Seeing Things Through Stuff How light bends when it goes in the opposite direction

1)Fill the semicircular container about three quarters full with water. Do L12 Refraction of Light Activity, From Water (More Dense) to Air (Less Dense).

2)Carefully move the container so that it lines up with the image on the protractor.

2)Carefully move the prism so that it lines up with the image on the protractor.

3)Rotate it so that a light ray…… Refraction Water into Air

3)Rotate it so that a light ray can be shone incident to the curved surface, along the normal to the curved surface.

3)Direct a single ray of light at the flat surface of the water along the normal. Make absolutely sure that the ray passes through the centre of the flat surface.

4)Measure the angle of refraction in air and record it in the table.

5)Repeat the procedure for angles of incidence of 10 , 20 , 30 , 40 , 50 , 60  and 70 , recording your observations in the table.

When finished recording your observations, answer the analysis questions. Answers follow. L12 Refraction of Light Activity From Water (More Dense) to Air (Less Dense)

1)When light travels from water into air along the normal ( ∠ i=0  ), what happens to it? When light travels from water into air along the normal ( ∠ i=0  ), it continues on without refracting ( ∠ R=0  ).

3)The incident and refracted rays are always located on (the same / opposite) sides of the normal? 2)When light travels from water into air at an angle of incidence greater than 0 , it is bent, (away from / towards) the normal.

4)Why does the incident ray not bend when entering the curved surface (at large arrow) in this lab? Recall from the previous activity, L10 Refraction of Light Activity – From Air (Less Dense) to Water (More Dense), if the circular region where the first incident ray meets the semi-circular prism is greatly magnified -

The curve would look like a straight line which is the same as the tangent to the semi-circle. The dotted line or radius is perpendicular to this and the incident ray would be along the normal. 4)Why does the incident ray not bend when entering the curved surface (at large arrow) in this lab?

Therefore, the incident ray would be along the normal to the surface ( ∠ i=0) and the refracted ray would not bend ( ∠ R=0). 4)Why does the incident ray not bend when entering the curved surface (at large arrow) in this lab?

5)The intensity of the reflected ray [gets more intense / gets less intense / stays the same] as the angle of incidence increases.

6)At an angle of incidence of approximately 45 , what happens?

At about ∠ i~45 , the refracted ray bends close to the flat surface of the semi-circular container ( ∠ R  90  ), OR the refracted ray disappears AND the reflected ray becomes very intense.

7)This angle is called the Critical Angle with the symbol (  c ). The Critical Angle (  c ) is the angle of incidence for which the angle of refraction equals 90 .

8)Draw the refracted and/or reflected rays. Angle of incidence less than Critical Angle ( ∠ i<  c ) If the angle of incidence is less than the Critical Angle ( ∠ i<  c ), as the light leaves the more dense medium, ……

8)Draw the refracted and/or reflected rays. Angle of incidence less than Critical Angle ( ∠ i<  c ) If the angle of incidence is less than the Critical Angle ( ∠ i<  c ), as the light leaves the more dense medium, it bends away from the normal……

8)Draw the refracted and/or reflected rays. Angle of incidence less than Critical Angle ( ∠ i<  c ) If the angle of incidence is less than the Critical Angle ( ∠ i<  c ), as the light leaves the more dense medium, it bends away from the normal and the reflected ray is faint.

8)Draw the refracted and/or reflected rays. If the angle of incidence is equal to the Critical Angle ( ∠ i=  c ), as the light leaves the more dense medium, ….. Angle of incidence equal to Critical Angle ( ∠ i=  c )

8)Draw the refracted and/or reflected rays. If the angle of incidence is equal to the Critical Angle ( ∠ i=  c ), as the light leaves the more dense medium, it bends close to the surface or the angle of refraction equals 90  ( ∠ R= 90  )…… Angle of incidence equal to Critical Angle ( ∠ i=  c )

8)Draw the refracted and/or reflected rays. Angle of incidence equal to Critical Angle ( ∠ i=  c ) If the angle of incidence is equal to the Critical Angle ( ∠ i=  c ), as the light leaves the more dense medium, it bends close to the surface or the angle of refraction equals 90  ( ∠ R= 90  ) and the reflected ray is intense.

8)Draw the refracted and/or reflected rays. Angle of incidence greater than Critical Angle ( ∠ i>  c ) If the angle of incidence is greater than the Critical Angle ( ∠ i>  c ), as the light leaves the more dense medium, ……

8)Draw the refracted and/or reflected rays. Angle of incidence greater than Critical Angle ( ∠ i>  c ) If the angle of incidence is greater than the Critical Angle ( ∠ i>  c ), as the light leaves the more dense medium, it totally reflects or there is no refracted ray.

8)Draw the refracted and/or reflected rays. The Critical Angle (  c ) is the angle of incidence for which the angle of refraction equals 90 . Angle of incidence less than Critical Angle ( ∠ i<  c ) Angle of incidence greater than Critical Angle ( ∠ i>  c ) Angle of incidence equal to Critical Angle ( ∠ i=  c )

When the angle of incidence is greater than the Critical Angle (  c ), the light is totally reflected. This is called Total Internal Reflection (TIR). Total Internal Reflection (TIR) reflects 100% of the light. This is better than mirrors which absorb some of the incident light.

9)What’s wrong with these diagrams? Draw the correct refracted rays.

If the angle of incidence is less than the Critical Angle ( ∠ i<  c ), as the light leaves the more dense medium, it bends away from the normal and the reflected ray is faint.

9)What’s wrong with these diagrams? Draw the correct refracted rays

9)What’s wrong with these diagrams? Draw the correct refracted rays. If the angle of incidence is greater than the Critical Angle ( ∠ i>  c ), as the light leaves the more dense medium, it totally reflects or there is no refracted ray.

9)What’s wrong with these diagrams? Draw the correct refracted rays.

9)What’s wrong with these diagrams? Draw the correct refracted rays When light travels from more dense into less dense along the normal ( ∠ i=0  ), it continues on without refracting ( ∠ R=0  ).

9)What’s wrong with these diagrams? Draw the correct refracted rays.

10)Draw the missing rays.

If the refracted ray bends close to the surface or the angle of refraction equals 90  ( ∠ R= 90  ) and the reflected ray is intense, then the angle of incidence is equal to the Critical Angle ( ∠ i=  c ).

10)Draw the missing rays. The incident ray is along the normal to the curved surface ( ∠ i=0); therefore, the refracted ray does not bend. In the more dense medium ∠ i=  c, as the light leaves, it bends close to the surface or the angle of refraction equals 90  ( ∠ R= 90  ) and the reflected ray is intense.

10)Draw the missing rays. The incident ray is along the normal to the curved surface ( ∠ i=0); therefore, the refracted ray does not bend on entering. In the more dense medium, the angle of incidence is less than the Critical Angle ( ∠ i<  c ). As the light leaves, it bends away from the normal and the reflected ray is faint.

10)Draw the missing rays. The incident ray is along the normal to the curved surface ( ∠ i=0); therefore, the refracted ray does not bend on entering. In the more dense medium, the angle of incidence is greater than the Critical Angle ( ∠ i>  c ). As the light leaves, it totally reflects or there is no refracted ray.

10)Draw the missing rays.