Question

The power of plane glass is (A) \(\infty\) (B) 0 (C) \(\overline{2 \mathrm{D}}\) (D) \(4 \mathrm{D}\)

Short answer

The power of plane glass is 0 (option B) since its parallel surfaces do not change the direction of incoming light rays, meaning it doesn't have any converging or diverging power.

Step-by-step solution

Understand Lens Power and Plane Glass Properties

Lens power is the property of a lens or optical system to converge or diverge incoming parallel rays of light. It is measured in Dioptres (D) and can be calculated using the formula: Power (P) = \(\frac{1}{f}\) where f is the focal length of the lens in meters. Plane glass has parallel surfaces which do not change the direction of incoming light rays, meaning it doesn't have any converging or diverging power.

Calculate the Power of Plane Glass

Since plane glass doesn't have any converging or diverging power, its focal length can be considered to be infinite. Plugging this into the power formula: Power (P) = \(\frac{1}{\infty}\)

Simplify the Result

Simplifying the expression: Power (P) = 0

Choose the Correct Option

Comparing the result with the given options, we can conclude that the correct answer is: (B) 0

Key concepts

Plane Glass

Plane glass refers to a flat piece of glass that has two parallel surfaces. It is commonly used in windows, picture frames, and various optical applications. Plane glass is significant in optics because it does not alter the path of light passing through it. When light rays enter and exit plane glass, they continue along the same path without getting bent or deviated.
This absence of bending is due to the lack of curvature in the glass surfaces. Therefore, plane glass does not have the capacity to focus or disperse light.

• Does not converge or diverge light
• Has two parallel flat surfaces
• Commonly used in everyday products

Understanding the nature of plane glass is essential for evaluating its optical power and how it differs from lenses with curved surfaces.

Diopters

Diopters are units of measurement used to describe the optical power of a lens or optical system. The optical power determines how strongly a lens can converge or diverge light. This measurement is particularly useful in eyeglass prescriptions and optical laboratory settings.
It is denoted by the symbol D and is calculated using the focal length of the lens in meters:
The formula is:
\[ P = \frac{1}{f} \]
where \( P \) is the power in diopters and \( f \) is the focal length in meters.

• Expresses lens strength
• Used in vision correction
• Important for lens design

In the context of plane glass, since it does not alter light paths, its diopter value is 0, confirming its inability to bend light.

Focal Length

Focal length is a critical concept in optics, defining the distance over which parallel rays of light are brought to a focus, or point. It is typically measured in meters and is inversely related to the optical power of a lens.
A shorter focal length means greater optical power, resulting in stronger bending of light rays. Conversely, an infinite focal length, as seen with plane glass, indicates zero optical power.

• Determines convergence point
• Inverse relationship with power
• Infinite for plane glass

By understanding focal length, you can better grasp why certain lenses are so effective at altering light paths, unlike plane glass, which leaves the light unchanged.

Parallel Rays

In optics, parallel rays refer to light rays that travel in parallel to each other, meaning they never converge or diverge. When these rays encounter an optical medium like plane glass, they pass through unchanged in direction if the surfaces are parallel.
This property is crucial in understanding lens behavior and the optical power they possess.

• Do not converge on their own
• Pass unchanged through plane glass
• Altered by lenses with curvature

When learning about optics, recognizing how parallel rays interact with different optical materials helps clarify why certain lenses can focus light into a point, while plane glass cannot.