Light slides

17.1 What is Light? ,[object Object],[object Object],[object Object],[object Object]

Speed of light ,[object Object],[object Object],[object Object],[object Object]

Speed of light ,[object Object],Cheetah 31.0 m/s Light in vacuum 300,000,000 m/s Space shuttle 7,780 m/s Earth in orbit around the Sun 29,780 m/s

Garden snail 0.04 m/s Jetplane 350 m/s Sound in air 330 m/s

How does light travel? ,[object Object],[object Object],Look at the flame of a candle through a straight hose. You should be able to see the light through the hose. Now, try looking through a bent hose. The light from the candle cannot reach your eyes. This shows that light does not bend, but travels in straight lines.

How does light travel? ,[object Object],[object Object]

Rays and beams ,[object Object],[object Object],[object Object],[object Object],Parallel beam Divergent beam (fan outwards) Convergent beam (merge to a point)

17.2 Reflection ,[object Object],[object Object],[object Object],Reflected images are very clear on a smooth surface. A parallel beam of light stays parallel after regular reflection.

17.2 Reflection ,[object Object],[object Object],[object Object],Although this page appears smooth, under a microscope, you can see how rough it is. Thus, there is no reflected image. A parallel beam of light hitting a rough surface gets scattered or reflected in an irregular manner.

Reflection in a mirror ,[object Object],[object Object],[object Object]

Reflection in a mirror ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

Reflection in a mirror ,[object Object],[object Object]

Tracing reflected light rays A ray of light AO strikes the mirror at point O , creating an angle i with the perpendicular line NO . AO is called the incident ray , and angle i is called the angle of incidence . The perpendicular line to the surface NO is also known as the normal . The light ray bounces off the mirror and leaves along the path OB . OB is called the reflected ray . This ray makes an angle r with the normal. This angle is known as the angle of reflection . O N A B Incident ray Reflected ray

Types of mirrors ,[object Object],[object Object],[object Object],[object Object]

Types of mirrors ,[object Object],[object Object],[object Object]

17.3 Refraction ,[object Object],[object Object]

17.3 Refraction ,[object Object],At A , the point where the ray enters, a normal is drawn. When light enters the glass block, it is moving from a less dense medium to a denser medium. Hence, the ray of light will bend towards the normal. When the ray of light exits the glass block at B , it is moving from a denser medium to a less dense medium. Hence, it will bend away from the normal. Normal incident ray Normal glass block B A emergent ray

Effect of refraction: Apparent depth ,[object Object],[object Object],[object Object],[object Object]

17.4 Dispersion of White Light ,[object Object],1. When a beam of white light passes through a prism, it is split into different colours. 2. This is because the different colours of white light bend towards the normal through diffferent angles when entering and leaving the prism. 3. A spectrum of colours is produced, which is made up of seven colours: red, orange, yellow, green, blue, indigo and violet. This splitting of white light is called dispersion .

17.5 Colours ,[object Object],[object Object],[object Object],[object Object]

17.5 Colours Green Blue Red White Cyan Yellow Magenta

17.5 Colours ,[object Object],[object Object],[object Object],[object Object],Green White Red White

17.5 Colours ,[object Object],[object Object],When white light is shone on these balls, each ball will reflect their respective colours. This is because white light contains all the colours of the spectrum. When red light is shone on the balls, only the red ball will reflect the red light. The green and blue balls appear black since they can only reflect green and blue light respectively.

17.5 Colours ,[object Object],[object Object],Under white light, a yellow ball appears yellow But if red light is shone on the yellow ball, it appears red. Yellow is a secondary colour, which consists of red and green. Thus, a yellow ball can reflect both red and green light.

Miscellaneous ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

Light slides

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