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Cork Institute of Technology
Bachelor of Engineering (Honours) in Structural Engineering – Stage 1
(NFQ – Level 8)
Summer 2007
Physics
(Time: 3 Hours)
Answer (^) FIVE questions (^) only. Show ALL working to gain full marks. Assume: g = 10.0 ms -
Examiners: Prof. P. O Donoghue Mr. P. Anthony Dr. M. E. Woods
Q1. (a) (i) What is a thermometric property of a thermometer?
(ii) State the thermometric property of ONE named thermometer. (4 marks) (b) The tungsten filament of a lamp has a length of 0.6 m and a radius of 20 μm. The power rating of the lamp is 50 W. Assume that the wire emits radiation equivalent to 80 % of that of a black body radiator at the same temperature.
(i) What is a black body? State its emissivity ( ε ) value. (3 marks)
(ii) Estimate the temperature of the filament. Assume that absorption of radiation from the surroundings is negligible. (9 marks) [Stefan’s Constant σ = 5.7 x 10-8^ Wm-2^ K -4^ ]
(c) A cavity wall of a house with an air gap emits 3.0 kW of heat through it walls which have an area of 90 m^2 when the internal temperature of the house is 28 o^ C and the external temperature is 3 o^ C. Determine the U-value of the wall. [4 marks]
Q2 (a) (i) Sketch a fully-labelled ray diagram of a refracting astronomical telescope operating in normal adjustment incorporating two converging lenses of focal length f (^) o and f (^) e [f (^) o > f (^) e]. Indicate all relevant distances, angles and images. [6 marks] (ii) State the location , orientation and nature of the final image. [3 marks] (iii) State the magnification equation for the telescope. [1 mark] (iv) What additional device is incorporated into a terrestrial telescope? How does this device affect the final image? [2 marks] (b) An object is placed 50 cm from a thin converging lens (lens1) and produces a real image at a distance of 75 cm from the lens. A second thin lens (lens 2) is then placed in contact with the first lens and the focal length of the combination is measured to be fc = + 80 cm (i) Calculate the individual focal lengths of the two lenses. [5 marks] (ii) State with a reason whether the second lens is diverging or converging. [1 mark] (iii) Calculate the magnification of lens1. [2 marks]
Q3 (a) Define the following categories of wave and name ONE physical property , which belongs to that type: (i) longitudinal wave (ii) transverse wave. [5 marks]
(b) A boat traveling along a river generates a progressive wave, whose displacement y is given by: y = Asin( 2 π (ft + x λ )) The water wave has a frequency of 0.3 Hz, an amplitude of 7.5 cm and a wavelength of 80 cm. (i) Sketch a labelled diagram of displacement (y) versus position (x) for the condition t = 0 s. Indicate the wavelength and amplitude on the plot. [4 marks] (ii) State the wave equation and hence determine the wave velocity (units: ms-1^ ). [4 marks] (iii) Determine the period (T) of the wave. [2 marks] (iv) State the equation for the particle velocity and determine its value (units: ms -1^ ) for x = 0 cm, t = 5.0 s. [5 marks]
Q6 (a) Define electrical current. [2 Marks]
(b) The emf of a battery is ε =12.0 V. The battery is connected to a 3 Ω resistor to form a circuit and the measured voltage is now found to be 10.2 V. Calculate: (i) the internal resistance [r] of the battery (ii) the power [P] dissipated in the 3 Ω resistor. [8 Marks]
(c) For the circuit in figure below calculate: (i) The equivalent resistance of the 60 Ω and the 100 Ω resistors. (ii) The equivalent resistance of the whole circuit. (iii) The current reading [I] on the ammeter. [10 Marks]
9V 30 Ω
A
Q7. (a) Define Specific Latent Heat of Fusion. [2 marks] (b) A section of the Greenland ice sheet of mass 6.5 x 10 6 kg at a temperature of -15 o^ C breaks off and falls into the North Atlantic. (i) Calculate the heat energy required to melt the ice (The specific heat capacity of ice is 2.03 kJ kg-1o^ C -1^ ; the specific latent heat of fusion of ice is 334 kJ kg-1^ ). (ii) Determine how long it takes for the iceberg to melt if the surroundings heat it at a rate of 150 MW on average. [13 marks] (c) A steel bridge of length 250 m expands when the ambient temperature changes from a minimum of 10 o^ C by night to a maximum of 32 o^ C by day. State the equation for linear expansion and hence determine the increase in length of the bridge from night to day. [The coefficient of linear expansion for steel α = 1.2 x 10-5^ K -1^ ] [5 marks]
