Question

Speed of electromagnetic wave is the same (A) for all wavelengths (B) in all media (C) for all intensities (D) for all frequencies

Short answer

The speed of electromagnetic waves is the same for all intensities (C), as it is not directly dependent on the amount of energy the wave carries. This holds true as long as the wavelength and medium do not change.

Step-by-step solution

Analyzing Option A: For all wavelengths

Electromagnetic waves can have different wavelengths, but, in a vacuum, their speed remains constant, and the frequency will adjust accordingly to maintain that speed. However, when they enter different media, the speed may change, so this statement is not always true.

Analyzing Option B: In all media

The speed of electromagnetic waves depends on the medium through which they travel. In a vacuum, the speed remains constant at \(3 \times 10^8 m/s\), but in other media such as air, water, or glass, the speed will generally reduce. This is due to the interaction between the waves and the atoms in the medium. Therefore, this statement is not true.

Analyzing Option C: For all intensities

The intensity of an electromagnetic wave refers to the amount of energy it carries. The speed of the wave is not directly dependent on its intensity. A higher intensity wave may have more energy, but it will still travel with the same speed if the wavelength and medium do not change. Therefore, this statement is true.

Analyzing Option D: For all frequencies

The speed of electromagnetic waves in a vacuum is constant, and the wavelength changes according to the frequency to maintain that constant speed. However, in different media, the speed may vary with frequency. So, this statement is not always true. Given the analysis above, the correct answer is: (C) for all intensities