2026 Science Chapter 4 (Separation Techniques) & Chapter 5 (Ray Model of Light)

Exploring diversity of matter using separation techniques o How to choose the appropriate separation technique(s) Applications: ▪ Evaporation is used to extend the shelf life of food such as ikan bilis and reduce food wastage ▪ Chromatography is used in food testing to ensure that food does not contain harmful substances and is safe for consumption ▪ In Singapore, filtration and evaporation are used in the recycling of used water to obtain potable water o The different constituents of mixtures retain their physical properties o The differences between these physical properties allows us to choose the separation technique(s) for separating the constituents of the mixtures o Other factors that should be considered when choosing a separation technique includes: ▪ Cost ▪ Reliability ▪ Environmental impact ▪ Example: Reverse osmosis helps us to obtain potable water in Singapore, however it is costly, therefore it may not be possible to use only reverse osmosis to obtain potable water o Separating a mixture of magnetic and non-magnetic substances ▪ Magnetic substances such as iron and steel are attracted to a magnet. ▪ Steel is a mixture of iron and other elements ▪ Other substances such as plastic and paper are non- magnetic ▪ Magnets can be used to separate magnetic substances from non-magnetic substances (Example: When a magnet is places near a mix of iron filings and sulphur, only the iron filings are attracted, the non-magnetic sulphur is left behind ▪ Magnetic attraction is used to separate magnetic and non-magnetic substances (Example: In Singapore, scrap metal is a waste material generated. Scrap metal contains a mixture of metals such as aluminium, copper and iron. Iron, being magnetic, can be removed from the mixture by passing a strong magnet over the scrap metal, the iron can then be reused or recycles, helping to reduce waste ▪ Separating a mixture of particles

Ray Model of Light - Used to explain why and how we are able to see things - Luminous objects emit light in all directions - The light rays travel in straight lines from the objects to our eyes, allowing us to see the object - Light from a light source can bounce off an object and enter our eyes Reflection - The bouncing of light is called reflection - Light travels in straight lines even when bouncing off objects (no matter what) - Incident ray: Ray that hits the reflecting surface - Angle of incidence (i) is the angle between the normal and incident ray - Normal: The line perpendicular to the surface at the point of incidence - Point of incidence: Point where the incident ray, normal and angle of reflection meet - Angle of reflection (r): Angle between the reflected ray and normal - Reflected ray: Light ray travelling away from the reflecting surface after bouncing off the surface - Angle of incidence (i) and the angle of reflection (r) are and will always be equal - - Mirrors: o Plane mirrors (Flat mirror):