Question 2 (10 marks) A sample of an unknown gas (gas A) has a volume of 3. 2 mm at a temperature of 10 co. Another sample of an unknown gas (gas B) has a volume of 4. 5 mm at a temperature of 250 co. Assuming that both gases obey Charles’ law at all temperatures and are at the same pressure, (a) Could gas A and gas B be samples of the same gas at different temperatures? (b) What is the volume of gas A at the following temperatures: -50 co, O co, 50 co, 100 co ? Question 3 (10 marks) The core temperature of an athlete is 37 co and his surface area is 1. 2. The thermal conductivity of his surface tissue, which is mm thick on average, is 0. Maw -1 K-1. If heat is transferred from his core to his skin at a rate of OWE, what is the average temperature of his skin surface? Question 4 (1 5 marks) A cyclist does 2 MS of mechanical work over the course of a day. His work efficiency is 20% and the metabolic energy of the food consumed during the day is MM]. (a) What is the net metabolic energy used during the day? (b) How much heat does the cyclist transfer to his surroundings during the day? (c)
How much extra food will the cyclist need to consume at the end of the day in order not to loose weight? Question 5 (9 marks) In a chemical reaction, the two ends of a 2. 45-mm-long DNA molecule acquire charges of +e and -e , respectively. What is the force between the two ends of the molecule? Question 6 (1 5 marks) Sodium ions (An+) are flowing through a cylindrical ion channel which has a diameter of 0. 85 pm and is 5 pm long. There is a potential difference of move between the ends of the channel. The sodium ions have a drift velocity through the channel of . Moms-1 and in a period of 1 ms a total of 15×106 ions exit the channel. (a) What total charge exits the channel in a time period of 1 ms? (b) What is the current in the (c) What is the ‘resistance’ of the channel to the flow of sodium ions? (d) What is the number density, n, of ions in the channel? (e) How many sodium ions are in the channel at any one time? Question 7 (16 marks) A defibrillator can be modeled as a capacitor which discharges through the patient, inducing an electrical current in the chest.
The resistance of the path which the electrical current takes through the chest of a typical adult is 50 k. A particular defibrillator has a capacitance of 16. 67 NFG and is designed to be charged to an electrical potential of 900 V before discharging. The defibrillator includes a ‘ballast’ resistor of 40 OK which is connected in series with the patient. (a) What is the maximum current Imax that will pass through the typical adult patient’s chest? (b) How long will it take the current passing through the typical adult patient’s chest to drop below 1. Mama?
You wish to redesign this defibrillator so it can be used on a child. The resistance of the typical child’s chest is around 40 OK and the maximum current that be allowed through the chest is AMA. The current must drop to 0. Main 4 ms. If the defibrillator is charged too maximum potential of 900 V as before, then (a) What is the required resistance that must be connected in series to the child patient’s chest? (b) What is the required capacitance of the defibrillator? Question 8 (1 5 marks) In a region of space there is a uniform magnetic field of magnitude 0. Mat pointing vertically straight down. A) If an electron is moving in the horizontal plane at a peed of 550 SMS-l , what will the radius of the resultant circular path be? (b) Will the electron be moving clockwise or counter-clockwise when viewed from above? (c) If a positron (same mass as an electron but with a charge of +CEQ ) is moving in the horizontal plane at speed of 550 SMS-l , what will the radius of the resultant circular path be? (d) Will the positron be moving clockwise or counter-clockwise when viewed from above? (e) How fast would an 0 particle 0 need to be traveling to have a path of the same radius as the electron in part (a)?