A resistor is an electronic component which has one simple job to do, which is to restrict current flow (cause resistance). The resistance of a resistor is measured in ohms. A resistor has no positive end or negative end and therefore can be wired up either way. It doesn't matter how it is wired up, it will still restrict current flow. But the amount of resistance to current flow is dependent on the resistor itself. There are a range of resistors. They are all similar in size but have different resister ratings. Resistors have colored bands drawn on them. Resistors can be identified by a code using the color and the position of the bands.
How to identify
The first two or three bands may be the numbers to write down.
Next band is the multiplier
The last band is the tolerance value
Here's the resistor color code chart
E.G: Say your resistor has these bands on it in this order. Brown, Red Orange, Gold.. This will give you a reading of 1,2,1000,5% which means 12,000ohms 5%
The 5% is the tolerance value. It means that the resistance of the resistor can vary plus or minus 5% of the actual value. In this case the tolerance will be 11,400ohms (lowest) and 12,600ohms (highest).
Diodes
A diode is an electronic component which conducts and lets current flow through in only one direction. From Anode (positive) to Cathode (negative).
In our practical class we did a few tests on a diode using a multimeter. The first test we did was we measured the diode's resistance in both directions. The result came out infinity (no circuit). This meant that there was no circuit either way of the diode. But why? A diode requires a small amount of voltage (theoretically 0.6V) to turn on, which our meter did not supply (only supplied 0.245V). Hence the diode didn't let current through and the result was an open circuit. We then set the meter on diode test mode and measured the diode in both directions. The readings we got was 0.808V (anode to cathode) and infinity (cathode to anode). These results meant that our diode only lets current through one way which is from positive to negative (anode to cathode). And that it requires 0.808V to turn on. We then did the same tests with another type of diode. A LED (light emitting diode). In the diode test mode the result for anode to cathode was 1.617V. This means that this diode requires 1.617V to turn on. But why? This is because compared with the other diode the LED produces an output as well as allow current flow. That output is light. Hence the LED requires more voltage to start up. These were the two diodes that we tested in class but we were briefly exposed to three other types of diodes. A SCR diode, Photo diode and a Zender diode.
Capacitor
A capacitor is an electronic component that stores electrical charge. It does this by providing ground when there is an open circuit (switch is open). This storage of electrical charge prevents voltage spikes from happening. A capacitor consists of two metal plates very close together. They are separated by an insulator. When connected to a battery or a power source electrons flow into the negative plate and charge up the capacitor. This charge still remains when the battery or the power source is removed. The amount of charge a capacitor can store depends on the capacitance of the capacitor (measured in Farads F).
In our practical class we wired up a capacitor in a circuit and then charged it. Every 10seconds voltage readings were taken from the capacitor. The capacitor was supplied with 16.81V for 210seconds. The results were then graphed. (see in worksheet). The graph showed us that the capacitor when first started charging gained voltage quite fast and then it gradually reduced its rate of charge. Why? This was due to the potential difference of the capacitor equalizing with the power source. As it equalizes the pressure voltage decreases hence the capacitor starts to slow down its rate of charge.
Relays
A relay is an electronic component that uses a low amperage circuit to switch on a higher amperage circuit. This low amperage circuit is called a control circuit. The control circuit will have a coil of wire that creates a magnetic field around it when the circuit is powered and earthed. The switching circuit (higher amperage circuit) will have a set point of contacts that are switched on and off by having the magnetic field pull (attract) the points over to connect with another set of points.
The control circuit of the relay usually gets its power from the battery. It will also have a switch that will turn on and off the circuit. This switch can either be on the positive side of the circuit or the negative side of the circuit. The circuit can be switched by either a switch, a sensor with a switch inside it, or an ECU (electronic control unit) that does the switching based on a logic circuit.
The switching circuit (high amp circuit) also gets its power from the battery and this circuit is connected to the component.
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