4. The Object placed in denser medium and image formed is virtual
Answers
Answer:
Refraction: The bending of light when it travels from one medium to another is known as Refraction. Normally, when a light travels from a denser medium to a rarer medium, the light changes its direction and moves away from the normal and while travelling from lighter medium to a denser medium it shifts its direction and moves closer to the normal.
Cause of Refraction: The main reason why the light changes its direction while travelling from one medium to another depends on the factor known as Refractive Index of the Material. As the refractive index is different for different medium, thus the speed of the light changes while travelling through them, resulting in the change of direction.
Optically Rarer and Denser Medium: A medium is said to be optically denser, when the speed of the light is more in that medium. Similarly when the speed of a light is less in a medium, it is said to be an optically rarer medium.
Laws of Refraction
(a) The incident ray, the refracted ray and the normal lies in the same plane.
(b) The sine of both the angles, that is, the angle of incidence to the angle of refraction is constant for the two media, the light is travelling through.
The refractive index of a medium can also be understood as the speed of the light in first medium through which the light is travelling to the speed of the light in the second medium, where the light gets refracted. The refractive index of the air is 1.0003.
Refraction by Spherical Lenses
Lens: A lens consists of two transparent glass surfaces on the same side. The portion which is curved inwards is known as Concave Surface and the portion which is bulged outwards is known as Convex Surface. These two together form a lens.
Refraction by Spherical Lenses
Optical Centre and Principal Axis of a Lens
The central point of a lens is known as Optical centre of Lens. The line passing through the optical centre of the lens is known as Principal Axis. The principal axis is perpendicular to the both concave and convex surface of the lens.
Principal Focus and Focal Length of a Convex Lens: A parallel beam of lights after travelling parallel to the principal axis and passing through the convex surface, converges at a point on the principal axis. This point is known as the Principal Focus. Since a lens has two convex surfaces, thus a lens is said to have two foci. Both the foci of a lens are at equal distances from the optical centre. The word foci is the plural form of Focus .
Principal Focus and Focal length of a convex lens
Principal focus and focal length of a Concave Lens: Principal focus is defined as the point on principal axis from which the light travelling parallel to the principal axis, appears to diverge after passing through the concave lens.
Principal focus and focal length of a Concave Lens
The distance between optical centre and principal focus is known as Focal Length.
Image formation by Lens
In order to determine the nature, position and size of an image formed by the spherical lenses, we need to know the basic rule of the image formation:
The basic rule are as follows:
A ray of light travelling parallel to the principal axis from the object after passing through the convex lens gets refracted and converges at the principal focus located on the other side of the lens. In case of concave lens, the ray of light after passing through the lens, diverges from the principal focus.
In convex lens a ray of light after travelling through the principal focus, will travel parallel to the principal axis. In case of concave lens, the rays of light from the object appear to meet at the principal focus of the lens and then travels parallel to the principal axis.
When a ray of light from the object passes through the optical centre in both concave and convex lens, it will travel through straight without getting deviated.