Electronics Chapter 53 What is Electronics? Electronics is the careful and exact control of very...
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Transcript of Electronics Chapter 53 What is Electronics? Electronics is the careful and exact control of very...
![Page 1: Electronics Chapter 53 What is Electronics? Electronics is the careful and exact control of very small electric currents. It is used in many small devices.](https://reader036.fdocuments.us/reader036/viewer/2022062516/56649dc55503460f94ab8490/html5/thumbnails/1.jpg)
Electronics
Chapter 53
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What is Electronics?
• Electronics is the careful and exact control of very small electric currents.
• It is used in many small devices such as Tv’s, computers, digital watches e.c.t.
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Relationship between voltage current and resistance
• The higher the resistance in a circuit, the lower the current that will flow.
• Voltage x Current = Resistance
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Diodes• A diode is a component that will allow current to
flow in one direction only.
• When the positive terminal of a battery is connected to the positive end of the diode, the diode is said to be forward biased and allows current to flow.
• When the positive terminal of a battery is connected to the negative end of the diode, the diode is reverse biased and no current can flow through it.
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Forward and reverse biased
• A forward biased diode conducts. The bulb lights
• A reverse biased diode does not conduct. The bulb doesn’t light.
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Forward Biased
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Reverse Biased
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Rectifier• The diode can act as a rectifier. It can change alternating
current to direct current.
• A diode will only allow the current through it when it is flowing in a forward direction. So the output will be direct current.
Uses of a diode
• Computers TV radios need a current that flows in the same direction(direct current). Therefore they need a diode to change ac to dc.
• Diodes can protect appliances. Computers and radios can be damaged if connected the wrong way round. With a diode in the circuit, no current would flow if connected wrongly and no damage would be done.
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Rectifier
The simplest kind of rectifier circuit is the half-wave rectifier. It only allows one half of an AC waveform to pass through to the load.
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Light emitting diodes(LED)
• A light emitting diode (LED) is a diode that gives out light when a current flows through it.
• An LED uses a small current and a resistor must be connected in series so that it is not damaged by too large a current.
• LED’s are used as indicators on many electronic devices such as computers TV’s and radio’s. Used to display the
numbers on digital clocks and calculators.
Symbol for LED
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LED
The FLAT side also indicates which leg is the negative
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LED display and meters
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Light dependent diodes.(LDR)
• A light dependent resistor (LDR) is a resistor whose resistance depends on light.
• When light falls on the LDR, its resistance decreases and the current in the circuit increases.
• LDR’s are used to control street lighting and used in light meters in cameras.
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A circuit showing a LDR
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Experiment: To test the polarity of a battery.
• Set up circuit as shown. Connect the two LED’s in the opposite direction.
• Connect the battery to be tested between A and B.
• Which LED lights?
• Which pole, A or B is positive?
• Reverse the connections?
• Which pole, A or B is negative?
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Results
Conclusion:
• If the red LED comes on, then the red LED is forward biased. Thus terminal A is positive and B is negative.
• If the green LED comes on, then the green LED is forward biased. Thus terminal B is positive and A is negative.