Waves from the Sun
Light and its relatives cross empty space.
Across empty space
Between the Sun and the Earth there is almost nothing, no air and no water. Yet the Sun's energy reaches us.
How might that energy travel?
What this lesson covers
The idea
Solar radiation travels as EM waves through vacuum at the speed of light, 3 × 10⁸ m s⁻¹; the EM spectrum runs from high-frequency, short-wavelength, high-energy gamma and X-rays to low-frequency, long-wavelength infrared and radio waves.
Across empty space
Between the Sun and the Earth there is almost nothing, no air and no water. Yet the Sun's energy reaches us.
How might that energy travel?
- As waves that need no medium
- As sound that needs air
- It cannot reach us
Waves and the spectrum
Press Next step.
EM waves do not need a medium
Sound waves are mechanical waves and need a medium. EM waves do not, so they can cross the vacuum between the Sun and the Earth. Light is one kind of EM wave, and its speed in a vacuum is 3 × 10⁸ m s⁻¹.
Solar radiation travels as EM waves through a vacuum at the speed of light, 3 × 10⁸ m s⁻¹. The EM spectrum runs from high-frequency, short-wavelength, high-energy gamma rays and X-rays to low-frequency, long-wavelength infrared and radio waves.
Notes
EM waves cross a vacuum at 3 × 10⁸ m s⁻¹. The EM spectrum goes from high-energy gamma rays and X-rays to long-wavelength infrared and radio waves.
Check yourself
What is the speed of light in a vacuum?
Which waves can travel from the Sun to the Earth through a vacuum?
Which radiation has high frequency, short wavelength and high energy?
Light travels 3 × 10⁸ m in one second in a vacuum. How far does it travel in 3 seconds? Give your answer as a number of 10⁸ m.
Answer: 9 × 10⁸ m
- 3 × 10⁶ m s⁻¹. The speed of light in a vacuum is 3 × 10⁸ m s⁻¹, which is 100 times larger than this.
- 3 × 10¹⁰ m s⁻¹. The speed of light in a vacuum is 3 × 10⁸ m s⁻¹, which is 100 times smaller than this.
- 3 × 10⁸ m s⁻¹ — correct. Yes!
- Electromagnetic waves — correct. Yes!
- Sound waves. Sound waves are mechanical waves and need a medium to travel.
- Any wave that needs air or water to carry it. Such waves are mechanical waves. Electromagnetic waves do not need a medium.
- Radio waves. Radio waves have low frequency and long wavelength.
- X-rays — correct. Yes!
- Infrared. Infrared has low frequency and long wavelength compared with X-rays.