✅ 7. Required Practical: Testing Reflection And Refraction (P12)

Question 1

Aim of this Practical

Answer 1

To investigate the reflection of light by different types of surface, and the refraction of light by different substances.

Question 2

Equipment for the Practical

Answer 2

• Marker Pen
• Ruler
• Protractor
• Whiteboard/Laminated Paper/ Paper
• See-through Block
• Mirror
• Light Fliter/Blocker/Slits
• Power Pack
• Ray Box
• Camera

Question 3

Method For This Practical

Answer 3

1. Set up a ray box, slit and lens so that a narrow ray of light is produced
2. Place a 30 centimetre (cm) ruler near the middle of a piece of plain A3 paper. Draw a straight line parallel to its longer sides. Use a protractor to draw a second line at right angles to this line. Label this line with an ‘N’ for ‘normal’.
3. Place the longest side of a rectangular acrylic polymer block against the first line. With the normal near the middle of the block, carefully draw around the block without moving it.
4. Use the ray box to shine a ray of light at the point where the normal meets the block. This is the incident ray.
5. The angle between the normal and the incident ray is called the angle of incidence. Move the ray box or paper to change the angle of incidence. The aim is to see a clear ray reflected from the surface of the block and another clear ray leaving the opposite face of the block.
6. Using a pencil on the paper, mark the path of:
   
   • The incident ray with a cross
   • The reflected ray with a cross
   • The ray that leaves the block with two crosses - one near the block and the other further away
7. Remove the block. Join the crosses to show the paths of the light rays.
8. Repeat steps 2 to 7 for a rectangular glass block.
9. Measure the angle of incidence, angle of refraction and angle of reflection for each block.

Question 4

Risk Assessment for this Practical

Answer 4

Hazard: Ray box gets hot
Consequence: Minor burns
Control Measures: Do not touch the bulb and allow time to cool

Hazard: Semi-Dark Environment/Room
Consequence: Increase hazard of tripping over
Control Measures: Ensure environment is clear of potential trip hazards before lowering lights

Question 5

Analysis of this Practical/What you do with the Results

Answer 5

You can:

1. Compare the angle of incidence with the angle of reflection for each block
2. Compare the angle of incidence with the angle of refraction for each block

Question 6

Results Tables for this Practical

Answer 6

For Both Results for the Reflection and Refraction fir the Glass Block:

I made three columns to record my results in, with each different angle in every row. In the left column, I recorded the ‘Angle of Incidence(°)’, in the middle I recorded the ‘Angle of Reflection (°)’, and on the right I recorded the ‘Angle of Refraction (°)’.

Question 7

Conclusion for this Practical - What Do The Results Show/Confirm

Answer 7

Overall, the results for reflection essentially follow the law for reflection, in that the incident ray is an equal angle (measured from the normal) to the reflected ray when reflected off of a plane mirror.

The results for refraction prove Snell’s Law (the law of refraction). Snell’s law is a formula used to describe the relationship between the angles of incidence and refraction, when referring to light waves (or other kinds of waves) that pass through a boundary of differing materials.

Question 8

Evaluation for this Practical - How Could It Be Improved (What Are The Limitations and How Can They Be Corrected)

Answer 8

On the whole, the experiment was quite accurate, meaning there is little that I would change to improve the acurracy of the results. However, there are some possibke limitations that can arise:

Seeing Light Rays Clearly
Do the experiment in a dark room to allow the light beams to be more visible.

Measuring Amounts/Measurements Wrong
Make sure that you are as accurate as possible when using the ruler and protractor, as you could make mistakes. Also, ensure that you measure the angles from the normal

Keeping The Mirror in the Correct Place
You could place a mirror on a stand and keep it in the same place to ensure it moves as little as possible when drawing the lines of reflection and refraction, as this will avoid getting any dogy measurements.

Question 9

What is an Independant Variable

Answer 9

In Independant Variable is the variable that is altered during a scientific experiment.

Question 10

What is a Dependant Variable

Answer 10

A Dependant Varibale is the variable being tested or measured during a scientific experiment.

Question 11

What is a Control Variable

Answer 11

A Control Variable is the variable that is kept the same during a scientific experiment.

Question 12

As the light enters the block, is the angle of refraction larger or smaller than the angle of incidence?

Answer 12

It is smaller

Question 13

As the light enters the block, does the ray refract towards or away from the normal when it first hits the block?

Answer 13

It bends towards the normal

Question 14

As the light emerges from the block, is the angle of refraction larger or smaller than the angle of incidence?

Answer 14

The angle of refraction is larger than the angle of incidence.

Question 15

As the light emerges from the block, does the ray refract towards or away from the normal as it passes into the air as it leaves the block?

Answer 15

The ray refracts away from the normal

Question 16

Is air more or less optically dense than glass?

Answer 16

Air is less optically dense than glass

Question 17

Make an overall conclusion about how a ray of light is refracted as it passes from air to glass and also from glass to air? Refer to the optical density of each medium.

Answer 17

As the light passes from air to glass, the light passes to an optically denser material. This means the light will bend towards the normal, with a smaller angle of refraction than incidence. As the light lasses back into air, the medium again becomes rarer. Also, the light bends away from the normal, with a larger angle of refraction than incidence.

Question 18

What do you notice about the incident and emergent rays?

Answer 18

Both are the rays are at the same angle

Question 19

a) It has been suggested that the ratio:

sin (i) / sin(r) =constant

Do your results agree with this?

b) You could find the ratio of angle of incidence to refraction that conforms to every angle and use the rule on that.
(Results: i,r
-35°,24°
-45°, 30°
-55°, 35°
-65°, 40°)

Answer 19

a)
sin(45)/sin(30) = 1.41
sin(55)/sin(35) = 1.42
sin(65)/sin(40) = 1.41

(All are approximately equal to 1.41)

Angle measuring is not perfect, yet results are close, so I do agree.

b)
You could find the ratio of angle of incidence to refraction that conforms to every angle and use the rule on that.

Question 20

What are the 2 rules of Refraction

Answer 20

The investigation should show that a light ray:

• Changes direction Towards the normal when it travels into glass. The angle of refraction, r, is smaller than the angle of incidence, i.
• Changes direction Away from the normal when it travels from glass into air. The angle of refraction, r, is greater than the angle of incidence, i.

Question 21

Describe an experiment that could be performed in order to investigate refraction of light at an air to glass boundary. Identify sources of inaccuracy in your method.

(Method + Possible Sources of Inaccuracy)

Answer 21

1. Place the glass or Perspex block in the centre of the piece of paper (landscape view) and draw around its edges.
2. Remove the block and draw a dotted normal line at right angles to the edge of one long side of the block, about half way along.
3. Draw a line to represent the incident ray (e.g, at 30°C) to the normal.
4. Place the block back on the rectangle you have drawn.
5. Switch on the ray box with a narrow slit in front of the bulb and shine the ray
   along the incident ray you have drawn.
6. Observe the path of the light through the block and out of the other side.
   7 Mark the path of the emergent light ray on the other side with a pencil line. Also mark any other ray you can see.
7. Remove the glass block. Draw a normal at the point where the light emerged from the glass block.
8. Draw a line to join the incident and emergent ray through the rectangle representing the glass block to give the refracted ray.
9. Measure the angles shown in the diagram using the protractor. Record your results in the table below.
10. Repeat for an angle of incidence of 40°, 50°, and another angles.

Possible Sources of Inaccuacy:

• Make sure you measure the correct angles when getting your results.
• Make sure your in a dark room in order to be able to judge where the ray passes better.
• Make sure that the light ray is thin enough to get accurate results.