When an electric field changes, what is the induced magnetic field in relation to the electric field?

When an electric field changes, what is the induced magnetic field in relation to the electric field?

• A. It becomes parallel to the electric field
• B. It becomes perpendicular to the electric field
• C. It cancels the electric field
• D. It remains unaffected

Answer: (B)

A changing electric field generates a magnetic field. This is described by Maxwell-Ampere law: curl B is proportional to the time rate of change of E (in vacuum, curl B = μ0 ε0 ∂E/∂t). Because curl B is aligned with how E changes, the magnetic field lines form around the axis of the changing E, placing B in a direction perpendicular to E. In a plane electromagnetic wave, E, B, and the direction of propagation are all mutually perpendicular, with B perpendicular to E. So the induced magnetic field is perpendicular to the electric field.

A changing electric field generates a magnetic field. This is described by Maxwell-Ampere law: curl B is proportional to the time rate of change of E (in vacuum, curl B = μ0 ε0 ∂E/∂t). Because curl B is aligned with how E changes, the magnetic field lines form around the axis of the changing E, placing B in a direction perpendicular to E. In a plane electromagnetic wave, E, B, and the direction of propagation are all mutually perpendicular, with B perpendicular to E. So the induced magnetic field is perpendicular to the electric field.