Hitesh Rana

The mean of 100 observations is 50. If one of the observation which was 50 is replaced by 150 then what will be the resulting mean?

Resistance is a concept used for DC (direct currents) whereas impedance is the AC (alternating current) equivalent. Resistance is due to electrons in a conductor colliding with the ionic lattice of the conductor meaning that electrical energy is converted into heat. Impedance is a more general term for resistance that also includes reactance. In other words, resistance is the opposition to a steady electric current. Pure resistance does not change with frequency, and typically the only time only resistance is considered is with DC (direct current -- not changing) electricity. Reactance, however, is a measure of the type of opposition to AC electricity due to capacitance or inductance. This opposition varies with frequency. For example, a capacitor only allows DC current to flow for a short while until it is charged; at that point, current will stop flowing and it will look like an open. However, if a very high frequency is put across that capacitor (a signal that has a voltage which is changing very quickly back and forth), the capacitor will look like a short circuit. The capacitor has a reactance which is inversely proportional to frequency. An inductor has a reactance which is directly proportional to frequency -- DC flows through easily while high-frequency AC is stopped. Impedance is the total contribution of both -- resistance and reactance. This is important for AC analysis and design. At DC, reactive elements can be replaced with their steady-state model (capacitor->open,inductor->short) and resistance can be considered. (this isn't true for transient analysis)