Y10 Electronics

What is the purpose of circuit symbols?

Circuit symbols provide a universal way to represent components in circuit diagrams, ensuring clear communication and understanding.

What is Ohm’s Law and its equation?

Ohm’s Law states that current (I) is directly proportional to voltage (V) and inversely proportional to resistance (R). The equation is: V=I×RV = I \times R

What are the standard SI units for voltage, current, and resistance?

• Voltage (V) is measured in Volts (V)

• Current (I) is measured in Amperes (A)

• Resistance (R) is measured in Ohms (Ω)

• Power (P) is measured in Watts (W)

• Capacitance (C) is measured in Farads (F)

• Frequency (f) is measured in Hertz

What are the three main groups of an electronic system?

1. Input – Detects external signals (e.g., sensors, switches).

2. Process – Modifies the input signal (e.g., microcontrollers, amplifiers).

3. Output – Produces a response (e.g., LEDs, motors, buzzers).

What is an open loop system?

The output responds directly to the input without feedback.

What is a closed loop system?

Uses feedback to adjust the input based on the output, improving accuracy and efficiency.

What are prototype boards used for?

Prototype boards, or breadboards, allow temporary circuit assembly by inserting component legs into pre-arranged holes, enabling rapid circuit testing without soldering.

What are the standard practices for breadboard wiring?

Red wire (+VE) on the top rail. Black wire (0V) on the top rail unless using a dual power supply. Pin 1 is always at the bottom left. Inputs are always on the left; outputs are always on the right. Wires should be kept flat and straight to maintain an organized circuit.

What are the different multimeter settings and their uses?

• DC Voltage Range: Measures direct current voltages.

• AC Voltage Range: Measures alternating current voltages.

• mA Current Range: Measures small currents, starting from the highest range.

• 10A Current Range: Measures high currents but is rarely used in electronics.

• Resistance (Ω) Range: Measures resistance and checks continuity.

How do you measure resistance with a multimeter?

1. Select the resistance (Ω) mode.

2. Place the probes across the resistor.

3. If resistance is greater than the selected range, a "1" is displayed, requiring switching to a higher range.

What is the importance of Ohm’s Law?

Ohm’s Law is fundamental in electronics, allowing the calculation of voltage, current, or resistance in a circuit: V=I×RV = I \times R

How do you calculate power in an electrical circuit?

• P = V × I

• P = I² × R

• P = V² / R

How do you calculate the total resistance in a series circuit?

R_total = R₁ + R₂ + R₃ …

How do you calculate the total resistance in a parallel circuit?

1/R_total = 1/R₁ + 1/R₂ + 1/R₃ …

How are resistor values determined using colour codes?

• Band 1 & 2: Significant digits Band 3: Multiplier Band 4: Tolerance

What are common types of input sensors in electronics?

• Light sensors (LDRs) – Change resistance based on light intensity.

• Temperature sensors (thermistors) – Change resistance with temperature.

• Moisture sensors – Detect water content.

• Pressure sensors – Detect applied force.

• Hall effect sensors – Detect magnetic fields.

• Sound sensors – Detect audio signals.

What is a relay?

A relay is an electromagnetic switch that allows a low-power circuit to control a high-power device.

How does a relay work?

When a power supply is applied to the coil, a magnetic field moves a metal switch, enabling the control of high-power devices like motors and lamps.

What is the function of a capacitor?

A capacitor stores electrical charge and releases it when needed, often used for smoothing voltage changes, providing time delays, and filtering signals.

What are the different types of capacitors and their characteristics?

• Electrolytic Capacitors – Large capacitance, polarized, used in power supply circuits.

• Ceramic Capacitors – Small capacitance, non-polarized, used in signal circuits.

• Tantalum Capacitors – Small, high stability, polarized.

• Film Capacitors – High voltage tolerance, non-polarized.

• Supercapacitors – Store large amounts of charge, used in energy storage applications.

How do capacitors provide a power boost?

When a circuit experiences a voltage drop, a charged capacitor can release stored energy to stabilize the voltage.

How does a capacitor reduce noise in circuits?

A capacitor can filter out high-frequency signals by allowing AC signals to pass while blocking DC components.

What happens during capacitor charging?

Voltage increases as charge builds up

What happens during capacitor discharging?

Voltage decreases as stored charge is released

What is the equation for capacitor charging?

The voltage across a charging capacitor follows: V=Vmax(1−e−tRC)V = V_{max} \left(1 - e^{-\frac{t}{RC}} \right)

What is the equation for capacitor discharging?

V=Vmaxe−tRCV = V_{max} e^{-\frac{t}{RC}} Where:

What happens when capacitors are connected in series or parallel?

Series: 1Ctotal=1C1+1C2+1C3\frac{1}{C_{total}} = \frac{1}{C_1} + \frac{1}{C_2} + \frac{1}{C_3} Parallel: Ctotal=C1+C2+C3C_{total} = C_1 + C_2 + C_3

What is a transistor?

A transistor is a semiconductor device used as an electronic switch or an amplifier to control the flow of current in a circuit.

What are the two main types of transistors?

Bipolar Junction Transistor (BJT) – Controlled by current at the base. Field-Effect Transistor (FET) – Controlled by voltage at the gate.

What are the three terminals of a BJT?

• Collector (C): Main current flows into this terminal.

• Base (B): Small current here controls the transistor.

• Emitter (E): Current flows out of this terminal.

How does a BJT work?

A small base current (I_B) controls a much larger current from collector to emitter (I_C). When base voltage V_BE ≥ 0.7V, the transistor turns ON.

What is transistor gain (h_FE)?

Gain (h_FE) is the ratio of collector current (I_C) to base current (I_B): hFE=ICIBh_{FE} = \frac{I_C}{I_B}

What are the two modes of BJT operation?

Switching mode: The transistor acts as an ON/OFF switch. Amplifier mode: The transistor increases the strength of a signal.

How do you protect a transistor from excessive current?

A current-limiting resistor is always included in series with the base.

What is transistor saturation and cut-off?

Saturation: When V_BE ≥ 0.7V, the transistor is fully ON (acts as a closed switch). Cut-off: When V_BE < 0.7V, the transistor is OFF (acts as an open switch).

What are the three terminals of a FET?

Gate (G): Controls the transistor. Drain (D): Current flows into this terminal. Source (S): Current flows out.

What is the advantage of an FET over a BJT?

An FET requires almost no input current, making it more efficient for digital circuits.

What is a MOSFET?

A Metal-Oxide Semiconductor Field-Effect Transistor (MOSFET) is a special type of FET used in power electronics.

How does a MOSFET function?

Applying voltage to the Gate (G) creates an electric field that allows current to flow from Drain (D) to Source (S). More Gate voltage means more Drain current.

What is transconductance in FETs?

Transconductance (g_m) measures how much the drain current changes when the gate-source voltage changes: Id=gm(Vgs−Vth)I_d = g_m (V_{gs} - V_{th}) I_d = Drain current. g_m = Transconductance (measured in Siemens). V_{gs} = Gate-source voltage. V_{th} = Threshold voltage.

What is the threshold voltage of a MOSFET?

The minimum voltage required at the gate to allow current to flow between the drain and source.

What are the two types of MOSFETs?

Enhancement Mode MOSFETs: Need a positive voltage to turn ON. Depletion Mode MOSFETs: Normally ON and turn OFF with a negative voltage.

When should you use a MOSFET instead of a BJT?

Use a MOSFET for high-speed switching and low power loss applications like digital circuits and power electronics.

What are some common uses of transistors?

Switching circuits (turning LEDs, motors ON/OFF). Amplifiers (boosting weak signals in audio devices). Voltage regulation (as part of power supplies). Oscillators (for generating clock signals).

How is a transistor used in a relay driver circuit?

A transistor acts as an interface between a low-power control signal (like from a microcontroller) and a high-power relay. When the transistor turns ON, it activates the relay.

What is a 555 timer IC?

A 555 timer is an integrated circuit used for timing, pulse generation, and oscillation in electronic circuits.

What is a monostable 555 timer circuit?

A monostable circuit has one stable state. When triggered, it switches to a HIGH state for a set time, then returns to LOW.

What are the components of a 555 monostable circuit?

Trigger (Pin 2): Activated when voltage drops below 1/3 Vcc. Threshold (Pin 6): Ends the HIGH pulse when voltage reaches 2/3 Vcc. Discharge (Pin 7): Discharges the capacitor when output goes LOW. Capacitor (C1): Controls the time duration. Resistor (R1): Sets the charge rate of C1.

What is the equation for monostable time delay?

T=1.1×R×CT = 1.1 \times R \times C Where: T = Time delay in seconds. R = Resistance in ohms. C = Capacitance in farads.

What happens when the trigger pin is activated?

The output goes HIGH for the calculated time delay, then returns to LOW automatically.

What is an astable 555 timer circuit?

An astable circuit continuously switches between HIGH and LOW, generating a square wave signal without requiring an external trigger.

What are the key components of an astable 555 circuit?

Resistors R1 and R2: Control charging/discharging. Capacitor C: Determines pulse width and frequency. Pin 3 (Output): Alternates between HIGH and LOW states.

What are the frequency and duty cycle equations for an astable 555 timer?

Frequency (f): f=1.44(R1+2R2)Cf = \frac{1.44}{(R_1 + 2R_2) C} Time HIGH (T_on): Ton=0.693(R1+R2)CT_{on} = 0.693 (R_1 + R_2) C Time LOW (T_off): Toff=0.693R2CT_{off} = 0.693 R_2 C Duty Cycle: D=TonTon+Toff×100D = \frac{T_{on}}{T_{on} + T_{off}} \times 100Where: R1, R2 = Resistors in ohms. C = Capacitance in farads.

What is the Mark/Space ratio?

The Mark/Space ratio compares the HIGH to LOW time in an astable circuit: Mark/Space Ratio=TonToff\, Mark/Space \, Ratio = \frac{T_{on}}{T_{off}}

How does changing R1 and R2 affect output frequency?

Increasing R1 or R2 → Decreases frequency. Decreasing R1 or R2 → Increases frequency.

What are common applications of 555 timers?

Monostable Mode: Used in timers, touch sensors, missing pulse detection. Astable Mode: Used in LED flashers, pulse generation, clock signals. PWM (Pulse Width Modulation): Used in motor speed control, dimmable LED circuits.

How does a 555 timer generate a Pulse Width Modulation (PWM) signal?

By varying R2 or a control voltage, the duty cycle can be adjusted, allowing control of power delivery to motors or LEDs.

How can a 555 timer be used as a frequency divider?

Connecting the output of one 555 timer to the trigger of another can create frequency division, where the second timer outputs a lower frequency.