NUMS — Medical & Dental Entry Test
Take the NUMS Physics — Waves, Sound, Optics and Thermodynamics (Set 3): 30 multiple-choice questions (40 minutes) with instant scoring and a full answer…
What this test covers
The first 5 questions of this test, with the correct answer and explanation.
Q1. A travelling wave is described by y = 0.02 sin(100πt − 5πx) in SI units. What is the speed of the wave?
Answer: D. 20 m/s
Explanation: v = ω/k = 100π/5π = 20 m/s.
Q2. A stretched string of linear mass density 0.010 kg/m is under a tension of 100 N. What is the speed of transverse waves on it?
Answer: C. 100 m/s
Explanation: v = √(T/μ) = √(100/0.010) = 100 m/s.
Q3. A string of length 0.50 m fixed at both ends carries transverse waves of speed 100 m/s. What is the frequency of its third harmonic?
Answer: B. 300 Hz
Explanation: f₁ = v/2L = 100 Hz; the third harmonic is 3f₁ = 300 Hz.
Q4. A pipe closed at one end and 0.85 m long is filled with air in which sound travels at 340 m/s. What is the frequency of its second resonance (first overtone)?
Answer: D. 300 Hz
Explanation: f₁ = v/4L = 340/3.4 = 100 Hz; a closed pipe has only odd harmonics, so the first overtone is 3f₁ = 300 Hz.
Q5. A 512 Hz fork and a second fork B together produce 6 beats per second. When the prongs of B are filed slightly, the beat frequency rises to 8 per second. What was the frequency of B before filing?
Answer: B. 518 Hz
Explanation: Filing the prongs raises B's frequency. From 506 Hz it would move closer to 512 Hz and the beats would fall below 6; from 518 Hz it moves further away and the beats rise to 8. So B was 518 Hz.
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Q6. A source emitting 500 Hz moves towards a stationary observer at 20 m/s. If the speed of sound is 340 m/s, what frequency does the observer hear?
Q7. The sound intensity at a point is 1.0 × 10⁻⁶ W/m². What is the sound level in decibels? (reference intensity I₀ = 1.0 × 10⁻¹² W/m²)
Q8. One machine produces a sound level of 40 dB at a point. What is the level when 100 identical machines operate together at the same point?
Q9. A 0.50 kg mass is attached to a spring of constant 200 N/m and set into simple harmonic motion. What is the period?
Q10. An oscillator has amplitude 0.10 m and angular frequency 20 rad/s. What is its speed when it is 0.06 m from the mean position?
Q11. What length must a simple pendulum have to have a period of 2.0 s? (g = 9.8 m/s²)
Q12. A particle in SHM has amplitude A. What fraction of its total energy is kinetic when the displacement is A/2?
Q13. A ray of light in air strikes a glass surface (n = 1.5) at an angle of incidence of 30°. What is the angle of refraction?
Q14. What is the critical angle for a transparent medium of refractive index 2 when light travels from it into air?
Q15. An object is placed 30 cm from a convex lens of focal length 20 cm. Where is the image formed and what is the magnification?
Q16. Two thin lenses of powers +5 D and −2 D are placed in contact. What is the focal length of the combination?
Q17. A convex mirror has a focal length of 15 cm. An object is placed 30 cm from it. At what distance is the image formed?
Q18. A hypermetropic person has a near point at 50 cm. What power of lens allows reading at the normal near point of 25 cm?
Q19. A compound microscope has an objective of focal length 1.0 cm and an eyepiece of focal length 5.0 cm. Using M ≈ (L/fₒ)(D/fₑ) with tube length L = 20 cm, final image at infinity and D = 25 cm, what is its magnification?
Q20. An astronomical telescope in normal adjustment has an objective of focal length 100 cm and an eyepiece of focal length 2 cm. What is its magnifying power?
Q21. In Young's double-slit experiment the slit separation is 0.30 mm, the screen is 1.5 m away and the light has wavelength 600 nm. What is the fringe spacing?
Q22. Light of wavelength 500 nm falls normally on a diffraction grating having 2200 lines per cm. What is the highest order of maximum that can be observed?
Q23. Unpolarised light of intensity I₀ passes through a polariser and then through an analyser whose axis makes 60° with that of the polariser. What is the final intensity?
Q24. An ideal gas expands isothermally and absorbs 250 J of heat from a reservoir. How much work does the gas do, and what is its change in internal energy?
Q25. Why does the temperature of an ideal gas rise when it is compressed rapidly (adiabatically)?
Q26. A gas expands at a constant pressure of 2.0 × 10⁵ Pa from 2.0 L to 5.0 L. How much work does it do?
Q27. A Carnot engine works between 127 °C and 27 °C. What is its efficiency?
Q28. By what factor does the rms speed of the molecules of a gas change when its temperature is raised from 27 °C to 927 °C?
Q29. How much heat is required to raise the temperature of 3 mol of helium gas by 40 K at constant pressure? (R = 8.314 J/mol K)
Q30. 600 J of heat flows spontaneously from a hot reservoir at 400 K to a cold reservoir at 300 K. What is the net change in entropy of the two reservoirs?