Electromagnetic Relay Question & Answers May 8, 2023 By Wat Electrical This article lists 50 Electromagnetic Relay MCQs for engineering students. All the Electromagnetic Relay Questions & Answers below include a hint and a link to the relevant topic wherever possible. This is helpful for users who are preparing for their exams, interviews, or professionals who would like to brush up on the fundamentals of the Electromagnetic Relay. An electromagnetic relay is an electrical switching device that uses an electromagnet to control the flow of electricity. It works by using a small current to control a larger current. The relay consists of a coil of wire that is wound around a core of magnetic material, called the armature. Armature winding is a type of winding used in electric machines, such as generators, motors, and alternators. When a current is passed through the coil, it creates a magnetic field that attracts the armature, causing it to move and complete a circuit. The relay has two circuits: the control circuit and the load circuit. The control circuit is where the coil is connected, and the load circuit is where the larger current flows. When a current is applied to the control circuit, it creates a magnetic field that pulls the armature towards it, causing the switch to close and complete the circuit in the load circuit. When the current in the control circuit is removed, the magnetic field collapses, and the armature returns to its original position, opening the switch and breaking the circuit in the load circuit. Electromagnetic relays are commonly used in applications where a low-voltage signal needs to control a high-voltage circuit, or where a circuit needs to be switched on or off remotely. They are also used in a variety of industrial and commercial applications, including control systems, automation, and safety systems. 1). Which one of the following relays consists of a coil, armature, and contacts, and uses an electromagnetic field to open and close the contacts? Reed relay Armature relay Polarized relay Solid state relay Hint 2). Who is credited with inventing the first electromagnetic relay? Nikola Tesla Thomas Edison Joseph Henry Michael Faraday Hint 3). Which application was the first to use electromagnetic relays? Telecommunications Power generation Transportation Military Hint 4). Who developed the first practical relay for industrial use? Charles Wheatstone Werner von Siemens Samuel Morse André-Marie Ampère Hint 5). Which type of relay was developed to improve reliability and reduce noise? Mercury-wetted relay Reed relay Polarized relay Solid-state relay Hint 6). Which type of relay uses a magnetic core to amplify the input signal? Polarized relay Reed relay Transformer relay Induction relay Hint 7). Which type of relay is used to protect power systems from faults? Overload relay Differential relay Time-delay relay Seal-in relay Hint 8). Which type of relay is used to control the switching of high-power circuits? Time-delay relay Control relay Overload relay Latching relay Hint 9). Which type of relay is used to control the speed of electric motors? Soft-start relay Latching relay Time-delay relay Overload relay Hint 10). Which one of the following relays uses a permanent magnet to polarize the armature, and a coil to create a magnetic field that attracts or repels the armature? Reed relay Armature relay Polarized relay Solid state relay Hint 11). In what year was the first electromagnetic relay invented? 1802 1835 1877 1901 Hint 12). Which type of relay is used to protect sensitive electronic equipment from power surges? Surge protection relay Solid-state relay Polarized relay Reed relay Hint 13). What was the main purpose of the first electromagnetic relay? To control lighting To control heating systems To control telegraph lines To control telephone lines Hint 14). Who improved the design of the electromagnetic relay and made it commercially viable? Samuel Morse Alexander Graham Bell Thomas Edison Charles Wheatstone Hint 15). What is the principle behind the operation of an electromagnetic relay? The magnetic effect of an electric current The electric effect of a magnetic field The thermal effect of an electric current The chemical effect of an electric current Hint Electromagnetic Relay MCQ for Exams 16). What is the purpose of an auxiliary relay in an electrical circuit? To provide additional power to the main relay To isolate the main relay from the circuit To enhance the sensitivity of the main relay To reduce the power consumption of the main relay Hint 17). Which of the following is not a type of auxiliary relay? Polarized relay Differential relay Time-delay relay Directional relay Hint 18). What is the purpose of a time-delay auxiliary relay? To provide a delay before activating the main relay To provide a delay before deactivating the main relay To provide a time delay between the activation of two main relays To provide a time delay between the deactivation of two main relays Hint 19). What is an auxiliary relay? A relay used for auxiliary power supply A relay used for switching high-power loads A relay used to perform a specialized function in a larger control system A relay used to protect against overvoltage conditions Hint 20). Which one of the following relays uses semiconductor devices such as thyristors, triacs, or transistors to switch the load circuit? Reed relay Armature relay Polarized relay Solid state relay Hint 21). Which of the following is a common application of an auxiliary relay in a power system? Overvoltage protection . Directional protection Differential protection Underfrequency protection Hint 22). Which type of auxiliary relay is used to detect and measure the phase angle difference between two voltage signals? Directional relay Synchronizing relay Differential relay Overcurrent relay Hint 23). Which of the following is a disadvantage of using auxiliary relays in a control system? They increase the complexity of the control system They are expensive and difficult to maintain They introduce delays in the control system They decrease the reliability of the control system Hint 24). What is a reed relay? A relay used in power systems to detect faults A relay used in telecommunications to switch low-level signals A relay used to control the operation of motors and generators A relay used to protect against overvoltage conditions Hint 25). What is the main advantage of using a reed relay over other types of relays? High current carrying capacity Low cost Low power consumption High reliability Hint 26). How does a reed relay switch signal? By using a magnetic field to move a mechanical armature By using an electromagnet to create a magnetic field By using a solid-state device to switch the signal By using a semiconductor to amplify the signal Hint 27). Which of the following is a disadvantage of using a reed relay? Limited switching speed High power consumption High cost Low reliability Hint 28). What is a common application of a reed relay in a telecommunications system? To switch high-power loads To detect faults in the power system To provide overvoltage protection To switch low-level signals between circuits Hint 29). What is the maximum switching frequency of a typical reed relay? 1 kHz 10 kHz 100 kHz 1 MHz Hint 30). Which one of the following relays uses mercury as the contact material, and a magnetic field to move the mercury droplets to complete the circuit? Reed relay Armature relay Polarized relay Mercury relay Hint Electromagnetic Relay MCQ for Quiz 31). What is a potential disadvantage of using reed relays? Limited contact life Low contact resistance High coil resistance Low sensitivity Hint 32). An electromagnet is a switching element of __________________ relay? Polarized relays Reed relays Armature relays Contact relays Hint 33). The mechanical contacts are a switching element of __________________ relay? Polarized relays Reed relays Armature relays Contact relays Hint 34). A coil of wire that produces a magnetic field when energized is known as _______________? Electromagnet Armature Contact Points Spring Mechanism Hint 35). A movable component within the magnetic field of the coil is known as ______________? Electromagnet Armature Contact Points Spring Mechanism Hint 36). Electrical contacts that are opened or closed by the armature is known as ___________________? Electromagnet Armature Contact Points Spring Mechanism Hint 37). A mechanism that returns the armature to its original position is known as ___________________? Electromagnet Armature Contact Points Spring Mechanism Hint 38). A protective casing that houses the components of the relay is known as ___________________? Electromagnet Armature Contact Points Housing Hint 39). The moving armature is a switching element of __________________ relay? Polarized relays Reed relays Armature relays Contact relays Hint Read more about DC Motor 40). Which of the following is not a type of electromagnetic relay? Induction type relay Thermal relay Solid-state relay Reed relay Hint 41). Which type of relay operates on the principle of electromagnetic attraction? Induction type relay Attraction type relay Induction disc type relay Balanced beam type relay Hint 42). Which type of relay is commonly used for high-speed protection of power systems? Induction type relay Differential relay Overcurrent relay Distance relay Hint 43). Which type of relay is used in applications where a low power signal is required to switch a high-power circuit? Induction type relay Solid-state relay Reed relay Balanced beam type relay Hint 44). Which type of relay is used for detecting faults in a transformer? Buchholz relay Differential relay Overcurrent relay Distance relay Hint 45). The reed switch is a switching element of __________________ relay? Polarized relays Reed relays Armature relays Contact relays Hint 46). The systems for transmitting and receiving information over long distances is known as _____________? Telecommunications Power systems Control systems Safety systems Hint 47). The systems for generating, transmitting, and distributing electrical power is known as _____________? Telecommunications Power systems Control systems Safety systems Hint 48). The systems for controlling and regulating the operation of machines and processes is known as _____________? Telecommunications Power systems Control systems Safety systems Hint 49). The systems for protecting people, equipment, and the environment from harm or damage is known as _____________? Telecommunications Power systems Control systems Safety systems Hint 50). Which one of the following protects people, equipment, and the environment from harm or damage? Telecommunications Power systems Control systems Safety systems Hint Time's up
