Behavioral
Tell me about yourself.
A 60-90 second "elevator pitch" covering their current major/year, a highlight of relevant coursework or projects, and a brief statement on why they are excited about this specific role.
What is the equivalent resistance of two 100-ohm resistors in parallel?
50 ohms. The formula is $R_{eq} = (R_1 \times R_2) / (R_1 + R_2)$, which simplifies to half the value when two identical resistors are in parallel.
What does PID stand for, and briefly explain what each of the three terms does to help a system reach its target?
PID stands for Proportional, Integral, and Derivative. A good candidate should explain them conceptually:
Proportional (Present): Reacts to the current error. It applies a corrective force proportional to how far off you are right now, but often leaves a small constant gap (steady-state error).
Integral (Past): Reacts to accumulated error over time. It eliminates steady-state error by continuing to push the system if it gets "stuck" near the target.
Derivative (Future): Reacts to the rate of change of the error. It acts as a damper, slowing the system down as it approaches the target to prevent it from overshooting.
Explain the difference between a low-pass filter and a high-pass filter.
A low-pass filter allows signals with frequencies below a certain cutoff frequency to pass through while attenuating higher frequencies. A high-pass filter does the exact opposite.
Convert the binary number 1011 to decimal.
11. (Calculated as $1\times 8 + 0\times 4 + 1\times 2 + 1\times 1$).
What is your greatest technical weakness?
A genuine answer (not "I work too hard") followed immediately by the actionable steps they are taking to improve it (e.g., "I haven't had much exposure to PCB layout yet, so I just joined the solar car team to learn Altium Designer").
Draw a voltage divider and state its output equation.
Solution: Two resistors ($R_1$ and $R_2$) in series between a voltage source ($V_{in}$) and ground. The output voltage ($V_{out}$) is taken between the two resistors. The formula is $V_{out} = V_{in} \times (R_2 / (R_1 + R_2))$.
If you plot a system's transfer function and find poles located in the right half of the s-plane, what does that tell you about the system?
The system is inherently unstable.
A multiplication operation in the frequency domain corresponds to what mathematical operation in the time domain?
Convolution
Describe the operational difference between a Stack and a Queue.
A Stack operates on a Last-In-First-Out (LIFO) basis (like a stack of plates). A Queue operates on a First-In-First-Out (FIFO) basis (like a line at a grocery store).
Tell me about a time you disagreed with a teammate on a project. How did you handle it?
Uses the STAR method (Situation, Task, Action, Result). The answer must demonstrate active listening, focusing on data/logic rather than emotion, and reaching a productive compromise.
State Thevenin's Theorem and explain the steps to find both the Thevenin voltage and Thevenin resistance for a given linear circuit.
The Theorem: Any linear circuit with voltage/current sources and resistors can be simplified down to a single equivalent voltage source ($V_{th}$) in series with a single equivalent resistor ($R_{th}$) connected across the load terminals.
Finding $V_{th}$: Remove the load and calculate the open-circuit voltage across those two terminals.
Finding $R_{th}$: Remove the load, turn off all independent power sources (short-circuit all voltage sources and open-circuit all current sources), and calculate the equivalent resistance looking into the open terminals.
Explain the Root Locus method and describe what it is used for in control systems design.
The Root Locus is a graphical method that plots the paths (loci) of the closed-loop poles of a system in the s-plane as a specific system parameter (usually the feedback gain, $K$) is varied from zero to infinity. It is used to quickly determine how changing that gain affects the system's stability (keeping poles in the left-half plane) and transient response (like settling time and overshoot).
What is the Nyquist-Shannon sampling theorem?
To perfectly reconstruct a continuous signal, it must be sampled at a rate strictly greater than twice its highest frequency component.
An oscilloscope can only directly measure voltage over time. If you only have an oscilloscope and standard passive components, how can you measure the current flowing through a circuit?
You place a resistor with a known, very small value in series with the circuit. You then use the oscilloscope to measure the voltage drop across that resistor and use Ohm's Law ($I = V/R$) to calculate the current.
Describe a time a project or experiment failed. What went wrong and what did you learn?
Demonstrates accountability. The candidate should take responsibility for their part, explain the root cause analysis, and detail how they adjusted their process for the next time.
How does an ideal capacitor behave at a DC steady-state, and how does it behave at very high AC frequencies?
At DC steady-state, a capacitor acts as an open circuit (blocks current). At very high AC frequencies, it acts as a short circuit (passes current easily).
Draw the magnitude Bode plot for a standard 2nd-order low-pass filter and describe its key features.
A flat line at 0 dB (or the DC gain) for low frequencies.
A potential resonant peak at the natural cutoff frequency ($\omega_n$), the height of which depends on the damping ratio ($\zeta$).
A high-frequency roll-off with a constant slope of -40 dB/decade (or -12 dB/octave) after the cutoff.
Describe the Fourier Transform of a continuous-time sine wave. What does it look like in the frequency domain?
The frequency spectrum consists of exactly two Dirac delta functions (impulses or spikes). One is located at the positive fundamental frequency ($+f_0$) and the other at the negative fundamental frequency ($-f_0$).
Why do we place decoupling (or bypass) capacitors right next to the power pins of microcontrollers?
Microcontrollers and digital ICs have transistors inside that switch on and off incredibly fast. When they switch, they pull sudden, sharp spikes of current from the power supply. Because the trace connecting the power supply to the IC has a small amount of parasitic inductance, the power supply can't deliver that sudden burst of current fast enough, causing the voltage at the pin to dip, which can reset the chip. We place decoupling capacitors as physically close to the power pins as possible to act as tiny, local energy reservoirs. When the IC suddenly needs current, it pulls it instantly from the capacitor instead of waiting for the main power supply.
Tell me about a time you had to use a tool or learn a concept not taught in your classes to finish a task.
Highlights resourcefulness and self-learning. Good answers mention reading documentation, looking up application notes, or seeking out subject matter experts, rather than just "I watched a YouTube video."
Describe the setup of an inverting operational amplifier and provide its gain equation.
The input signal is connected to the inverting (-) terminal through a resistor ($R_{in}$). A feedback resistor ($R_f$) connects the output back to the inverting terminal. The non-inverting (+) terminal is grounded. The gain is $-R_f / R_{in}$
Draw the phase Bode plot for a standard 2nd-order low-pass filter and describe its key features.
The phase starting at 0 degrees at low frequencies.
The phase passing exactly through -90 degrees at the natural cutoff frequency ($\omega_n$).
The phase asymptotically approaching -180 degrees at high frequencies. (The steepness of the transition depends on the damping ratio).
Suppose you want to sample an audio signal. What sampling frequency will you use and why? (Hint: Human hearing goes up to about 20 kHz).
You should choose a sampling frequency around 44.1 kHz or 48 kHz. According to the Nyquist theorem, you must sample at least twice the highest frequency (40 kHz) to accurately reconstruct the signal. However, because perfect "brick-wall" hardware filters don't exist, the extra frequency range provides a necessary transition band. This gives the analog anti-aliasing filter enough room to gradually roll off above 20 kHz before hitting the Nyquist limit.
Can you explain what pull-up and pull-down resistors are, and why we use them in digital circuits?
To fix this, we use pull-up or pull-down resistors. A pull-up resistor connects the pin to the supply voltage (like 3.3V or 5V). This guarantees that when the switch is open, the pin reads a solid HIGH. When the switch is closed, it connects directly to ground, reading LOW. A pull-down resistor does the exact opposite, connecting the pin to ground so it defaults to LOW. We usually use a value like 10kΩ so that it’s strong enough to hold the voltage steady, but high enough that it doesn't draw too much current when the switch is closed.”