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UNIVERSITY-LEVEL PHYSICS EXAM
. 1 The group velocity of a wave packet is defined as:
A. vg=ω/kv_g = \omega / kvg=ω/k B. vg=dω/dkv_g = d\omega / dkvg=dω/dk C. vg=k/ωv_g = k / \omegavg=k/ω D. vg=−dω/dkv_g = - d\omega / dkvg=−dω/dk Answer: B
. 2 The moment of inertia of a solid sphere (mass MMM,
radius RRR) about its diameter is:
A. 12MR2\frac{1}{2} MR^2 21 MR B. 25MR2\frac{2}{5} MR^2 52 MR C. 35MR2\frac{3}{5} MR^2 53 MR D. 75MR2\frac{7}{5} MR^2 57 MR Answer: B
3. The electric field inside a conductor in electrostatic
equilibrium is:
A. Zero B. Infinite C. Equal to the surface charge density D. Perpendicular to the surface Answer: A
4. The expectation value of position ⟨ x ⟩ \langle x \rangle ⟨ x ⟩
for a symmetric probability distribution about the origin
is:
A. Positive B. Negative C. Zero
D. Depends on normalization Answer: C
5. The Lorentz force is:
A. F⃗ =qE⃗ \vec{F} = q\vec{E}F=qE B. F⃗ =q(E⃗ +v⃗ ×B⃗ )\vec{F} = q(\vec{E} + \vec{v} \times \vec{B})F=q(E+v×B) C. F⃗ =q(v⃗ ⋅B⃗ )\vec{F} = q(\vec{v} \cdot \vec{B})F=q(v⋅B) D. F⃗ =ma⃗ \vec{F} = m\vec{a}F=ma Answer: B
6. For a Carnot engine, the efficiency is:
A. 1−ThTc1 - \frac{T_h}{T_c} 1 −TcTh B. 1−TcTh1 - \frac{T_c}{T_h} 1 −ThTc C. ThTc\frac{T_h}{T_c}TcTh D. 1+TcTh1 + \frac{T_c}{T_h} 1 +ThTc Answer: B
7. A photon’s momentum is given by:
A. p=mvp = mvp=mv B. p=mcp = mcp=mc C. p=E/cp = E / cp=E/c D. p=c/Ep = c / Ep=c/E Answer: C
8. In a hydrogen atom, the radius of the nth orbit (Bohr
model) is proportional to:
A. nnn B. n2n^2n C. 1/n1/n1/n D. 1/n21/n^21/n Answer: B
C. ΔxΔv=0\Delta x \Delta v = 0ΔxΔv= 0 D. ΔEΔt=0\Delta E \Delta t = 0ΔEΔt= 0 Answer: B
25. The speed of sound in a gas is proportional to:
A. 1 /T1/\sqrt{T}1/T B. TTT C. T\sqrt{T}T D. T2T^2T Answer: C
26. A transformer works on the principle of:
A. Coulomb’s law B. Faraday’s law C. Gauss’s law D. Conservation of momentum Answer: B
27. The Compton wavelength shift depends on:
A. The intensity of incident photons B. The scattering angle C. The temperature of electrons D. The magnetic field strength Answer: B
28. In fluid dynamics, Reynolds number determines:
A. Compressibility B. Turbulence C. Surface tension D. Buoyancy Answer: B
29. The fundamental mode (first harmonic) of a string
fixed at both ends has:
A. One node B. Two nodes C. Three nodes D. Infinite nodes Answer: B
30. The entropy of an isolated system:
A. Always decreases B. Always increases C. Remains constant D. Never stays the same Answer: B
31. The magnetic field of a long straight wire varies as:
A. B∝1/rB \propto 1/rB∝1/r B. B∝rB \propto rB∝r C. B∝r2B \propto r^2B∝r D. B∝1/r2B \propto 1/r^2B∝1/r Answer: A
32. When light enters a denser medium, its frequency:
A. Increases B. Decreases C. Remains the same D. Becomes zero Answer: C
33. The tunneling probability in quantum mechanics:
A. Increases with barrier width B. Decreases with barrier height C. Increases with particle energy
A. Ideal gases B. Metals at high temperature C. Solids at low temperature D. Radiation Answer: C
39. A wave on a string satisfies the wave equation only if:
A. The string is massless B. Tension is constant C. Frequency is zero D. Energy is zero Answer: B
40. The Fermi energy is defined as:
A. The energy of the highest filled state at T = 0 B. The energy of the lowest filled state C. The average electron energy D. Twice the band gap Answer: A
41. The force between two parallel currents in the same
direction is:
A. Repulsive B. Attractive C. Zero D. Infinite Answer: B
42. The classical electron radius is obtained by equating:
A. Electric field to magnetic field B. Electrostatic energy to rest mass energy C. Kinetic energy to potential energy D. Charge to mass ratio Answer: B
43. In special relativity, simultaneity is:
A. Absolute B. Independent of the observer C. Dependent on the reference frame D. Impossible Answer: C
44. The de Broglie wavelength of a particle is:
A. λ=p/h\lambda = p/hλ=p/h B. λ=h/p\lambda = h/pλ=h/p C. λ=hp\lambda = hpλ=hp D. λ=p2/h\lambda = p^2 / hλ=p2/h Answer: B
45. A driven harmonic oscillator exhibits resonance when:
A. Driving frequency = natural frequency B. Damping = zero C. Energy = zero D. Force is constant Answer: A
46. In a semiconductor, doping with pentavalent atoms
produces:
A. p-type material B. n-type material C. Intrinsic material D. Insulator Answer: B
47. The plasma frequency of electrons in a metal is
proportional to:
