Lens Flashcards
What is the definition of principal axis?
the line passing through the centre of curvature of the lens and which is perpendicular to the plane of the lens
What is the definition of optical centre? What is it labelled as?
the point on the principal axis that is the midpoint between the surfaces of the lens.
It is labelled as C
What is the definition of focal point? What is it labelled as?
a point on the principal axis where rays of light parallel to the principal axis meet after passing through the lens. it is labelled as F.
What is the definition of focal length?
the distance between the focal point and the optical centre of the lens
Given an upright illuminated object that emit light rays in all directions, what are the three distinct light rays that we are interested in?
- The light ray that passes through the optical centre undeviated (straight line that passes through the whole diagrram (draw two arrow head one at the left section of the converging lens and one on the right section of the converging lens)
- The light ray that is parallel to the principal axis.(after passing through the thin converging lens, it will converge and bend towards the focal point and then intersect with the first light ray in point 1 –> this is the position of your image
- The light ray that cuts the focal point at the left section of the converging lens. After passing through, it will be parallel to the principal axis.
Thin converging lens works on the principle of ______________.
(a) reflection
(b) refraction
(c) total internal reflection
b
Light rays bend towards the normal when it travels from ____________ medium to ______________ medium.
from optically less dense medium to optically denser medium.
Given that the angle of incidence in water is 40 degrees, what is a possible angle of refraction when the light ray passes from water to air medium?
0 degrees
29 degrees
40 degrees
59 degrees
59 degrees
What happens to the light ray when it passes through a clear plastic rectangular block at right angle?
The light ray does not bend and continues travelling horizontally through the clear plastic rectangular block since it enters the plastic from a right angle.
The figure shows an incident light ray on a thin converging lens.
What happens to this light ray after passing through the lens?
The incident ray will bend towards the normal when it passes through the lens due to refraction and bend away from the normal when it exits the converging lens as the emergent ray/. The light ray should bend towards the centre of the lens.
The figure shows an incident light ray on a thin diverging lens.
What happens to this light ray after passing through the lens?
(a) The light ray will bend above the undeviated light path.
(b) The light ray will bend below the undeviated light path.
(c) The light ray will travel along the undeviated light path.
(a)
Case 1: object is at infinity (a very distant object)
Visualise and describe the diagram of a light ray for an object that is at infinity (a very distant object)
Image location: ___________
Orientation: ___________
Image type: __________
Size: ___________
Which apparatus allows you to see a very distant object? ___________
1st light ray:
Parallel beam of light. Incident on the converging lens. After passing through, it will cut through the focal point.
2nd light ray:
Parallel to principal axis/ After passing through the optical centre, it will pass through undeviated.
3rd light ray:
Parallel to the principal axis as it passes through the converging lens, it will pass through the focal point.
The image will be at the focal point.
Image location: opposite side
Orientation: inverted
Image type: real
Size: diminished
Which apparatus allows you to see a very distant object? Telescope
Case 2: object is far away (further than 2F)
Visualise and describe the diagram of a light ray for an object is far away (further than 2F –> focal length away)
Image location: _______
Orientation: __________
Image type: __________
Size: ________
Object in the diagram is represented by an upright arrow
1st light ray:
light ray passes through the optical centre and after passing through it will pass through undeviated. (draw light ray arrows on both sides)
draw a light ray that comes from the top of the object, parallel to the principal axis, after passing through it will cut the focal point.–> intersection point –> you can see that it has an inverted image
Image location: between F and 2F
Image type: real
Orientation: inverted
Size: diminished
Which application results in a real diminished image? camera
Case 3: object is at 2F
Visualise and describe the diagram of a light ray for object is represented by an upright arrow and at 2f length away
Image location: _______
Orientation: __________
Image type: __________
Size: ________
draw a light ray that cuts the optical centre and pass through undeviated, with arrow head on both sections
draw a parallel light ray from the top of the object. Once it touch the converging lens, it will cut the focal point. (draw arrow head in both sections)
The image lands itself at 2 focal length away.
Image location: opposite side at 2F (focal length away)
Image type: real
Orientation: inverted
Size: same size
Which application results in a real image the same size as the object? Photocopier
Case 5: object is at F
Visualise and describe the diagram of a light ray for object is represented by an upright arrow and at F length away
Image location: _______
Orientation: __________
Image type: __________
Size: ________
1st light ray: from the top of the object passing through the optical centre, undevoated, with arrow head on both sections
2nd light ray: light ray from the top of the object, parallel to the principle axis, after passing through the light ray will converge to the focal point –> the 1st and 2nd light ray seems to be parallel. So you have to extend the 1st and 2nd light ray backwards from the 2nd section using dotted line –> therefore it shows that the light ray seems to come from behind the object
Image location at infinity
Image type: virtual
Orientation: upright
size: image magnified
Which application produces parallel beams of light? : spotlight
Object is between F and the lens.
Visualise and describe the diagram of a light ray for object is represented by an upright arrow.
Image location: _______
Orientation: __________
Image type: __________
Size: ________
1st light ray: from the top of the object –> passing through the optical centre –> pass through undeviated
2nd light ray: draw a parallel light ray, parallel to the principal axis, after passing through the lens, it will converge and bend towards the focal point.
The light ray after passing through the converging lens seems to be diverging –> if you place an user/observer eye at the right of the light ray –>the eyes will perceive these diverging light rays as though coming from behind the lens as represented by dotted line (extend the line backwards for both 1st and 2nd light ray).–> point of intersection –> this is where the virtual image represented by a dotted line is formed–> image
Image location: same side of lens
Orientation: upright
Image type:
A virtual image is formed
Size: magnified
Which application results in a upright magnified image? :magnifying glass
One of the property from the image formed from a thin converging lens, can be seen from the ____________________.
linear magnification factor (m)
It is the ratio of the image size to that of the object size
m = hi/ho
In the case of the image of the object being located at the opposite side as compared to the object:
measure the height of the object –> ho
height of the image: –> hi
In the case that the image of the object is located at the same side as the object:
m = v/u
v –> image horizontal distance to the optical centre
u –> object distance to the optical centre
An object is placed at a distance less than 1 focal length away from a thin converging lens, what is the type of image formed by this lens?
(a) diminished and virtual
(b) magnified and virtual
(c) diminished and real
(d) magnified and real
(b)
Which location should an illuminated object be placed along a thin converging lens in order to produce a parallel beam of light?
(a) less than 1 focal length away from the lens
(b) exactly at 1 focal length away from the lens
(c) exactly at 2 focal lengths away from the lens
(d) more than 2 focal lengths away from the lens
(b)
What are the characteristics of the image formed when an object is placed at 2 focal lengths away from a thin converging lens?
(a) real and diminished
(b) real and same size
(c) real and enlarged
(d) virtual and diminished
(b)
