## Cooling, undercooling and Latent Heat

In this experiment we will analyze the temperature variation of a sample of water through melting and solidification. For this I used a resistive thermometer into a test tube and connected to an analog pin on the Arduino board. To cool the sample I prepared a freezing mixture (ice, water and salt) in a thermos steel, which was maintained at about -7 ° C for several hours. A good explanation of why these temperatures are achieved with this mixture, we can find in this  link .

It is a known fact that suits wear light colors when it’s hot and we are exposed to sunlight. The reason is that light colors reflect more radiation they receive, than dark colors, which absorb more radiation than the first. By absorbing more radiation heat up faster, reach a higher temperature, and transfer more heat to the environment. This experience is intended to show what the relationship between the clear, as to the absorption of radiation, mainly dark colors and heat.

To realize we will expose two cans, one painted white and painted black, in the light of an incandescent bulb of 60 watts, which delivers enough heat to the environment (also can be made in the light of the sun) recording changes temperature until it is almost stable and then graph the results.

## Period of a pendulum

The period of a pendulum is the time it takes to perform this oscillation, ie, going back and forth.

In theory, this time depends directly on the length of thread and inversely on the acceleration of gravity, by the equation:

where T is the period, l the length of wire and g the acceleration of gravity, equal to .

In this experiment we use an infrared barrier to detect the passage of the thread through a point in his career. You can use any infrared barrier market but on teaching issues, we describe the assembly of that use.

## Charging a capacitor

A capacitor is a device capable of storing electrical charges. To load is applied a potential difference and accumulate charges to its full capacity. The maximum amount of charge that can accumulate divided potential difference is a property called capacitor capacitance , and is an indicator of the amount of energy it can store.