What type of bond would yot -5:yxff(mfz)r( gzuu expect for
(a) the $N_2$ molecule,
(b) the HCl molecule,
(c) Fe atoms in a solid?

Describe how the moled;.dtwjyygth// u,j ;0d dr i8cule $ \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 moleculeltc or/p. 5bs**u9eob $ \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 i)m(1y-dfxx 5qc ok j8anto four categories. What are they?

  Would you expect the mole.h/n:h6fx m tp ey.dy;cule $ \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 (n+vy/lhyd . p8$ Z=6 $) usually forms four bonds with hydrogen-like atoms.

If conduction electrons are free to roam about in a metal, why don't they leave gxnze4aga5 fry jy;2,d+71e8cvs5 jw the metal enn, ayceyj zxf+a1r;8j7554eg sv wgd2 tirely?

Explain why the resistivity of metals increases with temperature wher1f vp0:d owgudqp9 :3keas the resistivity of semi3opv1d qw0k 9ud fp::gconductors may decrease with increasing temperature.

(Fig. Below) shows a "bridge-type" fuleg fzj ;*k ueg+8;pgx9l-wave rectifier. Explain how the current 8 zuxgej;f *+gpek;9gis rectified and how current flows during each half cycle.

Compare the resistance of a pn junction diode connected in foeku)j9pylj +on:)fh6k h t ,3nrward bias to its resistance when connn n ho9j :lp63h,fu)+ek)tyjkected in reverse bias.

Explain how a transistor could be used asxl )c*4v5lhxc a switch.

What is the main difn u 7yyzju*5:yference between n-type and p-type semiconductors?

Describe how a pnp tras+h 54slbeboc16h6 ma nsistor can operate as an amplifier.

In a transistor, the base-emitter junction and the base-collector juncth :,8a +ltjcpryp,5 jeion are ess +,,jjrha5:e plct8yp entially diodes. Are these junctions reverse-biased or forward-biased in the application shown in (Fig. Below)?

A transistor can amplify an electrgu(1 xs93 zgk e7(mle)qrugiyv30wj0onic signal, meaning it can increase the power of an input signal. Whe 0gex uqirgkyjl(0ews)vg u3 917( 3mzre does it get the energy to increase the power?

A silicon semiconductor is doped wikuh ;5xro .gqbe6wb-+4s j.bk/n s v)pth phosphorus. Will these atoms be donors or acceptors?.bsp 6bxbr /o5;vw kjqh4.k+s-g)nu e What type of semiconductor will this be?

  Do diodes and transistors obey Ohm’s law? Explvt1 +tynfmw(y,h l;t erx) 9(fain. {yes|no}

  Can a diode be used to amplify a signal? Explg 9 hdn-9/ytj )pkjmm1ain. {yes|no}

  Estimate the binding energy of e :wos6k8udmu:)w z5d/*wzhe a KCl molecule by calculating the electrostatic potential energy when t)uw u 5wekzo/s*zw8h md:e:d 6he $ \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 KCb3czy3 u17bwliepsz+zm7*r (l is 4.43 eV. From the result of Problem 1, estimate the contribution to the binding energy of the repelling electron clouds3 7w pz*r71uzezc y(sibbml3+ at the equilibrium distance $ r_0 = 0.28\ \text{nm} $. $PE_{\text{clouds}} =$    $\ \text{eV}$

  Estimate the binding energy of tm(+c9( ; kq0c+zuu8btjz mbny ab:i2vhe $ \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 in7o2 s umo(a)hi kcal per mole, and then the binding energy in eV per molecule is calculated from that reo u7)2iha os(msult. 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 y n/wkdt(gupihqcj,+. (g v76similar to that in the text for the states in the formation ofq ,+kw.ydggvu(pc6 i(n7t h/j 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 quantitqic9m5k + 5t lv37odo.0ddc yjy $ \frac{\hbar^2}{2I} $ has units of energy.

  The so-called “characteristic rotat0i/.t(av/k *on jers vional 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 characterjri1gz 8dwm,lf dpa5/ s/.r/zistic 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 7prvubtu y r921t ao 5z--p;qbatoms 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 threg ,h a;o8uvebq(p.l 7ee successive wavelengths for rotational transitionepq,a ;.hog8 l 7bue(vs 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 estimd/x2hi-1r xc5 hzh. daate 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 Crr j( 6w gifks,nb4 g2clp;)8sl ions in a NaCl crystal is 0.24 nm. What is the spacing betweic6; rsj(np82r kls gwb,)4gfen two nearest neighbor Na ions? D =    nm

  Common salt, NaCl, ha .s4g62mi ztshs 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 KCj;shpii47w 2 4)vtndul whose density is $ 1.99\ \text{g/cm}^3 $. $s$ =    nm

Explain on the basis of energy bands why the sodium chl5auz 7ag,+xbk 44u 7x9x d0-ysfgsrwcoride crystal is a good insulator. [Hint: Consider the szu,xg+7ar4a sckwxdg 90yf u4b5 -x7shells of $ \text{Na}^+ $ and $ \text{Cl}^- $ ions.]

  A semiconductor, bombarded with lc s -2yms5l/7uiqzh8 kight of slowly increased frequency, begins to conduct when the wavelength of light is 640 nm. Estimate -57 k2m /yiulh8qcszsthe size of the energy gap $ E_g $. $ E_g $ =    eV

  Calculate the longest-wavelength photon that can cause an elect mc 5;tek w1 k7r --8imkzpgxm4qi;n(zron 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 cm6nw6t: l3 0ajnxo(lozi/ pg 4onduction bands in germanium is 0.72 eV. What range of wav0 oj6(onxgt3 :izlwal6 /pn4melengths 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;fh--f +qu,z bdnb3g g $ 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 b0 f-pf 7h*na2yvw (pbwt w9cz30ju rm+1x7jgsemiconductor is doped with phosphorus so that one silicon atow7*v cnahp 0 9pzf 0yxfr2bju-jg1wm (7twb3 +m 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 ma.gox gsla,d) enywn26c3 z6x*terial with an energy gap6zd e axycs6ng3) ,2gn *xl.wo $ E_g = 1.4\ \text{eV} $? $\lambda $ =    $\mu m$

  If an LED emits light of wavelengtzp d09 4px.os 5o65; ch;)tndql efgwd. cpv7eh $ \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 characte p;b, spdt3xwf7,(jdcristics are given in (Fig. Below), is connected in7bdf(;sdpp3j t c, wx, 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 connected in se9ms6ofy3z 1l:qtrzv1l1 +m g vries 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, l+ *dtdu/r l8: szv) ld.gcjg+for $ V > 0 $, for the diode shown in(Fig. Below).

  An ac voltage of 120 V rms is to be rectified. Estimate very rougha1 trjzi4wb) ,oca: 1oly the average current in the outp jozr1awa,tc )4i o1b:ut 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 siz17e8luj )dr1iy8oy m gnificant current only if the forward-bias voltage excezoj7le11 i)8rydmu 8 yeds about 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 voltage is to be rectifiufyi zpj; 78j;,-dqq ) / +ghhrobqhv3ed with a full-wave rectifier (Fig. Below,-y 3;fvq+hhb )7g rpjjiqzuo / q;h8d), 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 yvcain -s2c3qq(w 0g(for the relationship between the base current $ I_B $, the collector current $ I_C $, and the emitter current $ I_E $ (not labeled in the figure).

  Estimate the binding w7hl.2i u 98k4awpfhbenergy 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 kineisa c tg*+x)di) o)jy/om*x j,z( wy0ntic 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 distj1l .t7cnedv et;ys r4( q-p)nance 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 with arj, )x +jkbil6 weakly bound cubic lattice, with each atom connected to six neighbors, each bond having a bj,+kxr b)l6i jinding 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 activcp5zrdr /c4uut /jr2/ ation energy of 1.4 eV. When the molecule is disassociated, 1.6 eV of energy is released. Draw a potenti/ur25jt4c curdzp/r/al energy curve for this molecule.

  When EM radiation is inc7d/ z o)nz7.uvb lh-,xpasvt :ident on diamond, it is found that light with wavelengths shorter than 226 nm will cause the diamond to conduct. Whox7u :. -zdbvp,7nv/t)z h aslat 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 i5o12bjet (0as ixk qyv6 sck91ei(y )js not to react to visible light, could it make use of silicon as a "window" with its (y1coi i eqxvyjb9ajs(ks526)e1t0 k 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, assume04pc yi;ln,p p that the "extra" electron moves in a Bohr orbit about the arsenic ion. For this electron in the ground state, take into account thec0ypinpl4; , p 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 u:w :8n0zrx fua solar cell to absorb all this, what energy gap ought the materian wz: xf0uu8r:l have? $E_g$ =    eV

  For a certain semiconductor,ojv(xbyb-mh 4or . 22a the longest wavelength radiation that can be absorbed is 1. x2o o42yrbj m(-vbh.a92 mm. What is the energy gap in this semiconductor? $E_g$ =    $ \times 10^{-4}\ \text{eV}$

  Green and blue LEDs became available many years after red LEDs were qf 2xv* l+lviawu j)+(first developed. Approximately what e +2 qa )juvl+(vlfx*winergy 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 redgkmfr7n05087 d. bau (qj:sda 9c-l5yoil iv gulator 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?    $\ \text{k}\Omega \leq R_{\text{load}} < \infty$