# Welcome to Time Constant Learning Resource

## What do I learn in this resource?

There are many examples of the time constant in the world around us. For example, it takes time for objects to heat up and cool down. You wouldn't put your hand on a cooker just after you turned it off - you have to wait for it to cool down. The way it cools down is interesting - most of the cooling happens very quickly followed by a more gradual return to normal temperature. Then it is safe to touch. The time constant is a measure of how long this takes.

In this resource, you will learn the following:

• Why the above example and lots of others are known as first order systems
• What is meant by a step change to the input
• An example of a first order system, the RC circuit
• A definition of the Time Constant
• That it takes 5 time constants to reach steady state
• That 63% of the change has occured in the first time constant
• Describe an experiment to measure the time constant of a system

## How do I use this resource?

To use this resource fully you should go through each link on the banner at the top of the page. I've described them quickly below:

• Lesson 1 is a learning object on the RC Circuit which is an example of a first order system. Here, the input is the volage across R and C and is stepped by switching on the circuit. The output is voltage across C.
• Some of the terminology might get confusing so you can go to the Terminology page to check definitions you're not sure about.
• A demonstration of ???
• Some sample questions