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How much voltage or current should be applied for impedance measurement to a human body?
Since the objective is to find out the impedance between two points, it is advisable to have a meter that has a high input impedance; the higher the better. This is because when the probes are applied across the "impedance" to be measured, the input impedance of the meter is effectively in parallel with the measured impedance. So, if the input impedance of the meter is infinite, the accuracy of measurement will be 100%.
Now, let us take a look at the situation on the human body: If the 2 points for measurement are selected on the same acupuncture meridian, the impedance will be lower than if you select one point on the meridian and one point randomly on the other parts of the body. If you select 2 points (not on any meridian) randomly on the human body, the impedance will even be higher.
If you are using electrodes with sticky pads for skin contact, the result will be different from that measured with acupuncture needles puncturing the 2 points.
Hope this is helpful.
K. Kit Sum.
What else can I help you with?
When are voltage and current out of phase?
Because the impedance of the inductor and capacitor is not a real resistance / has an imaginary value that causes voltage and current to be out of phase. An inductor's impedance is equivalent to j*w*L (j = i = imaginary number, w = frequency in radians, L = inductance), while a capacitor's impedance is 1/ (j*w*C). The 'j' causes the phase shift.
What are voltage controlled voltage source?
when the magnitude of voltage of a source is controlled by another small voltage source in the circuit the former is called voltage controlled voltage source and the later is called controller voltage source.
Can impedence inversion be obtained by a short circuit stub?
No, impedance inversion cannot be achieved with a short circuit stub. A short circuit stub will have a low impedance at the point where it is connected, which will not invert the impedance at that point. Impedance inversion can be achieved using techniques such as a quarter-wave transformer or a transmission line with specific impedance characteristics.
What is the function of operator 'j' in alternating current?
The operator 'j' represents the imaginary unit in alternating current circuits. It is used to denote the phase difference or angular displacement between voltage and current waveforms in complex impedance calculations. The use of 'j' helps in simplifying mathematical calculations in AC circuits by treating the impedance as a complex number.
How much current would a 15W light bulb draw if it had 120 volts applied to it?
Basically, Power = Current*Voltage Current = Power/Voltage Current = 15/120 Current = 0.125A or 125mA
Impedance of electric circuit?
The impedance of electric circuit refers to the measure of the opposition that a circuit presents to a current when a voltage is applied.
Why LV side is shorted in short circuit test?
Transformer short circuit tests are used to determine the impedances (positive and zero sequence) of the transformer. A simple explanation: to do this one winding is shorted, and voltage is applied to another winding to circulate the normal full load current of the transformer. The impedance of the transformer is the applied voltage divided by the induced current. If one winding was not shorted, the voltage divided by induced current would not give the impedance of the transformer - the induced current would be much lower, giving a much higher impedance measurement that would be essentially meaningless.
Impedience of electric circuit?
The impedance of an electric circuit is the measure of the opposition presented by a circuit when the current and voltage is applied.
Does it matter if the voltage leads the current or the current leads the voltage?
Yes. If voltage leads the current, the impedance is inductive (this would be the case if the load is a motor). If current leads the voltage, the impedance is capacitive (this would be the case for a CFL light bulb).
Why does the ratio of the voltage to current in capacitor and inductor depend on frequence?
The ratio of voltage to current, or the impedance, of reactive elements such as capacitors and inductors depends on the frequency of the applied wave because they store energy, and the amount of energy they store is directly related to the frequency of the applied waveform. When a DC voltage is applied to a capacitor, the current through the capacitor initially will be large, and will decay down to zero as the capacitor charges. Also, the voltage across the capacitor will be small initially and will increase over time to be equal to the applied voltage. This behavior results in a varying impedance when an AC waveform is applied. At a very low frequency, the capacitor will charge up and discharge similarly to if a DC source was switched into the capacitor for a long period of time there would be a large voltage drop, and small current = high impedance). As the frequency increases, the capacitor will appear more like a DC source was initially switched into the capacitor (low voltage drop and high current = low impedance).
WHY does the ratio of the voltage to current in capacitor and inductor depend on frequency?
The ratio of voltage to current, or the impedance, of reactive elements such as capacitors and inductors depends on the frequency of the applied wave because they store energy, and the amount of energy they store is directly related to the frequency of the applied waveform. When a DC voltage is applied to a capacitor, the current through the capacitor initially will be large, and will decay down to zero as the capacitor charges. Also, the voltage across the capacitor will be small initially and will increase over time to be equal to the applied voltage. This behavior results in a varying impedance when an AC waveform is applied. At a very low frequency, the capacitor will charge up and discharge similarly to if a DC source was switched into the capacitor for a long period of time there would be a large voltage drop, and small current = high impedance). As the frequency increases, the capacitor will appear more like a DC source was initially switched into the capacitor (low voltage drop and high current = low impedance).
What is the output impedance of a constant voltage source and constant current source?
The output impedance is z= V/I, the ratio of the constant voltage and the constant current source.
What is the maximum current that can be drawn from a voltage source?
The maximum current that can be drawn from a voltage source is dependent on the impedance of that source, the impedance of the connections to the source, and the energy available from that source.
HOW TO CALCULATE THE IMPEDANCE FOR THE TRANSFORMER?
The term, 'percentage impedance', is a little misleading, as it is defined as 'the value of primary voltage that will cause rated current to flow in the secondary winding, expressed as a percentage of the rated primary voltage'. So, the test is carried out as follows: the secondary winding is short-circuited through an ammeter capable of reading the rated secondary current. A variable voltage is applied to the primary winding. The primary voltage is gradually increased until the ammeter indicates rated secondary current. That primary voltage is then expressed as a percentage of the rated primary voltage -and that value is the transformer's 'percentage impedance'.
Why infinite current flows when voltage applied is zero?
No current flows when the applied voltage is zero.
What is the impedance of a single phase inductive circuit having a voltage of 240volts and a current flow of 10amps?
Work it out for yourself. The equation is: Z = E/I, where Z is the impedance, E is the supply voltage, and I is the load current.
What is electrical impedence?
Electrical impedance is the total opposition to current flow. It includes both a resistive, or DC component and a reactive, or frequency-dependant component. Impedance is the same as resistance if the applied voltage is DC. For AC voltage, the reactive components opposition to current flow changes with frequency, so impedance is typically specified at a particular frequency.
