Holmarc's Liquid Lens Apparatus (Model No: HO-ED-O-01) is designed for the determination of refractive index of a given liquid. With its new design and features, one can easily understand the principles and practices involved.
The theory behind the liquid lens is based on the properties of one or more liquids to create magnifications within a small amount of space. The focus of a liquid lens is controlled by the surface of the liquid. The surface profile of the liquid determines the focal length of liquid lens system and how the liquid lens focuses light rays.
This apparatus consists of graduated vertical post with rigid base along with a light source and required optics. A pointer illuminated with LED is mounted on the vertical post. The illumination helps to conduct the experiment even in low light conditions. The pointer is free to move along the axis of the vertical post and can be easily clamped at desired positions.
The liquid lens arrangement is kept on a rigid base. The pointer is raised or lowered till the tip of its image coincides with the tip of the pointer without parallax. The distances of the pointer from the top and bottom of the lens are measured. The experimental setup includes three convex lenses of different focal lengths and a plane mirror. A petri dish carrying liquid is also included in this setup.
The focal length is the distance between the centre of the lens and the image.
Liquid lens is Plano-concave type. It is formed as a lens in between convex lens & mirror.
Let f1 be the focal length of the convex lens. If 'F' be the focal length of the combination of the convex and liquid lens, then the focal length of the liquid lens,
f2 = Ff1 / f1 - F
The refractive index of liquid,
n = 1 + R / f2
R is the radius of curvature.
Fig. Lens floated in mercury
Fig. Mechanical Drawing