Physics A 2 Flashcards
What is a refractive index?
The reflective index of a medium is the ratio of speed of light in a vacuum to speed of light in that medium
Define refraction
Refraction is when waves change direction as they enter a different medium.
What formula do we use to figure out the refractive index?
Refractive index (n) = sin I
—-
Sin r
I = incident ray R = refracted ray
List the properties of converging and diverging lenses.
The axis of a lens is a line passing through the middle of the lens
A converging lens is convex it causes parallel rays of light to converge
The principal focus of a converging lens is where rays hitting the lens parallel to the axis all meet
There is principal focus on each side of the lens
The distance from the centre of the lens to the principal focus is the focal length
A diverging lens is concave it causes rays of parallel light to diverge
What is the difference between a real and virtual image
A real image is where light from an object comes together to form an image on a screen.
A virtual image is when the rays are diverging so they appear to be coming from a completely
Where must and object being magnified be and what is the formula for magnification?
And what is the formula for figuring out the power of a lens
The object must be closer to the lens than the focal length
Magnification= image height \ object height
Power (d) = 1/focal length
List parts of the eye and what they do
The cornea is a transparent window with a convex shape it does most of the eyes focusing
The iris is the coloured part of the eye it is made up of muscles that control the size of the pupil. They control the intensity of light entering the eye.
The lens changes shape to focus light from objects at varying distances
Images are formed on the retina which is covered in light sensitive cells.
What is short sightedness and how can it be corrected
Short sighted people can’t focus on distant objects as their far point is closer than infinity.it is caused by the eyeball being to long.
To correct short sight you need a diverging lens (with a negative power)
What is long sight and how is it corrected?
Long sight is when you can focus on things that are near you because your near point is further away than normal( 25 cm or more. It is caused by the cornea being too weak or eyeballs being to short.
A converging lens with a positive power can correct long sight
What is total internal reflection
Total internal reflection is when light being shot through an optical fibre where the angle of incidence greater than the critical angle. So no light comes out as it’s all reflected internally.
