Lab Report 5 1i3k4q

PHYSICS LAB REPORT Prepared for Prepared by

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Date Report #5

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Mrs. Rubena Yusof Danny Basir Lynliana anak Unjan Noorfaizmira bt. Saleh Nashrul Haq b. Tagiling 07th May 2013 Multiple Reflections

(BS12110110) (BS12110330) (BS12110420) (BS12160788)

OBJECTIVES 1. To draw conclusions regarding the law of reflection as the light rays were reflected by the plane mirror. 2. To observe multiple reflections as light rays reflect from plane mirrors inclined at a certain angle. APPARATUS 1. Light Box & collimating lens. 2. Three slit former plates. 3. Set of 8 colour filters & plates. 4. Two sets of mirrors. 5. Protractor. THEORY Based on our basic understanding, a reflection is a reflected duplication of an object that appears identical but reversed. As an optical effect it results from reflection off of substances such as a mirror or water. There are several properties of reflection of light: 1. There are three rays that lies in the same plane and medium, which is the incident ray, the normal ray and the reflected ray 2. The angle which the incident ray makes with the normal is equal to the angle which the reflected ray makes to the same normal.

3. The reflected ray and the incident ray are on the opposite sides of the normal. 4. Lights path are reversible.

The diagram above shows to us what is incident, normal and reflected ray.

What is a multi reflection? When the light ray is made to reflect at different surfaces then the phenomenon of multi reflection of light came in to play. Let us imagine there are two mirrors AB and CD, inclined at an angle of 900 with each other. The when an object is placed in between them then the First image will be formed in mirror AB as X1. This image will act the object for mirror CD and its image will be X2. Also the object had image in mirror CD and that is X3. This image will also behave as object for AB and had image X4. But here the two images X2and X4 will overlap each other and will be identical as single image. So total 3 different images will be there for one object. In this, we can find the number of images when two mirrors are inclined at some angle.

Multiple reflections.

MULTIPLE REFLECTIONS TASK A Reflect a single ray from the plane mirror at an angle of incidence of 45 to 50 . Examine the reflections closely:  How many reflections are there? Three reflections. 

Which is the brightest? The middle reflected ray.

Look carefully down on the mirror from above and then make an enlargement drawing to show how the three reflected rays occur.  Is there something special in the angle of incidence being 90 ? There is no reflection in the angle of incidence of 90 . Experiment to discover if all three reflections occur at the other angle of incidence e.g 10 , 20 and so on to 90 . Angle 10° 20° 30° 40° 50° 60° 70° 80° 90°

Reflection(s) 2 2 3 3 3 3 3 1 No reflection

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Which reflected ray disappears and at which angle does this occur? Reflected rays become less than three at angles 10 , 20 (2 reflections) and 80 (1 reflection).

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Why is this reflection the faintest of the three? The faintest reflection can be observed at angle of incidence 10 . This is because the intensity of the reflected light decreases as the angle of incidence became smaller.

Place the rectangular slab of plastic in front of the mirror and repeat the experiment and observation.  How many reflections are there (angle of incidence 45 to 50 ) Three reflections. 

Which is the brightest? The middle reflected ray.

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Which reflected ray disappears and at which angle does this occur? (angle of incidence other than 45 to 50 ) Angle 10° 20° 30° 40° 50° 60° 70° 80° 90°

Reflection(s) 1 1 1 3 3 3 3 3 No reflection

Reflected rays become less than three, indicating them to be disappear at the angle of 10 , 20 and 30 . 

Why is this reflection the faintest of the three? The smaller the angle of incidence, the less intense the reflected light ray, causing it to be faint.

TASK B Place two mirrors at an angle of 90 to each other. Aim a single ray to strike one mirror at an angle, at point about 25 mm from the corner where the two mirrors meet.

Observe the principle reflected ray (not fainter secondary reflections), as it is reflected from both mirrors. Record this position.  What do you notice about the directions of the original ray and the emergent ray? The original and emergent ray are parallel to each other. 

Does this result occur at whatever angle you send the ray into the right angled mirror? Yes.

Look into the corner of the mirrors  What do you see? We will see the light reflected back to the source. 

If you shift your position, does the same thing occur? No.

If there is a larger plane mirror available, place it horizontally on the desk and stand the other two plane mirrors on it at right angles to each other, so that the mirrors are mutually perpendicular. A set of reflectors similar to this was placed on the moon by astronauts. Move aside, up and down, looking into the triple corner from all directions.  What do you see in the corner? Reflection occurs. Aim a beam light into the corner.  What do you notice about the reflection? The light ray is reflected back. Suggest why the reflector placed on the moon was a triple angled reflector.  What type of light beam was aimed at it and with what results? The reason that a triple angled reflector was placed at the moon because it offers the best chance to reflect any incident radiation back. The type of beam used was laser beam and the results was the laser beam being reflected three times, once by each of the reflector’s surface. 

Since scientists know this type of reflection occurs on Earth, what have they gained by placing the reflector on the moon? Since the main use of this triple angled reflector is for range finding, the astronauts can determine the distance between Earth and Moon.

Examine the reflector on the back of a car or bicycle  What is the shape of the dimples in the glass or plastic? Triangle or hexagon.

DISCUSSION Light, as we all know was to be reflected the moment it hits a mirror. The phenomenon that we studied was about multi reflections. Just like what has been said earlier and based on the results of the experiment, when an object was placed in between of two mirrors set up in a 90 position, it will produce two images on both mirrors respectively. The same case goes to light rays, when it was directed to one of the mirrors, it will be reflected back so the reflected ray will be parallel to the incident ray. When doing this experiment, there are some problems occurred. The result of the measurement value are not accurate at all because of some systematic error had occurred during the experiment. The parallax errors occur during taking the measurement for the angle. To avoid this problem, the eyes must perpendicular when taking the reading of angles. The lack of apparatus makes the experiment hard to do. In order to overcome this problem we have to borrow the apparatus from other group . The condition of the lab that is bright makes us hard to find the three reflected lines. To avoid this problem, we switch off the lamp to get the three lines form by the mirror. The source of light is nearer to the mirror produced different value. To overcome this problem, make sure before start the experiment, set up the source of light with standardized measurement so the other experiment will get precise value. CONCLUSION The results of the experiment showed to us that there are three rays of reflected light on a mirror plane. The right angle mirror test on the other hand showed that the emergent ray is parallel to the incident ray. In real life situation, reflections are very important to determine the distance and range. For example, the triple angled reflector or more known as the retroeflector or corner reflector is widely used in cars and also used by astronauts. Finally, and most important, the objective of the experiment was obtained as all the experiments obeys the law of reflection.