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Determine Magnification



Galileo’s first telescope magnified an object three times its size. He determined this fact by measuring the size of the object by the use of his eye alone, and then measuring its size again as it appeared through his telescope. Over the years, Galileo refined his telescopic lenses to the point where they magnified an object 30 times its original size.

MATERIALS
Ball or other objects for measuring
Metric ruler
Toy telescope, binoculars, or magnifying glass

Place the ball on a table. Stand a short distance away and look at it through the toy telescope. Hold the telescope in one hand and the ruler in the other. Position the ruler vertically next to the end of the telescope so that the ruler can be viewed in the telescope. The beginning end of the ruler should be at the top of the view of the ball. You will probably not be able to see the markings on the ruler, but place a finger across the ruler at the bottom of the ball. Put the telescope down and look where your finger is on the ruler. How big is the ball while looking through the telescope?

Now look at the ball without the aid of the telescope. Hold the ruler up at the same distance from your eyes as you previously did. The beginning end of the ruler should be at the top of the view of the ball. Place your finger across the ruler at the bottom of the ball. How big is the ball?

Compare your measurements. If the ball measured 3 centimeters with the telescope and 1 centimeter without the telescope, then the toy telescope magnifies an object 3 times its size. If the ball measured 2 centimeters with the telescope and 1 centimeter without it, the telescope magnifies an object 2 times its size. What is the magnification power of your toy telescope?

If using binoculars, only determine the magnification by looking through one lens at a time. You can also experiment with a magnifying glass by examining a small object up close. Place the ruler on top of the lens of the glass. What size is the object when it is magnified? Now measure the size of the actual object. Compare the measurements. What is the magnification power of your magnifying glass?