Core losses are energy losses in a transformer’s magnetic core caused by changing magnetic fields. In Principles of Physics II, they come from hysteresis and eddy currents, even when the transformer has no load.
Core losses in Principles of Physics II are the energy losses that happen inside the magnetic core of a transformer when the magnetic field keeps changing. You will also see them called iron losses, because they happen in the metal core that carries the magnetic flux.
These losses show up whenever a transformer is operating with alternating current. The core is constantly being magnetized and demagnetized as the AC current changes direction, and that repeated reversal is not free. Some energy is converted into heat inside the core instead of being transferred cleanly from the primary coil to the secondary coil.
There are two main parts to core losses. Hysteresis loss comes from the way the core material responds to magnetization. The magnetic domains in the material do not flip instantly and perfectly, so energy is spent each cycle. Eddy current loss comes from currents induced within the conducting core itself. Since the magnetic field is changing, loops of current are created in the core, and those currents heat the material.
That is why transformer design often tries to reduce these losses. Laminated cores break up the paths for eddy currents, so the circulating currents stay small. Core materials are also chosen for low hysteresis, which means they can magnetize and demagnetize with less wasted energy. A good transformer does not eliminate core losses completely, but it keeps them small enough that the device stays efficient.
A useful detail for this course is that core losses happen even when the transformer is not supplying a load. If the primary coil is connected to AC, the core is still cycling through magnetic changes, so the device still draws some power. That makes core losses a real part of the energy budget, not just a side effect when the transformer is doing useful work.
If you are working a problem or reading a circuit diagram, the presence of core losses usually means you are looking at a real transformer instead of an ideal one. Ideal transformer problems ignore them, but real transformer questions often bring them back when efficiency, heating, or power loss is the point of the question.
Core losses matter because they are part of the gap between an ideal transformer and the one you would actually build or use. In the perfect version of the model, all the input power gets transferred to the output side. In real life, some of that power is lost in the core as heat, so efficiency is always less than 100%.
This shows up directly in transformer efficiency questions. If a problem asks why a transformer gets warm, or why its output power is lower than expected, core losses are one of the first places to look. They also help explain why transformer design is not just about coil turns and voltage ratios, but also about the material and shape of the core.
Core losses connect the magnetic side of Physics II to the energy side. You are not just tracking fields, you are tracking where energy goes when fields change. That is a big idea in electromagnetism, and transformers are one of the clearest places to see it.
They also connect to the wider topic of power transmission. Large power systems rely on transformers to step voltage up and down efficiently, so even small losses matter when the devices run for long periods. Understanding core losses gives you a more realistic picture of why electrical systems are designed the way they are.
Keep studying Principles of Physics II Unit 8
Visual cheatsheet
view galleryHysteresis Loss
Hysteresis loss is one of the two main parts of core losses. It comes from the lag between the changing magnetic field and the way the core material actually responds. In a transformer, the domains in the core keep being reoriented as the AC current reverses, and that cycle wastes energy as heat.
Eddy Currents
Eddy currents are the circulating currents induced inside the transformer core by the changing magnetic field. They are the other major source of core loss. If the core is made of a conductive material, those loops can be strong enough to cause noticeable heating, which is why laminations matter.
Transformer Efficiency
Core losses are one of the reasons transformer efficiency is not perfect. When you compare input power to output power, some energy has already been lost in the core before it ever reaches the secondary circuit. Questions about efficiency often ask you to identify whether the loss is from the core or from the coils.
open-circuit test
The open-circuit test is a standard way to study transformer losses when the secondary coil is not delivering a load. Because the transformer still uses power even with no load, the test helps isolate core losses. That makes it a useful lab or problem-set tool for separating core loss from copper loss.
A quiz question may give you a transformer running with no load and ask why it still draws power from the source. The move is to identify core losses, especially hysteresis loss and eddy current loss, as the reason the primary still consumes energy. In problem sets, you may also compare ideal and real transformers and explain why real devices heat up. If the question mentions laminations or core material, connect that detail to reducing eddy currents or lowering hysteresis. In lab work, this concept often shows up when you interpret an open-circuit test or a transformer efficiency calculation. The key is to trace where the energy goes, not just repeat the voltage ratio.
Core losses happen in the magnetic core because of changing magnetic fields, while copper losses happen in the coils because the wire has resistance. Core losses can still appear with no load, but copper losses grow with current in the windings. If a question mentions heating in the core material, think core losses. If it mentions I²R heating in the coils, think copper losses.
Core losses are energy losses in a transformer’s magnetic core caused by alternating magnetic fields.
The two main parts are hysteresis loss and eddy current loss.
Core losses happen even when the transformer is not delivering a load, so they still affect energy use.
Laminated cores and low-hysteresis materials reduce these losses by limiting eddy currents and magnetic waste.
When a problem asks why a real transformer is less efficient than an ideal one, core losses are part of the answer.
Core losses are the energy losses that happen in a transformer’s magnetic core when the magnetic field keeps changing. They come from hysteresis loss and eddy current loss. In this course, they explain why a real transformer wastes some energy as heat even when the coil setup looks ideal on paper.
The two causes are hysteresis and eddy currents. Hysteresis comes from repeatedly magnetizing and demagnetizing the core material, and eddy currents are loops of current induced inside the conductive core. Both effects turn part of the electrical energy into heat.
Core losses happen in the magnetic core, while copper losses happen in the coil wires. Core losses are tied to changing magnetic fields and can happen even with no load. Copper losses depend on current through the windings and increase as the current gets larger.
A common way is to use a laminated core, which breaks up the paths for eddy currents. Transformer designers also choose materials with low hysteresis loss. Those changes reduce heating and improve efficiency without changing the basic voltage ratio of the transformer.