Intensity

Aaarghhh.. radiation - we're all gonna die... ahem

What is radiation? [1]
- Energy emitted from a source
  - What are some examples of ionising nuclear radiation? [3]
    - Alpha-rays
    - Beta-rays
    - Gamma-rays
  - What is an example of another ionising radiation? (not nuclear) [1]
    - X-rays
  - What is an example of a non-ionisng radiation? (not nuclear) [1]
    - Visible light, Radio Waves, Infra Red, etc
What exactly does the "Intensity" of Radiation mean? [1]
- "Intensity = the Rate of Energy Flow to a 1 m² Area"
  - So if the radiation carries more energy, will it be more intense? [1]
    - Yes - The more energy it carries, the more energy gets transferred when it hits an object
- ...or "Intensity = the rate at which Energy arrives at 1 m² of surface"
  - How does the surface area of the object affect the amount of radiation that smacks into it? [1]
    - A big object with a bigger surface area is going to catch more radiation than a small one
- ...or "Intensity = Power of radiation / Area it falls on"
  - How can you write that as a word equation? [1]
    - - How might you write that as a symbol equation? [1]
        
        I = P / A
        
        What are the units Intensity is measured in? [1]
        
        W/m²
        
        Eg: What is the intensity of radiation if the energy from a 100 W light bulb spreads over a surface of 4 m². [3]
        
        I = P / A
        
        I = 100 W / 4 m²
        
        I = 25 W/m²

How does distance affect Intensity? [1]
- The closer the source is to the surface, the higher the intensity of radiation that hits into it.
  - If you move twice as far away from the source, how much less would the intensity be? [1]
    - ¼ of the intensity
      - Why is it not ½ of the intensity? [1]
        
        Since the intensity of the radiation depends on the area it's spread over, if you move twice as far from the source, the same radiation is being spread over four the area. So you only receive ¼ of the energy over 1 m² surface area
        
        What would the intensity be if you move three times as far from the source? [1]
        
        1/9 of the intensity
      - What is this type of relationship known as? [1]
        
        The inverse square relationship
What's a medium? [1]
- The substance the radiation is passing through (e.g. air, water, glass, etc)
  - If the radiation is passing through a medium other than a vacuum, what might happen to some of the radiation before hitting the surface? [1]
    - It might get absorbed or scattered
  - How might this affect the intensity? [1]
    - It would be less than expected (e.g. sunglasses absorb some of the light, reducing the true intensity of the surroundings)

Homework
- What's the proper definition for radiation?
- What's the equation for Intensity of Radiation?
- The energy from a 1 kW electric heater radiates out evenly over a surface of 4m². Calculate the Intesity of the radiation at the surface
- What two factors affect the intensity of radiation you receive from a 40 W light bulb?

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Intensity

Aaarghhh.. radiation - we're all gonna die... *ahem*

What is radiation? [1]

What exactly does the "Intensity" of Radiation mean? [1]

How does distance affect Intensity? [1]

What's a medium? [1]

Homework

Aaarghhh.. radiation - we're all gonna die... ahem