Final answer:
A door lock requiring either a key or a passcode to open is an example of an XOR circuit since it unlocks exclusively with one input at a time, mirroring the XOR logic operation.
Step-by-step explanation:
A real-world example of an XOR (Exclusive OR) circuit would be option 3: A door lock that requires either a key or a passcode to open. This is because an XOR circuit operates on two inputs in such a way that it outputs a true (or 'on') signal only when the inputs are different from each other. In the case of the door lock, this means the door would unlock when either the key is used or the passcode is entered, but not both at the same time. The light switch, calculator, and traffic light examples do not behave in this exclusive manner and are therefore not examples of XOR circuits.
Modern digital devices extensively use integrated circuits with transistors to perform logical operations such as XOR. These devices manipulate data using binary code, which relies on the concept of transistors functioning as on-off switches. The XOR function is a fundamental part of digital logic and computing, helping in various tasks like data manipulation and decision-making processes within electronic devices.