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11TH GRADE · OPTICS

Reflection and refraction of light

Laws of reflection, refraction and total internal reflection.

24 minutes13 theory cards
Open interactive lesson

LESSON MATERIAL

Basic Concepts

3

Law of Light Reflection

The incident and reflected rays lie in the same plane with the normal, the angle of reflection is equal to the angle of incidence.

Both angles are measured from the normal to the surface, and not from the surface itself - this is a common source of error.

Law of light refraction

Relationship between the angles of incidence and refraction with the optical properties of two media.

When crossing the boundary, the frequency of light does not change, but the speed and wavelength change; so the beam turns.

Total internal reflection

Reflection of light from a boundary without a refracted ray upon transition from an optically denser medium.

It is possible only upon transition from an optically denser medium to a less dense one and at an angle greater than the limiting one.

LESSON MATERIAL

Physical quantities

7

Angle of incidence

α\alpha

The angle between the incident ray and the normal to the boundary.

Unit: radian · rad\mathrm{rad}

Reflection angle

β\beta

The angle between the reflected ray and the normal to the boundary.

Unit: radian · rad\mathrm{rad}

Angle of refraction

γ\gamma

The angle between the refracted ray and the normal to the boundary.

Unit: radian · rad\mathrm{rad}

Relative refractive index

nn

The ratio of the refractive indices of two media.

Unit: dimensionless quantity

Refractive index of the first medium

n1n_1

Optical characteristics of the first medium.

Unit: dimensionless quantity

Refractive index of the second medium

n2n_2

Optical characteristics of the second medium.

Unit: dimensionless quantity

Limit angle of total reflection

α0\alpha_0

The smallest angle of incidence at which total internal reflection begins.

Unit: radian · rad\mathrm{rad}

LESSON MATERIAL

Lesson formulas

3

Law of Reflection

α=β\alpha=\beta

The angle of reflection is equal to the angle of incidence.

Law of refraction

sin⁡αsin⁡γ=n=n2n1=v1v2=λ1λ2\frac{\sin\alpha}{\sin\gamma}=n=\frac{n_2}{n_1}=\frac{v_1}{v_2}=\frac{\lambda_1}{\lambda_2}

The ratio of the sines of angles is related to the refractive indices, velocities and wavelengths in the media.

Limit angle of total reflection

sin⁡α0=1n=n2n1\sin\alpha_0=\frac{1}{n}=\frac{n_2}{n_1}

The sine of the limiting angle is equal to the inverse relative refractive index.

Condition: Light comes from an optically denser medium to a less dense one.

DIRECTORY

Related formulas

Refractive indexn · dimensionless

PRACTICE

Tasks on the topic

Optics11 class · 12 problems