In an atom, orbits are group into energy bands know as shells. Each shell has a fixed maximum number of electrons at permissible energy levels. The shells are designated as K,L,M,N, and so on. The outermost shell is know as valence shell and the electrons in this shell are called valence electrons . These valence electrons contribute to chemical reactions and bonding.
Shells of orbital Electrons in an Atom 50 18 14 10 6 2 O 32 14 10 6 2 N 18 10 6 2 M 8 6 2 L 2 2 K Total g f d p s
the flow of electrons from an area high in electron excess to one of lower electron content.
the flow of energy in a wire (similar to the flow of water in a pipe) that is invisible, that causes the wire to become hot , causes a magnetic field to develop around the wire and can be put to work driving pumps, blowers, fans and so forth.
Electricity cannot be generated. It can neither be created nor destroyed. It can, however, be forced to move and thus transmit power or produce electrical phenomena.
1. Battery – a single unit capable of producing DC voltage by converting chemical energy into electrical energy.
2. Dynamo – a machine that converts mechanical energy to electrical energy and vice versa.
3. Motor – transformation from electrical energy to mechanical energy.
4. Generator – transformation from mechanical energy to electrical energy.
5. Solar energy – it converts solar energy from the sun through the use of solar cells.
Alternating Current (AC) and Direct Current (DC)
Direct current or DC is the first type of current because it is easy to produce. This current always flows in one direction. Its disadvantage is that it has an excessive voltage drop and power loss in the power lines for a long distance. Batteries are common sources of direct current.
Alternating current is the solution to the problem of DC. AC allows the flow of current in two directions. Today, it is possible to step up electricity to a power station, transmit it to any distant place and step it down for consumption. A transformer is the device used for stepping up and stepping down AC voltage.
Electronics test instruments are crucial instruments that are often use for troubleshooting, repairing and analyzing the operation of a specific device. The most frequently measured parameters are the voltage, resistance and current.
The multi-tester or multi-meter or sometimes called VOM(Voltmeter, Ohmmeter, Milliammeter) is best instrument that can measure voltage, resistance and current. But this instrument measures the numerical value, not the actual waveform, which is also important to know when troubleshooting and determining the frequency of the signal.
The analog multi-tester has a moving coil assembly which is characterized by a needle pointer. The advantage of analog multi-tester over digital multitester is a resistance test in testing electronic components such as capacitor and transistor.
Connect the test probe to the appropriate jack. The red probe to the + jack and black probe to the (-) common jack.
Check is the pointer rest exactly at the zero position or infinite position at the ohmmeter range. If not adjust the zero corrector screw.
Check the accuracy of the ohmmeter by touching the two test probe. Set the multitester to x1 ohm or x10 ohms selector range. Hold the two test probe simultaneously. The pointer should not deflect when holding the two test probe. If the pointer deflects, the ohmmeter range is defective.
4. Check the probes if they are OK. Set the multi-tester to corresponding selector resistance range. Short the two probes lead together. The pointer should deflect towards zero ohm reading. Adjust the ohm adjustment if the pointer could not rest exactly at “0” ohm reading. If nothing happen the possible cause is low powered battery
The ammeter scale is the same as the voltmeter scale. Apply the same procedure in measuring voltage. However, in current measurement , the meter must be connected in series with the circuit. Unlike in measuring voltage, the connection is parallel.
A device that stores electrons. The basic capacitor is made up of two conductors separated by an insulator, or dielectric. Depending on how the capacitor is built, the dielectric can be made of paper, plastic, mica, ceramic, glass, vacuum or any other non conductive materials. Capacitor storing ability is measured in Farad. 1 Farad is approximately 6,280,000,000,000,000,000 electrons.
A magnet is an object made of certain materials which create a magnetic field . Every magnet has at least one north pole and one south pole. By convention, we say that the magnetic field lines leave the North end of a magnet and enter the South end of a magnet. This is an example of a magnetic dipole ("di" means two, thus two poles). If you take a bar magnet and break it into two pieces, each piece will again have a North pole and a South pole. If you take one of those pieces and break it into two, each of the smaller pieces will have a North pole and a South pole. No matter how small the pieces of the magnet become, each piece will have a North pole and a South pole.
The ancient Greeks and Chinese discovered that certain rare stones, called lodestones, were naturally magnetized. These stones could attract small pieces of iron in a magical way, and were found to always point in the same direction when allowed to swing freely suspended by a piece of string. The name comes from Magnesia, a district in Thessaly, Greece
Headphones, stereo speakers, telephone receivers, phone ringers, microwave tubes, doorbell ringer solenoid, floppy disk recording and reading head, credit card, computer monitor deflection coil, computer hard drive recording, TV deflection coil, clothes washer and dryer, DVD spinner and head positioner, hard disk spinner, starter motor, A/C clutch, etc.
1. North poles point north, south poles point south.
2. Like poles repel, unlike poles attract.
3. Magnetic forces attract only magnetic materials.
4. Magnetic forces act at a distance.
5. While magnetized, temporary magnets act like permanent magnets.
6. A coil of wire with an electric current flowing through it becomes a magnet.
7. Putting iron inside a current-carrying coil increases the strength of the electromagnet.
8. A changing magnetic field induces an electric current in a conductor.
9. A charged particle experiences no magnetic force when moving parallel to a magnetic field, but when it is moving perpendicular to the field it experiences a force perpendicular to both the field and the direction of motion.
10. A current-carrying wire in a perpendicular magnetic field experiences a force in a direction perpendicular to both the wire and the field.
Permanent magnets are those we are most familiar with, such as the magnets hanging onto our refrigerator doors. They are permanent in the sense that once they are magnetized, they retain a level of magnetism. As we will see, different types of permanent magnets have different characteristics or properties concerning how easily they can be demagnetized, how strong they can be, how their strength varies with temperature, and so on.
Temporary magnets are those which act like a permanent magnet when they are within a strong magnetic field, but lose their magnetism when the magnetic field disappears. Examples would be paperclips and nails and other soft iron items.
An electromagnet is a tightly wound helical coil of wire, usually with an iron core, which acts like a permanent magnet when current is flowing in the wire. The strength and polarity of the magnetic field created by the electromagnet are adjustable by changing the magnitude of the current flowing through the wire and by changing the direction of the current flow.
Neodymium Iron Boron magnet = Nd2Fe14B or Nd15Fe77B8.
The magnitude of the electrostatic force between two point electric charges is directly proportional to the product of the magnitudes of each of the charges and inversely proportional to the square of the total distance between the two charges .
2. LED(light emitting diode) – it is made of gallium arsenide or gallium arsenide phosphide.
Operation: when the device is forward bias, electrons cross the pn junction from the n type material to p type material. When recombination takes place, the electrons release energy in the form of heat and light.