amirks

I'm thinking of getting the most out of gaming from my laptop with a new installation of Windows XP. I won't be browsing the Internet, reading emails or downloading and running files; just playing online mmo games. Is it okay if I don't install any security software (antivirus or firewall) and also do not update my windows (keep it at sp1) so to waste as less resources as possible? (I will be running hijackthis occasionally to make sure nothing fishy is going on)

Consider the case of a disk of radius a, carrying a surface charge density σ that varies linearly with the distance from the centre of the disk. If the disk rotates about its symmetry axis with an angular velocity of ω, calculate the magnetic field B a distance z above the midpoint of the disk. What is the electric field at the same point? so what I did was I said digma= cr c=constant and v=omega r so surface current I=sigma v = c omega r^2 now using amperian loop we have int (B.dl) = mu I(enc) i used an amparian loop with one vertical side corssing the centre with width of r and height of z above the disk (and below, and we have two vertical parts) so int (B.dl) = B4z and I(enc) = c omega r^2 r not sure if any of these are right, and also I thought of doing this by thinking of the disk as many narrow loops of charge and then find the current at each loop and then the field and .... plz helllp!!