Download Engineering Physics 1 Exams (PHYS 6003) at Cork Institute of Technology, Winter 2008 and more Exams Engineering Physics in PDF only on Docsity!
CORK INSTITUTE OF TECHNOLOGY
INSTITIÚID TEICNEOLAÍOCHTA CHORCAÍ
Semester 1 Examinations 2008/
Module Title: Engineering Physics 1
Module Code: PHYS 6003
School: School of Building & Civil Engineering School of Mechanical & Process Engineering
Programme Title: Bachelor of Engineering (Honours) in Mechanical Engineering – Year 1 Bachelor of Engineering (Honours) in Biomedical Engineering – Year 1 Bachelor of Engineering (Honours) in Structural Engineering – Year 1
Programme Code: EMECH_8_Y EBIOM_8_Y CSTRU_8_Y
External Examiner(s): Dr. Vincent Casey Internal Examiner(s): Mr. G. M. Croke, Dr. M. E. Woods
Instructions: Answer FOUR questions, ONE only from each section. Show ALL working to gain full marks.
Duration: 2 HOURS
Sitting: Winter 2008
Physical Constants Charge on electron ( e ) 1.60x10-19^ C Speed of light in a vacuum ( c ) 3.00x10^8 m s-
Avogadro’s No ( Ν Α) 6.02x10 23 mol-1^ Planck’s Constant ( h )^ 6.63x10-34^ Js
Rest mass of electron ( m e ) 9.11x10-31^ kg Stephan’s Constant ( σ) 5.67 x 10-8^ W m-2^ K -
Note to Candidates: Please check the Programme Title and the Module Title to ensure that you have received the correct examination paper. If in doubt please contact an Invigilator.
Section A: Answer ONE question only from this section
Q1 (a) Explain, with the aid of a schematic diagram, the principle of operation of a scintillation detector. Sketch the spectrum which would be obtained from a mono- energetic γ-ray source such as 137 Cs using such a detector and identify the principal features of the spectrum. (20 marks) (b) A photomultiplier tube (PMT) has a gain of 5.3 x 10^6. If the average secondary electron yield of the dynodes is 4.7, calculate the number of dynodes in the tube. (5 marks)
Q2 (a) Describe the properties of the strong force and the electromagnetic force and state their roles in maintaining the stability of an atom. What TWO other forces are present in the atom? Compare the relative strengths of these forces. (12 marks) (b) A sample of 22086 Rn(Radon) gas contains 4.5 x 10^21 nuclei and has a decay constant λ = 0.0127 s-1^. The radon decays by alpha emission into Polonium (symbol Po ). (i) State the decay equation for 22086 Rn.
(ii) Determine the half-life of 22086 Rn. (iii) Write down the Law of Radioactive Decay and hence determine how long it takes for the number of radioactive radon nuclei to reach a value of 6.0 x 10^20. (13 marks)
Section C: Answer ONE Question only from this section
Q5 (a) By considering a thin converging lens of focal length f and considering light rays from an object making a small angle of incidence onto the lens, derive the lens equation :
v
u
f
where u = object distance, v = image distance.^ (12 marks) (b) A thin biconvex converging lens of focal length 10.0 cm is placed in contact with a second thin lens. The focal length of the combination fc = + 25.0 cm. Determine the f ocal length f 2 of the second lens and state with a reason whether it is a converging or diverging lens. (7 marks) (c) What is the dispersion of light? Describe with the aid of a diagram one method of dispersing light. Explain the physical principal involved for this example. (6 marks)
Q6 (a) An experiment is set up to measure the refractive index of a glass block by determining the real and apparent depth of an object in the block. Derive an expression relating the refractive index of the glass to the real and apparent depth of the object (the desk surface) in the glass, when viewed from above. (10 marks) (b) When the experiment is carried out, it yields the following results: Scale reading with desk surface in focus (no glass): 12.50 ± 0. Scale reading with desk surface in focus through glass: 19.18 ± 0. Scale reading with upper surface of glass in focus: 30.28 ± 0. Using this data, calculate the refractive index of the glass block and its uncertainty, and display your result in an appropriate form. (10 marks) (c) Two rays propagate from the object and strike the top surface of the glass block from underneath, with angles of incidence of 30° and 50°. Using Snell's Law, or otherwise, determine how these rays travel after striking the top surface of the glass block. Comment on your results. (5 marks)
Section D – OPTION TOPICS: Answer ONE Question only from this section
Q7 (a) (i) State Wien’s Displacement Law ; (ii) Estimate the temperature of the Sun, which emits light whose peak is in the visible spectrum at about 500 nm. Wien’s Displacement Constant is 2.9 x 10-3^ metre Kelvin. (8 marks) (b) The double glazed window of a room has dimensions of 2.50 m wide by 1.50 m high. Each of the panes has a thickness of 4.0 mm and the air gap between them is 9.0 mm. The internal temperature of the room is 20.0o^ C and the external temperature is -4.0o^ C. The thermal conductivity of the glass = k 1 = 0.60 Wm-1^ K -1^ and the thermal conductivity of air = k 2 = 0.025 Wm-1^ K -1^. Determine the: (i) rate of heat loss [P] through the window; (ii) total heat loss [Q] in 20 minutes. (17 marks)
Q8 (a) A wood burning stove is operating at a temperature of 205o^ C. The stove heats a room, which reaches a temperature of 21o^ C. The surface area of the stove is 3.5 m^2 and its surface has an emissivity of 0.92. (i) Describe how the emissivity of a material relates to the radiation emitted or absorbed by that material. (ii) State the Stephan-Boltzmann equation. (iii) Determine the net power (P) radiated by the stove. (13 marks) (b) A road is to be constructed out of concrete slabs in the Nevada desert. Each slab is 16 m long when constructed at 20o^ C and has a mass of 16800 kg. There is an expansion gap between each slab as the road is designed to operate from a minimum of -20 o^ C to a maximum of + 50o^ C. The specific heat capacity of concrete C = 880 J kg-1^ K -1^ and the coefficient of linear expansion for concrete α = 1.2 x 10-5^ o^ C-^. (i) How much does a slab expand in length between the minimum and maximum design temperatures? (ii) How much heat energy would be absorbed by the concrete slab when expanding between the minimum and maximum design temperatures? (12 marks)
