Light Flashcards
(26 cards)
What is a luminous object?
Objects such as the sun, electric lamps and candles which make their own light.
What are non luminous objects?
Objects that do not make their own light but reflect it from a luminous source.
How does light travel and how do we see it?
Light travels in straight lines. The beams are visible because dust particles in the air reflect light into our eyes.
What is a beam? And what is a ray?
Beam: A stream of light and is shown by a number of rays.
Ray: the direction of the path in which light is travelling.
What are the types of beams?
Beams may either be parallel, diverging (spreading out) or converging (getting narrower)
How are shadows formed?
Because some objects which are said to be opaque do not allow light to pass through them. And because light travels in straight lines.
What is opaque?
not able to be seen through; not transparent.
What is transparent?
allowing light to pass through so that objects behind can be distinctly seen.
What is translucent?
allowing light, but not detailed shapes, to pass through; semi-transparent.
What is umbra?
the fully shaded inner region of a shadow cast by an opaque object, especially the area on the earth or moon experiencing the total phase of an eclipse.
What is penumbra?
the partially shaded outer region of the shadow cast by an opaque object.
Give an example for how light travels faster than sound?
A thunderstorm. The flash of lightning is seen before the thunder is heard.
What is the law of reflection?
The angle of incidence equals the angle of reflection.
Where is the normal of an angle found?
The perpendicular to the mirror at the point where the incident ray strikes
Where is the angle of incidence found?
Between the incident ray and the normal
Where is the angle of reflection found?
Between the reflected ray and the normal
What happens when a parallel beam of light falls on a plane mirror?
It is reflected as a parallel beam and a regular reflection occurs.
What happens when a parallel beam of light falls on a rough surface?
The light is reflected irregularly and the rays in an incident parallel beam are reflected in many directions.
What is a real image?
One which can be produced on a screen (as in a pinhole camera) and is formed by rays that actually pass through it.
What is a virtual image?
A virtual image cannot be formed on a screen and is produced by rays which seem to come from it but do not pass through it.
How does a kaleidoscope work?
A kaleidoscope works by reflecting light. Light travels in a straight line. When light bumps into something it changes direction. If light bumps into something shiny it reflects back in the direction it came from. In a kaleidoscope the two mirrors are usually kept at the same angle about 60 degrees and different designs are made by hundreds of tiny coloured beads which can be moved around between the mirrors.
What is refraction?
The bending of light when it passes from one material (called a medium) to another is called refraction.
What happens when a ray of light enters an optically denser medium at an angle ? (Air to glass)
The ray of light is bent towards the normal ie the angle of refraction is less than the angle of incidence.
What happens when a ray of light is bent away from the normal?
When it enters an optically less dense medium. (Glass to air)
