3. The three laws of geometrical optics (2p.)

Question 1

The law of rectilinear propagation

Answer 1

The law of rectilinear propagation states that in a homogenous medium light travels along straight paths. According to this, an opaque object (a ball) will cast a shadow (umbra) and half shadow (penumbra). If source of light is a point, only umbra will be cast.

Question 2

The law of reflection

Answer 2

The law of reflection states that for a light ray traveling in air and
incident on a smooth surface, the angle of reflection 𝜃’1 equals the angle of incidence 𝜃1 .
Both angles are defined with respect to the normal to the surface at the point of incidence.

Question 3

The law of refraction:

Answer 3

The law of refraction:

Light crossing a boundary as it travels from medium 1 to medium 2 is refracted or bent. The angle of refraction 𝜃2 is defined by the relationship:

sin 𝜃1/sin 𝜃2 = 𝑣1/𝑣2 = constant

Where 𝜃1 is the angle of incidence (padania) .

The index of refraction n of a medium is defined by the ratio: 𝑛 = c/v’, where c is
the speed of light in vacuum and v is the speed of light in the medium. In general,

n varies with wavelength and is given by 𝑛 = 𝜆/𝜆m
, where 𝜆 is the vacuum wavelength
and 𝜆m is the wavelength in the medium.
As light travels from one medium to another, its frequency remains the same.

Question 4

Snells’ law of refraction

Answer 4

If 𝜃 ! and 𝜃 ! are the angles of incidence and of refraction respectively, 𝑛 ! and 𝑛! are the indices of refraction in the two media, then Snell’s law states that:

𝑛1 * sin 𝜃1= 𝑛2 * sin 𝜃2