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Light igcse
for AQA certificate Light
Question | Answer |
---|---|
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. |