Chapter 38: Problem 34
Describe fully the image of an object that is \(10 \mathrm{~cm}\) high and 28 \(\mathrm{cm}\) from a diverging lens of focal length \(-7.0 \mathrm{~cm}\).
Short Answer
Expert verified
The image is 2 cm tall, virtual, erect, and 5.6 cm from the lens.
Step by step solution
01
Understand the Problem
We have an object that is 10 cm tall and located 28 cm from a diverging lens. The focal length of the lens is -7.0 cm. We need to find the characteristics (position, size, orientation, and type) of the image formed by the lens.
02
Use the Lens Formula
The lens formula is \( \frac{1}{f} = \frac{1}{v} - \frac{1}{u} \), where \( f \) is the focal length, \( v \) is the image distance, and \( u \) is the object distance. Here, \( f = -7.0 \) cm and \( u = -28 \) cm (we take the object distance as negative since the object is in front of the lens). Substitute the known values to find \( v \):\[ \frac{1}{v} = \frac{1}{f} + \frac{1}{u} = \frac{1}{-7} + \frac{1}{-28} \]
03
Simplify and Solve for the Image Distance
Calculate \( \frac{1}{v} \):\[ \frac{1}{v} = -\frac{1}{7} - \frac{1}{28} = -\frac{4}{28} - \frac{1}{28} = -\frac{5}{28} \]Thus, \( v = -\frac{28}{5} = -5.6 \) cm. The negative sign indicates that the image is virtual and on the same side of the lens as the object.
04
Determine the Magnification
The magnification \( m \) is given by \( m = \frac{v}{u} \). Substitute \( v = -5.6 \) cm and \( u = -28 \) cm:\[ m = \frac{-5.6}{-28} = \frac{5.6}{28} = 0.2 \]
05
Calculate the Image Height
The image height \( h' \) can be found using the magnification formula, \( m = \frac{h'}{h} \), where \( h \) is the object height. With \( m = 0.2 \) and \( h = 10 \) cm:\[ h' = m \times h = 0.2 \times 10 = 2 \text{ cm} \]
06
Analyze the Results
The image is 2 cm tall, virtual (since the image distance is negative), erect (since the magnification is positive), and located 5.6 cm on the same side of the lens as the object.
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Lens Formula
The lens formula is a crucial part of understanding how lenses form images. It is represented by the equation:
- \( \frac{1}{f} = \frac{1}{v} - \frac{1}{u} \)
- \( f \) is the focal length of the lens, which indicates how strongly the lens can converge or diverge light.
- \( v \) is the image distance, meaning the distance from the lens to the image formed.
- \( u \) is the object distance, which is how far the object is from the lens.
Diverging Lens
A diverging lens, also known as a concave lens, spreads out light rays that have been refracted through it.
These lenses are thinner at the center than at the edges.
The key features of a diverging lens include:
The key features of a diverging lens include:
- It has a negative focal length. This means it cannot converge parallel light rays to a single point.
- The images formed by a diverging lens are typically virtual, reduced in size, and erect.
Virtual Image
In optics, a virtual image is formed when the light rays diverge, and the image cannot be projected onto a screen. For diverging lenses, the image appears to be on the same side as the object. Characteristics of virtual images include:
- They have a negative image distance \( v \), indicating that they are formed on the same side of the lens as the incoming light.
- Virtual images are erect, meaning that the image has the same orientation as the object.
- They are reduced in size compared to the actual object.