# Solenoid time constant

Discussion in 'Physics' started by JardaK, Mar 20, 2015.

1. ### JardaK Thread Starter New Member

Mar 20, 2015
3
0
Hello,

I have a small problem.
Solenoid has a resistance of 14.2 ohms and an inductance 0.056H is connected in series with a resistance 2.2Ohm
Thus calculated is the Tau = L / R = 0,056 / (14.2 + 2.2) = 0.0034s
But the measured value is 0.02s
The measurement is done on an oscilloscope for resistance.
Source is a classic laboratory.

If I measure only air-core coil corresponds to the time constant.
How is it possible that tau is based on much more?

Solenoid Type:
Code (Text):
1.  http://docs-europe.electrocomponents.com/webdocs/001b/0900766b8001b732.pdf [/ code]
2.
3. Thank you for your response.

2. ### Alec_t AAC Fanatic!

Sep 17, 2013
7,010
1,450
Did you measure with the plunger extended or retracted? Plunger position will probably have a significant effect on inductance.

Edit: I don't think you should count the 14.2 Ohms as being in series with the coil when calculating Tau. So Tau = 0.056/2.2 = 0.025 s

Last edited: Mar 20, 2015
3. ### JardaK Thread Starter New Member

Mar 20, 2015
3
0
Why?
Coil having no core has a smaller inductance. This coil inductance and resistance 0.012H and 14.2Ohm
0.0012 / (14.2 + 2.2) result corresponds approximately

4. ### studiot AAC Fanatic!

Nov 9, 2007
5,005
519
Where did the inductance value come from?

Mar 20, 2015
3
0