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What is the focal length of a lens which has a power of 0.5? Find out in this quiz.

# Light - Lenses 2

This Physics quiz is called 'Light - Lenses 2' and it has been written by teachers to help you if you are studying the subject at senior high school. Playing educational quizzes is one of the most efficienct ways to learn if you are in the 11th or 12th grade - aged 16 to 18.

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When the word lens was first used, it was defined as 'a piece of glass to regulate light rays'. The word comes from the Latin name for the lentil plant as the lentils themselves have a similar shape to the bi-convex pieces of glass that were used at the time for magnifying things. Since that time (the end of the 17th century), many different forms of lens have been devised. They are also made from many different substances, including plastic and there are even gravitational lenses. These are objects in space that have such a large gravitational attraction that they can bend light.

1.
In the eye, which of the following parts does light NOT travel through?
The pupil
The lens
The cornea
The iris
The iris is the colored part of the eye which controls the size of the pupil. So allowing more or less light to enter the eye depending on the conditions
2.
What is the focal length of a lens which has a power of 0.5?
2 cm
2 m
0.2 m
0.5 m
This needs you to rearrange the lens power equation
3.
What is chromatic aberration?
Where light is split into constituent colors as it travels through a lens
Separate rays of colored light are converged into one beam of chromatic light
Where chromatic light is split into two colors after traveling through a lens
Chromatic aberration does not affect light
It decreases the quality of the image
4.
What part of the eye focuses the light?
The lens
The iris
Suspensory ligament
Retina
The iris limits the amount of light entering the eye, the suspensory ligament supports the eye and the retina is the 'screen'
5.
A lens which focuses light to a point is called a what?
A converging lens
A diverging lens
A meniscus lens
A biconvex lens
Converging means coming together
6.
What is the power of lens which has a focal point of 20 cm?
0.05
0.5
5
50
Remember that focal length needs to be changed into meters
7.
What is the power of a lens dependent on?
The type of wave incident on the lens
The focal length of the lens
The time of day
The way the lens is being held
The focal length depends on the curvature of the lens and the material from which it is made
8.
What is the unit of power for a lens?
Watt
Joule
Dioptre
Metre
The higher the number of dioptres, the more a lens will bend light rays
9.
Calculate the power of a converging lens of focal length 0.05 m.
20
-20
-2
2
The power for a converging lens is given a positive value and for a diverging lens it is given a negative value. A capital letter D is often used to signify dioptres but is not an official SI unit symbol
10.
The power of a lens (SI system) can be calculated using which of the following formulae?
Power = 1 / focal length (in m)
Power = focal length / 1
Power = 1 / focal length (in cm)
Focal length (m) = 1 / Power2
Remember to convert focal length to meters
Author:  Martin Moore