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15:21, 22 February 2019 (UTC)

2-8-19

Static Electricity

I skimmed all of the sections in Static Electricity and decided to read the section about lightning in depth.

Lightning starts by storm clouds polarizing. The top on the cloud is positively charged and the bottom is negatively charged. Two mechanisms can lead to polarization; Separation of charge and a freezing process.

In separation of charge, clouds contain water molecules moving around. Ground water then evaporates and forms water droplets that rise upwards and combine with the water droplets already in the cloud. When they collide, electrons are ripped off the rising droplets, causing a separation of negative electrons from the positively charged water droplets.

In a freezing process, rising moisture encounters colder temperatures as it evaporates, causing the water to freeze. The frozen particles cluster tighter together, and non frozen particles surround the frozen ones. The frozen part is negatively charged and the surrounding drops are positively charged. When they reach the cloud, the positively charged particles rise to the top of the cloud, and the negative ones stay on the bottom, which further polarizes the clouds.

Now that the cloud is polarized, its electric field stretches through the space surrounding it and causes the movement of electrons on earth. Electrons on the outer surface of the Earth are repelled by the negatively charged bottom of the cloud, which creates an opposite charge on Earth's surface. As static charge builds up, the electric field increases as well. The electric field around the cloud ionize the surrounding air and make it conductive. The lighting bolt begins to form from a step leader. Extra electrons on the bottom of the cloud travel through the conductive air to the ground as fast as 60 mph. These electrons zig-zag towards the ground, sometimes branching out in different areas. This is not the actual lightning strike, but the path that it will follow. As these electrons approach the ground, there is more repulsion of of electrons down on Earth's surface, and the positive charge on Earth's surface increases. The charges starts to migrate up through trees, buildings, people, etc. and this is known as a steamer. Then, if the steamer meets the step leader, lightning begins to form. The contact point between the two charges travels upwards at 50,000 miles per second. The initial strike is often followed by several strikes in close succession; So close that it only sounds like one lightning strike. The rapid flow of charge heats and expands the air surrounding the strike, which creates a shock wave that we hear as thunder.

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2-22-19

Current Electricity

I skimmed all of the sections in current electricity and decided to read the section about electric current in depth.

If the two requirements of an electric circuit are met (closed conducting path and energy supply), electricity will flow through it. Current is a physical quantity that can be measured and expressed numerically. Current is the rate at which charge passes by a point on the circuit or simply the ratio of quantity of charge and time. Mathematically it can be expressed as I=Q/t. Ampere is the standard metric unit for current, which is shortened to Amp or symbolized by A.

The particles that carry charge through wires are mobile electrons.The electric field direction within a circuit is the direction that positive test charges are pushed, so negatively charged electrons move in the direction opposite the electric field.

The direction of an electric current is the direction positive charges would move, so the current in the external circuit is directed away from the positive terminal and toward the negative terminal of a battery.

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3-1-19

Waves

I skimmed all of the sections in waves and decided to read the section about reflection, refraction, and diffraction in depth.

When waves meet the end of their medium, they don't just stop. Instead, it undergoes certain behaviors when it reaches the end of the medium. There will be some reflection off the boundary and some transmission into the new medium. You can study waves in two dimensions using a ripple tank. A ripple tank is a large glass bottomed tank of water that is used to study the movement of water waves. A light is shined down into the tank and on a white piece of paper under the tank. Some of the light is absorbed by the water as it passes through the tank, and the crest absorbs more than the trough, so bright spots represent troughs and dark spots represent crests. When water moves through the tank, the spots move as well, allowing you to observe the waves behavior.

1. ↑ "Lightning". www.physicsclassroom.com. Retrieved 2019-02-22.
2. ↑ "Electric Current". www.physicsclassroom.com. Retrieved 2019-02-22.