What type of bond would you expect for 4;pi.ogvlk gt9 *nv 0wb(kqc(
(a) the $N_2$ molecule,
(b) the HCl molecule,
(c) Fe atoms in a solid?

Describe how the molecule8 b5y zf6zh8zx $ \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 moleculewpy *h(auo5* b $ \text{H}_3 $ is not stable, the ion $ \text{H}_3^+ $ is. Explain, using the Pauli exclusion principle.

The energy of a molecy dr1go5eo ):uule can be divided into four categories. What are they?

  Would you expect thenqho3a:*c dko81 dn.g molecule $ \text{H}_2^+ $ to be stable? If so, where would the single electron spend most of its time?{yes|no}

Explain why the carbon b h p)0z43xnneatom ($ 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 leav zngkz3o;*t9tp/ n qg7e t97;okpz*g t3nz n t/gqhe metal entirely?

Explain why the resistira d6p5,ab +fyvity of metals increases with temperature whereas the resistivity of semiconductors may decreaserpybd+,a5a6f with increasing temperature.

(Fig. Below) shows a "br4 y4n 8ra;c/3jmqg, lxql: qnqidge-type" full-wave rectifier. Explain how the current is rectified and how current flows d8, jqq c g:l4/qyal;4x3m nqrnuring each half cycle.

Compare the resistance of y-dcmr)gaqr p9:: 0qm a pn junction diode connected in forward bias to its resistance when connecte rqdyra:)0 p qm-m:g9cd in reverse bias.

Explain how a transistor co v45k ldlkx.0luld be used as a switch.

What is the main difference betwee)q5eet6:/q coy qx8: d yus-asn n-type and p-type semiconductors?

Describe how a pnp transistor can operate tb,.v-)i2 j gx6c74x rkya+:7w wd.twzlunut as an amplifier.

In a transistor, the base-emitter junction and the base-collector junction if:d4 +xqzr4sare essentially diodes. Are these junctions reverse-biased or forwar4z+4f:d i qsxrd-biased in the application shown in (Fig. Below)?

A transistor can amplify an electronic signal, mjuq)cwd m/fp*dt;0aej1vgk-; l zi *0eaning it can increase the power of an input signal. Where does it get the energy to increase the powerg* d p*ml0/ ctedu1a kfjjwq;z0-;v)i ?

A silicon semiconductor is doped with phosphorus. Will t-1 nlda e8t8+r.k n dl9wwqhh:hese atoms be donors or acceptors? What type of s:8 tqd k+wwl1 n dr9lhen8ah-.emiconductor will this be?

  Do diodes and transistors obey Ohm’s eh5k dd h*npb.- 8j8unlaw? Explain. {yes|no}

  Can a diode be used to amplify a signal? Explai x0j3k)4laenb1-t ,r am4yj t6ldhi:mn. {yes|no}

  Estimate the binding energy of a KCl m;t:s j9 pky+ceav3n,solecule by calculating the electrostatic potential ac kst9ps,jne vy :;3+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. / +t1c(m *dxtnv4e,x8d yek ghFrom the result of Problem 1, estimate the contribution to the binding en81me ynh /v+tg k*x(xdd4e ,ctergy of the repelling electron clouds at the equilibrium distance $ r_0 = 0.28\ \text{nm} $. $PE_{\text{clouds}} =$    $\ \text{eV}$

  Estimate the binding energy*:cac. x pc0 vakn;0ky 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 experimentallx p-c34kco lv5y 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 molecu43-5pc vock lxle? 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 t w)p s)ja- q3 phhqujn p58db97hr*r(bhe formation of thpp qj3a7 h-br8*sr hj) unwqp(9)b 5dhe $ \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 b+q3k8fx,k4 8r43s jo/z n4krmjllmz $ \frac{\hbar^2}{2I} $ has units of energy.

  The so-called “characteristic rotational enetul d,1 hcku0+1yzs+ergy,” $ \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 cha o+ cca2d 7en3vjk*tz* 1x1pz7bchkz+ivmv6 7 racteristic 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 atow3wir:2cly+g hjn,g a v:6jf4 ms 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 NaClj4ulk;8jzeh d91 : 4xh/htekb molecule given that three successive wavelengths for rotational transitiokjld: x;94ee4ubjh/t 8hhzk1ns 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 estimate the62ogdy ;ql9 sm;x1ac gq8no,g 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 “ne;rvpyt2 w(l):q3 0 4cyfz c)rf h+becaarest neighbor” Na and Cl ions in a NaCl crystal is 0.24 nm. What is the spacing between twoc;(+ y0yh2w b rz3cl prf a4:)qcvt)ef nearest neighbor Na ions? D =    nm

  Common salt, NaCl, has a den up2j.mri46b )jy gc.zsity 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 density isfdn4ub g x v/4agz;a6(9vn zy5 $ 1.99\ \text{g/cm}^3 $. $s$ =    nm

Explain on the basis of energy bands why the sodium chloride crystal is a g8x7a;uo6r e dzood insulator. [Hint: 6ra78duz eox ;Consider the shells of $ \text{Na}^+ $ and $ \text{Cl}^- $ ions.]

  A semiconductor, bombarded with light of slowly increasedpt-cw oq5/1k 1csmq r(csow+. frequency, begins to conduct when the wavelength of light is 640 nm. Estimate the size of the energy rw1c.w - soks /mcqco5qt1p+(gap $ E_g $. $ E_g $ =    eV

  Calculate the longest-wavelength photon that ca (0epbs, rfxp/n 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 an4ye on9h;wac 5 jjal6,d conduction bands in germanium is 0.72 eV. What range of 6h594 nealja y;ocwj,wavelengths 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 art rnplq2baa0 j)6-wc9e $ 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 sl :8cn .rbzard 5,d(ozo that one silicon atom in 8da, zz5ror.lc: ndb($ 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 made from a material wixd9ctc/bgk .eaogm 8ol0jy) r;r 4/( gth an energy gadr(l/ ga cgcbj4o 8r0) xemkt;9 y/.ogp $ E_g = 1.4\ \text{eV} $? $\lambda $ =    $\mu m$

  If an LED emits light jg ykn-csc2(i q1zz0 4of wavelength $ \lambda = 650\ \text{nm} $, what is the energy gap (in eV) between valence and conduction bands? $e_g$ =    eV

  A silicon diode, whose curre i3 njemj f,h-sg+.*vsnt-voltage characteristics are given in (Fig. Below), is chfensv3,im g*.-sj j+onnected 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. Bzqa/pz78 atp;m1 3m. pkjy /ywelow) 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 o /6:xvabfy j)ef current, for $ V > 0 $, for the diode shown in(Fig. Below).

  An ac voltage of 120 V rms is tcq;8r1jsp lg*vco5 c 8o be rectified. Estimate very roughly the average current in the oujq881 copcgcvs5; rl *tput 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-biasnr.x5jxx.g)0v3 10uufwag ed ln/*oh voltage exceeds about 0.6 Vvx0 ghafgd)n .ruxj0ol3.5/n u1w*xe. 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 volta)h/l5of 8e;xd(3jqru fm 5: ec/or6*isd o orrge is to be rectified with a full-wave rectifier (Fig. Below), wco5q;)eroirre/xfj6 sd(o 3/mlh or5:ud 8 *f 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 v;qoyqq9+w55b, ttx v equation 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 ef) d:ttzmkp1 x6(w5rcnergy 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 molecule is abouj9x n:uj pagf;mz1-dm ps. ,y/t $ 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 separa go2g3beik*bxw 5u qlaqk,ch: h9hnt+n /- 0c3tion 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 with a weakly bound cubic qy j 9bcve.yd2cuge b8r9h(5 (f+/ uqglattice, with each atom connected to six nyd8y9qu/v uh fe(qc2e9(cg b+.r g5bj eighbors, 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 activationr6bi hidw+ip o(q(u9 , energy of 1.4 eV. When the mo orii6dbw (hi+qu( 9,plecule is disassociated, 1.6 eV of energy is released. Draw a potential energy curve for this molecule.

  When EM radiation is incident on diamondg6n k60xzz npdk )nxt p4:5kb,, it is found that light with wavelengths sz4g6xtn p kzkd6nx:bpk, )n 05horter than 226 nm 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 I88pck v,awx2pl:.z ol R light. If the detector on the TV set is not to react to visible light, could it make use of silic,o 2p8ll k:wpc.xv az8on 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, assume that the "b20mbs 58(xn.l yr u5s;q kzldextra" electron moves in a Bohr orbit about the arsenic ion. For this electron in the ground state, take into accou2kl dr;z(blx yubmsn8 q5s 5.0nt 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 huev8nxkes 100(2 rqaxas wavelengths shorter than 1000 nm. For a solar cell to absorb a kxerq8va10(0 u2nxesll this, what energy gap ought the material have? $E_g$ =    eV

  For a certain semiconductor, the longest wavelength rdw)rc*pkdj 7jcl9 ), qadiation that can be absorbed is )r,d cwkdl )9jpj7c*q1.92 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 L zo7ef gzv, z987zlc;va/ pgl+EDs were first developed. Approximately what energy gaps would you expect to find 9g,/vvzgz c7zzp;o8l fae7l+ 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. Be*; jrkcl7qq- u;p*gummh(8pylow). 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?    $\ \text{k}\Omega \leq R_{\text{load}} < \infty$