Question

Electromagnetic waves are produced by (A) a static charge (B) a moving charge (C) an accelerating charge (D) chargeless particles

Short answer

The correct answer is (C) an accelerating charge, as it results in a changing electric and magnetic field, which is necessary for the generation of electromagnetic waves. Static charges, moving charges, and chargeless particles do not produce the required changing fields.

Step-by-step solution

Understanding Electromagnetic Waves

Electromagnetic waves are a type of wave that consists of oscillating electric and magnetic fields. These fields are perpendicular to each other and to the direction of the wave's propagation. In order to create an electromagnetic wave, we need a changing electric or magnetic field.

Evaluating Options A, B, and C

To determine which type of charge produces electromagnetic waves, we need to examine the behavior of static charges, moving charges, and accelerating charges. (A) A static charge is not changing in time, and thus cannot create the changing electric and magnetic fields required for an electromagnetic wave. (B) A moving charge, while not static, still has a constant velocity. This means that the electric and magnetic fields will also not change with time, and therefore, this charge cannot produce an electromagnetic wave. (C) An accelerating charge, on the other hand, is changing its velocity which results in a changing electric and magnetic field. As a result, an accelerating charge can generate electromagnetic waves.

Evaluating Option D

(D) Chargeless particles do not inherently possess electric or magnetic fields. As a result, they cannot produce electromagnetic waves.

Conclusion

Based on the analysis of the behavior of static charges, moving charges, accelerating charges, and chargeless particles in relation to their ability to produce electromagnetic waves, the correct answer is (C) an accelerating charge.

Key concepts

Oscillating Electric and Magnetic Fields

Electromagnetic waves are fascinating phenomena that involve interlinked electric and magnetic fields. These fields oscillate, meaning they change in magnitude and direction with time. This oscillation occurs at right angles to each other, as well as to the direction in which the wave travels. When an electric field changes, it induces a magnetic field, and conversely, a changing magnetic field will induce an electric field. This dynamic interplay allows electromagnetic waves to maintain their propagation through space.

The self-sustaining nature of electromagnetic waves is what sets them apart from other types of waves. Unlike sound waves, which require a medium like air or water to travel, electromagnetic waves can move through the vacuum of space. This remarkable feature is why we can receive sunlight from the sun, or radio signals from distant stars, across the void. Understanding this crucial aspect helps explain why sources of varying electric and magnetic fields are essential for generating electromagnetic waves.

Accelerating Charges

Electromagnetic waves originate from accelerating charges. Not just any charge will produce these waves; it needs to be accelerating. When a charge accelerates, it means it is changing its velocity. This change can be a speed increase or decrease, or a change in direction.

As the acceleration alters the charge's electric field, it causes the field to oscillate. This oscillation is key in producing electromagnetic waves. A moving charge with constant velocity won't create these oscillations, just like a static charge remains inactive.

To visualize, consider electrons in an antenna. When these electrons accelerate back and forth, they produce oscillating electric and magnetic fields. This results in the emission of electromagnetic waves, like the radio waves that carry all your favorite tunes.

Wave Propagation

Wave propagation refers to the movement or travel of waves through a medium or space. Electromagnetic waves are unique because they do not need a medium to travel. They can move efficiently through the vacuum of space as well as through materials.

The propagation of electromagnetic waves is governed by their oscillating electric and magnetic fields, which continually regenerate each other as they move forward. This true synergy ensures that once generated, electromagnetic waves can sustain their transmission over vast distances.

Propagation depends on the frequency and wavelength of the wave. Shorter wavelengths tend to have higher frequencies and can penetrate materials more effectively, leading to a wider range of applications. Longer wavelengths, such as radio waves, can traverse kilometers in open space, making them ideal for communication across long distances.