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\(A-150 \times\) microscope has an eyepiece whose focal length is \(4.4 \mathrm{~cm}\). If the distance between the lenses is \(20 \mathrm{~cm},\) find the focal length of the objective.

Short Answer

Expert verified
The focal length of the objective lens is approximately 0.76 cm.

Step by step solution

01

Understanding the Microscope Magnification Formula

To find the focal length of the objective lens in a compound microscope, we use the formula for total magnification: \( M = \frac{D}{f_o} \times \frac{25}{f_e} \), where \( M \) is the total magnification, \( D \) is the tube length (distance between lenses), \( f_o \) is the focal length of the objective lens, and \( f_e \) is the focal length of the eyepiece.
02

Assign Known Values

From the problem, we know that the total magnification \( M = 150 \), tube length \( D = 20 \text{ cm} \), and the focal length of the eyepiece \( f_e = 4.4 \text{ cm} \). We need to find \( f_o \), the focal length of the objective lens.
03

Rearrange the Microscope Formula

First, rearrange the formula to solve for \( f_o \):\[ f_o = \frac{D \times 25}{M \times f_e} \]
04

Substitute Values into the Formula

Now, substitute the known values into the rearranged formula:\[ f_o = \frac{20 \times 25}{150 \times 4.4} \]
05

Calculate the Focal Length of the Objective Lens

Perform the calculation:1. Compute the numerator: \( 20 \times 25 = 500 \).2. Compute the denominator: \( 150 \times 4.4 = 660 \).3. Divide the numerator by the denominator to find \( f_o \):\[ f_o = \frac{500}{660} \approx 0.7576 \text{ cm} \]
06

Round to Appropriate Significant Figures

Based on the precision of the provided values, the objective lens focal length should be expressed to 2 significant figures: \( f_o \approx 0.76 \text{ cm} \).

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Microscope Magnification
Microscope magnification is a key feature that defines how much larger an object appears under the microscope compared to its actual size. In a compound microscope, magnification is achieved through the combined power of two lenses: the objective lens and the eyepiece lens. The total magnification, often represented by the letter \( M \), is the product of the magnification of these two lenses.
For instance, if an objective lens magnifies 40 times and an eyepiece lens magnifies 10 times, the total magnification would be \( 40 \times 10 = 400 \) times. This makes small details visible, allowing us to observe specimens with great clarity and detail. Understanding magnification is crucial for anyone using a microscope for scientific and educational purposes.
When tackling problems related to microscopes, it's important to understand that the magnification can be influenced by the distances or lengths of the lenses which are expressed in the formula. Each lens has its own focal length which contributes to this magnifying capability.
Focal Length of Objective Lens
The objective lens is an essential part of a compound microscope, with its primary role being to magnify the image of the specimen. The focal length of the objective lens, denoted by \( f_o \), determines the degree of magnification that lens offers. A shorter focal length means higher magnification, as the lens is able to focus light from the specimen more effectively.
Usually, in a compound microscope, the objective lens has a short focal length compared to the eyepiece lens. This is why objective lenses are typically positioned close to the specimen being observed.
In many problems, such as finding the focal length, one needs to understand how the total magnification and the eyepiece's properties play into this calculation. Knowing your objective lens qualities can greatly influence your microscope's usability and results.
Eyepiece Focal Length
The eyepiece, also known as the ocular lens, is the part of the microscope that you look through. Its function is to further magnify the image created by the objective lens. The focal length of the eyepiece, represented by \( f_e \), is typically longer than that of the objective lens.
This focal length is critical because it impacts the degree to which the specimen is magnified. In the given exercise, where the eyepiece focal length is given as 4.4 cm, it shows how this value plays a part in calculating the total magnification. Generally, the longer the focal length of the eyepiece, the lower the magnification it provides.
When working with microscopes, understanding the eyepiece focal length helps you choose the right combination of lenses for the desired magnification. It's crucial for achieving the best possible view of the specimen.
Microscope Formula
The microscope formula is a mathematical representation aiding in the calculation of microscope magnification. This formula is invaluable for determining various components of a microscope's optical system. The general equation is given by:\[ M = \frac{D}{f_o} \times \frac{25}{f_e} \] where:
  • \( M \) is total magnification.
  • \( D \) is the distance between the lenses, also called the tube length.
  • \( f_o \) is the focal length of the objective lens.
  • \( f_e \) is the focal length of the eyepiece lens.
This formula stands as the backbone of understanding how these individual components work together to achieve magnification. The concept of calculating a lens's properties through such a formula enables students and professionals to make precise judgments in the field of microscopy. It helps align the different lenses to achieve a balanced and focused view, thereby enhancing our exploration of the microscopic world.

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Most popular questions from this chapter

A person is prescribed with contact lenses that have powers of \(-3.0 \mathrm{D}\). What type of lenses are these? What is the lenses' focal length?

The amount of light that reaches the film in a camera depends on the lens aperture (the effective area) as controlled by the diaphragm. The f-number is the ratio of the focal length of the lens to its effective diameter. For example, an \(f / 8\) setting means that the diameter of the aperture is one- eighth of the focal length of the lens. The lens setting is commonly referred to as the \(f\) -stop. (a) Determine how much light each of the following lens settings admits to the camera as compared with \(\mathrm{f} / 8\) : (1) \(\mathrm{f} / 3.2\) and \((2) \mathrm{f} / 16 .\) (b) The exposure time of a camera is controlled by the shutter speed. If a photographer correctly uses a lens setting of \(\mathrm{f} / 8\) with a film exposure time of \(1 / 60 \mathrm{~s}\), what exposure time should she use to get the same amount of light exposure if she sets the f-stop at \(f / 5.6 ?\)

An astronomical telescope has an objective and an eyepiece whose focal lengths are \(60 \mathrm{~cm}\) and \(15 \mathrm{~cm}\), respectively. What are the telescope's (a) magnifying power and (b) length?

A woman cannot see objects clearly when they are farther than \(12.5 \mathrm{~m}\) away. (a) Does she have (1) nearsightedness, (2) farsightedness, or (3) astigmatism? Explain. (b) Which type of lens will allow her to see distant objects clearly, and of what power should the lens be?

A telescope has an angular magnification of \(-50 \times\) and a barrel \(1.02 \mathrm{~m}\) long. What are the focal lengths of the objective and the eyepiece?

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