Ray diagrams for concave mirror

If an object is in front of a concave mirror that reflecting light, the concave mirror will form the image of the object. If the position of the object in front of the concave mirror is known, how to draw the image formation of the object? To clarify this, suppose an object is in front of a concave mirror as shown below.

Ray diagrams for concave mirror 1Orange line = concave mirror

Blue lines = the principal axis

Arrow (green) = object

R = center of the curvature of the concave mirror

f = focus of the concave mirror

Images of objects can be produced by drawing all the beams of light passing through objects, but this is less practical because there will be many lines representing light beams. For simplicity, just a few beams of light are chosen to represent all the beams of light passing through the object. Since this event involves the reflection of light, the law of reflection of light must be obeyed when drawing the image formation.

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Ray diagrams

1 :

Ray diagrams for concave mirror 2Ray 1 or light beam 1 that comes into the concave mirror is drawn parallel to the principal axis and touches the upper end of the object, then reflected by a concave mirror where the reflected light beam must pass through the focal point (f). The incoming rays and reflected rays that are drawn must fulfill the law of reflection of light, where the angle of incidence equals the angle of reflection.

2 :

Ray diagrams for concave mirror 3Ray 2 or light beam 2 that comes to the concave mirror is drawn as having to pass through the focal point and touch the upper end of the object then reflected by a concave mirror where the reflected light beam must be parallel to the principal axis. The incoming rays and reflected rays that are drawn must fulfill the law of reflection of light, where the angle of incidence equals the angle of reflection.

3 :

Ray diagrams for concave mirror 4Ray 3 or the light beam 3 that comes towards the concave mirror are drawn must pass through the center point of the mirror curvature (R) and touch the upper end of the object, then reflected by a concave mirror where the reflected ray coincides with the incident ray. The incoming rays and reflected rays that are described must fulfill the law of reflection of light, where the angle of incidence equals the angle of reflection. If the light beam comes to coincide with the reflected beam, the beam of light must be perpendicular (90o) with the concave mirror surface that passes through the beam of light so that the angle of incidence of 90o is equal to the angle of reflection of 90o.

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Image formation (two rays)

The image formation for an object can be drawn using only two rays, as shown below. If using two rays, there are three possible images formation.

Ray 1 and ray 2

Ray diagrams for concave mirror 5

Ray 1 and ray 3

Ray diagrams for concave mirror 6

Ray 2 and ray 3

Ray diagrams for concave mirror 7

The image formation for an object drawn using only two rays needs to be adjusted by the distance of the object from the concave mirror. If the distance of the object from the concave mirror as in the figure above, there are three ways to draw an image formation using only two rays. If the distance of the object from the concave mirror is different from the figure above, for example, the object is between the focal point and the center of curvature, then there are only two ways to draw.

If you draw an image formation by a concave mirror, you can choose one method and not have to use two or three ways.

Image formation (three rays)

The image formation for an object can be drawn using three rays, as shown in figure below.

Ray diagrams for concave mirror 8

If the distance of the object from the concave mirror is not like the one above, for example, the object is between the concave mirror and the focal point, or the object is between the focal point and the center of curvature of the concave mirror, then the image formation for an object can be drawn using three ways as shown in the figure above. There can only be two ways to draw the image formation. Please observe the example of the image formation by a concave mirror, where the distance of objects from concave mirrors varies, on the topic of the image formation of the concave mirror.

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