Light and Optics: Key Terms (Form 4 SPM Physics)

Terms and definitions

• 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.
• Scalar quantity, A physical quantity that has magnitude only, with no direction, such as distance, speed and mass. (related term from another chapter)
• Vector quantity, A physical quantity that has both magnitude and direction, such as displacement, velocity and force. (related term from another chapter)
• SI unit, The internationally agreed system of units for physical quantities, based on the seven SI base units such as the metre, kilogram and second. (related term from another chapter)
• Prefix, A word or symbol placed before a unit to indicate a multiple or fraction of it, such as kilo- (10³) or milli- (10⁻³). (related term from another chapter)

Content standards these terms come from

• 6.1 Refraction of Light
• 6.2 Total Internal Reflection
• 6.3 Image Formation by Lens
• 6.4 Thin Lens Formula
• 6.5 Optical Instruments
• 6.6 Image Formation by Spherical Mirrors

How to learn them

1. Cover the definition, say it aloud, then check the unit.
2. Pair each term with a formula or experiment from the chapter.
3. Write the Malay term alongside the English one, SPM papers are bilingual.

More Light and Optics resources

• Chapter overview: Light and Optics
• Revision Notes
• Common Mistakes
• Practice Questions
• Paper 2 Answering Guide
• Paper 3 Guide
• Calculation practice sets

Source: DSKP KSSM Physics Form 4 and 5 (Versi English), Sijil Pelajaran Malaysia: Format Pentaksiran mulai 2021, Fizik (4531) (Bahagian Pembangunan Kurikulum (BPK), KPM)