Meaning & use
time constant
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Meanings
nouncountablephysicstechnical
A measure of how quickly a system responds to a change, defined as the time it takes to complete about 63 percent of its change.
Grammar: Countable and usually singular with the: the time constant of the circuit. Often followed by of.
Patterns
- the time constant of something
- a time constant of five seconds
The time constant of the circuit is the product of its resistance and capacitance.
A larger time constant means the voltage rises more slowly.
The sensor has a time constant of two seconds, so it reacts slowly to sudden changes.
nouncountablebiologytechnical
In biology and medicine, a similar measure of how quickly a process, such as a nerve cell's electrical response, settles.
Grammar: Used with the cell or process being described: the membrane time constant.
Patterns
- the membrane time constant
The membrane time constant tells how fast a neuron responds to a signal.
Researchers measured the time constant of the muscle's response.
A short time constant means the cell reacts quickly.
Word forms
| plural | time constants |
|---|
Common combinations
- an RC time constant
- The RC time constant sets how fast the capacitor charges.
- measure the time constant
- Students measured the time constant using an oscilloscope.
- a long time constant
- A long time constant makes the signal change gradually.
- a short time constant
- The sensor has a short time constant, so it responds quickly.
- the thermal time constant
- The thermal time constant of the oven is several minutes.
Synonyms and how they differ
- response time
- Response time is a looser term for how long a system takes to react, while time constant is a precise value for exponential change.
- decay time
- Decay time refers to a falling signal, whereas time constant covers both rising and falling changes.
- lag
- Lag is an everyday word for a delay and does not imply any specific mathematical value.
Word family
- constant noun
- a quantity that does not change
- constant adjective
- staying the same over time
- exponential adjective
- increasing or decreasing at a rate proportional to the current value
- half-life noun
- the time for a quantity to fall to half its value
Commonly confused: time constant or half-life?
time constant vs half-life
Half-life is the time to fall to 50 percent, while the time constant marks about 37 percent remaining, or 63 percent completed.
Practice
In a circuit, doubling the time constant will do what to the speed of the response?
Choose one answer.
A larger time constant means the system takes longer to reach its final value, so the response is slower. It does not stop the response or change nothing.
Make it your own
Write a sentence using “time constant”, then check it and compare it with the examples above.