# Light

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## Reflection of Light

- the normal at a point on a mirror is a line drawn perpendicular to the mirror

- the law of reflection states that the angle of incidence = the angle of reflection

- for a light ray reflected by a plane mirror:

...the angle of incidence is the angle between the incident ray and the normal

...the angle of reflection is the angle between the reflected ray and the normal

- specular reflection is reflection in a single direction without scattering, diffuse reflection is refletcion from a rough surface that scatters the light

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## Refraction of Light

- refraction is the change in direction of waves when they travel across a boundary from one medium to another

- when a light ray refracts as it travels from air into glass, the angle of refraction is less than the angle of incidence

- when a light ray refracts as it travels from glass into air, the angle of refraction is more than the angle of incidence

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## Light and Colour

- the wavelength of light increases from red to violet across the visible spectrum

- the colour of a surface depends on the pigments of the surface materials and the wavelengths of light the pigments absorb

-  a translucent object lets light pass through it but scatters or refracts the light inside it

-  a transparent object lets all the light that enters it pass through it and does not scatter or refract the light inside the object

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## Lenses

- a convex lens focuses parallel rays to a point called the principle focus

- a concave lens makes parallel rays spread out as if they had come from a point called the principal focus

- a real image is formed bya convex lens if the object is further away than the principal focus, a virtual image is formed by a convex lens if the object is nearer than the principal focus

- magnification = image height / object height

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## Using Lenses

- a ray diagram can be drawn to find the position and nature of an image formed by a lens

- when an object is placed between a convex lens and its principal focus F, the image formed is virtual, upright, magified and on the same side of the lens as the object

- a camera contains a convex lens that is used to form a real image of an object

- a magnifying glass is a convex lens that is used to form a virtual image of an object

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