Which statement is true about radiation generation, per the stated rules?

Which statement is true about radiation generation, per the stated rules?

• A. A time-varying current or acceleration of charge is required
• B. A static charge radiates freely
• C. No current is ever needed for radiation
• D. Radiation occurs only in magnetic fields

Answer: (A)

Radiation arises when the electromagnetic field is driven to change by moving charges. A time-varying current or acceleration of charge makes the electric and magnetic fields vary with time, producing waves that propagate away. A static charge maintains a steady field and does not emit radiation. Likewise, a charge moving at constant velocity has no acceleration, so it doesn’t radiate. The key idea is that changing currents or accelerating charges generate the changing fields needed to radiate; radiation isn’t confined to magnetic fields alone but is about the time variation of the fields caused by the moving charges.

Radiation arises when the electromagnetic field is driven to change by moving charges. A time-varying current or acceleration of charge makes the electric and magnetic fields vary with time, producing waves that propagate away. A static charge maintains a steady field and does not emit radiation. Likewise, a charge moving at constant velocity has no acceleration, so it doesn’t radiate. The key idea is that changing currents or accelerating charges generate the changing fields needed to radiate; radiation isn’t confined to magnetic fields alone but is about the time variation of the fields caused by the moving charges.