Site Logo Home
 
rOm
Quest
Glossary
 
Random
Page
Search
Site
Lush
Sim
Class
Subject
Images
 
Help
FAQ
Sign
Up
Log
In
AS Level     >Timing<     RC Timing     Schmitt NOT Astable    

Timing


Site for Eduqas/WJEC - Go to the AQA site.

  AS Level    RC Timing   0 of 3    Question 6    RC Time Constant 
Score 0/0 
Not attempted  
Last Answer  
Deadline not set1 of 3    Question 592    RC Time Constant 
Score 0/0 
Not attempted  
Last Answer  
Deadline not set2 of 3    Question 593    RC Time Constant 
Score 0/0 
Not attempted  
Last Answer  
Deadline not set3 of 3    Question 594    RC Time Constant 
Score 0/0 
Not attempted  
Last Answer  
Deadline not set  Questions 0 to 3   -->  View All  

Use a resistor and a capacitor to make a timing circuit.
Time Constant:   T   =   R C   =   The time for the capacitor to charge or discharge by 63%.

View the RC timer in the Lushprojects Simulator

The time constant calculations below are needed for designing timing circuits.

In this circuit, when the switch is flipped, the voltage across the capacitor changes quite fast and the current flowing is larger. As the capacitor approaches full charge (or discharge) the voltage changes more slowly and the current is smaller. The current is proportional to the rate of change of voltage.

Here is a Flash animation of a water analogy. The container represents the capacitor. It takes time to fill or empty. When the tank is nearly full or empty, the level changes much more slowly. Capacitors behave the same way.

RC Timing Calculations

Charging

Capacitor Charging Graph
  • R = 1000000 Ohms.
  • C = 1 Microfarad.
  • R C = 1 Second.
0% T = 0 Seconds
50% T = 0.69 R C Seconds
63% T = R C Seconds
66.6% T = 1.1 R C Seconds (555 Monostable)
100% T = 5 R C Seconds

 

Discharging

Capacitor Discharging Graph
  • R = 1000000 Ohms.
  • C = 1 Microfarad.
  • R C = 1 Second.
100% T = 0 Seconds
50% T = 0.69 R C Seconds
37% T = R C Seconds
0% T = 5 R C Seconds

 

Experiment

The aim is to measure the voltage across a charging capacitor at regular time intervals. Once the capacitor is fully charged, repeat the measurements while it is discharging. These results should be plotted on a graph. The graph should then be marked up with the key positions listed above.

Capacitor Charging Experiment

Capacitor-Charging-Experiment-Layout.gif

Tasks

Plot and Label the Graph

Charging ...

Discharging

Leakage

Picoscope Traces for a Faster Timing Circuit

Capacitor Charging Picoscope Measurements

Subject Name     Level     Topic Name     Question Heading     First Name Last Name Class ID     User ID    

fff
Home
<<<
ppw
Pg Up
<<
ppp
Up
<
|||

>|<
nnn
Down
>
nnw
Pg Down
>>
lll
End
>>>

Close
Escape
X

Q: qNum of last_q     Q ID: Question ID         Score: num correct/num attempts         Date Done    

 

Submit
Enter

 

Question Text

image url

 


Help Link

Add     Delete     Clone     Edit     Hardness

Help Text
Debug


 

 

 

Contact, Copyright, Cookies and Legalities: C Neil Bauers - reviseOmatic V4 - © 2016/17

Hosted at linode.com - London