<p> Physics 112 HW15 Due Friday, 17 October 2014</p><p>VIR02. Consider the circuit at right. The (non-ideal) voltmeter has a resistance of 900 kΩ. Calculate the voltage the voltmeter reads (the voltage across resistor R) if a) R = 10 Ω, b) R = 10 kΩ, and c) R = 10 MΩ. d) Repeat parts a – c if the voltmeter is ideal (it has essentially infinite resistance). Does the finite resistance of voltmeters matter?</p><p>VIR03. Consider the circuit at right. Both voltmeters and the ammeter are ideal; the “r” represents the internal resistance of the battery. The switch is initially open, and the voltmeter V1 reads 10 volts. a) What does ammeter A read? b) What does voltmeter V2 read? c) What is the voltage of the battery’s ideal voltage source? The switch is now closed. V1 now reads 9V, V2 now reads 3V, and the ammeter reads 0.5A. d) Determine the values of r, R1, and R2. Open the switch and replace the two voltmeters with crappy non-ideal voltmeters each with an internal resistance of 100Ω. Also replace the ideal ammeter with a non- ideal ammeter with internal resistance 1Ω. The resistors r, R1, and R2 have the values you determined in part d above. e) Determine what V1, V2, and A read now. Close the switch. f) Determine what V1, V2, and A read now.</p><p>K02. (Wolfson, Ch. 25 Problems 75 and 76) The figure at right below shows a portion of a circuit used to model the electrical behavior of long, cylindrical biological cells such as muscle cells or the axons of neurons. a) Find the current through the “battery” V3, given that all resistors have the same value R = 1.5 MΩ and V1 = 75 mV, V2 = 45 mV, and V3 = 20 mV. Be sure to specify the direction of the current. b) An electrochemical impulse traveling along the cell changes the value of V3 so that now it supplies an upward current of 40 nA. Assuming the rest of the circuit remains as described in part a), what is the new value of V3?</p>