Determining the constants R and L of a coil

In summary, the values of R and L for the given voltage readings at 60 Hz are R = 5 ohms and L = 26.5mH. The current is found to be 2A by using Ohm's law. The coil is treated as an ideal inductor with impedance wL and resistance R in series. The resistance of the coil adds to the total resistance of the circuit. To calculate the resultant impedance of an inductor and a resistor connected in series, phasor magnitudes should be used as the voltages are measured at different times and are in RMS form.
  • #1
viciado123
54
0
We determined the constants R and L of a coil by placing it in series with a standard resistor of 10 ohms and reading the voltages on the terminals of Rs, the coil and the series circuit complete. What are the values of R and L for the following voltage readings at 60 Hz:
Vrs = 20; Vcoil = 22,4; Vt = 36

Answer:
R = 5 ohms
L = 26,5mH

I find the current
Vrs = I . Zr
20 = I . 10 I = 2A
Now I do not know how to find R and L
 
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  • #2


Is this an experiment you've done? Do you have a circuit diagram for this? I'm curious because those voltages don't agree with each other. (if they are measured at the same time, and the circuit is what I think it is)

A diagram is almost a necessity for any circuit question since a small change might significantly alter how current and voltage behave.
 
  • #3


Is this an experiment you've done? Do you have a circuit diagram for this? I'm curious because those voltages don't agree with each other. (if they are measured at the same time, and the circuit is what I think it is)

A diagram is almost a necessity for any circuit question since a small change might significantly alter how current and voltage behave.
 
  • #4


viciado123 said:
I find the current
Vrs = I . Zr
20 = I . 10 I = 2A
Now I do not know how to find R and L

The current is OK. You know that in Ac circuits, the voltage is impedance times current.
Usually the ohmic resistance of a coil can not be ignored, so you need to treat the coil as an ideal inductor with impedance wL and resistor R in series.

This resistance of the coil adds to the resistance of the total circuit,
too.

Do you know how to calculate the resultant impedance of an inductor L and a resistor R connected in series?

ehild
 
  • #5


All right, I get it now. The question should mention that those are the AC peak voltages. You should use phasor magnitudes in your calculations. So they aren't measured at the same time.
 
  • #6


cartonn30gel said:
All right, I get it now. The question should mention that those are the AC peak voltages.

Or rather RMS voltages. The AC voltmeters read the RMS voltage usually.

ehild
 

1. How do I determine the constant R of a coil?

To determine the constant R of a coil, you can use the formula R = V/I, where V is the voltage across the coil and I is the current passing through it. You can measure the voltage and current using a multimeter and then calculate the value of R.

2. What is the significance of the constant R in a coil?

The constant R, also known as the resistance of a coil, measures the opposition of the coil to the flow of electric current. It is an important parameter in determining the behavior of the coil in an electrical circuit.

3. How can I find the constant L of a coil?

The constant L of a coil, also known as the inductance, can be found by measuring the rate of change of current passing through the coil when a known voltage is applied. This can be done using an oscilloscope or a function generator.

4. What does the constant L represent in a coil?

The constant L represents the ability of the coil to store energy in the form of a magnetic field when a current passes through it. It is a crucial parameter in determining the behavior of the coil in an electrical circuit, especially in AC circuits.

5. How can I accurately determine the constants R and L of a coil?

To accurately determine the constants R and L of a coil, you can perform various experiments and measurements using different techniques and equipment such as multimeters, oscilloscopes, and function generators. It is important to take multiple measurements and calculate the average values to ensure accuracy.

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