Topic 5a - Refraction Waves Flashcards
What is refraction?
The change in direction of a wave, due to a change in density, causing a change in speed
Describe what happens to light as it passes from air into glass
The light refracts as it slows down and changes direction towards the normal
Explain how the soldiers walking onto sand from the road explains thr process of refraction
What is the critical angle?
Angle of incidence in the denser medium that causes an angle of refraction of 90 degrees in the less dense medium
(As for sin(Theta c) to be less than 1 then the refractive index of n1 must be greater than that of n2
A high refractive index means what about the speed of light in one medium compared to another?
Refractive index = speed of light/ speed in the medium
So a high refractive index = a lovw speed in the medium
Draw the shape of a convex lens and explains what this lens does to rays of light
Light converges on the principal
Focus
Draw the shape of a concave lens and describe what this type of lens does to rays of light
Increasing what thing increases the angle of deviation?
Distance of ray from principal axis,as this increases angle of incidence
Incident rays which travel parallel to the principal axis converge where?
At the focal point
Which rays converge at the focal point of a convex lens
Rays travelling parallel to the principal axis
Explain how a convex lens focuses a beam of light travelling parallel to the principal axis
- going from the centre of the lens to the top the angle of incidence on the lens increases
So the angle of deviation increases
So all rays cross the principal axis at the principal focus
How can you get effectively parallel rays of light incident on objects
Very distant objects emit light rays that can be treated as parallel to the principal axis
Thicker lenses have a greater what
Greater refraction - so parallel rays converge closer to the lens
If the refraction of a lens is higher than how will this affect the distance of teh focal point from the lens
It decreases the distance
What is the principal focus
The point on the principal axis where rays parallel to the principal axis will converge
What is the focal length?
The distance between the centre o f the lens and the principal focus
Is the focal length negative or positive for converging lenses? And diverging lenses?
Positive, then negative
If we view a distant object with a convex lens, where does the image form?
At the focal point
Describe the image seen if you view a distant object with a convex lens?
Real, inverted, diminished
How do we know if an image is real?
It can be projected on a screen\and it is behind the lens (relative to object)
Describe the image formed if you view an object through a lens at a distance less than the focal length?
Magnified, upright, virtual
Explain how to estimate the focal length of a convex lens
Measure the distance to the image formed by viewing an object at a distance
What is the symbol for a convex lens?
An arrow with the heads pointing outwards
What does u mean in the thin lens equation
Distance object to lens
What kind of line do you use to draw virtual rays?
Dotted line
What is a real image?
Image formed from real light rays converging to a point where the image is formed
What is a virtual image
The rays don’t pass through the image position - formed by the apparent divergence of light rays from a. Single point
When is no image formed by a convex lens
When the object is the focal length away from the lens
When the convex lens is acting as a magnifying glass what kind of rays are forming the image?
Virtual rays
Convex lens: if the object distance from lens is greater than focal length what image is formed?
Real, inverted and magnified or diminished
What kind of image is formed when the object distance from lens is equal to focal length for a convex lens?
No image
What kind of image is formed when the object distance from lens is less than focal length for convex lens
Virtual, upright, magnified
What kind of image is always formed by a concave lens
Virtual, diminished, upright
Distances to real objects and real images are positive or negative
Positive
Distances from lenses to virtual objects and images are positive or negative
Negative
If a ray emerges from a medium into the same medium that it was in before it changed mediums - what can we say about the angle of incidence and the angle at which it emerges?
They are equal
