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Light - Lenses 01
A converging lens would be a good choice to use for the purposes of magnification.

Light - Lenses 01

This GCSE Physics quiz about light looks at lenses. You will no doubt know someone who wears lenses, or you may even wear them yourself if you own a pair of spectacles. However, lenses are used in other ways too. Lenses are a crucial part of our modern lives, they allow us to correct people's vision, view the stars and examine bacteria.

Lenses are not new, the oldest lens known dates back almost 3000 years. The first written evidence from history of the use of lenses comes from Greek and Roman times. They were used by craftspeople to carry out fine work, for checking that official seals were authentic and occasionally to help with vision. They were also used as 'burning glasses' to concentrate the Sun's heat onto wood or other inflammable items to light fires. These early lenses were made from a naturally transparent material known as rock crystal which is a type of quartz.

What is refraction?
The manipulation of light to form bright and dark spots by passing it through a narrow slit
The change in direction of light as it passes from one medium to another
The ability of light to spread out to fill a room
The ability of light to penetrate solid objects
As light travels from one medium to another, it either speeds up or slows down. This change in speed means that any light entering at an angle will bend due to one side of the beam hitting the medium before the other
How does a lens work?
It forms an image by refracting light
It forms an image by diffracting light
It forms an image by diffusing light
It takes a picture with a digital camera and tags it on Facebook for you to see
Because it has a curved surface, most of the light entering the lens hits at an angle and is therefore refracted
Consider a convex lens - parallel rays of light are brought to a focus at which point?
Secondary focus
Primary focus
Principal focus
Focal place
The principal focus or focal point is the point at which a lens focusses the light which is incident upon it
What is the distance from the lens to the principal focus called?
Focal width
Focal height
Focal length
Focal point
Less curved lenses have longer focal lengths
Which formula correctly states how refractive index is related to the angles of incidence and refraction?
refractive index = sin isin r
refractive index = sin rsin i
refractive index = sin i2 sin r
refractive index = 2 sin isin r
It is a ratio and therefore has no units
What does i represent in the above equation?
The normal
The angle of refraction
The angle of incidence
The refractive index
In optics, the incoming light hitting any surface is called the incident light
What does r represent in the above equation?
The angle of incidence
The angle of refraction
The normal
The refractive index
In addition, on a ray diagram, the normal line is a line drawn at the point at which the light beam enters the material and is drawn perpendicular to the surface of the material
The nature of an image produced by a lens is defined by which attributes?
The relative size of the image
Whether the image is upright or inverted relative to the object
Whether the image is real or virtual
All of the above
Make sure that you know how to describe images from lenses and other optical devices
Which type of lens would be a good choice to use for the purposes of magnification?
Diverging lens
A concave lens
A converging lens
Bi concave lens
Concave lenses cause rays of light passing through them to diverge. The image is always virtual and diminished
What is the refractive index of a medium when light is incident upon it at 45o to the normal and the angle of the refraction is 30o from the normal?
You need to find the sine of each angle and then you can substitute the values into the refractive index equation
You can find more about this topic by visiting BBC Bitesize - Lenses

Author:  Martin Moore

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