A company demonstrates wireless power transmission across a room. How is this explained by electromagnetic theory?

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Question: A company demonstrates wireless power transmission across a room. How is this explained by electromagnetic theory?

Option a: A static electric field pushes charges to the receiver.
- This is incorrect for wireless power transmission over a distance. Static electric fields imply a constant, non-propagating field between conductors. In practical wireless power transfer, the charges at the receiver are not maintained by a stationary field at a distance; instead, energy transfer involves time-varying fields and coupling between circuits.

Option b: The air becomes ionized and transmits electrons.
- Ionization of air would create a plasma and is associated with breakdown or spark/COVID-19-like arcing, which is highly inefficient and dangerous for continuous power transfer. Wireless power transfer relies on non-ionizing regimes to avoid gas discharge. Therefore this description does not match the typical EM mechanism used for wireless power transmission.

Option c: Oscillating electric and magnetic fields form a self-sustaining electromagnetic wave that carries energy.
- This aligns with the standard electromagnetic theory of wireless power transfer. An alternating current in a transmitter coil creates time-varying magnetic flux, which, via mutual inductance or resonant coupling, generates oscillating electric and magnetic fields. These fields propagate as an electromagnetic wave or couple energy through near-field/resonant modes to a receiver, delivering energy without direct contact. The key ideas are time-varying fields, propagation, and energy transport by EM waves or modes, not static fields or ionization.

Option d: Sound waves trigger movement in electric circuits.
- Sound waves do not carry electrical energy and are not the mechanism by which wireless power is transmitted. They are mechanical waves and would not couple efficiently into electrical energy in typical wireless power systems. This option confuses acoustics with electromagnetism and energy transfer.

In summary, the physically consistent explanation involves time-varying electric and magnetic fields that propagate or couple energy to the receiver, rather than static fields, ionization, or acoustic effects.

SPH4U - Physics 12 (2025-26) - A

A company demonstrates wireless power transmission across a room. How is this explained by electromagnetic theory?

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