40CHAPTER 2. OHM’S LAWEIRIf you know E and I, and wish to determine R, just eliminate R from the picture and seewhat’s left:EIREIR =If you know E and R, and wish to determine I, eliminate I and see what’s left:EIREI =RLastly, if you know I and R, and wish to determine E, eliminate E and see what’s left:EIRE = I REventually, you’ll have to be familiar with algebra to seriously study electricity and elec-tronics, but this tip can make your ﬁrst calculations a little easier to remember. If you arecomfortable with algebra, all you need to do is commit E=IR to memory and derive the othertwo formulae from that when you need them!• REVIEW:• Voltage measured in volts, symbolized by the letters ”E” or ”V”.• Current measured in amps, symbolized by the letter ”I”.• Resistance measured in ohms, symbolized by the letter ”R”.• Ohm’s Law: E = IR ; I = E/R ; R = E/I2.2An analogy for Ohm’s LawOhm’s Law also makes intuitive sense if you apply it to the water-and-pipe analogy. If we havea water pump that exerts pressure (voltage) to push water around a ”circuit” (current) through