Light summary in progress 🙂
Light – Reflection
Tag Archives: Topic Light
Not just the 3 rays
Critical Angle
Disappearing test tube
Demonstration of Reflection, Refraction and TIR using light source with a slit
Reflection of light using a mirror
Refraction of light using various shaped optical mediums
Total Internal Reflection (TIR) using a semi-circular perspex
For Total Internal Reflection (TIR) to occur:
1) angle of incidence i is greater than the critical angle c
2) the light is travelling from an optically denser medium towards a less dense medium
Types of images formed by a thin converging lens
Liters of light for shanty homes
Refer to the following post on the physics concepts involved.
Waves – Confuse with V, f and lamda?
Mirror Reflection and Kinematics
Solutions: Option C
Lens – Ray Diagram
Solutions: Option C
N2010P1Q23 Lens
Answer is A.
Many thought it is a diverging lens due to the ray which seems to diverge out. If you refer to the sketch esp the highlighted ray in pink, you will realise that it is converging lens.
Likewise you will be able to see that object is less than focal length in order to have such ray.
Next Generation Broadband Network (NGNBN)
Optical fibre network technology allows us to surf net approximately 100 times faster than our current Internet connections.
Optical fiber cables are thin strands of glass, about the thickness of a human hair, that permit the transmission of data using light over longer distances and at higher connection speed of 1Gbps and above. The blue and red cables in the photo are the optical fibre cables.
The transmission of light through the optical fibre cable uses physics concept of Total Internal Reflection (TIR).
For TIR to occur,
1) light must be traveling from a denser to less dense medium.
2) incidence angle is greater than critical angle.
N98 P1 Q20 Light Reflection – Technique to remember
The diagram shows four lamps in front of a plane mirror. The card prevents the observer at X from seeing the lamps directly, although the image of one lamp can be seen in the mirror.
Which lamp’s image can be seen?
Solution: B
PP N2002P1Q19: Lens – to form a sharp image on screen
A lens forms a blurred image of an object on a screen.
How can the image be made sharp and in focus on the screen?
A)Â Â Â Â By moving the object away from the lens and screen.
B)Â Â Â Â By moving the screen away from the lens and object.
C)Â Â Â Â By using a brighter object at the same position.
D)Â Â Â Â By using a lens of longer focal length at the same position.
Solutions: Option DÂ (refer to the video on why the image is blurred and how to form a sharp image)
A and B will create a more blurred image.
C – brighter object will not create a shape image.
D – using a lens of longer focal length, when light rays pass through the lens, it will converge to a point further away from the lens. Hence the sharp image will be formed on the school.
Alternatively, you can move the screen nearer to the lens such that the position of the screen is at the intersection of the rays.
Innovative guy using light concepts to brighten one’s life
Thank you Yue Jie (5N1 2011) for sharing!
Explanation
Sent from my iPad
Innovative guy using light concepts to brighten one’s life
Thank you Yue Jie (5N1 2011) for sharing!
Explanation
Sent from my iPad
Concave mirror
These photos are taken in Sentosa Resort World – Festive Hotel.
In some hotels, they have cosmetic mirror like the one you see in the photos. There are 2 sides of the mirror which you can use. Law of reflections are obeyed on both mirrors.
On one side, it is a normal plane mirror. Your 5 characteristic of mirror image apply here.
On the other side, it is a concave mirror, which creates a magnified image for you to see the ‘flaws’ on your face =)
N2010 P1 MCQ Q12 Sci Physics 2010 O-Level
Which distance is equal to the focal length of a lens?
A. The distance between a distant object and its image.
B. The distance between the image of a close object and the centre of the lens.
C. The distance between the image of a distant object and the centre of the lens.
D. The distance between two principal foci.
Solution: Option C.
Recall that only reflected rays from distant object (object placed far away) are considered parallel. When these parallel light rays pass through the converging lens, they converge to a point, Focal Point (F).
Only then, the distance between the (sharp) image of distant object to the centre of the lens, optical centre (C), is known as focal length (f).
Refer to the diagrams below.
Also refer to another question on lens: http://evantoh.posterous.com/2010/11/09/converging-lens-important-concepts
Refraction of Light
An example of Total Internal Reflection
Some designer lightings like that one show in the video make use of total internal reflection. This was taken at Spring Maternity @NEX Jul 2011.
An Example of Total Internal Reflection from evantoh on Vimeo.
Each strand is actually make of transparent plastic-like material, which is flexible and has higher optical density than the air.
Recall the 2 conditions for total internal reflection to take place
1: light is traveling from denser medium (plastic) to the less dense medium (air)
2: angle of incidence is greater than critical angle
Hence from the centre light source, light can total internal reflection and comes out from the other end of each strand. There you have it! A unique designer lighting, just making use of physics!
Sent from my iPad
Refraction of Light in Glass Block
Refraction is the bending of light as light travels from one medium to another medium of different refractive index.
As light travels from less dense medium (air) to the denser medium (glass), it bends towards the normal as the speed of light decreases in the medium.
The video below show how the refraction takes place in the glass block and how to position the needles in line.
<p>Refraction of Light – Glass Block + Needles from evantoh on Vimeo.</p>
Refraction
This is not magic! As both the water and crystal balls have the same refractive index (optical density), light will pass through without bending as if both are of the same medium. Hence you are not able to see the crystal balls.
Converging Lens – Which ray is correct after passing through the lens
Which of the following light rays behaves correctly when it passes through the converging lens?
Solutions: Option C
Refer to the following diagrams and recall the basic.
From the diagram above, only when parallel beam of light passes through the converging lens and converge to a point, that point is known as focal point, F. Only then, the distance between F and optical centre, C, is known as the focal length, f.From the diagram above, note that when light ray from object is parallel to principal axis, it will pass through F after passing the converging lens.When light ray passes optical centre, it will pass straight. When light ray passes F and then the converging lens, it will be parallel to the principal axis.
A is wrong as it should be parallel to principal axis after passing through the lens.D is wrong as if after the lens the ray is parallel to principal axis, it must pass through F initially before entering the lens.
The 3 rays shown in the previous diagram are not the only rays from object. In fact, light shines on any point on the object, light is reflected in all direction. We usually concentrate on the 3 rays from drawing of image and its properties (as mentioned above).
For the other rays likewise, all reflected light from that particular point on object will be converged to the same particular point on the image.Hence, B is wrong as did not pass through F before hitting the lens, the light will definitely not pass through F on the other side.Only C is correct.Another important concept, when a parallel beam of light strikes the lens, the light rays will converge to a point which falls along the focal place. Refer to diagram below.
Click the following posts for other lens concepts:
Light – Two mirrors in parallel
The diagram below shows a object O placed at the middle of two parallel mirrors. Which of the following is not a possible position of image of O?
Solutions:Â Option D
Based on the concept of characteristics of mirror image – Distance of object to mirror is equal to Distance of image to mirror.
Object O at the centre of two mirrors, based on the above characteristic, B and C are possible positions of image of O.
Consider A. Treating C as the object now and using the mirror on the left, distance of C to left mirror is equal to distance of A to left mirror.
Hence A is a possible position of image of O.
Consider D. Treating B as object and using the mirror on the right, distance of B to right mirror is not equal to distance of D to right mirror.
Hence D is not a possible position of image of O.
N2007P1Q20 Light – Mirror Image through Periscope
The diagram shows an object O viewed using two mirrors. A person looks into the mirrors as shown. At which position is the image of O seen.
Solutions: Option D
To solve this kind of question, you have to do in stages.
1) Consider the object O and the mirror at the top. The image formed will be equal distance perpendicular to the mirror (follows the 5 characteristics of mirror image). Let the image be O’.
2) Now treat O’ as the new object and consider the mirror at the bottom. Likewise apply the same principle, the image of O’ is now at position D. Alternatively, a fast and simple way is based on the concept that to our eyes, light seems to travel in straight line. Hence to our eyes, the image of O is directly in front.
Reflection – Min. length of mirror to see the wall behind
Man is standing at the middle facing the mirror wall. What is the minimum length of mirror on AB that is required to see the whole wall CD?
Use Maths concept on Similar Triangles to solve such questions. If the man is at other positions instead of standing at middle, the min. length of mirror needed can still be solved using Similar triangles.
Evan's Space 