Download Coefficient of Linear Expansion - Physics - Exam Paper and more Exams Physics in PDF only on Docsity! 5 Question 1 [12 Marks] (a) Define the average coefficient of linear expansion for a material in terms of its fractional change in length and the change in temperature. If your definition includes an equation, define all terms used in it. (b) A circular disk has a concentric circular hole cut out of its middle, as in the diagram. Explain, giving your reasoning, what happens to both the disk and the hole as the disk is heated. Suppose that r0=5.0cm, r1=10cm and the coefficient of linear expansion is 2.0x10-5 °C-1. What is the change in the area of the material that makes up the disk for a 30°C increase in its temperature? (c) R T C Water at temperature 25°C flows from a tap T into a heated container C. The container has a heating element (a resistor R) which is supplied with electrical power, P, that may be varied. The rate of flow of water F = 0.030 litres per minute. The electrical power is sufficient that the water in the container is boiling. What is the minimum power that must be supplied in the steady state so that the amount of liquid water in the container neither increases nor decreases with time? You may neglect other losses of heat, such as conduction and radiation from the container to the air. For water, c=4,200 J kg-1 K-1, Lvap=2.30x106 J kg-1, ρ=1,000 kg m-3. ro r1 6 Question 2 [15 Marks] (a) Write down an equation that describes the First Law of Thermodynamics. What quantity is being conserved? Make sure that you fully describe any symbols that you use. (b) In the last four columns of the following table fill in the boxes with a –, + or 0 depending on whether the quantities decrease, increase, or remain (approximately) unchanged, respectively. Provide brief explanations as to your choices. Situation System Heat Work Done Change in Internal Energy Change in Temperature Rapidly letting air out of a bicycle tire Air in the pump Covered pan of hot water sitting on a bench top at room temperature Water in the pan (c) The figure shows a cylinder containing a gas which is closed by a moveable piston. The cylinder is submerged in an ice-water mixture, and the gas is initially in thermal equilibrium with the ice-water. The piston is pushed down very quickly from position 1 to position 2. It is then held at position 2 until the gas is again in thermal equilibrium with the ice-water. The piston then is slowly raised until it returns to position 1. Sketch a Pressure-Volume diagram showing the changes that have taken place, and indicate briefly what thermodynamic processes are taking place at each stage around one complete cycle. If 200g of ice are melted during one cycle, how much work has been done on the gas? Lfusion=3.33 x 105 J/kg. ice and water
