# Energy stored in fields

How to intuitively think of energy stored in a magnetic/electric field?

Kindly answer in a bit simple terms without referring to mathematics.

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Energy is a quantity; it is a number together with a unit. To talk about "quantities" is to talk "quantitatively" which is pretty much the same thing as "referring to mathematics". It's really the point of energy that it isn't a potato or bumblebee or anything with a specific shape; it "only" has the number which is what makes it important. In the international units, energy is counted in joules. You may imagine a joule is a bumblebee except that it looks like nothing of the sort. I wonder: what leads you to insist that you want to avoid mathematics? That's not a way to understand Nature. – Luboš Motl Apr 22 '13 at 10:47
@ Luboš Motl The way I wanted to ask is , I can kind of see kinetic energy ,understand it . But how is energy stored in a field , I can't understand ? – kumar gaurav Apr 22 '13 at 14:19

## 1 Answer

Energy is a scalar quantity, a single number, that doesn't change in physical systems where all interactions are inside the system.

For a number of particles that only interact with one another at the same location, kinetic energy is this single number that's conserved. When they interact at a distance via the electromagnetic field, the total kinetic energy of the particles is no longer conserved. However, we can still add a quantity associated with the electromagnetic field; electromagnetic energy, to the total kinetic energy of the particles, that still gives us a conserved number called the total energy.

It turns out that the electromagnetic energy is a mathematical expression involving the electric and magnetic fields evaluated over the whole of space, whereas the kinetic energy of a particle is evaluated at one location. Hence there is this picture some people have of electromagnetic energy being "stored" in the electromagnetic field. This is just a confusing, outdated interpretation, influenced by the past when this electromagnetic energy was once seen as stored in an electromagnetic substance called the ether.

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