- Refraction of light
- The bending of light as it passes from one transparent medium to another because of a change in its speed.
- Refractive index
- A measure of how much a medium slows down light, equal to the speed of light in a vacuum divided by its speed in the medium.
- Angle of incidence
- The angle between an incident ray and the normal at the point where the ray meets a surface.
- Critical angle
- The angle of incidence in the denser medium for which the angle of refraction in the less dense medium is 90°.
- Total internal reflection
- The complete reflection of light back into the denser medium when the angle of incidence exceeds the critical angle.
- Converging lens
- A lens that is thicker at the centre and brings parallel rays of light together at a focal point.
- Focal length
- The distance between the optical centre of a lens (or mirror) and its focal point.
- Thin lens formula
- The relationship linking object distance u, image distance v and focal length f of a thin lens: 1/f = 1/u + 1/v.
- Linear magnification
- The ratio of the height of the image to the height of the object, equal to image distance divided by object distance.
- Real image
- An image formed where light rays actually meet, which can be captured on a screen.
- Virtual image
- An image formed where light rays only appear to come from, which cannot be captured on a screen.
What "Light and Optics" terms cover
This group collects the 11 SPM Physics terms in Light and Optics. Getting these definitions exactly right is some of the cheapest marks in Paper 2, a "define" or "state" question wants one precise sentence with the correct unit.
The key terms to get right
- Refraction of light, The bending of light as it passes from one transparent medium to another because of a change in its speed.
- Refractive index, A measure of how much a medium slows down light, equal to the speed of light in a vacuum divided by its speed in the medium.
- Angle of incidence, The angle between an incident ray and the normal at the point where the ray meets a surface.
- Critical angle, The angle of incidence in the denser medium for which the angle of refraction in the less dense medium is 90°.
- Total internal reflection, The complete reflection of light back into the denser medium when the angle of incidence exceeds the critical angle.
- Converging lens, A lens that is thicker at the centre and brings parallel rays of light together at a focal point.
- Focal length, The distance between the optical centre of a lens (or mirror) and its focal point.
- Thin lens formula, The relationship linking object distance u, image distance v and focal length f of a thin lens: 1/f = 1/u + 1/v.
- Linear magnification, The ratio of the height of the image to the height of the object, equal to image distance divided by object distance.
- Real image, An image formed where light rays actually meet, which can be captured on a screen.
- Virtual image, An image formed where light rays only appear to come from, which cannot be captured on a screen.
How this vocabulary is examined
These terms appear as define/state items in Paper 1 and Paper 2, and inside explain and calculate questions where using the wrong word costs marks. Learn each term with its unit and one example of correct use.
Source: DSKP KSSM Physics Form 4 and 5 (Versi English) (Bahagian Pembangunan Kurikulum (BPK), KPM)