Physics

Light Reflection Issues


Fundamentals

1. In the scheme below, O is the observer and F It is a point source of light.

Using the laws of reflection, represent the ray of light, the angle of incidence and the image point. F '.

According to the 1st law of reflection, the incident radius, the reflected radius and the normal line to the mirror surface must belong to the same plane, ie the radii and angles are represented in the given scheme in actual size.

According to the 2nd law of reflection, the incidence and reflection angles must be equal. Therefore, there is only one possible point of incidence.

This radius can be plotted by using the image point F ', which is located by the flat mirror symmetry. The reflected radius is the link between the image point and the observer.

We can still calculate the angle value α, considering each division as a unit of measure:

2. In the figure, the flat mirrors E1 and E2 are perpendicular. A light beam strikes mirror E1 forming 30 ° with the reflective surface as shown:

Represent the light's trajectory until it leaves the mirror system.

Using the two laws of reflection, we can find the angles of each ray with the mirror.

The angle of incidence on mirror E2 is calculated using the property of triangles, of which the sum of all internal angles must be 180 °.

Flat mirrors

1. A vertical flat mirror combines the image of a standing observer 1 m from the mirror. Moving the mirror 2 m away from where you were, how far is the first from the second image?

The displacement of the image is twice the displacement of the mirror itself, ie:

Another way to get to this value is by the equation:

Where d is the distance from the object to the mirror in each case:

2. In a car, the driver sees the image of a roadside tree in the rearview mirror. Knowing that the apparent travel speed of the tree in the mirror is 120 km / h, how fast is the car moving?

The image offset is twice the mirror offset, so: