3.2.1 - 3.2.6 - Reflection and Refraction Flashcards
What type of wave is light?
Visible light is a part of the electromagnetic spectrum which means it is a transverse wave
This means the direction the light particles vibrate is perpendicular to the direction of the energy transfer
Light can undergo:
Reflection
Refraction
All waves in the electromagnetic spectrum can be reflected and refracted
What are sound waves?
Sound waves are vibrations of air molecules
When a sound wave comes into contact with a solid those vibrations can be transferred to the solid
What type of waves are sound waves?
Sound waves are longitudinal waves
This means the direction the particles vibrate is parallel to the direction of the energy transfer
Hence, it consists of:
Compressions - regions of higher density
Rarefactions - regions of lower density
How does reflection occour in a wave?
A wave hits a boundary between two media and does not pass through, but instead stays in the original medium
When does refraction occour in a wave?
A wave passes a boundary between two different transparent media and undergoes a change in direction
What is the law of reflection?
Angles are measured between the wave direction (ray) and a line at 90 degrees to the boundary
The angle of the wave approaching the boundary is called the angle of incidence (i)
The angle of the wave leaving the boundary is called the angle of reflection (r)
The angles are the same, so the law of reflection can be written:
Angle of incidence (i) = Angle of reflection (r)
How are angles measured?
Angles are measured between the wave direction (ray) and a line at 90 degrees to the boundary
How can you draw a ray diagram?
When drawing a ray diagram an arrow is used to show the direction the wave is travelling
An incident ray has an arrow pointing towards the boundary
A reflected ray has an arrow pointing away from the boundary
The angles of incidence and reflection are usually labelled i and r respectively
What are refraction ray diagrams
Refraction occurs when light passes a boundary between two different transparent media
At the boundary, the rays of light undergo a change in direction
The change in direction depends on the difference in density between the two media:
From less dense to more dense (e.g air to glass), light bends towards the normal
From more dense to less dense (e.g. glass to air), light bends away from the normal
When passing along the normal (perpendicular) the light does not bend at all
Why does the ray change direction?
The change in direction occurs due to the change in speed when travelling in different substances
When light passes into a denser substance the rays will slow down, hence they bend towards the normal
The only properties that change during refraction are speed and wavelength – the frequency of waves does not change
Explain Core practical core Investigating Refraction?
To investigate the refraction of light using rectangular blocks, semi-circular blocks and triangular prisms
Place the glass block on a sheet of paper, and carefully draw around the rectangular perspex block using a pencil
Switch on the ray box and direct a beam of light at the side face of the 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
Draw a dashed line normal (at right angles) to the outline of the block where the points are
Remove the block and join the points marked with three straight lines
Replace the block within its outline and repeat the above process for a ray striking the block at a different angle
Repeat the procedure for each shape of perspex block (prism and semi-circular)
What are the results for the different blocks?
The final diagram for each shape will include multiple light ray paths for the different angles of incidences (i) at which the light strikes the blocks
This will help demonstrate how the angle of refraction (r) changes with the angle of incidence
Label these paths clearly with (1) (2) (3) or A, B, C to make these clearer
i and r are always measured from the normal
For light rays entering the 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
What errors could occour in this experiment?
An error could occur if the 90° lines are drawn incorrectly
Use a set square to draw perpendicular lines
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
How do light rays change through different mediums?
When light enters a denser medium (such as glass) it slows down and bends towards the normal
How much the light bends depends on the density of the material
If light travels from a less dense to a more dense medium (e.g. air to glass), r < i (bends towards the normal)
What is snells law?
Refractive index of material = angle of incidence / angle of refraction of the light
What is Total internal reflection?
The angle of incidence is greater than the critical angle and the incident material is denser than the second material
Therefore, the two conditions for total internal reflection are:
The angle of incidence > the critical angle
The incident material is denser than the second material
