Chapter 26: Problem 117
A converging lens \((f=12.0 \mathrm{cm})\) is held \(8.00 \mathrm{cm}\) in front of a newspaper that has a print size with a height of \(2.00 \mathrm{mm}\). Find (a) the image distance (in \(\mathrm{cm}\) ) and (b) the height (in \(\mathrm{mm}\) ) of the magnified print.
Short Answer
Expert verified
Image distance is -24.0 cm (virtual), and the height of the print is 6.00 mm.
Step by step solution
01
Identify Given Values
The problem provides us with the following values: the focal length of the lens \( f = 12.0 \ \mathrm{cm} \), the object distance \( d_o = 8.00 \ \mathrm{cm} \), and the height of the object (print size) \( h_o = 2.00 \ \mathrm{mm} \).
02
Use the Lens Formula
The lens formula is \( \frac{1}{f} = \frac{1}{d_o} + \frac{1}{d_i} \). We will rearrange this formula to solve for the image distance \( d_i \).
03
Solve for Image Distance
Rearrange the lens formula to \( \frac{1}{d_i} = \frac{1}{f} - \frac{1}{d_o} \), and substitute the known values: \( \frac{1}{d_i} = \frac{1}{12.0} - \frac{1}{8.00} \). Calculate this to find \( \frac{1}{d_i} = \frac{1}{12.0} - \frac{1}{8.00} = \frac{2}{24.0} - \frac{3}{24.0} = -\frac{1}{24.0} \), thus \( d_i = -24.0 \ \mathrm{cm} \).
04
Determine the Image Nature
Since \( d_i \) is negative, it suggests that the image is virtual and located on the same side as the object.
05
Calculate the Magnification
The magnification \( m \) is given by \( m = -\frac{d_i}{d_o} \). Substitute the known values to find \( m = -\frac{-24.0}{8.00} = 3.0 \).
06
Find the Image Height
Using the magnification equation which also relates to height, \( m = \frac{h_i}{h_o} \), we substitute \( m = 3.0 \) and \( h_o = 2.00 \ \mathrm{mm} \) to get \( h_i = 3.0 \times 2.00 = 6.00 \ \mathrm{mm} \).
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Converging Lens
A converging lens, often referred to as a convex lens, is a lens that brings light rays together at a point. This type of lens is thicker in the middle than at the edges.
A simple way to describe its shape is that it bulges outward. Converging lenses have several key concepts:
A simple way to describe its shape is that it bulges outward. Converging lenses have several key concepts:
- They have a focal point, which is the point where parallel light rays meet after passing through the lens.
- The distance from the lens to the focal point is called the focal length, often denoted by \( f \).
- These lenses can produce both real and virtual images depending on the object's position relative to the lens.
Image Distance
The image distance, denoted by \(d_i\), is the distance between the lens and the image it forms. This is essential to determine what type of image is produced - whether it is real or virtual.
The sign and magnitude of \(d_i\) inform us about the image nature:
The sign and magnitude of \(d_i\) inform us about the image nature:
- If \(d_i\) is positive, the image is real and inverted, formed on the opposite side of the object.
- If \(d_i\) is negative, the image is virtual and upright, appearing on the same side as the object.
Lens Formula
The lens formula is an equation that relates the focal length \( f \), the object distance \( d_o \), and the image distance \( d_i \). It is given by:\[ \frac{1}{f} = \frac{1}{d_o} + \frac{1}{d_i} \]This formula is fundamental in optics as it helps in determining the image's location and properties based on the given object and focal lengths.
In our exercise:
In our exercise:
- The object's distance \(d_o\) is \(8.00 \, \text{cm}\).
- The focal length \(f\) is \(12.0 \, \text{cm}\).
Magnification
Magnification is a measure of how much larger or smaller the image is compared to the object. It is given by the formula:\[ m = -\frac{d_i}{d_o} \]This equation also relates the image height \( h_i \) to the object height \( h_o \):\[ m = \frac{h_i}{h_o} \]In our problem:
- The calculated magnification is \( m = 3.0 \), meaning the image is three times larger than the object.
- The object height \(h_o\) is \(2.00 \, \text{mm}\).
- The image height \(h_i\) is then calculated as \(6.00 \, \text{mm}\) using the magnification relationship.