Rainy Night

Click the blank space above to see the animation.

In the previous lesson, we learned about the way light travels. Light travels in a straight path, but can reflect off of surfaces and refract through certain ones. In the picture above, the traffic light is reflecting off the wet ground, creating horizontally polarized light. Because the surface of the ground is wet, the light is able to reflect off of it. The angle of incidence and the angle of reflection (separated by the dotted line or normal) are equal to each other as you can see in the animation.

Cheeky Music

In our past unit of physics, we learned about waves! There are two types of waves: longitudinal and transverse. We learned a little bit about sound waves which are actually longitudinal waves made by air compressions/rarefactions. So anyways, for my blog today, I decided to make some music using my cheek flicking skillz.

How it works:
Flicking your cheek (or any part of your body for that matter) causes a tiny sound. When you slap a table, sound is heard. When you slap a can sound is heard. On certain objects, a slap can produce a nice ringing sound. In order for that to happen, the object has to have at least one open side where the sound waves can escape. We learned that the harmonic equation for a wave in a closed pipe is fn=n(v/4L) and the equation for the open pipe is fn=n(v/2L). Now that you know wave movement in a closed pipe and open pipe is possible (due to the equations), we can proceed with explaining what I did in this video.

As I flicked my cheek, my cheek vibrates. Vibration creates waves! So what waves are being created in this video? Well, because my cheek is vibrating, the air around it resonates with my cheek. HUH?! In laymen terms, the air feels the vibration and moves. So the air moves around just like it would in a closed pipe. Now why do I call this a closed pipe? Well, I actually have no idea if it is an open pipe or a closed pipe. I just assume it is a closed one because the waves eventually travel out of my mouth. I guess technically the waves could travel down my esophagus but that would still end up being a closed pipe because the waves would eventually hit my stomach acid and then bounce right back out of me......ANYWAYS! So its a closed pipe. And the waves are created by me flicking my cheek. So how am I changing the note? I developed a feel for the notes and my mouth automatically adjusts the size of its opening based on the note I want to play. Cool huh? **Feel free to check the "Brian is Awesome" tab below!

Motor: The Microwave Turntable

Almost every household appliance that moves uses a motor. This includes computers, microwaves, phones, washing machine, dryer, fans, etc... The microwave has a turntable inside which uses a motor to produce the rotating motion (well, at least my microwave has a motor that can do that :P). We learned that motors use coiled wires and magnets. The current within the coil and the electric field inside the coil determines the speed of the motor. The spinning motion is produced because the coil feels a force created from the magnetic field of the magnet.

Turntables are just one way a motor is shown at work. The speed of the turntable can be adjusted by increasing or decreasing the amount of current that flows through the coils (in the case of the microwave).

Electricity and Children

Last week we learned about electricity! We learned about current flowing through wires when a change in voltage is present in a closed circuit. Here is a picture of a tag that I found on my extension cord.  There are several conditions the tag advises not to do during use of the cord.

- Keep Away from Water: Water can conduct electricity. This means that the current flowing through the wire can also travel through water. If the water happens to be touching you, you will get shocked.

- Do not use when wet: (see above).

- Keep Children and Pets Away from Cord: Both children and pets have several things in common, but most notably in this situation, inexperience and teeth. Children do not know how to handle the cord, thus if they touch any exposed wire, current will flow through them. The current will flow through them, from the outlet of 120V into the ground,with 0V. The child will get shocked and so will the animal. Aside from not being able to handle the cord properly, the child/pet may think the cord is food! (probably noodle-like). Eating the cord will cause the child/pet to touch exposed/metallic parts and they will get shocked.

- Covering the cord with metals won't do anything if the plastic covering is still on the wire, however if any exposed wiring touches the metal, the metal will have a current flowing through it, becoming potentially dangerous.

There are several other conditions but they all relate to what not to do with a cord. These guides are to prevent one from getting shocked by the cord. Now that we have finished the chapter of electricity, I can understand the labels I am reading on various electronic devices!

Don't try this at home

This chapter, we are learning about electrons jumping from one object to another. We excess charge can occur if an object isn't grounded. In the case of an outlet, when the outlet gives electricity to the plug of an object and the plug is taken out while the outlet is still giving electricity, an excess charge is created. Some plugs have a third prong which grounds the plug, neutralizing the excess charge. Most conventional, lower powered household items don't have the third prong, therefore the excess charge will form. in this video, my iron is plugged into the wall. As electricity flows through it, I pull out the plug, creating a visible excess charge of electrons in the form of a spark. I performed this in the dark so it would be easier to see the electrons jumping from the wall to the plug. Here is also a picture of what the outlet looks like in the light.