AQA · A-Level · Physics
Course version: 7408 · Version from Sept 2016
Students are expected to show awareness of safety issues associated with…
Full specification wording
Interference: Students are expected to show awareness of safety issues associated with using lasers.
Lasers used in interference experiments produce narrow, intense, monochromatic beams that can damage eyes.
Checked against the AQA 7408 specification (opens in a new tab) on .
- Point 4 of 7
- 4 key terms
Study notes
From the checked teaching notes for this specification point.
The idea
Lasers used in interference experiments produce narrow, intense, monochromatic beams that can damage eyes. Even a brief exposure to a direct or reflected beam can cause permanent retinal injury because the lens focuses the beam onto a small area of the retina. Safety awareness means never directing a laser beam towards anyone’s face, keeping the beam below eye level, removing reflective objects from the beam path, and using the lowest power laser suitable for the demonstration. A beam stop should absorb the beam, and the experiment should be arranged so that the direct beam and stray reflections cannot reach observers.
What earns the marks
- States that laser light can damage eyes, particularly the retina, because the beam is intense and focused by the eye.
- Explains that the beam should be kept below eye level and directed away from people.
- Describes the need to remove or avoid reflective surfaces that could send the beam into someone’s eye.
- States that a beam stop should be used to absorb the laser beam safely.
- Mentions using the lowest practical laser power and following laboratory safety rules or warning signs.
Common mistakes and how to put them right
Treating laser safety as only about not looking directly into the beam.
Put it right: Reflected beams are also hazardous and reflective objects must be kept out of the beam path.
Assuming that a low-power laser is completely safe for eyes.
Put it right: Even low-power lasers can cause eye damage, so all beams should be handled with care.
Ignoring the beam after it passes the slits.
Put it right: The direct beam and any stray reflections must be terminated safely with a beam stop.
Exam tips
- Give specific precautions rather than a general statement that lasers are dangerous.
- Link each precaution to the hazard it reduces, such as keeping the beam below eye level to avoid direct eye exposure.
- Mention both the direct beam and reflected beams, because reflections are a common source of accidents.
Try the lesson
The start of the Interference: Students are expected to show awareness of safety issues associated with using lasers. lesson, made from checked teaching notes for this specification point.
Have a go first
A student sets up a laser double-slit experiment on a bench. Which combination of precautions best reduces the risk of eye damage?
Listen
Lasers used in interference experiments produce narrow, intense, monochromatic beams that can damage eyes. Even a brief exposure to a direct or reflected beam can cause permanent retinal injury because the lens focuses the beam onto a small area of the retina. Safety awareness means never directing a laser beam towards anyone’s face, keeping the beam below eye level, removing reflective objects from the beam path, and using the lowest power laser suitable for the demonstration. A beam stop should absorb the beam, and the experiment should be arranged so that the direct beam and stray reflections cannot reach observers. A strong answer earns marks for these points. States that laser light can damage eyes, particularly the retina, because the beam is intense and focused by the eye. Explains that the beam should be kept below eye level and directed away from people. Describes the need to remove or avoid reflective surfaces that could send the beam into someone’s eye. States that a beam stop should be used to absorb the laser beam safely. A common slip: Treating laser safety as only about not looking directly into the beam. Instead, reflected beams are also hazardous and reflective objects must be kept out of the beam path. Exam tip: Give specific precautions rather than a general statement that lasers are dangerous.
See it
Key words
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Hazard identification
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Risk reduction in practical work
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Eye safety with electromagnetic radiation
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Responsible laboratory practice
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See every definition
- Hazard identification
- Showing awareness of safety issues associated with using lasers, whose narrow, intense, monochromatic beams can damage eyes.
- Risk reduction in practical work
- Never directing a laser beam towards anyone's face, keeping the beam below eye level, removing reflective objects from the beam path and using the lowest power laser suitable for the demonstration.
- Eye safety with electromagnetic radiation
- Even a brief exposure to a direct or reflected laser beam can cause permanent retinal injury because the lens focuses the beam onto a small area of the retina.
- Responsible laboratory practice
- Following local rules, such as warning signs and restricted access, and never looking directly into the beam or its reflection.
Label the diagram
Some boxes have lost their names. Pick the right name for each number.
1Box 1
2Box 2
3Box 3
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