HEC USAT Physics Flashcards

24 sample cards from the Physics deck

Sampled from the end of the deck, so these are different cards from the ones shown on the syllabus page.

1. Distinguish between transverse and longitudinal waves, giving one example of each.

   In transverse waves the particles vibrate perpendicular to the direction of wave travel (e.g., light, water surface waves). In longitudinal waves the particles vibrate parallel to the direction of travel (e.g., sound waves).

2. Define wavelength and frequency of a wave.

   Wavelength is the distance between two consecutive points in phase (e.g., crest to crest). Frequency is the number of complete waves passing a point per second, measured in hertz (Hz).

3. Name the four main wave phenomena.

   Reflection, refraction, diffraction, and interference.

4. What is the difference between constructive and destructive interference?

   Constructive interference occurs when waves meet in phase, producing a larger amplitude. Destructive interference occurs when waves meet out of phase (antiphase), reducing or cancelling the amplitude.

5. Approximately what is the speed of sound in air at room temperature, and how does it compare with its speed in solids?

   About 340 m/s in air at room temperature. Sound travels faster in liquids and fastest in solids; it cannot travel through a vacuum.

6. What property of a sound wave determines its loudness and which determines its pitch?

   Loudness is determined by the amplitude of the wave; pitch is determined by its frequency.

7. Define the Doppler effect.

   The Doppler effect is the apparent change in the observed frequency (or wavelength) of a wave due to relative motion between the source and the observer — frequency increases as they approach and decreases as they move apart.

8. What is an echo and what causes it?

   An echo is a reflected sound heard distinctly after the original sound; it is caused by the reflection of sound waves from a hard, distant surface, with a delay long enough for the ear to distinguish the two.

9. Define the audible frequency range for humans and the terms ultrasound and infrasound.

   The human audible range is about 20 Hz to 20,000 Hz. Ultrasound is sound above 20,000 Hz; infrasound is sound below 20 Hz.

10. What is temperature, and name three common temperature scales.

    Temperature is a measure of the average kinetic energy of the particles of a substance (its degree of hotness or coldness). Three scales: Celsius (°C), Fahrenheit (°F), and Kelvin (K).

11. Convert between Celsius and Kelvin, and give the value of absolute zero.

    K = °C + 273.15. Absolute zero is 0 K = −273.15 °C, the lowest possible temperature.

12. Give the formula for linear thermal expansion of a solid.

    ΔL = αL₀ΔT, where ΔL is change in length, α is the coefficient of linear expansion, L₀ is original length, and ΔT is change in temperature.

13. State the First Law of Thermodynamics and its formula.

    Energy is conserved: the heat added to a system equals the increase in its internal energy plus the work done by the system. ΔU = Q − W (or Q = ΔU + W).

14. State the Second Law of Thermodynamics.

    Heat flows spontaneously from a hotter body to a colder body, never the reverse without external work; the entropy of an isolated system tends to increase. No engine can convert all heat into work.

15. What is internal energy of a system?

    Internal energy is the total energy contained within a system — the sum of the kinetic and potential energies of all its molecules.

16. Name and describe the three modes of heat transfer.

    Conduction: heat transfer through direct contact of particles (mainly in solids). Convection: heat transfer by the bulk movement of a heated fluid (liquids and gases). Radiation: heat transfer by electromagnetic waves, requiring no medium.

17. What is thermal conduction and in which state of matter is it most effective?

    Conduction is the transfer of heat through a material by particle vibrations/collisions without bulk movement of the material. It is most effective in solids, especially metals (good conductors).

18. Why is heat transfer by radiation different from conduction and convection?

    Radiation transfers heat as electromagnetic waves and does not require a material medium, so it can occur through a vacuum (e.g., heat from the Sun). Conduction and convection both require matter.

19. State Coulomb's law and give its formula.

    The electrostatic force between two point charges is directly proportional to the product of the charges and inversely proportional to the square of the distance between them: F = kq₁q₂/r² (k ≈ 9×10⁹ N·m²/C²).

20. What is the SI unit of electric charge, and what is the charge on a single electron?

    The SI unit of charge is the coulomb (C). The charge on an electron is −1.6×10⁻¹⁹ C (the proton carries +1.6×10⁻¹⁹ C).

21. State Ohm's law and give its formula.

    At constant temperature, the current through a conductor is directly proportional to the potential difference across it: V = IR, where R is the resistance.

22. Define electric current and give its SI unit.

    Electric current is the rate of flow of electric charge: I = Q/t. Its SI unit is the ampere (A), where 1 A = 1 C/s.

23. How do total resistances combine for resistors in series and in parallel?

    In series: R_total = R₁ + R₂ + R₃ + … In parallel: 1/R_total = 1/R₁ + 1/R₂ + 1/R₃ + … (parallel total is less than the smallest resistor).

24. Give two formulas for electrical power dissipated in a resistor.

    P = VI; and using Ohm's law, P = I²R or P = V²/R.

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