precautions in reflection of light experiment

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Lab 10 - Reflection and Refraction

Introduction

Discussion of principles, reflection by a plane mirror.

Figure 1 : Reflection in a plane mirror

Refraction at a Plane Surface

Figure 2 : Reflection and refraction of light at air-glass and glass-air boundaries

Figure 3 : Sketch showing path of rays through glass plate

Figure 4 : Sketch showing geometry of the setup

• Glass plate
• Optic bench
• Vernier caliper
• Angular translator
• Rotational stage

Description of Apparatus: Laser

Description of apparatus: optical bench.

Figure 5 : Optic bench

Description of Apparatus: Angular Translator

Figure 6 : Side and top views of the angular translator

Alignment of Apparatus

Figure 7 : Side and top view of glass plate on rotating surface

Figure 8 : Photo showing rotation of glass plate

Procedure A: Measurement of Angle of Reflection

Procedure b: measurement of index of refraction.

Figure 9 : Photo showing the two reflected images on the scale

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Science project, reflecting light.

On the informational level, the student becomes acquainted with the law of reflection as it pertains to plane mirrors. First, the student experiences how a plane mirror creates an image that is flipped from left to right. Second, the law of reflection is used to explain the position of an image seen in a mirror in using a toy. The reflection of the toy appears to be behind the mirror! This is due to the fact that our brain tells us that light travels in straight lines coming from the toy, but when we see the toy reflected in the mirror, this is not actually the case. We are fooled when we perceive the cat as being behind the mirror. What we see is called a virtual image.

How does a person's mirror image differ from their actual image? How are virtual images constructed?

• Plane mirror
• Source of light
• Gather the materials which you require for this project. These include a plane mirror (the larger, the better), a toy, and a source of light.
• Copy the chart that you will use to record all of your observations.
• Do not look in the mirror! Start by recording on your chart how you expect a mirror image of your face will be different from an image of your actual face. Do you think it will be identical? If not, how will it differ?
• Now, look at your face in the mirror. Pretend that you are looking at a stranger who happens to be looking back at you. On your chart, record what you observe.
• Touch your left ear with your left hand. Look into the mirror. On which side of the mirror is your left hand? Record your observation.
• Touch your right ear with your right hand. Observe and record. On which side of the mirror is your right hand?
• Put your fingertip on the right-hand side of the mirror. On which side of the mirror is the reflection of your finger? Observe and record.
• Based on your observations, what conclusion do you reach? What kind of a reversal are you experiencing? Record your response.
• Place your toy in front of the mirror. Look carefully into the mirror. Where does it appear to be? In the front? In the back?
• Study the image of the toy; does the image appear to be the same distance behind the mirror as the actual distance the toy sits in front of the mirror? Is this a real or a virtual image?
• What do you conclude from this investigation? Is your brain playing games? How does the law of reflection enter this picture?
• Write up your report. What do you conclude about how our brain and the law of reflection influence our perception of the toy being behind the mirror when we “know” it is in front of the mirror? How do we explain virtual images?

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GCSE Physics Required Practical: Investigating Reflection and Refraction of Light

• 1.1 Meaning
• 1.2.1 Method
• 1.2.2 Improving Accuracy
• 1.3.1 Method
• 1.3.2 Improving Accuracy

Key Stage 4

Investigate the reflection and refraction of light .

Experiment 1: Reflection from a Plane Mirror

• Place a plane mirror in the centre of a piece of paper and draw a pencil line along its reflective side.
• Use a ray box and a slit to allow a single beam of light to be incident on the surface of the mirror at an angle less than 90°.
• Place a pair of x's on the incident ray and along the reflected ray .
• Remove the ray box and mirror .
• Use a ruler to join the x's with a pair of lines leading to the mirror to show the direction of the incident and reflected rays.
• Use a protractor and ruler to draw a normal line at right angles to the surface of the mirror at the point the light rays meet the mirror .
• Use the protractor to measure the 'i' the angle of incidence and 'r' the angle of reflection .
• Repeat this procedure for a number of different angles of incidence .

Improving Accuracy

Experiment 2: refraction from a rectangular glass block.

• Place a rectangular glass block in the centre of a piece of paper and draw a pencil line around the outside.
• Use a ray box and a slit to allow a single beam of light to be incident on the surface of the glass block at an angle less than 90°.
• Place a pair of x's on the incident ray and along the emergent ray .
• Remove the ray box and glass block.
• Use a ruler to join the x's with a pair of lines leading to the glass block to show the direction of the incident and emergent rays.
• Join the emergent ray and the incident ray with a line to represent the refracted ray .
• Use a protractor and ruler to draw a normal line at right angles to the surface of the glass block at the point the light rays meet the glass block.
• Use the protractor to measure the 'i' the angle of incidence and 'r' the angle of refraction .

Law of Reflection Lab

↘︎ Apr 18, 2010 … 6′ … download ⇠ | skip ⇢

To develop an understanding of the Law of Reflection, to apply the Law of Reflection to finding images formed by plane and spherical mirrors, and to learn to draw ray diagrams to assist in predicting the locations of images formed by spherical concave mirrors.

According to the Law of Reflection, the angle of incidence will equal the angle of reflection when light is shone off a flat reflecting surface. When light is shone off a spherical mirror, it will converge at a focal point. Light will converge at a real focal point in front the concave mirror, and light will converge at a virtual focal point somewhere behind the convex mirror. An object placed beyond the curvature of a mirror will cast an inverted, shrunken, real image. An object placed at the curvature of a mirror will project and inverted, true to size, real image. Finally, an object placed between the curvature and focal point will project an inverted, magnified, real image.

Labeled Diagrams

See attached sheet.

Focal length of mirror f = 5.5 cm

1. What statement can you make regarding the relative positioning of the normal, the incident ray and the reflected ray?

The angle between the incident ray and the normal is equal to the angle between the reflected ray and the normal.

2. Do your observations validate the Law of Reflection?

Yes, the observations validate the Law of Reflection as θ i = θ r or the values are extremely close in all trials.

3. Using your data above, create a graph in Graphical Analysis of pq vs. p + q. Your graph should appear linear. Perform a linear fit on the graph.

See graphs section.

4. There is an equation in geometrical optics called the mirror equation. It relates the object distance p and the image distance q to the focal length of the mirror f: 1/p + 1/q = 1/f. The mirror equation can be used to determine a mirror’s focal length. Solve the above equation algebraically for f.

In the instance of case 1, for trial 1 f = 4.0 cm, for trial 2 f = 4.1 cm, and for trial 3 f = 3.8 cm. In the instance of case 2, for trial 1 f = 4.1 cm. In the instance of case 3, for trial 1 f = 4.0 cm, for trial 2 f = 4.2 cm, and for trial 3 f = 4.3 cm. The average value for f is 4.1 cm.

5. How is your answer to Question 4 related to the slope of your graph from Question 3?

The slope of the graph from Question 3 is 4.0 cm, so these values are strikingly similar.

6. What is the percent difference between your slope and the focal length of the mirror that you measured?

The percent difference between the slope, 4.0 cm, and the focal length of the mirror that was measured, 5.5 cm, is 32%.

7. The magnification of the image of an object from a spherical mirror can also be expressed as the ratio –q/p. Calculate this ratio for each of your object and image distances and record in your data table.

See data table.

8. How does the ratio of –q/p compare to your calculated magnifications h i /h o for each entry? What is the percent difference?

In regards to case 1, the values for both h i /h o and –q/p are negative, but the values for h i /h o are more negative than that of –q/p. The percent difference for trial 1 is 126%, for trial 2 is 132%, and for trial 3 is 153%.

Case 2 shares the same characteristics of case 1. The percent difference is 112%.

In regards to case 3, the values are quite dissimilar because all h i /h o values are positive while all –q/p values are negative. The percent difference for trial 1 is 1200%, trial 2 is 700%, and trial 3 is 569%. It is thought that the images were recorded as upright when they were really inverted, which caused this error, but it cannot be validated by repeating the laboratory procedure at this time.

9. Do your data verify the prediction from your ray diagrams?

In regards to case 1, the values for –q/p verify the predictions made from the ray diagram, as when the object was moved further away from the mirror, the images became smaller. The values for h i /h o dot not support this claim however, as they say that the image way magnified, but in reality the projected image was smaller. The images were also inverted as told by the negative sign.

In regards to case 2, neither the value for –q/p nor h i /h o verifies the prediction made from the ray diagram. The magnification should have been 0.

In regards to case 3, the values for –q/p do verify the predictions made from the ray diagram, as when the object was moved closer to f, the images became more magnified. The images were recorded as being upright, but in reality were probably inverted as suggested by theory and the negative sign the –q/p value carries.

For part 1 of the experiment, the reflection of light from a plane mirror was measured. Equipment was set up on the optics bench so that light shone through a slit plate and slit mask onto a plane mirror. A ray table was used to measure the angle at which the line hit and reflected off the mirror. The ray table was rotated from 0 o to 90 o at 10 o intervals. The angle of incidence and angle of reflection were measured for each trial. The measured angles were identical or nearly identical in all trials, which seem to confirm the Law of Reflection. Any discrepancy in the measurements may be attributed to the ray optics mirror not being perfectly aligned on the ray table; without any way to secure it in place, it may have shifted slightly during some of the trials. This would have caused a difference in the angles of incidence and reflection.

For part 2 of the experiment, the focal points of a concave and convex mirror were measured. Equipment was set up on the optics bench so that light shone through a parallel ray lens and then through a slit plate and then onto the concave or convex mirror situated on a ray table. The parallel ray lens had to be adjusted to make the light rays project in a parallel fashion onto the mirror. Once parallel, the mirror was situated so that the centermost light ray would hit the center of the mirror perpendicularly. The light rays converged at a focal point which was measured and recorded. In the case of the convex mirror, a piece of paper was place underneath the mirror and the projected light rays were draw onto the piece of paper. The paper was then removed and the lines were extended to find the focal point which was located behind the mirror. In the case of the concave mirror, the focal point was in front of the mirror. The focal length of the concave mirror was 0.060 m and the focal point of the convex mirror was 0.058 m. This slight discrepancy could be attributed to difficulty tracing the lines projected by the convex mirror, but these values are rather close in value, which is expected.

For part 3 of the experiment, the cases of 3 ray diagrams were tested. Equipment was set up on the optics bench so that light shone through a crossed arrow target onto an angled spherical mirror which then reflected an image onto a viewing holder. The focal length of the mirror was first determined by placing the mirror as far away from the crossed arrow as target as possible. The viewing screen was moved to locate the point where the image of the target was focused, and that was designated as the focal point. In the case of this experiment, the focal length was 5.5 cm. The target was then placed at three positions beyond the curvature, directly on the curvature, and then at three positions between the curvature and the focal length. The viewing screen was situated in each trial to find the point where the projected image was focused. The distance from object to mirror, distance from image to mirror, height of the object, and height of the image were measured in each trial.

The results from this part of the experiment are not very consistent. In case 1, the values for both h i /h o and –q/p were both negative, but the values for h i /h o were more negative than that of –q/p. The percent difference for trial 1 was 126%, for trial 2 was 132%, and for trial 3 was 153%. The values for –q/p seems most reasonable as they predict that the image was shrunken and inverted, which was actually the case. The values for h i /h o suggest that the images were magnified and inverted, which was not what was observed. Case 2 shares the same characteristics of case 1, in that the value for both h i /h o and –q/p was negative, but the value for h i /h o was more negative than that of –q/p. The percent difference was 112%. During this case, it was predicted that the image would be inverted, but would be life size; not magnified or shrunken. In regards to case 3, the values were quite dissimilar because all h i /h o values were positive while all –q/p values were negative. The percent difference for trial 1 was 1200%, trial 2 was 700%, and trial 3 was 569%. It is thought that the images were recorded as upright when they were really inverted, which caused this discrepancy, but it cannot be validated by repeating the laboratory procedure at this time. The values for –q/p are most logical, as they suggest that the image was inverted and magnify, which is also what theory suggests.

The error from this part of the experiment came from the inability to distinguish when the image on the viewing screen was focused. Many times it was thought that the image was focused, but may not have truly been focused; there was not way to tell with certainty if it was focused or not. The viewing screen could be moved a few centimeters in either direction and the image would look about the same. All measurements for the height of the image are in question as well. The spherical mirror was placed at an angle in order to view the image, but this angle was never taken into consideration in any of the equations. The undoubtedly is what caused all the h i /h o values have such a stark difference from the –q/p values. It was not stated in the lab manual how to take that angle into consideration, and thus those values should most likely be thrown out. The –q/p values are most representative of the projected image, though the values for –q/p and h i /h o should have been equal.

1/p + 1/q = 1/f

Magnification = -q/p = h i /h o

Percent Difference = |x 1 – x 2 | / (x 1 + x 2 )/2 x 100%

circa 2018 (30 y/o)

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Light Refraction Experiment

March 30, 2020 By Emma Vanstone Leave a Comment

This light refraction experiment might be one of the most simple to set up science experiments we’ve ever tried. It is a bit tricky to explain, but impressive even if you can’t quite get your head around it!

If you like this activity don’t forget to check out out our other easy science experiments for kids .

Materials for Light Refraction Experiment

Paper or card

Instructions

Fill the glass almost to the top.

Draw arrows on one piece of of card or paper. Place the paper behind the glass and watch as the arrow points the other way.

Now try to think of a word that still makes sense if you put it behind the glass.

We tried bud , the green ( badly drawn ) plant is on the opposite side when the paper is not behind the glass.

NOW works well too 🙂

How does this work?

Refraction ( bending of light ) happens when light travels between two mediums. In the refraction experiment above light travels from the arrow through the air, through the glass, the water, the glass again and air again before reaching your eyes.

The light reaching your eye (or in this case our camera) coming from the arrow is refracted through the glass of water. In fact the glass of water acts like a convex lens (like you might have in a magnifying glass). Convex lenses bend light to a focal point . This is the point at which the light from an object crosses.

The light that was at the tip of the arrow is now on the right side and the light on the right side is now on the left as far as your eye is concerned (assuming you are further away from the glass than the focal point.

If you move the arrow image closer to the glass than the focal point it will be the way around you expect it to be!

More Refraction experiments

Create an Alice in Wonderland themed version of this too!

Find out how to make your own magnifying glass .

We’ve also got a fun disappearing coin trick .

Or try our light maze to learn about reflection .

Last Updated on February 22, 2021 by Emma Vanstone

Safety Notice

Science Sparks ( Wild Sparks Enterprises Ltd ) are not liable for the actions of activity of any person who uses the information in this resource or in any of the suggested further resources. Science Sparks assume no liability with regard to injuries or damage to property that may occur as a result of using the information and carrying out the practical activities contained in this resource or in any of the suggested further resources.

These activities are designed to be carried out by children working with a parent, guardian or other appropriate adult. The adult involved is fully responsible for ensuring that the activities are carried out safely.

What are the precautions in the reflection experiment?

You will need to take the time to wear protective gear. Protect your eyes so that they do not get harmed.

In a reflection experiment, precautions include ensuring a clean and smooth reflecting surface, minimizing ambient light to reduce interference, using a stable light source with a known wavelength, and measuring the angle of incidence and reflection accurately. It is also important to avoid touching the reflecting surface to prevent smudges or damage.

Add your answer:

What is the reflection experiment?

A reflection experiment involves observing how light or sound waves bounce off a surface and change direction. By studying the angle of incidence and the angle of reflection, researchers can better understand the behavior of waves and how they interact with different materials. This experiment is commonly used in physics and optics to explore the principles of reflection.

What are the necessary conditions for a surface to give an accurate reflection in the experiment of the laws of reflection?

The surface should be smooth and flat to give an accurate reflection in the laws of reflection experiment. A rough or curved surface may distort the reflection, making it difficult to observe and verify the angle of incidence equals the angle of reflection. Additionally, the surface should be clean and free from any dirt or smudges that could interfere with the reflection.

Source of error in a reflection experiment?

One common source of error in a reflection experiment is not positioning the mirror or reflective surface perfectly perpendicular to the incident light source, resulting in an inaccurate angle of reflection. This can lead to errors in measuring the angle of reflection and calculating reflection properties like the law of reflection. Regular calibration and ensuring proper alignment can help minimize this error.

What are the precautions in compound pendulum?

Ensure the length of the pendulum is accurately measured to maintain the accuracy of the experiment. Take precautions to minimize air resistance by conducting the experiment in a controlled environment. Ensure the pivot point is frictionless to reduce energy losses and improve the accuracy of the results.

Write an Experiment to verify laws of reflection of sound?

Set up a sound source and a microphone on opposite sides of a smooth, hard surface. Emit a sound wave from the source and measure the angle of incidence and angle of reflection using a protractor. Repeat the experiment for different angles of incidence and observe that the angle of incidence is equal to the angle of reflection, confirming the law of reflection of sound.

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