The use of lenses

Recall what type of lens or lenses the telescope Galileo used to observe objects in the night sky had.

• A single concave lens to gather light

• A single convex lens to focus light

• A convex lens to gather light and a concave lens to focus it

• A concave lens to gather light and a convex lens to focus it

• I'm not sure

Recall the type of lens or lenses the first microscopes, designed by the Janssens in the late 1500s, used.

• A single convex lens

• A single concave lens

• Two convex lenses

• Two concave lenses

• I'm not sure

The Janssens' microscope could magnify objects by 9 times. Calculate how long it would make a 2 mm-long ant appear.

• 9 mm

• 11 mm

• 1.8 cm

• 2 cm

• I'm not sure

The function of the ocular lens in the modern microscope is to magnify the image created by the light-gathering objective lenses. From this information, what can you infer about the ocular lens. Hint: Check the diagram 3 minutes into the video.

• concave, since it diverges light

• concave, since it converges light

• convex, since it diverges light

• convex, since it converges light

• I'm not sure

In your own words, explain why telescopes and microscopes have been so important in advancing scientific knowledge. Give an example of a discovery that depended on them.

Answer explanation

Telescopes and microscopes have revolutionized scientific knowledge by making visible what was once invisible.

Telescopes have revealed very large, distant objects such as the Moon, the planets, stars and galaxies. These objects were (and manystill are) too distant for our eyes to see in any detail.

Microscopes have revealed very small objects that might have been under our noses all along. These objects are too small to see with thenaked eye. Examples of important discoveries (from the video) include living cells, bacteria and even atoms.

The polymer droplets described in the Introduction can turn your smartphone into a microscope. They have a magnification of 160x. Imagine you use this microscope to view a 5-cent coin, which has a diameter of 19.4 mm. Describe how big the coin would appear.

Answer explanation

19.4 mm x 160 = 3,104 mm = 3.1 m

So the coin would appear to be about twice the height of an average human being.

In the photo above, the images of the scientist's head in the polymer droplets appear upside down. Use your knowledge of lenses to explain why.

Answer explanation

The polymer droplets are convex lenses because they are thicker in the middle and thinner at the edges.

Convex lenses produce upside-down images when the object being viewed is more than two focal lengths from the lens. So thescientist's head must be more than two focal lengths from the polymer droplets.

Smaller polymer droplets allow higher magnifications. Use your knowledge of lenses to explain why.

Answer explanation

Smaller polymer droplets are more curved than larger droplets, in the same way that a small sphere is more curved than a large sphere.

Convex lenses that are more curved cause light rays to converge more because the light rays hit the surface at a higher angle. This meansthat the image they produce for an observer is larger. In other words, they have higher magnification.

Every solution to a problem has advantages and limitations. Identify some of these for the use of the smartphone microscope and the origami microscope to diagnose malaria in the developing world.

Answer explanation

Smartphone microscope

Advantages: Very cheap.

Easy to carry and use in remote locations. Images can be sent away for analysis.

Disadvantages: Smartphone access may be limited in developing countries.

Smartphones are more likely to break and would need protective cases.

Origami microscope

Advantages: Very cheap.

Easy to carry and use in remote locations. Durable, so not likely to break.

As powerful as many research microscopes. Doesn't need a power supply and lasts up to 50 hours.

Disadvantages: Images cannot be captured digitally and then sent away for analysis.