Home › Subjects › O-Level Pure Physics › Light
O-Level Light
What the O-Level syllabus expects for Light, and how to practise it.
What the syllabus expects
- When describing reflection, recall and apply: normal, angle of incidence and angle of reflection.
- State that in reflection the angle of incidence equals the angle of reflection, and use this in constructions, measurements and calculations.
- When describing refraction, recall and apply: normal, angle of incidence and angle of refraction.
- Recall and use the relationship sin i / sin r = constant in unfamiliar situations or problem solving.
- Define a medium's refractive index as the ratio of the speed of light in a vacuum to that in the medium.
- Explain what is meant by critical angle and by total internal reflection.
- Apply total internal reflection to optical fibres in telecommunication and medicine, noting the advantages of using them.
- Describe how a thin converging lens acts on a beam of light.
- Define focal length for a converging lens.
- Draw ray diagrams showing how a thin converging lens forms real and virtual images of an object.
- Describe the characteristics of images formed by a thin converging lens, such as real/virtual, magnified/diminished and upright/inverted.
How it's examined
About 7% of the past-paper style questions in Rae's bank for this subject sit in this topic.
Worked examples
Example 1 (2 marks)
A lit object sits 32.0 cm from a convex lens L, and a clear image appears on a frosted screen positioned 36.0 cm from the lens. (b) Using the grid provided, construct a ray diagram showing how the lens produces the image. Label clearly the object, the image, two light rays and where the lens is placed.
Show the worked answer
Draw a horizontal principal axis with the convex (double-convex) lens standing vertically at the centre. Place the object as an upright arrow on the axis 32.0 cm to the left of the lens, and the screen 36.0 cm to the right. From the top of the object draw two rays: (1) a ray parallel to the axis that refracts through the far principal focus F, and (2) a ray straight through the optical centre of the lens (undeviated). The two refracted rays cross at 36.0 cm on the far side; that crossing point is the top of the image, which is real and inverted (slightly magnified, m = 36/32 = 1.13). Label object, image, lens and the two rays.
More O-Level Pure Physics topics
Physical Quantities, Units and Measurement · Kinematics · Dynamics · Turning Effects of Forces · Pressure · Energy · all of O-Level Pure Physics