iGCSE Physics (0625) 3.3 Electromagnetic spectrum-Exam Style Questions- New Syllabus
▶️ Answer/Explanation
Detailed solution:
All electromagnetic waves, including X-rays and visible light, travel at the same speed in a vacuum, approximately $3.0 \times 10^{8} m/s$.
The electromagnetic spectrum is ordered by increasing frequency and decreasing wavelength: radio, microwave, infrared, visible, ultraviolet, X-ray, and gamma ray.
Since X-rays have a much higher frequency than visible light, they must have a shorter wavelength according to the wave equation $v = f \lambda$.
Microwaves, conversely, have a lower frequency and thus a longer wavelength than visible light.
Option D is correct because it accurately identifies that X-rays travel at the same speed as visible light but possess a shorter wavelength.
▶️ Answer/Explanation
Detailed solution:
Infrared radiation is an electromagnetic wave, which travels at the speed of light in a vacuum, c=3.0×10 8 m/s.
The refractive index n of a medium is defined by the ratio n= v c , where v is the speed in the medium.
Rearranging the formula to solve for the speed in glass, we get v= n c .
Substituting the given values, v= 1.5 3.0×10 8 m/s .
This calculation yields v=2.0×10 8 m/s.
Therefore, option B is the correct speed of the radiation within the glass medium.
▶️ Answer/Explanation
Detailed solution:
Light is an electromagnetic wave, and all waves in the electromagnetic spectrum travel at a constant high speed in a vacuum.
According to the syllabus, this speed is exactly 3.0×10 8 m/s.
While light slows down slightly when passing through transparent media, the speed in air is considered approximately equal to its speed in a vacuum.
Option A (300 m/s) is incorrect as it approximates the speed of sound in air, not light.
Option B and D use incorrect units or magnitudes that do not align with the standard physical constant.
Therefore, the correct approximate value is 3.0×10 8 m/s, which corresponds to Option C.