Electronic components

On a circuit board, five electronic components numbered from 1 to 5 are observed:

1. A small cylinder with colored bands.

2. A cylinder with two leads and a side stripe indicating the negative pole.

3. A transparent component with two leads that emits light when current passes through it.

4. A component with three leads and a black plastic body.

5. A black rectangular package with two parallel rows of metal pins.

Identify each element and briefly explain what function it performs within a circuit.

Explain what a short circuit is and why it is dangerous to connect the two terminals of a battery directly with a wire.

You are assembling a circuit for a precision temperature sensor that requires a resistor whose actual value is strictly between $540\ \Omega$ and $600\ \Omega$; if the value falls outside this range, the sensor reading becomes uncalibrated. In the component drawer, you find a resistor with the color bands green - blue - brown - gold.

1) Interpret the color code indicating the nominal value of the resistor and its tolerance percentage.

2) Calculate the actual range of values (minimum and maximum) that this resistor can have in practice.

3) Reasonably justify whether it is technically safe to use this component in the circuit or if you should replace it with a higher-precision resistor (with a brown tolerance band, of $1\ \%$), arguing your decision.

Explain what function a resistor serves and what function an LED serves in a circuit, and explain why an LED is almost never connected alone, but rather with a resistor in series.

A red LED and a blue LED do not operate at the same voltage. Explain why this matters when designing the circuit and what can happen if both are powered using the same resistor calculated for only one of them.

You have a $9\ \text{V}$ battery and two identical LEDs whose technical specifications are: forward voltage $V_F = 2,2\ \text{V}$ and nominal operating current $I_F = 20\ \text{mA}$. You want to connect them in series using a single current-limiting resistor so that they operate at their nominal current. In the workshop, you have standard commercial resistors of $150\ \Omega$, $220\ \Omega$, $330\ \Omega$, and $470\ \Omega$.

1) Justify using Ohm's law what exact theoretical resistance is required and which of the available values you should choose to ensure maximum brightness without exceeding the safe current limit.

2) If someone mistakenly connects the two LEDs in series with the $150\ \Omega$ resistor, calculate the current that will flow and predict the thermal and operational consequences for the diodes.

A transistor is said to work as a current-controlled switch. Explain this idea using the example of a circuit that turns on an LED when it gets dark: a light sensor (LDR) controls the base of the transistor.

To make a car's interior light stay on for a few seconds after closing the door (opening the switch contact), a person connects a $2200\ \mu\text{F}$ capacitor directly in parallel with a $12\ \text{V}$, $6\ \text{W}$ light bulb. When testing it, they find that the bulb turns off almost instantaneously.

1) Justify by calculating the bulb's resistance and the time constant $\tau = R \cdot C$ why their circuit fails.

2) Propose and describe a modification to the circuit using an NPN transistor and an additional resistor, technically justifying how this new configuration does allow prolonging the illumination for several seconds with that same capacitor.

The digital output of a school microcontroller delivers $5\ \text{V}$ with a safety current limit of only $20\ \text{mA}$. A student connects a small $5\ \text{V}$ direct current motor that draws $250\ \text{mA}$ at full load directly to that pin. Upon activation, the microcontroller freezes and turns off immediately.

1) Technically justify why it is not viable to power the motor directly from the digital output.

2) Design the necessary switching stage using an NPN transistor as a switch (indicating how to connect the base, collector, and emitter with respect to the digital pin, the motor, and the power supply).

3) Explain what function the base resistor serves and predict what electrical disaster would occur to the transistor when turning off the motor if a flyback diode is not placed in reverse parallel across its terminals.

An LDR has high resistance when there is little light and low resistance when there is a lot of light. Reason how to use it so that a circuit "knows" whether it is day or night, indicating what would happen to the current in each case.

Explain what a potentiometer is and how it allows you to adjust the volume of a loudspeaker or the brightness of a lamp without changing any circuit components.

In a workshop practical, a team builds a direct current power supply by connecting a transformer and a diode bridge rectifier, obtaining at the output a pulsating DC voltage with a peak value of $18\ \text{V}$. To filter the ripple, they connect an electrolytic capacitor whose casing reads: $1000\ \mu\text{F}\ /\ 16\ \text{V}$, connecting the short lead (marked with a gray longitudinal stripe) to the positive terminal of the rectified output. A few seconds after turning on the power supply, the capacitor begins to hiss, heats up sharply, and bulges at the top.

Identify and justify in detail the two serious mistakes made in the assembly, explaining what physical or electrochemical phenomenon occurs inside the component in each case, and specify what minimum voltage and connection characteristics the new capacitor should have to operate completely safely.