To solve this problem, we need to understand where the eddy current effect is utilized.$\\$Eddy currents are loops of electric current induced within conductors by a changing magnetic field.$\\$They are used in various applications due to their heating effect and magnetic damping properties.$\\$Let's analyze each option:$\\$• Induction furnace:$\\$ - Eddy currents are used to heat the metal by induction heating.$\\$• Magnetic braking in train:$\\$ - Eddy currents are used to provide a braking force by creating opposing magnetic fields.$\\$• Electromagnet:$\\$ - While eddy currents can occur, they are not the primary effect utilized in electromagnets.$\\$ - Electromagnets primarily use direct current to generate a magnetic field.$\\$• Electric heater:$\\$ - Electric heaters typically use resistive heating elements, not eddy currents, to generate heat.$\\$From the analysis, we see that the electric heater does not use the eddy current effect.$\\$Therefore, the correct option is 4: Electric heater.