Electrical & Electronics: interview questions and learning guide

Circuits & power basics

Electricity is simple until something goes wrong, and then safety and method matter most.

Ohm's law links voltage, current and resistance, and power is voltage times current. Kirchhoff's laws describe how current and voltage behave in circuits. Power systems use AC, transformers and three-phase supplies, and protection devices stop faults from causing harm.

Interview tip: Always mention safety steps such as isolation and lockout.

Electronics & embedded systems

Small chips run huge parts of modern life, and they all start with a clean circuit.

Electronics uses parts such as diodes, transistors and capacitors to control signals. Microcontrollers read sensors with an ADC, drive devices with PWM and talk to other chips with buses such as I2C and UART. Stable power and good grounding prevent noisy readings.

Interview tip: Describe one project: the board, the sensor, the code and the result.

Industrial automation & electrical safety

Automation keeps factories running, and electrical safety keeps the people running them safe.

A PLC reads inputs from sensors and switches, runs ladder logic and drives outputs such as motors and valves. SCADA and HMI screens let operators monitor and control the process. Earthing, protective devices and lockout tagout protect people during operation and maintenance.

Interview tip: Name the PLC brands and software you have used.

AC/DC machines and transformers

A motor is a magnet that keeps chasing another magnet, and a transformer is a quiet gearbox for voltage.

Electrical machines turn electrical power into motion or the other way round. A DC motor uses a commutator to keep torque in one direction. An induction motor makes a rotating field in the stator and drags the rotor behind it, so the rotor always runs a little slower than the field. A transformer moves power between windings using a changing magnetic flux, and the turns ratio sets the voltage ratio. Losses show up as heat in copper and iron.

Interview tip: Always link slip to torque: no slip means no torque in an induction motor.

Power systems and protection

The grid is a giant river of power, and protection is the set of gates that closes the right one fast.

A power system has generation, transmission, distribution and loads. Power is sent at high voltage so current and line loss stay low. Faults such as short circuits and earth faults raise current sharply, so relays sense them and trip breakers. Good protection is selective: it isolates only the faulty part and keeps the rest running. Engineers also track voltage, reactive power and power factor to keep supply healthy and bills low.

Interview tip: Explain protection with the words selectivity, speed and sensitivity.

Microcontrollers and embedded C

A microcontroller is a tiny computer with its pins wired straight to the real world.

A microcontroller holds a CPU, memory and peripherals on one chip. Embedded C code reads inputs, decides, and drives outputs through registers. Peripherals such as timers, ADC and serial ports do work in hardware so the CPU stays free. Interrupts let urgent events pre-empt the main loop. Good firmware is small, deterministic and careful with memory because there is no operating system to rescue it.

Interview tip: Show you know to keep interrupt routines short and to mark shared variables volatile.

Sensors and signal conditioning

A sensor is the sense organ of a machine, and signal conditioning is the nerve that carries the message clean.

A sensor turns a physical value like heat, force or position into an electrical signal. That raw signal is often tiny, noisy or non-linear, so a conditioning stage amplifies, filters and linearises it. Industry likes the 4-20 mA loop because it resists noise and a broken wire shows as 0 mA. Choosing a sensor means checking range, accuracy, response time, environment and output type. Calibration keeps readings trustworthy over time.

Interview tip: Mention calibration and accuracy versus resolution when asked how you pick a sensor.

SCADA, drives and HMI

SCADA is the control room window, and the drive is the throttle for every motor on the floor.

A PLC runs the control logic, an HMI shows it to operators, and SCADA collects data from many PLCs across a plant or site. A variable frequency drive changes motor speed by changing supply frequency and voltage, which saves energy on pumps and fans. Devices talk through industrial protocols such as Modbus or Profibus. Alarms, trends and logs help operators and maintenance find problems early. Cyber security matters because these networks run real machines.

Interview tip: Link every drive or SCADA feature to a business gain such as energy saving or less downtime.

Isolate and lock out the supply, test that it is dead, follow the permit, wear PPE and confirm earthing.

Check the supply and fuses, the starter and overload relay, then test the motor windings and connections.

A microcontroller is a small chip embedded in products, while a PLC is a rugged industrial controller with standard inputs, outputs and ladder logic.

It shows how much current does useful work, and a low value wastes capacity and can raise bills, so capacitors are used to improve it.

A fuse melts once and must be replaced. A circuit breaker trips and can be reset.

A safe path for fault current to the ground so that metal parts do not stay live and breakers trip quickly.

A transformer changes voltage levels with no moving parts. A motor converts electrical energy into mechanical rotation.

A resistor that holds an input at a high level when nothing drives it, so the input does not float.

Common ones are UART, I2C and SPI. Explain which wires they use and when you chose each.

Pulse width modulation switches a signal on and off quickly, changing the duty cycle to control motor speed or LED brightness.

Check supply and fuses, overload relay, control circuit, connections and windings with a meter, isolate power first.