## Physics Tutorial

#### Intro

In this tutorial, we will look at how we can transfer heat from a low temperature region to a high temperature region.

#### Sample Problem

Heat flows from a high temperature region to a low temperature region. Is it possible to transfer heat from a low temperature region to a high temperature region?

#### Solution

Yes. Air-conditioner works in this way.

When heat flows from a high temperature region to a low temperature region, it happens naturally. No energy is required in this process. To transfer heat from a low temperature region to a high temperature region, we need energy.

Air-conditioner requires electricity to operate. Electricity is the source of energy for transferring heat from our home (a low temperature region) to outside air (a high temperature region). Besides, we need a medium for heat transfer which is called refrigerant. Liquid refrigerant absorbs heat inside our home at the evaporator. After absorbing heat, it evaporates and becomes a gas. The gas is then compressed and is delivered to a condenser which is located outside our home. At the condenser, gaseous refrigerant loses heat to the outside air and condenses to form liquid. The liquid refrigerator then flows back to the evaporator and the whole cycle repeats.

The key concept in here is that heat flows naturally from a high temperature region to a low temperature region but energy is required to transfer heat from a low temperature region to a high temperature. When we turn on air-conditioning, we are consuming energy. In order to save energy, we should reduce the use of air-conditioning.

The above concept can also be applied to chemistry. Diffusion from high concentration to low concentration is a natural process. Separation process such as distillation requires energy.

Can you now explain the difference between diffusion and active transport in biology?