Right here's an apology: - I'm sorry! I really should have forseen that someone would want to know what these words mean - in this context. I can/will add to this list as we may progress. For now just these: -
RESISTANCE - This is a measure of how well a DC (& sometimes an ac) current can flow in a circuit. We say that when 1 Volt causes a current of 1 Amp to flow the resistance in the circuit is 1 OHM. This then, is OHMS LAW. To get POWER in WATTS multiply the current (I) by the Volts (V).
CONDUCTANCE is the reverse of that with a unit called a MHO (mho) Get it? Don't worry about this, it rarely crops up!
IMPEDANCE - Still measured in ohms this is the complex ratio of sinusoidal (ac) voltage to current in a component or circuit consisting of two parts. The real & the imaginary. The real part is the RESISTANCE which will dissipate heat, the REACTANCE part is "imaginary" and does not dissipate.
REACTANCE - Measured in ohms this is the ac only part of any circuit or component. Characterised by the storage of energy rather than by Wattful dissipation.
NOTE:- Bear in mind that most/all practical electrical/electronic components are not "pure" in the sense that they have elements of all in them. In that regard, and for most practical circumstances, we can regard RESISTANCE as being for both DC & ac, but IMPEDANCE as being for ac circuits which are much less than pure. Usually containing INDUCTANCE and/or CAPACITANCE.
RMS - Root Mean Square. DC is what you get from a battery. It has a fixed polarity. Ohms law works! In ac power they use slip-rings on the generator to collect the current instead of a commutator - as in a motor or DC dynamo. There are advantages which outweigh the cons. Less arcing, less brush wear AND because the polarity keeps reversing (50Hz here - 60Hz in America), it is much safer for us! Muscles don't get held in relentless contraction. You can alter voltages up or down with a transformer. You can't do that with DC. The shape of the reversing wave is sinusoidal - that is relating to the cyclic operation of the generator. We need to know when this varying, & reversing voltage has the same heating effect as an equivalent DC voltage. Hence an average of what power is delivered. There's a formula which relates to the ROOT of 2. That's 1.414. The peak voltage will have to be 1.414 times higher than its DC equivalent to give the same heating effect. That means that a a 240Vac supply will have a peak of 1.414 X 240 = 339.6 Volts. In BOTH directions! That makes the Peak to Peak (p to p) Voltage = 679.4
The wave shape is traced in time like the valve on a wheel as it rolls. If the axle is at zero, the valve goes higher and lower than that describing a sine wave. Rotations / second is Hz. Think about it!
RESISTANCE - This is a measure of how well a DC (& sometimes an ac) current can flow in a circuit. We say that when 1 Volt causes a current of 1 Amp to flow the resistance in the circuit is 1 OHM. This then, is OHMS LAW. To get POWER in WATTS multiply the current (I) by the Volts (V).
CONDUCTANCE is the reverse of that with a unit called a MHO (mho) Get it? Don't worry about this, it rarely crops up!
IMPEDANCE - Still measured in ohms this is the complex ratio of sinusoidal (ac) voltage to current in a component or circuit consisting of two parts. The real & the imaginary. The real part is the RESISTANCE which will dissipate heat, the REACTANCE part is "imaginary" and does not dissipate.
REACTANCE - Measured in ohms this is the ac only part of any circuit or component. Characterised by the storage of energy rather than by Wattful dissipation.
NOTE:- Bear in mind that most/all practical electrical/electronic components are not "pure" in the sense that they have elements of all in them. In that regard, and for most practical circumstances, we can regard RESISTANCE as being for both DC & ac, but IMPEDANCE as being for ac circuits which are much less than pure. Usually containing INDUCTANCE and/or CAPACITANCE.
RMS - Root Mean Square. DC is what you get from a battery. It has a fixed polarity. Ohms law works! In ac power they use slip-rings on the generator to collect the current instead of a commutator - as in a motor or DC dynamo. There are advantages which outweigh the cons. Less arcing, less brush wear AND because the polarity keeps reversing (50Hz here - 60Hz in America), it is much safer for us! Muscles don't get held in relentless contraction. You can alter voltages up or down with a transformer. You can't do that with DC. The shape of the reversing wave is sinusoidal - that is relating to the cyclic operation of the generator. We need to know when this varying, & reversing voltage has the same heating effect as an equivalent DC voltage. Hence an average of what power is delivered. There's a formula which relates to the ROOT of 2. That's 1.414. The peak voltage will have to be 1.414 times higher than its DC equivalent to give the same heating effect. That means that a a 240Vac supply will have a peak of 1.414 X 240 = 339.6 Volts. In BOTH directions! That makes the Peak to Peak (p to p) Voltage = 679.4
The wave shape is traced in time like the valve on a wheel as it rolls. If the axle is at zero, the valve goes higher and lower than that describing a sine wave. Rotations / second is Hz. Think about it!
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