Interference 2
Physics: AQA A Level, topic 3.2.2
Laser Safety
Lasers are dangerous and need careful handling and use.
Laser safety
- To be safe with lasers you should:
- Not point the laser in people's eyes.
- Wear protective clothing and eyewear as necessary.
- Make sure that internationally agreed signage is used outside and inside laboratories.
- Stick to institutional safety requirements.
Danger of lasers
- We need to be safe with lasers because they are highly luminous over a very small area.
- The major risk with lasers is eye injury.
- With high powered lasers, the body's natural aversion reflex (the eye will automatically look away from a bright source) is too slow to prevent damage to the retina.
Understanding EM Radiation
Scientists have changed and updated their understanding of the nature of electromagnetic radiation over time. Newton, Huygens, Young and Einstein are prominent scientists in the theory of light.
Newton's corpuscles
- In the 1600s Isaac Newton theorised light as made up of "corpuscles", little packets of light.
Huygens' waves
- Huygens stated his wavefront theory in the 1600s.
Young's double slit experiment
- Young, with his double-slit experiment, provided evidence of Huygens' wavefront principle.
Einstein's photons
- Einstein provided evidence, through the photoelectric effect, supporting Newton's corpuscular theory.
- This was the beginnings of quantum theory.
Compton's scattering experiment
- Further on in the 20th century, Compton scattering (a photon scattering off an electron) provided more evidence for the quantisation of light.
Interference of Sound Waves
Interference can be observed in all types of waves, including sound waves.
Experimental set up
- To observe interference in sound waves, we can use the above set up.
- The two sources need to be coherent, meaning that the same sound must be played at the same time in each speaker.
Move microphone
- By moving the microphone from one side to the other, we can measure constructive and destructive interference by whether the noise is loud or quiet.
Test yourself on Interference 2
Which of these must you do when using lasers?
History of EM Radiation
What experiment did Einstein conclude meant that light was made up of photons?
When measuring the interference from two sound waves what do the quiet areas correspond to?
Why do the sound waves from both speakers have to be coherent?