Glasses, more than meets the eye

As many of you know, I wear glasses because I am nearsighted, meaning I cannot easily see objects that are far away. In order to correct this, I wear glasses that help to bring faraway images to a focus at the retina in the back of my eye, so my brain can receive and interpret them with maximum clarity. Because I am nearsighted, I see images at twenty feet that other people can see at say fifty or sixty feet (I'm not quite sure what my prescription is) away. When images enter my eye they are created at some distance in front of my retina whereas images in the eyes of farsighted people are focused behind the retina. In order to move the focus of images in my eye backward, I need to wear diverging lenses that cause incoming light rays to intersect at a point farther from the source as they diverge (get farther apart by refraction) while coming through the lens, thus they do not meet until they reach a father back location. On the other hand, if I were farsighted, I would have to wear converging lenses that cause rays to intersect closer after leaving the lens as they in a way push the rays of light closer as they are refracted at a smaller angle as they go through the lens.

Transformer

There are many transformers in my neighborhood as I suspect is the same in any neighborhood. Without these transformers our homes would not get the power that they need and nothing electrical would work. The need for transformers is due to the fact that power comes from the plant through electrical lines at very high voltages, into the tens of thousands! Most household appliances, however, operate on only a few hundred volts. So, there needs to be a way to reduce the power from its high voltage to a more usable voltage. This is where a transformer helps. Inside a transformer there are many coils, but lets just focus on two for the general concept. The two coils are separated by an iron core and as the full high voltage from the plant comes into the first coil a magnetic field is generated through the iron to the second coil and an emf is induced. This in turn creates a current in the second coil and this passes through a resistor and the emf becomes what is necessary for the resistor. The number of coils in the first and second coils also varies. The equation V1/V2=N1/N2 shows this as V is the emf and N is the number of loops, showing that the emf decreases proportionally to the number of loops on each side of the transformer.

Hand-Cranked Radio

Yesterday during the tsunami warning my parents found our hand-cranked radio that could run without electricity or batteries. But what really makes this radio run? Physics, of course! Recently we have been studying electromagnetism and so now I can explain how something can have power with no power source. Inside this radio (I'm assuming) there is a coil of wire attached to the radio. This wire will act as a generator and the person turning the crank will supply the necessary energy. As the mechanism is cranked energy is supplied and the small wire moves in a magnetic field. Because this wire moves in a magnetic field an emf is induced and thus a current is created. Since power equals current times voltage, the radio has power and can turn on. The power can be stronger due to more loops in the wire, turning the crank faster (greater angular velocity), a greater area within the wire, and more time. Conservation of energy applies here but some energy is lost to heat.

Flashlight Circuit

A flashlight is a good example of a simple

circuit. Inside this flashlight there are two batteries

connected in series along with a light builb and

metal connecting all of the components. The

flashlight's on-off switch completes the circuit when

it is switched on by moving a piece of metal into

place, thus completing the metal circuit relaying the

battery potential difference to the light bulb.

The amount of current running through the circuit

is found with the equation V=IR where V is the

voltage of the battery and R is the resistance across

the light bulb. Because the batteries are connected

in series the power or P=IV of the light bulb is greater than it would be with just one battery. In

order for the light bulb to stay lit, the circuit must remain completed by the on switch so that the

current is able to flow and complete the circuit.

Also, the Potential difference or voltage across the battery must be countered by the resistance in

the lightbulb so the voltage in the wire as it returns to the battery is 0V.

The Oven and Stove Top

Today as my mom and I were baking cookies to eat during the Super Bowl, I realized that our oven is a great representation of Physics concepts. A convection oven heats and cooks by convection which is heating through a fluid medium by movement of fluid. In an oven the heat that comes off of the coils rises and the surrounding heat sinks. This motion repeats and eventually cooks whatever is in the oven.

Also, the top of the oven shows the concepts of resistance and power. The coils that you place pans and pots on while cooking heat up due to electric current. The power that goes into the stove is equal to the current times the voltage. The coils then heat up due to this power. The heat that eventually comes off of the coils to heat up the food is equal to the current squared times the resistance of the coils. As the coils heat up, the resistance increases as shown in the equation P=I^2R. This heat is transfered to the food by conduction and as a side effect of the increase in temperature of the coils the resistance increases.

Electrical Wires

Electrical wires are an everyday thing, but after studying electrostatics, I am now able to better explain how they work. These are some of the wires that power my TV, DVD player, etc. Obviously, in order to power electrical devises, a charge must be carried to them. To do this, a conductor such as the copper in an electrical cord, is needed to allow the charge to flow from the outlet to the TV. The cords must be capable of handling enough current to power the TV without shorting the circuit, as happens with an overload of current.

As a little kid, whenever I unplugged something, I was always told to pull the cord out of the socket by pulling on the plastic part. This was because the plastic covering on the electrical cord "insulates" the cord and stops the charge from flowing from the copper to my hand or any other substance, and keeps people safe from electric shock.

If you have ever seen an electric shock, lightning, or some kind of electric spark, it can also be explained with electrostatics. The visible transfer of charge results in the "spark" or lightning that we see in such energy transfers. Such visible transfers are simply made by an extreme change in the electric potential of a system where a large number of charged particles are transferred to an area with less charged particles such as the ground, a lightning rod, the air, and even a person's hand. I have had many personal experiences with lightning and it is amazing to think that the enormous lightning bolt that flashes through the sky is really made up of a lot of, singularly invisible, charges.

Staticky Hair

Many times, especially during the winter, you will find your hair standing on end due to "static electricity". Even though we usually associate this phenomenon with rubbing a balloon on your head to create static, I have found that this also occurs on airplanes or while wearing a winter hat. Often when moving after leaning back on an airplane headrest or taking off a winter hat, my hair will stick to the previously mentioned surface. This is due to the opposite charges of my hair and the object. When two objects are rubbed together, they can become charged as electrons move from one object to the other. In the situation with hair, electrons probably move out of the chair or hat, making it positively charged with excess protons, and into my hair giving it an excess of electrons and making it negatively charged. Since the two objects are then oppositely charged, they attract, sticking together as I try to pull them apart. Throughout this process, charged is conserved as electrons are transferred between objects and not lost.