Lesson Notes By Weeks and Term v4 - SHS 3
APPLICATIONS OF ELECTRONICS
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APPLICATIONS OF ELECTRONICS
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Subject: Physics
Class: SHS 3
Term: 2nd Term
Week: 15
Grade code: 3.3.4.LI.2
Strand code: 3
Sub-strand code: 4
Content standard code: 3.3.4.CS.1
Indicator code: 3.3.4.LI.2
Theme: ELECTRIC FIELD, MAGNETIC FIELD AND ELECTRONICS
Subtheme: APPLICATIONS OF ELECTRONICS
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This lesson introduces learners to one of the most fundamental circuits in electronics: the full-wave rectifier. In Ghana, the power supplied to our homes and schools by the Electricity Company of Ghana (ECG) is alternating current (AC). However, most of our personal electronic devices, like mobile phones, laptops, radios, and LED lights, require direct current (DC) to operate. A rectifier is the electronic circuit that converts AC to DC. Understanding how this conversion works is crucial for anyone interested in electronics, engineering, or even basic appliance repair.
2.1. Recap: Alternating Current (AC) and Direct Current (DC) Alternating Current (AC): This is the type of current supplied to our homes. Its magnitude and direction change periodically. It is represented by a sinusoidal wave (sine wave). One complete cycle consists of a positive half-cycle and a negative half-cycle. Direct Current (DC): This is the type of current required by most electronic devices. Its magnitude and direction are constant. It flows in only one direction. Batteries provide DC.
Why convert AC to DC? Electronic components like transistors and integrated circuits (chips) in our phones and computers are designed to work with a steady, one-directional current (DC). Feeding them AC would damage them. Therefore, we must convert the AC from the wall socket into DC. This process is called rectification. 2.2. The Key Component: The P-N Junction Diode
The magic of rectification is made possible by a simple component: the P-N Junction Diode. Symbol: `----|>|----` (The arrow `>` points in the direction of conventional current flow). The flat line `|` is the Cathode (n-type side). The base of the triangle `---` is the Anode (p-type side). Function: A diode acts like a one-way street for electric current. Forward Bias: When the voltage at the anode is higher than at the cathode, the diode allows current to pass through it easily (it has very low resistance). It's like an open gate. Reverse Bias: When the voltage at the cathode is higher than at the anode, the diode blocks the flow of current (it has very high resistance). It's like a closed gate. 2.3. From Half-Wave to Full-Wave Rectification
A simple rectifier can be made with just one diode. This is called a half-wave rectifier. It works by allowing only the positive half-cycles of the AC input to pass and blocking the negative half-cycles. Disadvantage: It is inefficient because it throws away the entire negative half-cycle of the AC wave, wasting half the power.