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.2
Indicator code: 3.3.4.LI.2
Theme: ELECTRIC FIELD, MAGNETIC FIELD AND ELECTRONICS
Subtheme: APPLICATIONS OF ELECTRONICS
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In our daily lives in Ghana, we are constantly surrounded by amplified sound and signals. Think about the powerful speakers at a church service, the sound system at a school speech day, or even the way your small mobile phone can receive a radio signal from a station miles away. All these devices rely on a fundamental process called amplification. Amplification is the process of taking a weak signal (like a person's voice into a microphone) and making it much stronger without changing its basic information. The electronic component at the heart of this process is the transistor. Today, we will learn how to design a simple but powerful amplifier using an NPN transistor.
a) What is Amplification? Amplification is the process of increasing the amplitude (strength, power, or voltage) of a time-varying signal. The device that performs this is an amplifier. Input Signal: The original, weak signal (e.g., from a microphone). Output Signal: The strengthened, amplified signal (e.g., going to a speaker). Gain: The measure of how much the signal is amplified. Voltage Gain (Av) = (Change in Output Voltage) / (Change in Input Voltage) Current Gain (Ai) = (Change in Output Current) / (Change in Input Current)
An amplifier does not create energy. It uses energy from a power source (like a battery or a DC power supply) and shapes it to create a larger copy of the input signal. b) The NPN Transistor: The Heart of the Amplifier A transistor is a semiconductor device with three terminals that can be used to amplify or switch electronic signals. We will focus on the NPN Bipolar Junction Transistor (BJT). Structure: It consists of a thin layer of P-type semiconductor sandwiched between two layers of N-type semiconductor. Terminals: Emitter (E): Emits charge carriers. Base (B): Controls the flow of charge. Collector (C): Collects the charge carriers. Symbol:
*(Note: The arrow on the emitter points outwards for NPN)*
The Key Principle of Transistor Amplification: A very small current flowing into the base (Base Current, `Ib`) controls a much larger current flowing from the collector to the emitter (Collector Current, `Ic`). This relationship is defined by the transistor's current gain, called Beta (β) or `hFE`.