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# Light igcse

### for AQA certificate Light

What is the normal? Line at 90 degrees to boundary.
Which is the incident ray? the ray of light coming IN from the source of the light.
Where do you measure the angle of incidence? Between the incident ray and the normal.
Where do you measure the angle of reflection? Between the reflected ray and the normal.
What can you say about angle of incidence and angle of reflection? Angle of incidence equals angle of reflection.
Which way up is the image in a plane mirror - erect or inverted? erect.
Where is the image in a plane mirror? Same distance behind mirror as object is in front.
Is the image in a plane mirror real or virtual? Virtual.
Define a real image. Rays of light truly go to it, you can catch it on a screen.
Define a virtual image. Rays of light do NOT really go to it, you cannot catch it on a screen.
How do you show a virtual ray on a diagram? Dotted lines.
How do you show a virtual image on a diagram? Dotted lines with an arrow to show which way up it is.
How do you define magnification? Size of image divided by size of object.
Is the image in a plane mirror magnified or diminished? No, it is the same size as the object.
What does light is refracted mean? The ray of light changes direction because of change of speed.
Light goes from air to glass. Which way does the ray bend? towards the normal.
Light goes from air to glass. Which angle is bigger - incidence or refraction? angle of incidence
If you divide (sin i) by (sin r) what do you get? refractive index
Light goes from glass to air. Which way does the ray bend? away from the normal.
Light goes from glass to air. What is the biggest possible angle of emergence? 90 degrees.
Light goes from glass to air. What angle in the glass makes the angle of emergence = 90 degrees? the critical angle.
Light tries to go from glass to air. What happens if the angle in the glass is bigger than the critical angle? Total Internal Reflection
Name two uses of Total Internal Reflection e.g. Optical fibres and reflecting prisms.
Name two uses of optical fibres e.g. communications and seeing inside bodies.
How do you calculate refractive index from the critical angle? 1 divided by (sin C)
How do you calculate refractive index of water from light speed? speed in air (or vacuum) divided by speed in water
What is dispersion? Dispersion is when a prism splits light into a spectrum of colours because each wavelength has a different refractive index.
Is a bi-convex lens converging or diverging? converging.
Is a bi-concave lens converging or diverging? diverging.
Which kind of lens can ONLY make virtual images. Concave or diverging.
Which way up are images formed by a diverging lens? Images made by a diverging lens are erect.
Which way up are REAL images formed by a converging lens? Real images made by a converging lens are inverted.
Which way up are virtual images formed by a converging lens? Virtual images made by a converging lens are erect.
What do we call the place where parallel rays of light (that are parallel to the principal axis) are focussed? Principal focus, F
What letter do we use for the distance from object to lens? Object distance = u
What letter do we use for the distance from image to lens? Image distance = v
What letter do we use for the focal length? focal length = f
What do we calculate if we work out 1/f? power of lens
If the focal length is in metres, then 1/f calculates power in Dioptres.
The sign of the power of a converging lens is positive.
The sign of the power of a diverging lens is negative.
1/u + 1/v = ? 1/f
The ray of light that goes through the centre of the lens goes straight on, does not change direction.
A ray of light from the object that goes parallel to the principal axis until it hits the lens goes through the principal focus the other side.
For a convex lens to act as a magnifying glass the object must be closer to the lens than the principal focus.
If a converging lens is acting as a magnifying glass the image is virtual and ... erect and magnified.
Are the images made by the lenses in cameras and eyes real or virtual? Real (cast on screen)
What part of the eye does the same job as the film or CCD array in a camera? retina
What part of the camera does the same job as the pupil in an eye? aperture
How does a camera focus on objects at different distances from the camera? lens moves in and out.
How does an eye focus on objects at different distances from the eye? Ciliary muscles change shape of lens.
How does a camera adjust for bright and dim light? e.g. shutter speed and aperture size
How does an eye adjust for bright and dim light? pupil size
What changes to change the size of the pupil or aperture? the iris
What carries messages about light to the brain? Optical nerve
If someone's eyeball is too long (lens and cornea too powerful) they are short sighted (myopic)
If someone's eyeball is too short (lens and cornea not powerful enough) they are long sighted.
Long sighted people cannot see things clearly if they are near to them.
Short sighted people cannot see things clearly if they are far away.
The lenses that help long sighted people are ... converging lenses for long sight.
The lenses that help short sighted people are ... diverging lenses for short sight.
The closest you can see things clearly is called your near point.
The furthest away that you can see things clearly is called your far point.
Is the image on your retina magnified or diminished? Diminished image on retina.
Is the image on your retina inverted or erect? Inverted image on retina.
Created by: waslancing

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