Chapter 26: Problem 128
Suppose the radius of curvature of the mirror is \(5.0 \mathrm{cm}\). (a) Find the object distance that gives an upright image with a magnification of \(1.5 .\) (b) Find the object distance that gives an inverted image with a magnification of -1.5 .
Short Answer
Expert verified
For both magnifications (1.5 and -1.5), the object distance is 1.875 cm.
Step by step solution
01
Understanding the Relationship
The magnification formula for mirrors is given by: \[ m = -\frac{q}{p} \] where \(m\) is the magnification, \(q\) is the image distance, and \(p\) is the object distance. Rearrange to find \(q\):\[ q = -mp \].
02
Identify Mirror Type
Since the radius of curvature \(R\) is given as \(5.0 \text{ cm}\), we can find the focal length \(f\) using the relation: \[ f = \frac{R}{2} = \frac{5.0}{2} = 2.5 \text{ cm} \]. The focal length indicates that this is a concave mirror (since \(f > 0\)).
03
Using Mirror Equation
Use the mirror equation: \[ \frac{1}{f} = \frac{1}{p} + \frac{1}{q} \]. Substitute \(q = -1.5p\) for the upright image:\[ \frac{1}{2.5} = \frac{1}{p} - \frac{1}{1.5p} \].
04
Solve for Object Distance (Upright Image)
Simplify and solve for \(p\) from the equation in the previous step:\[ \frac{1}{2.5} = \frac{1}{p} - \frac{1}{1.5p} \]\[ \frac{1}{2.5} = \frac{1.5 - 1}{1.5p} \]\[ \frac{1}{2.5} = \frac{0.5}{1.5p} \]\[ p = \frac{0.5 \times 2.5 \times 1.5}{1} = 1.875 \text{ cm} \]. The object distance for an upright image with magnification 1.5 is \(1.875 \text{ cm}\).
05
Substitute for Inverted Image
Now consider \(q = 1.5p\) for the inverted image with magnification -1.5:\[ \frac{1}{2.5} = \frac{1}{p} + \frac{1}{1.5p} \].
06
Solve for Object Distance (Inverted Image)
Simplify and solve for \(p\) from the equation:\[ \frac{1}{2.5} = \frac{1 + 1/1.5}{p} \]\[ \frac{1}{2.5} = \frac{2.5}{1.5p} \]\[ p = \frac{2.5 \times 1.5}{2} = 1.875 \text{ cm} \]. The object distance for an inverted image with magnification -1.5 is also \(1.875 \text{ cm}\).
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Concave Mirror
A concave mirror, also known as a converging mirror, is shaped like the inner surface of a sphere. These mirrors have the ability to converge light rays that are incident upon them, focusing them at a single point known as the focal point.
Here are some important features of concave mirrors:
Here are some important features of concave mirrors:
- They can produce both real and virtual images, depending on the position of the object.
- When the object is placed between the focal point and the mirror, the image appears larger and upright.
- If the object is beyond the focal point, the image is smaller, inverted, and real.
Magnification Formula
The magnification formula is a mathematical formula used to relate the size of an image to the size of the object and their respective distances from a mirror. It is expressed as:\[ m = -\frac{q}{p} \]where:
Magnification shows how much larger or smaller the image is compared to the object. A value greater than one means the image is larger than the object, whereas a value less than one means it is smaller.
- \( m \) is the magnification value.
- \( q \) signifies the image distance from the mirror.
- \( p \) represents the object distance from the mirror.
Magnification shows how much larger or smaller the image is compared to the object. A value greater than one means the image is larger than the object, whereas a value less than one means it is smaller.
Radius of Curvature
The radius of curvature \( R \) is the distance between the center of curvature and the mirror's surface. For spherical mirrors, the radius of curvature is twice the focal length (\( f \)). It is directly related to how strongly the mirror converges or diverges light.The radius of curvature helps determine the mirror's focal length using the relation:\[ f = \frac{R}{2} \]A concave mirror with a small radius of curvature will have a shorter focal length, indicating it is highly curved and will more sharply bend incoming light rays.
Focal Length
Focal length (\( f \)) is the distance between the focal point and the mirror. It is a crucial concept in understanding how concave mirrors work and is calculated from the radius of curvature using:\[ f = \frac{R}{2} \]For a concave mirror:
- When the object is placed at the focal length, the rays parallel to the principal axis converge at a point on the opposite side.
- It affects the size and nature (real or virtual) of the image formed by the mirror.