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DC vs. AC

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In the Current Electricity section, you learned about electric charge, current, voltage and other related topics. But, just because you have a voltage does not mean electric current will flow. Electrons also need a complete loop of conductive material to flow, called a closed circuit . Let's look at a light switch. When you turn the switch "on", the switch creates a path that conducts electricity and electrons start to move—meaning electric current flows—and the light turns on. As soon as you turn the switch "off", the path is broken and electrons can no longer flow. The switch is like a drawbridge; switching it on is letting down the bridge so the electrons can cross (just like cars crossing a bridge) and provide energy to the light bulb. Illustration of how electric current can move through a closed loop of conductive material (left figure) but stops flowing whenever the loop is broken (right figure). This figure shows how a light bulb l...
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Magnetism

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In ancient times Greece people found a rock that attracts iron, nickel and cobalt. They call them as “magnet “and magnetism comes from here. These rocks were used later by Chinese people to make compasses. Later scientists found that, magnets have always two poles different from electricity. Magnets have two ends or faces called “poles” where the magnetic effect is highest. In last unit we saw that there is again two polarities in electricity, “-“charges and “+” charges. Electricity can exist as monopole but magnetism exists always in dipoles North Pole (represented by N ) and South Pole (represented by S) . If you break the rock into pieces you get small magnets and each magnet also has two poles N and S. Same poles of the magnet like in the electricity repel each other and opposite poles attract each other. Strengths of these forces depend on the distance between the poles and intensity of the poles. Types of Magnets In nature Fe 3 O 4 is used as magnet. However, th...
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magnetism part 2

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Magnetic Fields  Force On A Current Carrying Wire In A Magnetic Field You will be familiar with the basic notion of a magnetic field , in which magnetic materials experience a magnetic force.  However it is worth revising some of the basic ideas that you will have come across in early secondary school. Revision Magnetic fields can be shown by field lines, which go from North to South. The field lines in a strong magnetic field are more closely packed than in a weak field. Unmagnetised materials are attracted to either pole. Like poles repel; unlike poles attract. In the Earth’s magnetic field, the North pole will align itself to point to the North, if the magnet is allowed to swing freely. The Earth has a magnetic field like a bar magnet.  Notice that the S-pole is under the North geographic pole.  Be careful not to be confused by ...
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