photoelectric effect

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We looked at the photoelectric effect last week.  This video has a similar demonstration to the gold leaf electroscope experiment I showed you in class and includes an explanation of the process.

Click on the picture below to download the simulation we used to investigate the effect of irradiance on frequency on photocurrent.

You can change the metal under investigation (we used zinc in class).  You can also vary the wavelength and irradiance of the light.   Notice that below the theshold frequency you can’t get any photoelectrons, even if you set the light to its brightest setting.

star classification

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We know that our sun is a fairly common star.  In fact, the fanciest thing about our sun is probably the fact that the 3rd planet (Earth) in its solar system has life!

In this video, astronomers talk about how they can use the line spectra from stars to classify them into different categories.

electric motors

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image by explainthatstuff

We’re finishing off the electricity unit by looking at electric motors.  The page I used in class to help explain how a simple electric motor works is available here.

Here is another nice animation that shows the key parts of an electric motor.  It will stop after a few rotations but just reload the page to see it again.

Real electric motors have a few modifications;

  • they use field coils instead of a bar magnet – the field coils form a strong electromagnet when current passes through them.  The field coils do not rotate.
  • the single rotating coil is replaced by several rotating coils
  • there are more contacts on the commutator – each pair connects to a different rotating coil
  • the brushes are often made from carbon instead of metal – the carbon conducts electricity and can withstand high temperatures.  Carbon also moulds to the shape of the commutator to give a good electrical contact

image by marrrci