Exploring Fluorescence using a Laser

Thursday May 22, 2014

If you’ve ever wondered how glow in the dark toys stay bright even in the dark, this activity is just for you! When light hits a material, it’s either reflected, transmitted, or absorbed as we discovered with the gummy bear activity earlier. However, certain materials will absorb one wavelength and emit an entirely different wavelength, and when this happens it’s called “fluorescence”.  Let’s do an experiment first, and then we’ll go over why it does what it does.


Please login or register to read the rest of this content.

Measure your Hair Width with a Laser

Sunday April 21, 2013

Do you have thick or thin hair? Let’s find out using a laser to measure the width of your hair and a little knowledge about diffraction properties of light. (Since were using lasers, make sure you’re not pointing a laser at anyone, any animal, or at a reflective surface.)


Please login or register to read the rest of this content.

Laser Microscope

Thursday June 30, 2011

Did you know that you can use a laser to see tiny paramecia in pond water? We’re going to build a simple laser microscope that will shine through a single drop of water and project shadows on a wall or ceiling for us to study.


Please login or register to read the rest of this content.

Laser Basics

Wednesday February 3, 2010

Did you know that the word LASER stands for Light Amplification by Stimulated Emission of Radiation? And that a MASER is a laser beam with wavelengths in the microwave part of the spectrum? Most lasers fire a monochromatic (one color) narrow, focused beam of light, but more complex lasers emit a broad range of wavelengths at the same time.


In 1917, Einstein figured out the basic principles for the LASER and MASER by building on Max Planck’s work on light. It wasn’t until 1960, though when the first laser actually emitted light at Hughes Research Lab. Today, there are several different kinds of lasers, including gas lasers, chemical lasers, semiconductor lasers, and solid state lasers. One of the most powerful lasers ever conceived are gamma ray lasers (which can replace hundreds of lasers with only one) and the space-based x-ray lasers (which use the energy from a nuclear explosion) – neither of these have been built yet!


Please login or register to read the rest of this content.

Laser Maze

Wednesday February 3, 2010

By using lenses and mirrors, you can bounce, shift, reflect, shatter, and split a laser beam. Since the laser beam is so narrow and focused, you’ll be able to see several reflections before it fades away from scatter. Make sure you complete the Laser Basics experiment first before working with this experiment.


You’ll need to make your beam visible for this experiment to really work.  There are several different ways you can do this:


Please login or register to read the rest of this content.

Easy Laser Light Show

Wednesday February 3, 2010

Lasers are cool, but what can you do with one? This is a great introductory activity into what lasers are, how they work, and how different mediums (like glass, feathers, mirrors, etc.) can change the direction of the beam.


Lasers are a monochromatic (one color) concentrated beam of light. This means that when compared with a flashlight, the laser delivers more punch on a light detector. The alignment is more critical (as you’ll find out when you zig-zag a laser through several mirrors), so take your time and do these experiments in a steamy, dark bathroom after a hot shower. That way, you’ll be able to see the beam and align your optics easily.
Please login or register to read the rest of this content.


Electric Eye

Wednesday February 3, 2010

This is a super-cool and ultra-simple circuit experiment that shows you how a CdS (cadmium sulfide cell) works. A CdS cell is a special kind of resistor called a photoresistor, which is sensitive to light.

A resistor limits the amount of current (electricity) that flows through it, and since this one is light-sensitive, it will allow different amounts of current through depends on how much light it "sees".

Photoresistors are very inexpensive light detectors, and you'll find them in cameras, street lights, clock radios, robotics, and more. We're going to play with one and find out how to detect light using a simple series circuit.

Materials:

  • AA battery case with batteries
  • one CdS cell
  • three alligator wires
  • LED (any color and type)

Please login or register to read the rest of this content.

This is a super-cool and ultra-simple circuit experiment that shows you how a CdS (cadmium sulfide cell) works. A CdS cell is a special kind of resistor called a photoresistor, which is sensitive to light.

A resistor limits the amount of current (electricity) that flows through it, and since this one is light-sensitive, it will allow different amounts of current through depends on how much light it "sees".

Photoresistors are very inexpensive light detectors, and you'll find them in cameras, street lights, clock radios, robotics, and more. We're going to play with one and find out how to detect light using a simple series circuit.

Materials:

  • AA battery case with batteries
  • one CdS cell
  • three alligator wires
  • LED (any color and type)

Please login or register to read the rest of this content.


Laser Burglar Alarm

Wednesday February 3, 2010

This is a beefier-version of the Electric Eye that will be able to turn on a buzzer instead of a LED by increasing the voltage in the circuit. This type of circuit is a light-actuated circuit. When a beam of light hits the sensor (the “eye”), a buzzer sounds. Use this to indicate when a door closes or drawer closes… your suspect will never know what got triggered.
Please login or register to read the rest of this content.


Laser Door Alarm

Wednesday February 3, 2010

If you’ve already made the Laser Burglar Alarm (which is highly recommend doing FIRST), then you’re probably wondering how to make the circuit act in the opposite way… meaning how do you make it so that the buzzer sounds when the light is turned off?


This circuit requires more patience and parts, but it’s totally worth it. It uses the same parts as the previous experiment (plus a few more) with a couple of extra twists and turns in the circuit to let the buzzer know when it’s time to turn off. Use this in doorways or as an invisible trip wire trigger across hallways.


Materials:


  • Red laser pointer
  • 9V battery or two AA’s in a AA battery pack
  • 7 alligator clip leads
  • CdS Cell
  • 9V Battery OR 2 AA’s in a battery holder
  • NPN Transistor 2N3904 or 2N222A
  • 4.7k-ohm resistor
  • Buzzer (3-6V)
Please login or register to read the rest of this content.

Laser Light Show

Wednesday February 3, 2010

ss-laserWhat happens when you shine a laser beam onto a spinning mirror? In the Laser Maze experiment, the mirrors stayed put. What happens if you took one of those mirrors and moved it really fast?


It turns out that a slightly off-set spinning mirror will make the laser dot on the wall spin in a circle.  Or ellipse. Or oval.  And the more mirrors you add, the more spiro-graph-looking your projected laser dot gets.


Why does it work? This experiment works because of imperfections: the mirrors are mounted off-center, the motors wobble, the shafts do not spin true, and a hundred other reasons why our mechanics and optics are not dead-on straight.   And that’s exactly what we want – the wobbling mirrors and shaky motors make the pretty pictures on the wall!  If everything were absolutely perfectly aligned, all you would see is a dot.


Here’s how to do this experiment:


Please login or register to read the rest of this content.

Please login or register to read the rest of this content.


Flashlight Laser Tag

Wednesday February 3, 2010

This super-cool project lets kids have the fun of playing tag in the dark on a warm summer evening, without the "gun" aspect traditionally found in laser tag. Kids not only get to enjoy the sport but also have the pride that they build the tag system themselves - something you simply can't get from opening up a laser tag game box.

While real laser tag games actually never use lasers, but rather infrared beams, this laser tag uses real lasers, so you'll want to arm the kids with the "no-lasers-on-the-face" with a 10-minute time-out penalty to ensure everyone has a good time. You can alternatively use flashlights instead of lasers, which makes the game a lot easier to tag someone out.

This game uses a simple two-transistor latching circuit design, so there's no programming or overly complicated circuitry to worry about. If you've never built this kind of circuit before, it's a perfect first step into the world of electronics.

I've provided you with three videos below. This first video is an introduction to what we are going to make and how it works. Here's what you need:

NOTE: We updated this circuit in 2023 to reflect "best practices" when using transistors. 

Be sure to build this project as shown in the schematic and breadboard diagrams, and not as shown in the video.

The material list below is based on the new design as shown in the schematic and breadboard diagrams on this page.

The videos show how to build the old circuit, but are still very useful.


Please login or register to read the rest of this content.


Sunlight Alarm

Wednesday February 3, 2010

Wouldn’t it be nice to wake up your brother or sister using an alarm you build yourself, triggered by natural sunlight? The happy news is now you can, using your Flashlight Laser Tag circuit you already built!


Since your circuit is already sensitive to light, you can transform it easily into an alarm clock that will buzz or light up when hit by the sun’s rays.


Note – you can also use your Laser Door Alarm for this as well, since it’s also triggered by light. However, the Burglar Alarm will not work, because it gets triggered by darkness, so unless you want your alarm to sound just as your drifting off to sleep, you’ll want to use the Laser Door Alarm or the Flashlight Laser Tag circuit. Here’s what you need to know (it’s really simple…):


Please login or register to read the rest of this content.

Crystal Radio

Wednesday February 3, 2010

xtal3In addition to laser experiments, I thought you’d like to learn how to pick up sound that’s traveling on a light wave. A crystal radio is among the simplest of radio receivers – there’s no battery or power source, and nearly no moving parts. The source of power comes directly from the radio waves (which is a low-power, low frequency light wave) themselves.


The crystal radio turns the radio signal directly into a signal that the human ear can detect. Your crystal radio detects in the AM band that have been traveling from stations (transmitters) thousands of miles away. You’ve got all the basics for picking up AM radio stations using simple equipment from an electronics store. I’ll show you how…


The radio is made up of a tuning coil (magnet wire wrapped around a toilet paper tube), a detector (germanium diode) and crystal earphones, and an antenna wire.


One of the biggest challenges with detecting low-power radio waves is that there is no amplifier on the radio to boost the signal strength. You’ll soon figure out that you need to find the quietest spot in your house away from any transmitters (and loud noises) that might interfere with the reception when you build one of these.


One of things you’ll have is to figure out the best antenna length to produce the clearest, strongest radio signal in your crystal radio. I’m going to walk you through making three different crystal radio designs.


You’ll need to find these items below.


Here’s what you do:


Please login or register to read the rest of this content.