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Review Questions for Chapter 20.2 – Telescopes and the Electromagnetic Spectrum

Electromagnetic Spectrum

  1. What do all the energies in the electromagnetic spectrum have in common?

  2. They travel at the same speed – the speed of light, 300,000 km/sec – and all travel in waves
  3. What is frequency?

  4. The number of waves that pass a given point in a given time.
  5. What is wavelength?

  6. The distance between crest to crest, or trough to trough.
  7. In the visible light spectrum, which color has the highest frequency? The Lowest?

  8. The highest frequency would be violet, the lowest would be red.
  9. What is the relationship between frequency and wavelength?

  10. As wavelength increases the frequency will decrease, and vice versa.
  11. As wavelength decreases, does the energy in the waves become more dangerous, or less dangerous?
    As wavelength decreases the frequency will increase. Higher frequency wavelengths such as Xrays and gamma rays are more dangerous than low frequency wavelengths such as radio waves.

Visible Light

  1. What instrument is used to break light up into individual wavelengths?

  2. Spectrascope
  3. What can be learned from the spectra of visible light coming from stars and outer space?

  4. The composition of stars can be determined by their emission spectra. Also the temperature and distance of stars can be determined, but we have not discussed that yet.
  5. What are the three different spectras?
  6. Continuous – such as from sunlight

    Bright line or emission spectra – such as emitted from hydrogen or helium burning

    Dark-line spectra also known as absorption spectra – when a gas or the atmosphere absorbs certain wavelengths.

  7. What type of spectra is the result of absorption of some of the wavelengths?
  8. What type of spectra is sunlight?
  9. What type of spectra is the result of the unique emissions from an element?

Doppler Effect and the Red Shift

  1. What is red shift? And blue shift?

  2. The Red Shift is behind the theory that the universe is expanding. Spectra of one star will move toward the red end of the spectrum after being viewed month after month. This means the wavelength is increasing, which means that the object giving off the spectra is moving away from us. Blue shift is the opposite of that concept. Things that are moving closer produce spectra that shifts towards the blue end of the visible spectrum, meaning the wavelength is decreasing.
  3. How does the Doppler effect of sound relate to the red shift?
    The Doppler Effect is similar to the Red Shift, but dealing with pitch in sound waves. A train’s pitch gets higher and louder as it comes closer to you because the wavelengths are getting compressed – the frequency is increasing. (Remember the internet demo?) As the train passes you and moves away from you, the train’s pitch gets lower and softer, because the wavelengths are getting longer and the frequency is decreasing.