Before we begin to understand the two types of images, let us first understand the image concept. In optics, an image can be defined as the collection of multiple focus points of light rays incident from an object.
In this article, we’ll understand the concept and distinguish between Real Image and Virtual Image with examples, but there are some terms that we should be aware of.
Some basic terms in optics
- Object- It is a thing that is viewed.
- Screen- The place where the image is formed.
- Focus point- it is also known as image point. It is the point where light rays emanating from a point on the object intersect. A well-converged image is said to be in focus if the light from the object converges as much as possible, and it is said to be out of focus if the light is not well converged.
- Focal length- The focal length is the distance between focus and the mirror or lens on the principal plane.
- Centre of curvature- It is a point that lies on the centre of the sphere from which the mirror is cut.
- Diverging rays- The rays that move apart in different directions. They never intersect.
- Converging rays- The rays that travel towards each other. They eventually intersect at the focus point.
- Incident ray- On the surface of the mirror, It is the ray of light that falls.
- Reflected ray– In this also, it is a ray of light which is reflected by the mirror.
- Normal line- It is an imaginary line perpendicular to the surface of the mirror. It is drawn from the point on the mirror where the reflected ray strikes. It divides the angle between the reflected ray and the incident ray into two equal angles.
- The angle of incidence- This angle is between the normal and incident ray. It is denoted by theta i.
- The angle of reflection- The angle between the normal and the reflected ray. It is denoted by theta r.
- Image location- In this, it is the location in space where it seems to have all observers as though the reflected light is coming from.
Laws of reflection:
- Rays shooting from the point of incidence reflected rays, and normal rays lie in the same plane.
- Another law of reflection is that the angle of incidence is always equal to the angle of reflection.
A real image is the collection of focus points made by converging rays. To put it simply, the image formed when the rays of light after reflection or refraction converge at a point before the screen is known as a real image.
Real images are formed with the help of a Convex lens and concave mirror.
Examples of real images
The image formed on the camera’s photographic film.
- Let’s try to understand with an example how the real image is formed:
- Let’s keep a lighted candle in front of a concave mirror. The Light rays emanate, and some light rays bounce off the candle and extend in all directions.
- These are the incident rays, many of which will be incident on the mirror. Every incident ray follows the same law of reflection as it reflects off the mirror.
- As we can see in the diagram below, the reflected rays emerge from the mirror at different locations and converge at a focus point(s) in front of the mirror to form an image.
- We can see the image of a candle in the mirror as the reflected light travels to our eyes.
- The image thus formed is called the real image.
- It is inverted and formed on the same side as the object.
- The size of the image formed by the concave mirror varies depending upon the location of the object.
- In this case, the object is located beyond the centre of curvature, resulting in the image’s reduced size.
Hence, the size of the image formed is smaller than the size of the object. When the object is located at the centre of curvature, the size of the image is the same as that of the object.
When the object is located between the centre of curvature and the focus point, the image is formed beyond the centre of curvature. And the size of the resulting image is larger than the size of the object.
Properties of a real image:
- It is formed when the light rays actually intersect.
- A real image is always inverted with respect to the object.
- A real can be obtained on a screen.
- It is formed on the same side of the object.
The virtual image is the collection of focus points made by extensions of diverging rays. In simple words, a virtual image is formed when the actual diverging light rays appear to meet at focus points behind the lens or mirror.
To form a virtual image the object which is the source of light and the screen where the image is formed must lie on the same plane.
A plain mirror forms a virtual image. Concave mirrors sometimes form a virtual image.
Let’s try understanding it with an example:
- Suppose you are standing in front of a plane mirror.
- The Light rays fall on our body and then bounce off and extend in all directions, many of which will fall on the mirror. These rays are called incident rays.
- Each incident ray follows the law of reflection as it reflects off the mirror.
- So as we can see in the diagram below, the reflected rays emerge from the mirror at different locations. Unlike in the case of a concave mirror, here they’re getting diverged.
- However, we know that the reflected rays have to meet at a focus point(s) to form an image, so they must meet somewhere.
- To achieve this, as shown in the diagram below, we’ll extend the reflected rays in the opposite direction such that they converge.
- Then the point(s) where they converge is called the focus point, where the image is formed.
We can see the image of ourselves in the mirror as the reflected light travels to our eyes. The size of the image formed is the same as the size of the object. It is erect and laterally inverted. The distance of the image obtained is seen as the distance between the object and the mirror.
Properties of a virtual image:
- It is formed by the imaginary intersection of the light rays.
- A virtual image is always erect with respect to the object.
- A virtual image cannot be achieved on a screen. The image appears to be formed behind the screen.
- It is formed on the side opposite of the object.
Therefore, we hope you now have a clear idea regarding the concept of real and virtual images and their properties.