# Homework 3/2/99

Q4.  The following circuit will permit a single light to be turned on/off by either of two switches.  How would you expand this circuit so a single light can be turned on/off by any of three or four or more switches?

Q 7.  In an automobile a single wire goes from the positive terminal of the battery to each of the electrical appliances in the vehicle.  The electricity returns to the battery through the "ground."  The second terminal of each device is connected to the metal body of the vehicle and the negative terminal of the battery is also connected to the metal body to make this return through the "ground" possible.

Q 8.  The arguement that P must decrease as R increases based upon the equation P = V2/R,  assumes that V is held constant as R increases.  The arguement that P must increase as R increases based upon the equation P = I2R assumes that the current is held constant as R increases.  In fact, both cannot be simultaneously held constant.   If V is held constant because a battery supplies the power, only the arguement based upon P = V2/R is valid.  In P = I2R, I decreases (due to I = V/R) and R increases.  Since the I2 factor is squared, its decrease is much greater than the increase in the R factor.  The net effect is a decrease in P which is the same as that predicted by P = V2/R.

Q11.  A 100W lightbulb draws more current than a 50W bulb.  Since P = VI and since V is the same in both cases, I = 100W/120V is greater than I = 50W/120V.
The 100W light bulb has a smaller resistance than the 50W bulb.  Since P = V2/R and since V is the same in both cases, R = 120Vx120V/100W is smaller than R = 120Vx120V/50W.