my;a 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 thee+ ,xs0lyr+i:j -lfn1db8c n b states in the formation of bd icl81: +-,erlsyfb+nn xj0 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 quantij5x,ef.fg.4ikr q )ir ty $ \frac{\hbar^2}{2I} $ has units of energy.

  The so-called “characteristic rotational encq jk*lshbu nsl*9r80jx2+ 7oergy,” $ \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 charaekdch. dqg)g.ox0 o5,e :jbp/r: z6jecteristic 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+z7.,vjlv le y, iety99rf cn. 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 vthrv lmz5+*hoo2: 0 gNaCl molecule given that three successive wavelengths for rotational transitions are 0tvrh+*5go2: vmh olz23.1 mm, 11.6 mm, and 7.71 mm. $r = $    $\times 10^{-10}\ \text{m}$

  (a) Use the curve of (Fig. Below) to estimate the stif-6g oj. f0feb4*kae9jml nw k+fness 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 r35syehk2+sd:w ( kw fin a NaCl crystal is 0.24 nm. What is the spackdry( +2h 5fkswswe3: ing between two nearest neighbor Na ions? D =    nm

  Common salt, NaCl, has a densi*mj.3rgb:wp1 ep qe8qj q+6xnty 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 /g(7q. 1dqceos.ym8pok ;x bvk,qi4obb,1mq whose density is $ 1.99\ \text{g/cm}^3 $. $s$ =    nm

Explain on the basis of energy bandsqa9q ,7ik4r y(cp :mqlw/v uo/ why the sodium chloride crystal is a good ins9vai ro qu/lkq/mcwy ,4(q7:p ulator. [Hint: Consider the shells of $ \text{Na}^+ $ and $ \text{Cl}^- $ ions.]

  A semiconductor, bombarded with light of qa2 ktir- m3rsz+qy9h:-f*)w gx(gx wslowly increased frequency, begins to cof a9r32)ggx q zkytmr+w s-q -(:x*whinduct 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 g jju f(.7wg1c) u6ww(h0) :jkyjapm belectron in silicon ($ E_g = 1.14\ \text{eV} $) to jump from the valence band to the conduction band. $\lambda $ =    $\mu m$

  The energy gap betweedx5c/pzcn(i u9/p8lnx8(fg gcffu +; n valence and conduction bands in germanium is 0.72 eV. What range of wavelengths can a photon have to excit (8id+plx9ffu /zcnf 8x5/ ucp(gg;cne 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 are1 opmo9 8c kqe-e2csza8ql.5c $ 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 silico*rjpylf/ jg7 /so+fw2n semiconductor is doped with phosphorus so that one silicon a /r*jj fw/2gfoyp7ls+ 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 madev*.88og a0jsa9ncs uh from a material with an energy gap ncvusj0h 8osag *a .89$ E_g = 1.4\ \text{eV} $? $\lambda $ =    $\mu m$

  If an LED emits light of wavele*ospw,0dv:skat l 3l2ngth $ \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 (Fo / 5 1oolwfqm5jt)azr8ws ((jig. Below), is connected in series with a battery andzm(8s5wr1/w5(of l)aj qot j 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 * .qed 3l v4yzr8kxy:cu:8hjyin 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 currencao)c.3ky;pw wg9v; z t, for $ V > 0 $, for the diode shown in(Fig. Below).

  An ac voltage of 120 V rms is to be rectified. Estimate very roughly the j6cnkbk dir,d c*6;sqm8j;+ gaverage current in the out;*km+d 8dk6jcjgi,nbsr; 6qc put 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 voltage p bpis/ 8: iztfd9v4ce,w:jg4exceeds about 0.6jfi 8v449d,ps :e/gz biw:c pt 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 voltage i t2zyu,+zx ;f9w+ q,ecjl(f- 1 xzhfkfs to be rectified with a full-wave rectifier (Fig. Below), u1txxf2l(,kz+fcw;jz,+fyf9h zeq - where $ 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 bl9crt,,bttecg:25+hrtg;ghi wr n0 4 etween the base current $ I_B $, the collector current $ I_C $, and the emitter current $ I_E $ (not labeled in the figure).

  Estimate the binding energy okgi:wp1)ox o.p-6ymaf 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 az,ecx, zez-4sk; u4 kkbout $ 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 ve7.8n eeonw: d0ap*-(w geyqseparation 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 withs uy79b*/ud; uy( okiw a weakly bound cubic lattice, with each atom connected to six neighbkiu ws7o9 uu ;(*/bdyyors, 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 activation energy kw do,9.qvep 1of 1.4 eV. When the molecule is disassociated, 1.6 eV of energy is released. De.q1k,9 pdvo wraw a potential energy curve for this molecule.

  When EM radiation is incident on diamond, it is found that light wi0 xrobza*qnlh 29wc 93th wavelengths shorter than 226 nm 0zw3b c rqa9h o9xnl2*will cause the diamond to conduct. What is the energy gap between the valence band and the conduction band for diamond? $E_g$ =    eV

  A TV remote control emits IR light. If the detector on the TV set is not to rc6abn*djx ;l 73 oj3xteact to visible light, could it make use of silicon as a "window" w6c;7xa jxl n3 d*bot3jith 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, ass 2iqmubawa (8:ume that the "extra" electron moves in a Bohr orbit about the arsenic ion. For this electron in the ground wmau:qabi2( 8 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 shor prlf5+bl9)9e p rihq t5(zzp-ter than 1000 nm. For a solar cell to absorb all thi(eb5+r h9i95rtz l) -lpzppfqs, what energy gap ought the material have? $E_g$ =    eV

  For a certain semiconductor, the longest wavelength radiation thatxvd97ji r mc* ch0*k6m can be absorbed is 1.h7m90jxk6r cmvd i c**92 mm. What is the energy gap in this semiconductor? $E_g$ =    $ \times 10^{-4}\ \text{eV}$

  Green and blue LEDs became available many years aft 6kqu: 0aghvwwvc+8 17zp wn)ner red LEDs were first developan1w +pzh nu kw87qv6wc): v0ged. 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 i(6pmk8tar 9jzq4l0e regulator 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?    $\ \text{k}\Omega \leq R_{\text{load}} < \infty$