Required Practical: Investigating Reflection & Refraction

How many pieces of equipment are required in the practical:  Investigating Reflection & Refraction

7

list the pieces of equipment required in the practical:  Investigating Reflection & Refraction

• ray box

• mirror with stand

• protractor

• sheet of paper

• pencil

• ruler

• perspex box

purpose of the ray box?

to provide a narrow beam of light to reflect in the mirror

purpose of the mirror with stand?

to provide a reflective surface

purpose of the protractor?

to measure the light beam angles

purpose of the sheet of paper?

to mark with lines for angle measurement

purpose of pencil?

to draw lines on paper

purpose of the perspex block?

to refract the light beam

what is the resolution of measuring equipment

• Protractor = 1°

• Ruler = 1 mm

what is the aim of Experiment 1: Reflection of Light in a Mirror

To investigate specular reflection off a smooth surface

what is the independent variable of Experiment 1: Reflection of Light in a Mirror

Independent variable = angle of incidence, i

what is the dependent variable of Experiment 1: Reflection of Light in a Mirror

Dependent variable = angle of reflection, r

what are the control variables of Experiment 1: Reflection of Light in a Mirror

• Control variables:

  • Distance of ray box from mirror

  • Width of the light beam

  • Same frequency / wavelength of the light

how many steps are there to the method of Experiment 1: Reflection of Light in a Mirror

10

step 1 : Experiment 1: Reflection of Light in a Mirror

Set up the apparatus as shown in the diagram

step 2 : Experiment 1: Reflection of Light in a Mirror

In the middle of the paper use a ruler to mark a straight line of about 10 cm long

step 3 : Experiment 1: Reflection of Light in a Mirror

Use a protractor to draw a 90° line that bisects (cuts in half) the 10 cm line

step 4 : Experiment 1: Reflection of Light in a Mirror

Place the mirror on the first line as shown in the diagram above

step 5 : Experiment 1: Reflection of Light in a Mirror

Switch on the ray box and aim a beam of light at the point where the two drawn lines cross at an angle

step 6 : Experiment 1: Reflection of Light in a Mirror

1. Use the pencil to mark two positions of the light beam:

   • A point just after leaving the ray box

   • The point on the reflected beam about 10 cm away from the mirror

step 7 : Experiment 1: Reflection of Light in a Mirror

Remove the ray box and mirror

step 8 : Experiment 1: Reflection of Light in a Mirror

Use a ruler to join the two marked positions to the point where the originally drawn lines crossed

step 9 : Experiment 1: Reflection of Light in a Mirror

Use the protractor to measure the two angles from the 90° line. The angle for the ray towards the mirror is the angle of incidence, and the other the angle of reflection

step 10 : Experiment 1: Reflection of Light in a Mirror

Repeat the experiment three times with the beam of light aimed at different angles

list all the steps to the method of Experiment 1: Reflection of Light in a Mirror

1. Set up the apparatus as shown in the diagram

2. In the middle of the paper use a ruler to mark a straight line of about 10 cm long

3. Use a protractor to draw a 90° line that bisects (cuts in half) the 10 cm line

4. Place the mirror on the first line as shown in the diagram above

5. Switch on the ray box and aim a beam of light at the point where the two drawn lines cross at an angle

6. Use the pencil to mark two positions of the light beam:

   • A point just after leaving the ray box

   • The point on the reflected beam about 10 cm away from the mirror

7. Remove the ray box and mirror

8. Use a ruler to join the two marked positions to the point where the originally drawn lines crossed

9. Use the protractor to measure the two angles from the 90° line. The angle for the ray towards the mirror is the angle of incidence, and the other the angle of reflection

10. Repeat the experiment three times with the beam of light aimed at different angles

what variables would you include in a results table?

angle of incidence → angle of reflection

analyse the results of Experiment 1: Reflection of Light in a Mirror

• The law of reflection states:

i = r

• Where:

  • i = angle of incidence in degrees (°)

  • r = angle of reflection in degrees (°)

• If the experiment was carried out correctly, the angles should be the same, as shown below:

what is the aim of Experiment 2: Refraction of Light By A Perspex Block

To investigate the refraction of light by a perspex block

what is the independent variable of Experiment 2: Refraction of Light By A Perspex Block

Independent variable = angle of incidence, i

what is the dependent variable of Experiment 2: Refraction of Light By A Perspex Block

Dependent variable = angle of refraction , r

what are the control variables of Experiment 2: Refraction of Light By A Perspex Block

• Control variables:

  • Use of the same perspex block

  • Width of the light beam

  • Same frequency / wavelength of the light

how many steps are there to the method Experiment 2: Refraction of Light By A Perspex Block

6

step 1 : Experiment 2: Refraction of Light By A Perspex Block

Place the glass block on a sheet of paper, and carefully draw around the block using a pencil

step 2 : Experiment 2: Refraction of Light By A Perspex Block

Switch on the ray box and direct a beam of light at the side face of the block

step 3: Experiment 2: Refraction of Light By A Perspex Block

Mark on the paper:

• A point on the ray close to the ray box

• The point where the ray enters the block

• The point where the ray exits the block

• A point on the exit light ray which is a distance of about 5 cm away from the block

step 4 : Experiment 2: Refraction of Light By A Perspex Block

Draw a dashed line normal (at right angles) to the outline of the block where the points are

step 5 : Experiment 2: Refraction of Light By A Perspex Block

Remove the block and join the points marked with three straight lines

step 6 : Experiment 2: Refraction of Light By A Perspex Block

Replace the block within its outline and repeat the above process for a ray striking the block at a different angle

what would be the variables in Experiment 2: Refraction of Light By A Perspex Block

angle of incidence → angle of refraction

analyse the results of Experiment 2: Refraction of Light By A Perspex Block (5)

• i and r are always measured from the normal

• For light rays entering perspex block, the light ray refracts towards the central line:

i > r

• For light rays exiting the perspex block, the light ray refracts away from the central line:

i < r

• When the angle of incidence is 90° to the perspex block, the light ray does not refract, it passes straight through the block:

i = r

• If the experiment was carried out correctly, the angles should follow the pattern, as shown below:

identify and rectify the systematic errors (2)

• An error could occur if the 90° lines are drawn incorrectly

  • Use a set square to draw perpendicular lines

• If the mirror is distorted, this could affect the reflection angle, so make sure there are little to no blemishes on it

identify and rectify the random errors (2)

• The points for the incoming and reflected beam may be inaccurately marked

  • Use a sharpened pencil and mark in the middle of the beam

• The protractor resolution may make it difficult to read the angles accurately

  • Use a protractor with a higher resolution

list 3 of the safety considerations

• The ray box light could cause burns if touched

  • Run burns under cold running water for at least five minute

• Looking directly into the light may damage the eyes

  • Avoid looking directly at the light

  • Stand behind the ray box during the experiment

• Keep all liquids away from the electrical equipment and paper

• Take care using the mirror

  • Damages on the mirror can affect the outcome of the reflection experiment