Physics

# Why does the focal length of a lens increase when it is put in water?

###### Wiki User

Light changes direction when it goes from one medium to another for two reasons. One is because it is a wave and other is because the light travels different speeds in the two mediums.

Light travels the speed c in vacuum and it travels the slower speed 3/4c in water and even the slower speed 2/3c in glass.

When the lens is in air the difference in speed is 2/3c versus c. When it is in water the difference in speed is 2/3c versus 3/4c. The difference in speed is smaller when it is in water and so the light bends less. The light bending less corresponds to a longer focal length.

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## Related Questions

### Which of the two has a greater power a lens of short focal length or a lens of large focal length?

A lens of short focal length has a greater power (than a lens of large focal length)

### How focal length of a lens change when apparatus immersed in water?

Yes , because when lens is deeped in water its R.I changes &amp; hence focal length is increased

### What is the focal length of a lens?

The focal length of a lens refers to the distance from the centre of the lens to the principal foci.

### Whats the focal length of a lens?

The focal length of a lens is the distance from the principal foci to the center of the lens.

### How do you find the new focal length when the lence is put in to the water?

to find the new focal length when the lens is put into water it becomes the 4 times the focal length in air.

### What will happen to the focal length of a lens if it is cut into half vertically?

When the lens is cut vertically then the focal length of the lens will increase.the focal length will become approx double.

### Which lens has a greater power convex lens of focal length 10 cm or a convex lens of focal length 20cm?

Power is inversely related to the focal length. So convex lens of focal length 20 cm has less power compared to that having focal length 10 cm

### When does lens convexity increase?

when the degree of convergence of a convex lens placed in air increases, we say its convexity has increased. as the power of a lens is the measure of degree of its convergence or divergence, we can increase the convexity of a lens increasing its powerthis is further achieved by decreasing its focal length.as focal length is inversly proportional to the refractive index of lens we have to decrease in order to increase its convexity.

### If a telescope has an objective lens of 3 inches what is the focal length?

The size (diameter) of a lens does not determine its focal length. The amount of curvature of the lens does. Citing a diameter for a lens doesn't help us find the focal length. Lenses are ground to specifications that allow short or long focal length. The more curved the lens, the shorter the focal length. You can see this if we specify a given curvature and then start to "flatten" the lens. The focal length will get longer and longer as the lens is flattened. When the lens is flat (has to curvature) the lense has an infinite focal length, just like a piece of flat glass.

### What is the focal length of a convex lens?

The distance from the centre of the lens to the focal point.

### Explain how the focal length of a convex lens changes as the sides of the lens become less curved?

The focal length of a lens is the distance from the center of the lens to the point at which it focuses light rays. The bigger the focal length, the more powerful the lens. ChaCha!

### Which lens in a refracting telescope has a shorter focal length?

The eyepiece will have a shorter focal length than the objective lens has.

### How does change in the thickness of lens change the focal length of lens?

Not at all. The focal length is determined by the curvature of the surfaces.

### Does the focal length of a spherical mirror or lens change when placed under water?

i do not think so because a mirror an a lens is two same things except that mirrors can reflect the water and the lens may refract or bend the water so that can change the focal length between the mirror and the lens

### How does thickness of convex lens affect focal length?

The thicker the lens is, the shorter the focal length will be, and the bigger the image produced will be.

### What is the focal length formulae?

For a lens ... 1/image distance + 1/object distance = 1/focal length of the lens

### Will the focal length of a lens change when put in water?

A careful reading of the question raises the uncomfortable suspicion that it might be very difficult to put the focal length in water. However, it's quite possible to put the lens itself in water. When that's done, it's quite likely that the lens's focal length has changed. The refractive indexes of both materials ... the substance of which the lens is made and the medium around it ... are both involved in determining its focal length.

### Difference between focal point and focal length?

The focal point is the point where light converges after it passes through a concave lens. The focal length is the distance of the focal point to the lens. Same for a convex lens, except that the focal point is the imaginary point from where light deflected from lens seems to have emerged.

### How can you calculate the focal length of a lens?

Basically, the focal length is the distance from the center of the lens to the focal point or the principal foci.The calculations will depend on the curvature of the lens, the lens thickness, and the refractive index of the material that the lens was made out of. Wikipedia has a great description of lens focal length, see the link to this article in the related link section below.

### Why does the focal length of a mirror not depend on the mirror material when the focal length of a lens does depend on the lens material?

The focal length for a mirror is determined by the law of reflection from the mirror surface. This law is not governed by the material that the mirror is made by. This means that the focal length depends only on the radius and curvature. Conversely, the focal length of a lens depends on the indices of refraction of the lens meterial and the surrounding medium.

### Will focal length of a convex lens change when immersed in water?

yes. By lens formula the relative refractive index will change. hence the focal lenght increases.

### Will the focal lengths of concave and convex lens change in water?

No. Because the medium remains the same and hence the lens' or mirrors' focal length doesnt change

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