Why does water magnify objects

A ruled scale at the back enabled the experimenter to read the size of the adjusted square. Three chin-rests were used, two in front of the tanks and one in front of the adjustable square. The chin-rests were placed at a suitable height typically 30 cm to enable the observer to look at the target square and the adjustable square from a horizontal viewpoint.

The chin-rests were located so that the observer's eyes were The adjustable square was located further away than the furthest target, rather than nearer as in most experiments , because of limits on the size of the tanks and on visual accommodation at very close distances. A swivel chair with adjustable height was provided to enable the observer to turn quickly between the observation tanks and the adjustable square.

The experiment was carried out in a well-lit room 4 x watt fluorescent tubes , and took approximately 30 minutes to complete for each observer. The observers were seated in front of the apparatus and were provided with a written description of the details of the experimental procedure. They were asked to make both size and distance judgements of the various target presentations.

They were instructed to keep their head as still as possible and their chin against the chin-rest whilst making judgements. The targets were suspended singly at one of three distances 15, 20, and 25 cm along the support rods. Each of the three targets 2. Semi-random presentation orders were used. For each target presentation, the observer was asked to make three judgements. Binocular vision was used for the first two judgements distance and linear size , and monocular vision for the third angular size.

The observer was required to move the marker hidden beneath the stand until it was felt to be directly underneath the target square which was constantly visible in the tank. The movement was always started from the front of the tank, but the observer was allowed to overshoot and undershoot till satisfied with the match. The observer was required to vary the size of the adjustable square initially set at 0 until it appeared to be the same physical linear size as the target square; that is, both squares would measure the same with a ruler.

Only the last measure was used in the data analysis. The number of visual size comparisons was limited in order to capture first impressions, and to standardise the time taken by different observers.

The observer was required to vary the size of the adjustable square until it appeared to subtend the same angular size as the target square; that is, both squares would be the same size in a photograph.

The procedure was the same as for linear size judgements, except that monocular vision was used in order to assist the perception of angular rather than linear size. The observer placed the preferred eye in front of the viewing hole of the tank, and used the same eye for the adjustable square.

Ten observers used the left eye and 10 the right. After the 18 trials were completed, the observers were asked to fill in a brief questionnaire regarding their awareness and understanding of the optical effects of looking into water: the answers showed that few observers had much awareness or made any conscious correction for supposed effects.

The purpose of the experiment was then explained in more detail, and any questions were answered. The mean settings for perceived distance within the tank are shown for air and water in Figure 4.

The optical distance of the targets in water was calculated as 0. The settings in air correspond very closely to the physical distance, and those in water to the optical distance. The mean linear and angular size matches in air and water are shown in Figure 5 as a function of target size.

The angular means were slightly smaller than the linear means, but this trend was the opposite of the predicted direction and was not significant on a 2-tailed test.

The same data are shown in Figure 6 as a function of target distance. The true linear size required for an angular match in both air and water is also indicated in Figure 5 , and is very much greater than the obtained values. The true angles subtended at different distances by the mean target size 2. The adjustable square at a viewing distance of Classical SDI did not hold precisely in air: the targets were judged to be close to their physical distance, but slightly smaller than their linear size.

Classical SDI held better in water: the targets were judged to be close both to their optical distance and to their true linear size. The water judgements were thus not a simple optical transformation of the air judgements.

The relationship is illustrated in Figure 7 , where the ratio of judged to true linear size is plotted against the ratio of judged to true total viewing distance in air or to the equivalent optical distance in water, plus The air and water ratios are clearly not part of the same distribution, and the water ratios are closer to SDI than the air ratios. It is clear that perceptual SDI did not hold at all in this experiment, and cannot be used to explain discrepancies in classical SDI.

The matched angular sizes scarcely differed from the matched linear sizes, and were much smaller than required for a true angular match Figure 6. They were also much smaller than required for consistency with perceptual SDI. For example, the mean linear size judgement in air was 2. Similar arguments apply in water: the mean linear size judgement was 2.

The discrepancy from classical SDI can also be seen by comparing the water and air judgements with each other, and disregarding the physical values. The linear size ratio was 1. The angular size ratio was 1. The distance settings were very close to the true distance in air and the optical distance in water. This is to be expected for hidden tactile reaching at close range, with binocular vision for the target.

The errors found in other experiments usually arise from the use of numerical estimates or further viewing distances.

The size settings in air were inconsistent with classical SDI in that the linear size judgements were too small in relation to the slight underestimation of distance. Under-size matches may have occurred because the adjustable and standard targets differed in some physical aspect that made the adjustable target appear relatively large. One possible factor is luminance contrast: the black adjustable square was surrounded by bright white plastic, whereas the standard targets were displayed as isolated black squares against distant backgrounds of dull white cardboard.

Another possible factor is size contrast: the adjustable target was presented within a white surround 20 x 20 cm at the same distance as the target No clear predictions can be made for either contrast effect.

Other reasons for under-size matches might be procedural rather than visual. Starting position may have had an effect. The observers always adjusted the variable target upwards from zero at the start; but any bias would be small, because they typically made several adjustments before settling on a match.

Another procedural bias is the "error of the standard" - the different values obtained depending on which of two targets is adjusted and which is the standard see discussion by Kaufman and Rock However, there is usually a tendency to overestimate the standard, which is the opposite of our result.

This error is often confounded with the distance of the adjustable target, which is normally closer than the standard. Our experiment was unusual in reversing the distances, and this may be a very important factor. Measurements of perceived angular size show an increase with viewing distance , and this could explain the relatively large perceived angular size or relatively small settings of the distant adjustable target.

The discrepancy between these and previous findings may be entirely due to the reversal of the usual relative distances of the standard and adjustable targets. Whatever the reason for the slight underestimation of the linear size of the targets, perceptual SDI might have been upheld if the angular judgements were proportionately smaller than the true angle.

In fact, they were disproportionately smaller, being slightly smaller than the linear matches instead of larger. The observers appear to have had great difficulty in making angular matches, despite the use of only one eye. We have to conclude that angular size cannot be consciously perceived at such close distances, or that it cannot be measured by the method we employed The linear size judgements in water were greater than the air judgements by a factor of 1. These results differ from the experiments reported in the introduction Table 1 , where linear size in water was overestimated less than was the optical distance.

However, distance judgements were obtained for only four of these experiments, and the findings may vary with the method of measurement.

Alternatively, the difference may be due to the very short viewing distances used in the present experiment. The ratios of water to air judgements in this experiment give little support to either classical or perceptual SDI. Classical SDI was not supported because the linear size ratios were larger than the negligible overestimation of the optical distance.

It could be argued that perceptual SDI was supported because the ratio of water to air angular judgements was similar to that for linear judgements. However, this argument is not convincing because the linear and angular judgements were almost identical, and the angular judgements were much smaller than the required values. The likelihood of establishing the truth of perceptual SDI remains small unless a satisfactory measure of perceived angular size can be devised.

Attempts to measure SDI rest on the assumption that there exists a unitary perceptual spatial metric that obeys the rules of geometry. The only problem, then, is how to obtain accurate and commensurate measures of perceived linear size, angular size and distance.

On this view, the breakdown of SDI results from flawed measurement procedures. The image is also magnified , or enlarged. As magnification increases, any distortions are alsoexaggerated. The water drop works as a magnifyingglass by refracting light. A magnifying glass is asingle convex curved outward lens that is used toproduce a larger image of an object. Similarly, why do lemons look bigger in water?

A lemon in a glass of water appear bigger than its actual size is due to refraction of light". Reason: Light is refracted as it passes from water into air. Here, Tumbler with water acts as convex lens which curvesoutward in the middle and can focus light rays to magnifyobject.

Because light refracts when it crosses the water -air boundary - it does not travel in a straightline. Snell's law is the math behind this phenomenon - basically, water has a higher index of refraction than air, so theangle of the light with respect to the boundary is larger onthe air side than the water side. Magnifying glasses make objects appear larger because their convex lenses convex means curved outward refractor bend light rays, so that they converge or cometogether.

Asked by: Inar Moos medical health eye and vision conditions How does water magnify? Last Updated: 6th July, The reason that objects sometimes appear magnified when under water has to do with thecurvature of the water surface. The curved surface, unlike aflat surface, bends the light as it comes out from the water , and causes this magnification effect.

Marce Dubinsky Professional. Why do pencils look bigger in water? Because the light can 't travel as quickly in the water as it does in the air, the light bends aroundthe pencil , causing it to look bent in the water.

Basically, the light refraction gives the pencil a slight magnifying effect, which makes the angle appear bigger than it actually is , causing the pencil to look crooked. Amanat Palermo Professional.

Do fish look bigger underwater? Why Fish Look Bigger Underwater. Aissata Muhlenhardt Professional. How does water act like a mirror? Specifically to your question, the surface of water is able to make a reflected image, because gravity andsurface tension force it into an approximately flat plane, likea mirror , with which images can be formed. This is because the mirror acts as an open end. Angelia Shaban Explainer. What is a water lens? Definition of water lens.

Maysaa Haindl Explainer. What is water drop lens? Amazing Water Drop Lenses. Bruno Berge, physicistand inventor, has created liquid optical lens by a processknown as electro-wetting.

In this process, a water drop isdeposited on a metal substrate and covered by a thin insulatinglayer. In this practical, students experiment with magnification by placing water drops on top of lettering. Recently, you have managed to trade one of your paintings for a jeweled bracelet. When you return to your workshop you place the bracelet in a box with some drachma. When you look at the bracelet again, in one of the gems you can see an image of letters on the coins.

However, something unexpected has happened to the letters. Like all good ancient Greek science-artists, you decide to investigate further…. It may be easier to use a straw to place a few grains of salt or sugar onto the microscope slide or ruler. To do this, dip the end of the straw into the salt or sugar and scrape along the salt or sugar to get a few grains into it. Then carefully place the end of the straw onto the slide or ruler and tip them very gently onto it. Surface tension is the name for the attractive forces between the particles or molecules in water, which make the water drops become ball shaped or spherical.

This is because the molecules inside a drop are attracted to each other in all directions, from the surface inward. The outward curvature of the water droplet is similar to the curved surface of a lens. The more outwardly curved the lens, the stronger its magnification. This is because it is bending or refracting more light in a shorter space. This type of outwardly curving lens is called a convex lens. A convex lens bends the light rays to focus on a point in space somewhere beyond the lens as you can see in the diagram below:.

By moving the lens toward and away from the object, you can adjust where the point of magnification strikes your eye. When light strikes your eye, the cornea and lens project it onto your retina, as shown in the diagram below. You should find the water drop magnifies by a factor of 4 - 5.

The smaller the droplet the more the magnification, but it is also harder to look through and focus. This was the principle behind the early microscopes, such as that used by the 17th century Dutch trader and scientist Anton van Leeuwenhoek He perfected these early microscopes by using carefully prepared glass beads, similar in shape to your water droplet.

Although difficult to use, these microscopes were powerful, able to magnify up to x. This topic could start with a group discussion about magnifying glasses during which the teachers introduce the following ideas especially the words in bold.

Small things can be magnified to appear larger than they really are. This can be done using a magnifying glass , lens or a combination of lenses in a microscope. A water droplet can act as a simple lens and magnify an object. Pupils will make their own magnifiers out of a drop of water and learn how a magnifier works by exploring some properties of water, such as its ability to bend or refract rays of light , and form spherical droplets under surface tension. All ages can take part in this activity since the aim is to gain some understanding of the thinking of the scientist when investigating artefacts in close detail.

It links with:. Always be careful when handling glass and sharp objects. You can get a magnification using a clear transparent plastic ruler.

It might also be prudent to remind pupils they should never look directly at the Sun with or without a lens. It might be useful to have some petroleum jelly available so the pupils can create a circle of jelly and place the water drop inside the circle. This is because sometimes the slide still has soap on it and this causes the water droplet to spread out and wet the glass surface rather than forming a spherical drop.