What type of bond would you expect for prukd;jt: jo +/b.w) 2b ssu2u
(a) the $N_2$ molecule,
(b) the HCl molecule,
(c) Fe atoms in a solid?

Describe how the mole d69 tqe 6/r;eoy,kazucule $ \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 qtcfznx:i2 50 46mw zp$ \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 categorie10 yt7 qv90d:myw npfws. What are they?

  Would you expect the molecu i.tx9:3frcpule $ \text{H}_2^+ $ to be stable? If so, where would the single electron spend most of its time?{yes|no}

Explain why the carboko2/d 6gjlt)qoyezwn0o (p;4 n atom ($ Z=6 $) usually forms four bonds with hydrogen-like atoms.

If conduction electrons are free to roak6z nql (k6n(2wt;wnh m about in a metal, why don't they leave the metal entirely?knnl(6; tz qk2wn h(6w

Explain why the resistivity of metals increases with tempers 5u*xjg9a .vooge* 3hature whereas the resis35 ju*hg.*aoo vgx9se tivity of semiconductors may decrease with increasing temperature.

(Fig. Below) shows a "bridge-type" full-wave rectifier. cn2 8n7az*l euplve1oj 7.3ey Explain how the current is rect e.78y17p vnl2uacl *ejeo z3nified and how current flows during each half cycle.

Compare the resistance of a pn junction diode connected in forward;4*kr bs*4crfxxlavn;g w4 8 s bias to its resistance when connectaslxx 4frgscvk4b n;8*;*w r4ed in reverse bias.

Explain how a transistor cn sj:a/u1w6z2 h* norgould be used as a switch.

What is the main difference betocxhr)h*xku3f(c . i2ween n-type and p-type semiconductors?

Describe how a pnp transistor can operate as avn8uku;4 aaza hz/p 0:n amplifier.

In a transistor, the base-emitter junction and the base-collectoraqz: ig-g+v mecwh;): junction are essentially diodes. Are these junctions reverse-biased or forward-biased in the application shown in (Fig. Belq:)g emvc;ihza+:gw- ow)?

A transistor can amplify an electronic signal, xzf1xy;0upu 4 meaning it can increase the power of an input signal. Where does it get theuu4 ;1xf0xzpy energy to increase the power?

A silicon semiconductor is dopedv s w4cdze6:8f,o,rrv with phosphorus. Will these atoms be donors or acceptors? What type od,cerz84 f :w6v,o rsvf semiconductor will this be?

  Do diodes and transistors obey Ohm’s law? tl0o2xzh+io: qen..z Explain. {yes|no}

  Can a diode be used to amr2(l **u3ruwekj r0ygx 9s -xvplify a signal? Explain. {yes|no}

  Estimate the binding7:t xw5x9j*rzx ,s 8fiebxo6w energy of a KCl molecule by calculating the electrostatic potential energy t9 ,r*f sxie75x jxwzw6bo:8xwhen 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 3z xlk8*wiba: .k2xtr4.43 eV. From the result of Problem 1, estimate the contribution to the8atkk.2x*r:3bxl wzi 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 en7a1ga ,j ,dvb-sz6o htergy 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 ofte4f op8x)n n) +. x3pujlviw(ayn measured experimentally 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? What is the binding env 4fi .n xxjpwul y3n)pao+)8(ergy 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 form2/z .cq upac49 ky6;h p:rnfspq-t.q sation o /6fp.pncqqya 4s9 zc:-rs;t2p .qkh uf 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 quantit*wgr7qffs /pek:xq i ;gk 528qy $ \frac{\hbar^2}{2I} $ has units of energy.

  The so-called “characteristic rotationdyn5-,e; py,5z kpylib8. iaaal 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 characteriz6joa8 rlj;d 1stic 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 in rid n4os/uzk1n;9r;8yw(suwmd z80 i 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 givenei 4tca xja1juu3(*7d that three successive wavelengths for rotational transitions are 23.1 mm, 11.6 mm,1*uue(3dji7 x a4acjt and 7.71 mm. $r = $    $\times 10^{-10}\ \text{m}$

  (a) Use the curve of (Fig. Below) to estimanf-4 wu,gv9b k/i(i)q-p-bp1 ff vv oxte 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 Ckzvnawg:b ws9*yv*(13 ;xi i wl ions in a NaCl crystal is 0.24 nm. What is the spacing between two nearest neighbor Na*wbvnww 1ksi9; 3i(y:g*vz xa ions? D =    nm

  Common salt, NaCl, has a denk :kzcwv2 do)9sity 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 KClqf;-by )r ad 7iaz2b2k whose density is $ 1.99\ \text{g/cm}^3 $. $s$ =    nm

Explain on the basis of energy bands why the sodium chloride crystal is a good ib.:odz8c uj 6*nnvp2 pnsulator. [Hint: Considedo. pu:v6*jn8 c2znbp r the shells of $ \text{Na}^+ $ and $ \text{Cl}^- $ ions.]

  A semiconductor, bombarded with light of slowly increased frequency,op0(w *h ldsu2 16eiff begins to conducteup6 1io(d0ls*f 2hfw when the wavelength of light is 640 nm. Estimate the size of the energy gap $ E_g $. $ E_g $ =    eV

  Calculate the longest-wavelength photo-ov eoz34 cv 6.mtn*aw ki/-zon 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 bands in gi x 0;hv. +af(uyf r9-npj f,s2hyn2axermanium is 0.72 eV. What range of wavelengths can a photon have to excite an electron from the top of the valence band into the conduction ba;h vna-pi,fh r.x 2 +n(0uyxy9a2 jsffnd? $\lambda \leq$    $ \ \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 aru bl), z/ypm)rveu7b/e $ 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 phosphorukala4xqfb8,k ob f9a0lq 0t4 ,s so that one silicof40k 0faa,xotkqa9bq l8l, b4n atom 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 fr*:yrugt pmy;7oof-6r om a material with an energy gap 7ogtf;yyr -u :*rpo6m$ E_g = 1.4\ \text{eV} $? $\lambda $ =    $\mu m$

  If an LED emits light of wavelens3wjx -oj/k .4bn7kuggth $ \lambda = 650\ \text{nm} $, what is the energy gap (in eV) between valence and conduction bands? $e_g$ =    eV

  A silicon diode, whose current-volbzmbb*k+t 5y7yp/wpl 87bdu *qq)6zd hgo ) q-tage characteristics are given in (Fig. Below), is connected in series with a battery and ))bhpduwqztd5 6/y qlqy7zmb8*- bk+bp o 7g*a $ 960-\Omega $ resistor. What battery voltage is needed to produce a 12-mA current? $V_{\text{battery}}$=    V

  Suppose that the diod /,al eitfrp/( ((iduie of (Fig. 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 function of tx8 re(yh9f5p current, for $ V > 0 $, for the diode shown in(Fig. Below).

  An ac voltage of 120 V rms is to be rectified. Estimate very rougy vrn7k.k7oq hi)0l ,phly the average current in the out)y77k ,hvp.lnq r io0kput 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 .el86qa* jfxmonly if the forward-bias voltage exceeds about 0.6 V. Make a rough estimate of the average current in the output resistofe*am.8 xql 6jr $ 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 full-wave rectifier (Fig. Behm l8efosl;t d5,*/q0nu 2e bffu8;f lht/,obm5eq 0 dlsen2* low), 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 betau4 /pcj uh25rween the base current $ I_B $, the collector current $ I_C $, and the emitter current $ I_E $ (not labeled in the figure).

  Estimate the binding energygjiacv 7,.rht5kgmu-t7ewz4 -cw 0 k) 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 -9syz 7fv+: gncl,6mawunt u+kinetic 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 ionzso (jc0abtrj g(xe/;w6p8q sk0s( 9 ds 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, wz4 aw rclkpzxd:;qc1 3 +7ybbr5.p vv/ith each atom connected to six neighbors, each bond havinglkx45wd/aqzr .3 r+1y v;bb v:7pzcpc 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 of 1.4 eV. Whenwi 1td)* 5te9wj ;rbzk,zr9 wz the molecule is disassociated, 1.6 eV of energy is released. Draw a potential energy curve for this molecule.;eji9 dz)r w*w,9ztrzt1 kb5w

  When EM radiation is incident on diamond, it is found that light with wavel n(1 ,,vlh6 4gnetwknoengths shorter than 226 nm will cause the diamond to conduct. What is the energy gap between the valence band and the conduction band for diamk(,egnv ,1 o twn64lhnond? $E_g$ =    eV

  A TV remote control emits IR l1p6s)g2shzb)e 3kaqgight. If the detector on the TV set is not to react to visible lighg2bs z a13qse) hg)pk6t, 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 in a dt :8u+d7a tc+o -4:aropv30mgmxrj nqoped silicon semiconductor, assume that the "extra" electron moves in a Bohr orbit about the arsenic ion. For this electron in the ground state, take into accountmj c r adortp: 7a80gu+qvo +:t-3x4nm 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 wavelength*+ 81ax7wdymbty2a q bs shorter than 1000 nm. For a solar cell to absorb all this, what energy gap ought the material have? b 1aw2 8*xqd7 tyybm+a$E_g$ =    eV

  For a certain semiconductor, the longest wavelength radiation t)fp tucln/d2.z-vt0si1kf : z 5n4 tkwhat can be absorbed is 1 d 5)-4.kpn/sw:zl zft 0kcu ft2nvit1.92 mm. What is the energy gap in this semiconductor? $E_g$ =    $ \times 10^{-4}\ \text{eV}$

  Green and blue LEDs became available many years after red LEDs were fivd1o0uq/oyz/ hi id51 rst developed. Approximately what en/1i10h5v zi uq/dod oyergy 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 shown in (Fiwjz qr:q- sdn:*0jw,os8p rr.g. 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?    $\ \text{k}\Omega \leq R_{\text{load}} < \infty$