Fizeau's Speed of Light Experiment

• What did scientists previously believe about the speed of light?

  Light covered distance instantaneously
• What did some astronomical observations suggest about light's speed?

  They contradicted the belief of instantaneous speed
• Who measured a finite speed for light?

  Hippolyte Fizeau
• How did Fizeau measure the speed of light?

  By shining light at a distant mirror
• What device did Fizeau use in his experiment?

  A toothed wheel spinning at high speed
• What effect did the toothed wheel have on the light beam?

  It created regular pulses of light
• What was the total path length of the light in Fizeau's experiment?

  2d
• What does the variable c represent in Fizeau's experiment?

  The speed of light
• What is the formula for the total time for light to pass through the toothed wheel?

  t = $\frac{2d}{c}$
• What happens at a certain speed of the toothed wheel?

  The observer sees no light returning

  
• What occurs when the wheel's rotational speed is increased slightly?

  The returning light passes through the next gap
• How does the toothed wheel's design affect the light pulses?

  It allows periodic bursts of light
• How many gaps and teeth does the toothed wheel have?

  n gaps and n teeth
• What is the relationship between time period T and frequency f?

  Time period is the reciprocal of frequency
• What is the formula for the time taken for a gap to be replaced by a tooth?

  t = $\frac{T}{2n}$
• What does the equation $\frac{2d}{c} =$$\frac{1}{2nf}$ represent?


  The time for light to travel to the mirror
• How did Fizeau calculate the speed of light?

  By rearranging the equation to c = 4dnf
• What did Fizeau find about the speed of light in water?

  It was slower than in air
• What theory did Fizeau's findings contradict?

  Newton's corpuscular theory
• What are the steps to derive Fizeau's equation for the speed of light?

  1. Identify the time for a gap to be replaced by a tooth.
  2. Use the relationship between time and distance.
  3. Rearrange to find c = 4dnf.
• How does Fizeau's method for measuring light speed work?

  • Light is shone at a mirror.
  • A toothed wheel creates light pulses.
  • The speed of the wheel is adjusted.
  • Light returns through gaps in the wheel.
• What are the implications of Fizeau's findings on light speed in different media?

  • Light travels slower in denser media.
  • Contradicts Newton's theory.
  • Supports wave theory of light.
• What happens when Fizeau increases the toothed wheel's speed?

  The light reappears at maximum brightness
• How does the new frequency relate to the original frequency in Fizeau's experiment?

  The new frequency is twice the old frequency
• What is the significance of finding alternative methods to verify answers in exams?

  It confirms the accuracy of calculations