Uses of lenses and correcting sight
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The teaching part (1 min) is free to watch. A free account opens the whole lecture: 2 worked examples, 5 practice questions, 2 real past-paper questions with the answers explained, the mistakes that lose marks, the full-marks tip, a one-card summary and a quick quiz.
What this lecture covers
- Why do glasses work?
- Three lens instruments
Read the transcript of the teaching part
Last time
Before we start: last time, in Lenses, magnification and correcting sight, you learned these points. Here they are again on one card. Keep them in mind, because today builds on them.
Why do glasses work?
About half the people in a classroom wear glasses or contact lenses. Their eyes do not focus light correctly onto the back of the eye. A lens placed in front of the eye bends the light just enough to fix it. You can work out which type of lens, using the ray diagrams from the last lesson.
Three lens instruments
A camera: the object is beyond 2F. The image is real, inverted and smaller, and falls on the sensor. A projector: the slide is between F and 2F. The image is real, inverted and magnified, and falls on the screen. A magnifying glass: the object is inside F. The image is virtual, upright and magnified.
How often it comes up
How often Cambridge has asked each part, counted by ExamYard from every past paper in its question bank: Uses of lenses and correcting sight.
Chapter 3.2: Light
- Reflection by a plane mirror 7 min
- Refraction and refractive index 5 min
- Critical angle and total internal reflection 5 min
- Thin lenses, ray diagrams and magnification 6 min
- Uses of lenses and correcting sight 5 min
Also for O Level Physics 5054
Which topics come up most in O Level Physics 5054 past papers, counted from every paper since 2004.