Quick Answer / Short Answer Questions. (Estimated time per problem: 3-4 minutes). (Maybe 5-6 problems like these will be on the first part of the exam.) 1) How much energy does it take to run 20mA of current from a 3V potential to a 5V potential for 3 seconds? 2) A 2nC charge is 4mm away from a 3nC charge. What's the magnitude of the force on an electron halfway between those two charges? 3) A conducting ball is placed near a strong negative charge. Which will be at a higher potential: The side of the ball near the charge, or the side of the ball opposite the charge (or neither)? WHY? (2/3rds of the points are usually for the "why".) 4) Three identical lightbulbs are connected in parallel to a 12 Volt battery. 100mA runs through the battery. What's the resistance of each lightbulb? 5) A lightbulb is connected to a constant emf source. After it turns on, it heats up, increasing its resistance. As it heats up, does the the bulb's brightness (the power used) increase, decrease, or stay the same? WHY? 6) Air becomes conducting at an electric field of 3 million volts/meter. What's the maximum charge you can put on a 2mm-radius sphere? (before it leaks off through the air) 7) A parallel plate capacitor with 1cm x 1cm size plate is hooked up to a constant emf source. As the distance between the plates is decreased by 20%, what happens to the total charge on the plates? 8) A neuron is made up of chains of 1mm-long "axons" which have both a capacitance (1.6pF) and a resistance (25M2). If they are to send an electrical signal, one axon has to charge up before it can send that signal to the next axon. Estimate the speed at which the signal can propagate down the neuron, from axon to axon. (Hint: think of the charging process in terms of a resistor in series with a capacitor.) 9) How strong is the electric field 10cm off the axis of a long copper cylinder? The cylinder is 4m long, a radius of 1cm, and carries a total charge of 1mC. (spread out evenly) 10) Two protons are 1nm apart. How much energy would it take to position a third proton halfway between them? (Bring the proton in from infinity; give answer in eV.)

Quick Answer / Short Answer Questions. (Estimated time per problem: 3-4 minutes). (Maybe 5-6 problems like these will be on the first part of the exam.) 1) How much energy does it take to run 20mA of current from a 3V potential to a 5V potential for 3 seconds? 2) A 2nC charge is 4mm away from a 3nC charge. What's the magnitude of the force on an electron halfway between those two charges? 3) A conducting ball is placed near a strong negative charge. Which will be at a higher potential: The side of the ball near the charge, or the side of the ball opposite the charge (or neither)? WHY? (2/3rds of the points are usually for the "why".) 4) Three identical lightbulbs are connected in parallel to a 12 Volt battery. 100mA runs through the battery. What's the resistance of each lightbulb? 5) A lightbulb is connected to a constant emf source. After it turns on, it heats up, increasing its resistance. As it heats up, does the the bulb's brightness (the power used) increase, decrease, or stay the same? WHY? 6) Air becomes conducting at an electric field of 3 million volts/meter. What's the maximum charge you can put on a 2mm-radius sphere? (before it leaks off through the air) 7) A parallel plate capacitor with 1cm x 1cm size plate is hooked up to a constant emf source. As the distance between the plates is decreased by 20%, what happens to the total charge on the plates? 8) A neuron is made up of chains of 1mm-long "axons" which have both a capacitance (1.6pF) and a resistance (25M2). If they are to send an electrical signal, one axon has to charge up before it can send that signal to the next axon. Estimate the speed at which the signal can propagate down the neuron, from axon to axon. (Hint: think of the charging process in terms of a resistor in series with a capacitor.) 9) How strong is the electric field 10cm off the axis of a long copper cylinder? The cylinder is 4m long, a radius of 1cm, and carries a total charge of 1mC. (spread out evenly) 10) Two protons are 1nm apart. How much energy would it take to position a third proton halfway between them? (Bring the proton in from infinity; give answer in eV.)