P6 Revision Flashcards
What do you have to remember about CONCAVE (diverging) lenses?
The image will always be:
-Diminished (smaller)
-Upright
-Virtual (as the focal point is behind the lens, lines only appear to cross behind lens but don’t actually)
What do you have to remember about drawing CONCAVE ray diagrams?
-The symbol for the concave lens is a V shape at the top
-The rays diverge (spread out) after passing through the lens
-The lines drawn backwards from the diverged lines must be dotted as the lines don’t actually meet there (they only appear to come from the virtual focus)
-CONCAVE lenses are thicker at edges than at centre
-Where the FIRST ray drawn from the top of the object, which passes through the centre without changing direction, and the virtual line drawn backwards from the refracted ray, which is refracted from the ray also drawn from the top of the object which is parallel to the principal axis, meet that is where the virtual object is positioned
-Distance from centre of lens to virtual focus is focal length
What happens when light waves enter a more optically dense medium from a less optically dense medium (from air to glass)?
The light wave refracts as it enters the glass from the air, the light wave slows down and bends towards the normal.
Define Refraction
The change in direction of a wave at entering a transparent material/medium.
Why does the wave change direction when entering a more/less optically dense medium?
Because their speed changes
What happens when light waves enter a less optically dense medium from a more optically dense medium (from glass to air)?
The refracted ray refracts again as it exits from the glass into the air, the light wave speeds up again and moves away from the normal.
What do you have to remember about drawing CONVEX ray diagrams?
-The symbol for the convex lens is a ^ shape at the top
-The rays converge (meet together at a point called the focal point/focus)
-The rays are drawn parallel to each other on the left of the lens (not the case when drawing a ray diagram but is the case when drawing a convex diagram)
-The central ray passes through the lens without being refracted due to it passing directly along the normal (we say ray is passing along principal axis)
-Distance from centre of lens to the focus is focal length
Describe the image of an object once the object is placed at least 2 Focal Lengths (F) away from the lens in a CONVEX ray diagram?
-Image is diminished (smaller than object)
-Inverted (upside down)
-Real (the rays actually meet at a point and this is down on the right side of the lens)
Describe the image of an object once the object is placed between
1 focal length and 2 Focal Lengths (F) away from the lens in a CONVEX ray diagram?
-Image is magnified (larger than object)
-Inverted
-Real
Describe the image of an object once the object is placed between 1 focal length (F) and the lens in a CONVEX ray diagram?
You use dotted lines (because these don’t represent actual path of rays)drawn backwards from the two lines that are drawn from the object through the lens to find the location of the top of the image and that’s where the two lines cross.
-Image is magnified
-Image is upright
-Image is virtual (not real because rays don’t actually meet at a point they only appear to meet)
The image is located behind 2 focal lengths (F)
When is the only time a convex lens produces a virtual image?
When it is being used as a magnifying glass.
What is the equation for magnification and does magnification have units?
magnification=image height/object height
Magnification is a ratio so has no units. You would just say magnification is 7x.
