# Week 28 (Mar. 3 - 7)

**Reading:**Finish our work on DC circuits.

**DC circuits laboratory, Joule heating, charging and discharging of a capacitor**

Key Topics:

Key Topics:

**Lab:**Finish electronic circuits lab. This must be handed in by Friday, March 8 night at midnight. Your write-up should include all three experiments you did: (1) the resistors in parallel and series, (2) measuring the V vs I characteristics for a single resistor, and (3) measuring the V vs I characteristics of a tungsten light bulb. For each experiment, you must describe (1) the equipment and experimental setup, including a circuit diagram, (2) the procedure for carrying out your experiment, (3) plots of your data (for the second two experiments) and (4) explanation of your results (i.e. did you measure what you expected? if not, why not?)

**Week 28 Homework Problems:**

**Circuit analysis:**Consider three light bulbs with resistances 1, 2 and 3 ohms. The 1 and 2 ohm are placed in parallel. This parallel combination is then placed in series with the 3 ohm bulb. The whole thing is then placed between the terminals of a 120 volt battery. Find (a) the voltage across each bulb, (b) the current flowing through each bulb, and (c) the power dissipated (in Watts) in each bulb.**Charge stored on capacitors:**Find the charge stored by two 1muF capacitors charged up using a 1 kV power supply when they are arranged (a) in parallel and (b) in series. Generally speaking, which stores more charge: a parallel or a series arrangement of capacitors?**Adding capacitors:**Suppose you have three capacitors on your lab bench: 1 muF, 2 muF, and 4 muF. How many possible capacitances can you form with these? You can use any combination in series, parallel or alone.**Time to charge a capacitor:**A circuit consists of a battery (10 volts) in series with a resistor (1 mega-ohm) and then a capacitor (5 micro-farads). The battery can switched on in order to charge up the capacitor. First, make a sketch of your electronic circuit. Next, find (a) the time constant of the circuit, (b) the maximum charge on the capacitor when fully charged, and (c) the current flowing out of the battery at time t = 10 seconds after the battery is turned on. Finally, make a sketch of the (d) the voltage across the capacitor as a function of time and (e) the current flowing out of the battery as a function of time.