Cork Institute of Technology
Bachelor of Engineering (Honours) in Mechanical Engineering – Stage 1
(NFQ – Level 8)
Autumn 2006
Physics
(Time: 3 Hours)
Answer FIVE questions Examiners: Mr M.J. Howard
All questions carry equal marks Mr. J.E. Hegarty
Prof. M. Gilchrist
Physical constants
Charge on electron: e- = 1.6 x 10-19 C
Permittivity vacuum: ε0 = 8.85 x 10 -12 C2 N-1 m-2
Density of water: ρ = 1000 Kg m-3
Speed of light: 3 x 108 ms-1
Specific Heat Capacity of water: 4200 J Kg-1 K-1
Planck’s Constant: 6.626 x 10-34 Js
Rest mass of electron: 9.11 x 10-31 Kg
Velocity of sound in air: 343 ms-1
Q1 (a) What are the physical mechanisms that produce laser light and give a detailed
description of how a He-Ne laser works. Include its design and internal features.
(5 marks)
(b) What is the intensity ratio of two sounds if one is 90dB and the other is 93dB?
(3 marks)
(c) What is the Doppler Effect and how does it work? (5 marks)
(d) A +high speed train is travelling at a speed of 100mph and sounds its warning siren at
415Hz. What frequency and wavelength is perceived by a stationary observer as (i) the
train approaches, (ii) the train recedes? (7 marks)
