### Video Transcript

A plane electromagnetic wave travels northward. At one instant, its electric field has a magnitude of 6.0 volts per meter and points eastward. What is the magnitude of the magnetic field at this instant?

Weโre told in this statement that, at one instant in time, the magnitude of the electric field is 6.0 volts per meter, which weโll call capital ๐ธ. At that same moment in time, we want to know the magnetic field, which weโll call capital ๐ต.

To begin our solution, letโs recall a relationship between electric and magnetic field magnitude. At any moment in time, the magnitude of the electric field ๐ธ is equal to the magnitude of the magnetic field ๐ต times the speed of light ๐.

In our scenario, wanting to solve for ๐ต, we can rearrange this equation so it reads ๐ต is equal to ๐ธ divided by ๐, where we take ๐ to be exactly 3.00 times 10 to the eighth meters per second.

When we enter these values into our equation and calculate this fraction, we find that ๐ต at this moment equals 2.0 times 10 to the negative eighth tesla. Thatโs the strength of the magnetic field when the electric field is 6.0 volts per meter.