2.2 Size of Specimens

This section focuses on understanding and applying the concept of magnification when working with specimens in biology. It introduces the formula used to calculate magnification and its practical applications.

Magnification

Magnification is the increase in the apparent size of an object when viewed through a magnifying lens or microscope. It allows us to observe details that are too small to see with the naked eye.

Formula for Magnification

The magnification of a lens or instrument is calculated using the following formula:

$$ \text{Magnification} = \frac{\text{Image Size}}{\text{Actual Size}} $$

Where:

• Magnification is a number that indicates how much larger the image appears compared to the actual object.
• Image Size is the size of the image seen through the lens.
• Actual Size is the real size of the specimen.

Using the Formula

The formula can be rearranged to find either the image size or the actual size if the other two values are known.

1. To find the Image Size: $$ \text{Image Size} = \text{Magnification} \times \text{Actual Size} $$
2. To find the Actual Size: $$ \text{Actual Size} = \frac{\text{Image Size}}{\text{Magnification}} $$

Example

Suppose you use a microscope with a magnification of 400x to view a bacterium. If the actual size of the bacterium is 2 micrometers (µm), what is the image size?

Using the formula: Image Size = Magnification × Actual Size

Image Size = 400 × 2 µm = 800 µm

Therefore, the image of the bacterium will appear to be 800 micrometers in size.

Table of Common Magnifications

Instrument	Magnification
Naked Eye	1x
Hand Lens	2x - 10x
Microscope (Low Power)	40x
Microscope (High Power)	400x
Microscope (Very High Power)	1000x

Understanding the size of specimens and how magnification works is crucial for accurate observation and measurement in biology. It allows us to study microscopic organisms and structures effectively.