First, we learned about charges. There are three ways to make something charged: Thru contact (the transferring of electrons), friction (stealing electrons), or induction (charging without contact).
Friction is the reason that your hair stands up after taking off a winter hat. When you pull the hat off, it steals electrons from your hair, giving your hair a slightly positive charge. Since like forces repel, your slightly positive hairs stick up and apart in attempt to get away from each other.
Friction also causes your clothes to stick together in the drier. While being dried, they rub together, creating friction. This makes some of your clothes to gain electrons, making them negative, and some of your closes loose electrons, making them positive. Since opposite charges attract, the clothes stick together.
*Drier sheets eliminate this problem by absorbing electrons, making the clothes slightly positive and thus, repel each other.
Both friction and induction causes lightening. First, the clouds rub together, and become charged through friction. The top of the cloud becomes slightly positive, and the bottom of the cloud becomes slightly negative. The ground then become positive through induction from the negative clouds. Finally, the negative cloud charges and the positive ground charges creep towards each other through the air, and if the path is completed, energy (heat, light, and sound) will move form the ground to the cloud, creating lightening.
A picture of induction at work from Paul G Hewitt
Lightening rods are placed on tall buildings in case of lightening. Should lightening strike the building, it will be attracted to the rod, as charges are attracted to pointy objects. The lightning rod will run the charges along the building and into the ground, eliminating any damage to the building.
Next, we talked about polarization. When objects become polarized, the charges within the object separate, allowing one side to become positive and one side to become negative. Polarization is the reason that plastic wrap sticks to ceramic or glass bowls, but not to metal bowls.
When the plastic wrap is removed from its container, it becomes charged by friction and becomes slightly negative. When it is brought towards the plastic or ceramic bowl, the bowl polarizes. The positive charges in the bowl move towards the negative charges in the plastic wrap, and the negative charges in the bowl move further away. The plastic wrap sticks because the opposite, attractive force between the plastic wrap and the positive charges of the bowl is stronger than that between the similar, repulsive force between the plastic wrap and the negative bowl charges. We know this due to Coulomb's law, which states that the smaller the distance, the greater the force, and the greater the distance, the smaller the force. This is represented by the equation below. Thus, the plastic wrap sticks to the bowl.
Coulomb's law
The next topic is Electric Fields. An electric field is an area of influence around a change. Below is a helpful video, made by yours truly, about electric fields.
Electric Shielding is the reason electronics are encased in metal. While inside a metal box, the electric field is 0, meaning that a charge inside will not be pushed or pulled by outside electric charges. Metals allow the charges to distribute evenly, therefore everything inside the box will be pulled in one direction but will have equal and opposite forces pulling them in the other direction.
Capacitors are two oppositely charged plates.
Camera flashes are an example of capacitors. Two oppositely charged plates are continuously given charges, and the force between them continuously increases, as shown by Coulomb's law. As the forces increase, the energy between them also increases. When the plates are briefly connected, the energy rushes through the connecting wire and is released as light. This process takes time, therefore flashes cannot work continuously.
Before moving on to circuits, we learned some important vocabulary.
Voltage is a difference in electric potential.
Volts are electric potential. It's symbol is "V".
Current is energy being carried through the wire with charges, and is caused by voltage. It is measured in Amperes, and is represented by "I".
Electric Potential Energy is energy stored in electric fields.
Resistance is the ability of current to flow in a wire. A wire with a high resistance is typically long, narrow, and hot. Lower resistance wires are wide, short, and cold. Resistance is represented by the "R" and measured in ohms, the symbol Ω.
We also leaned some formulas.
Ohm's law: I=V/R. Essentially, Current is directly proportional to Voltage and inversely proportional to Resistance.
Power=Current x Voltage
Electric potential= potential energy/charge
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As seen above, when there is a difference in electric potential, voltage is created. Voltage causes current, and when voltage travels through a closed, completed circuit, electricity is created! However, there are a few factors that affect current.
Current is affected by Voltage and Resistance. The more voltage, the more current. The more resistance, the less current. Resistance is affected by three things: thickness of wire, length of wire, and temperature of wire. A long, narrow, hot wire will have a greater resistance, and thus a decreased current. A short, wide, cold wire will have a lower resistance, and thus a higher current.
Lightbulbs burning out is directly related to current, voltage, and resistance. When first turned out, the lightbulb's filament is cold, decreasing the resistance and increasing the voltage and current. Often, it is this rush of current and lack of resistance that breaks an old lightbulb's filament.
Current, voltage, and resistance are also the reason it is dangerous to plug an American appliance into a European outlet. American outlets are typically built with lower resistance, as they are plugged into outlets with lower voltages. However, European outlets have a higher voltage, so when American appliances are plugged in, they are given more current than they can handle, often starting fires and power outages.
There are two types of wire currents. Alternating currents, or AC, where electrons are constantly moving back and forth. AC are what we use when we are plugging things into wall outlets. Direct Currents, or DC, are when the electrons are moving in one direction. This is the type of current that batteries use.
For more on currents and circuits, here is a helpful video.
Current, voltage, and resistance are also the reason it is dangerous to plug an American appliance into a European outlet. American outlets are typically built with lower resistance, as they are plugged into outlets with lower voltages. However, European outlets have a higher voltage, so when American appliances are plugged in, they are given more current than they can handle, often starting fires and power outages.
There are two types of wire currents. Alternating currents, or AC, where electrons are constantly moving back and forth. AC are what we use when we are plugging things into wall outlets. Direct Currents, or DC, are when the electrons are moving in one direction. This is the type of current that batteries use.
For more on currents and circuits, here is a helpful video.
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