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In the measurement of the focal length \(f\) of a concave mirror, the object distance \(u=40 \pm 0.1 \mathrm{~cm}\) and image distance \(v=20 \pm 0.2 \mathrm{~cm}\). The maximum \(\%\) error in the measure of \(f\) is : (a) \(1.75\) (b) \(0.75\) (c) \(0.3\) (d) \(2.25\)

Short Answer

Expert verified
The maximum percentage error in measuring \( f \) is 1.25%, not listed in the options.

Step by step solution

01

Write the Mirror Formula

The mirror formula for a concave mirror is given by \[ \frac{1}{f} = \frac{1}{u} + \frac{1}{v} \]where \( f \) is the focal length, \( u \) is the object distance, and \( v \) is the image distance.
02

Differentiate the Mirror Formula

To find the maximum error, we need to differentiate the mirror formula. Differentiating with respect to \( u \) and \( v \), we have:\[ -\frac{1}{f^2} \cdot \Delta f = -\frac{1}{u^2} \cdot \Delta u - \frac{1}{v^2} \cdot \Delta v \]where \( \Delta u \) and \( \Delta v \) are the errors in \( u \) and \( v \), respectively.
03

Calculate Relative Errors

From the differentiated equation, we can express the relative errors as:\[ \left|\frac{\Delta f}{f}\right| = \left|\frac{\Delta u}{u}\right| + \left|\frac{\Delta v}{v}\right| \]We know \( u = 40 \pm 0.1 \) cm and \( v = 20 \pm 0.2 \) cm.
04

Substitute and Calculate

Substitute the given errors and distances:\[ \frac{\Delta u}{u} = \frac{0.1}{40} = 0.0025 \]\[ \frac{\Delta v}{v} = \frac{0.2}{20} = 0.01 \]Adding these gives the total relative error:\[ \left|\frac{\Delta f}{f}\right| = 0.0025 + 0.01 = 0.0125 \]
05

Convert to Percentage Error

To find the percentage error, multiply the total relative error by 100:\[ \mathrm{Percentage\ Error\ in\ } f = 0.0125 \times 100 = 1.25\% \]

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Key Concepts

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

Mirror Formula
The mirror formula is a fundamental equation that helps describe the relationship between the object distance, image distance, and focal length in mirrors, especially in the case of concave mirrors. The formula is expressed mathematically as:\[ \frac{1}{f} = \frac{1}{u} + \frac{1}{v} \]where:
  • \( f \) represents the focal length of the mirror.
  • \( u \) is the object distance, the distance from the object to the mirror.
  • \( v \) is the image distance, the distance from the image to the mirror.
This formula is pivotal in optical physics as it allows us to determine one variable, given the other two. It’s particularly useful in understanding how concave mirrors converge light to a focal point, which is critical in many applications like telescopes and certain types of cameras.
Error Analysis
Error analysis is crucial when conducting any scientific measurement or experiment. When you're dealing with measurements, there's always uncertainty due to limitations in precision. In the context of the concave mirror exercise, the object and image distances \( u \) and \( v \) have specific allowed errors, \( \Delta u \) and \( \Delta v \), respectively. Calculating these errors involves determining how much the potential inaccuracy of each measurement can affect the final calculation of the focal length.The error is processed through the differentiation of the mirror formula, leading to the expression:\[ \left|\frac{\Delta f}{f}\right| = \left|\frac{\Delta u}{u}\right| + \left|\frac{\Delta v}{v}\right| \]This equation shows that the relative error in the calculation of the focal length \( f \) is the sum of the relative errors of \( u \) and \( v \). Understanding and calculating error helps ensure that conclusions drawn from experiments are reliable and that the uncertainty is kept within acceptable limits.
Focal Length Measurement
Determining the focal length of a concave mirror is a common and essential task in physics classes and laboratories. Focal length, \( f \), is the distance from the mirror to the focal point where parallel rays converge after reflection.In the experiment setup, you measure the object distance \( u \) and the image distance \( v \) and apply them in the mirror formula to solve for the focal length. Here’s how it's done: 1. Rearrange the mirror formula to solve for \( f \):\[ f = \frac{uv}{u+v} \]2. Substitute the values of \( u \) and \( v \) you measured.Accurately measuring \( u \) and \( v \) is crucial, as errors can lead to incorrect calculations of \( f \). Precision instruments should be used to minimize error, and multiple measurements can be taken to increase accuracy.
Differentiation in Physics
Differentiation is a powerful mathematical tool used in physics to understand and analyze changes concerning different variables. In the context of the mirror formula, differentiation is applied to assess how small changes in object and image distances \( u \) and \( v \) translate to changes in the focal length \( f \).By differentiating the mirror formula:\[ -\frac{1}{f^2} \cdot \Delta f = -\frac{1}{u^2} \cdot \Delta u - \frac{1}{v^2} \cdot \Delta v \]we identify how errors in measurements propagate through calculations. The differentiated terms show the relationship between potential measurement errors (\( \Delta u \) and \( \Delta v \)) and their impact on \( \Delta f \), the change in focal length.In optics and broader physics applications, understanding this relationship helps in error analysis—you can predict and compensate for measurement inaccuracies, enhancing the precision and reliability of experimental results.

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Most popular questions from this chapter

A flat mirror revolves at a constant angular velocity making 2 revolutions/sec. With what velocity will a light spot move along a spherical screen with a radius of \(10 \mathrm{~m}\), if the mirror is at a centre of curvature of the screen? (a) \(251.2 \mathrm{~m} / \mathrm{s}\) (b) \(261.2 \mathrm{~m} / \mathrm{s}\) (c) \(271.2 \mathrm{~m} / \mathrm{s}\) (d) \(241.2 \mathrm{~m} / \mathrm{s}\)

A concave mirror produces an image \(n\) times the size of an object. If the focal length of the mirror is ' \(f^{\prime}\) and image formed is real, then the distance of the object from the mirror is : (a) \((n-1) f\) (b) \(\frac{(n-1)}{n} f\) (c) \(\frac{(n+1)}{n} f\) (d) \((n+1) f\)

A man of height \(1.8 \mathrm{~m}\) stands infront of a large vertical plane mirror. The distance of the image from the man if he stands at a distance of \(1.5 \mathrm{~m}\) from the mirror is : (a) \(1 \mathrm{~m}\) (b) \(2 \mathrm{~m}\) (c) \(3 \mathrm{~m}\) (d) \(4 \mathrm{~m}\)

A car is moving towards a plane mirror at a speed of \(30 \mathrm{~m} / \mathrm{s}\). Then the relative speed of its image with respect to the car will be : (a) \(30 \mathrm{~m} / \mathrm{s}\) (b) \(60 \mathrm{~m} / \mathrm{s}\) (c) \(15 \mathrm{~m} / \mathrm{s}\) (d) \(45 \mathrm{~m} / \mathrm{s}\)

A man is running towards a plane mirror with some velocity. If the relative velocity of his image with respect to him is \(4 \mathrm{~m} / \mathrm{s}\), then the velocity of a man is : (a) \(2 \mathrm{~m} / \mathrm{s}\) (b) \(4 \mathrm{~m} / \mathrm{s}\) (c) \(8 \mathrm{~m} / \mathrm{s}\) (d) \(16 \mathrm{~m} / \mathrm{s}\)

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