True North vs Magnetic North vs Geographical North

True north

True north (geodetic north) is the direction along the earth's surface towards the geographic North Pole.True geodetic north usually differs from(The direction a compass points toward the magnetic north pole), and from grid north (the direction northwards along the grid lines of a map projection). [1]Geodetic true north also differs very slightly from Astronomical true north (typically by a few arc seconds) because the local gravity may not point at the exact rotational axis of the earth.The direction of astronomical true north is marked in the skies by the north celestial pole. This is within about 1 degree of the position of Polaris, so that the star appears to trace a tiny circle in the sky each day. Due to the precession of the Earth's axis, true north rotates in an arc with respect to the stars that takes approximately 25,000 years to complete.

Magnetic North

The North Magnetic Pole is the point on the surface of Earth's Northern Hemisphere at which the planet's magnetic field points vertically downwards.

The North Magnetic Pole moves over time due to magnetic changes in the Earth's core.In 2001, it was determined by the Geological Survey of Canada to lie near Ellesmere Island in northern Canada at 81.3°N 110.8°W. It was situated at83.1°N 117.8°W in 2005.[2] In 2009, while still situated within the Canadian Arctic territorial claim at 84.9°N 131.0°W,it was moving toward Russia at between 34 and 37 miles (55 and 60 km) per year.As of 2012, the pole is projected to have moved beyond the Canadian Arctic territorial claim to 85.9°N 147.0°W.

Its southern hemisphere counterpart is the South Magnetic Pole. Since the Earth's magnetic field is not exactly symmetrical, the North and South Magnetic Poles are not antipodal: i.e., a line drawn from one to the other does not pass through the geometric centre of the Earth.

Geographical Pole

A geographical pole (also geographic pole) is either of the two points—the north pole and the south pole—on the surface of a rotating planet (or other rotating body) where theaxis of rotation (or simply "axis") meets the surface of the body. [3]The north geographic pole of a body lies 90 degrees north of the equator, while the south geographic pole lies 90 degrees south of the equator The Earth's actual physical North Pole and South Pole vary cyclically by a few meters over the span of each few years. This phenomenon is distinct from the precession of the equinoxes of the Earth, in which the angle of the planet (both axis and surface, moving together) varies slowly over tens of thousands of years.

Reference

1. ^ ^a b World Data Center for Geomagnetism, Kyoto. "Magnetic North, Geomagnetic and Magnetic Poles". Retrieved 2012-07-03.
2. ^ North Magnetic Pole Moving East Due to Core Flux, National Geographic, December 24, 2009
3. ^ "The Magnetic North Pole". Ocean bottom magnetology laboratory. Woods Hole Oceanographic Institution. Retrieved June 2012.

THE FUN ENERGY BALL

                           

During class we participated in group experiments. With the experiment, we were given an array of questions to answer. Making the energy ball work you must place two fingers on both of the metal contacts on the energy ball, being able to conduct electricity. This results in current that makes the ball flash and hum. This works because humans make pretty good electrical conductors.

There was one question that asked how to make one of two energy balls light up when one path of the circuit was broken. The solution is to make a parallel circuit instead of a series circuit. As you may know, there is a large difference between parallel and series. Before we learn about series and parallel we need to learn what a circuit is. Stated in the textbook, a circuit is ‘the path of electric current flow from and to the power supply' (1). A simple circuit includes an energy source, a load and a conductor. These are pictures of the two types of circuits, series circuit and parallel.

The major differences in Parallel vs. Series Circuits:

       In a series circuit, all devices are connected in series, which means there is only one pathway for charge flow. If one of the devices is broken, the circuit is referred to be an opening circuit and the charge would stop flowing.

In a parallel circuit, each device is placed in its own branch, which means there are multiple pathways for charge flow. If one of the devices is broken, other devices are normally working.

Some individuals could not make the energy ball work probably due to the dry hands or some non-conductor on hands, such as hand cream, which could not conduct electricity. Charges pass through all the conductors from negative to positive in a circuit. If it is added in a non-conductor, charges could not flow. Therefore the circuit becomes a opening circuit and the energy ball could not work.

Self-reflection

       From the experiment, I have learned that human bodies could conduct electricity. Because of human bodies are mainly made by water and salt ^[3]. In addition, I have learned the differences between series circuit and parallel circuit as well. The major difference of these two circuits is that series circuit has the only one pathway for electric charge flow, but the parallel circuit has separate pathways. Also I think, the most important part for studying physics is the attitude. Even if there are questions that I could not understand, I have a good attitude which could lead me to find the final solution.

Reference

[1] “Electronics and You”, (2009). Fig - 1: Series Circuit, Retrieved September 10, 2011

from http://www.electronicsandyou.com/circuit/analog_circuits.html

[2] “Electronics and You”, (2009). Fig - 1: Parallel Circuit, Retrieved September 10, 2011

from http://www.electronicsandyou.com/circuit/analog_circuits.html

[3] H. A. Harper, V. W. Rodwell, P. A. Mayes (1977). Review of Physiological Chemistry, 16th ed.,

Lange Medical Publications, Los Altos, California.