91Ó°ÊÓ

When discussing light, one of the fundamental properties to consider is its wavelength. Wavelength refers to the distance between consecutive peaks (or troughs) of a wave. In the context of light, this distance is often measured in angstroms (Ã…), where 1 Ã… equals 10^{-10} meters. Light with a wavelength of 5000 Ã… is typical for visible light, which ranges approximately from 3800 Ã… to 7500 Ã….

One vital point to understand about wavelength is that it does not change when light reflects off a surface. This means if light with a certain wavelength, like our 5000 Ã…, strikes a mirror, the light maintains this wavelength upon reflection. Reflection ensures that both the incident and the reflected light share identical wavelengths, a concept crucial for maintaining color consistency in mirrors.

Frequency is another core concept when working with light. It represents how many wave peaks pass a given point each second. Measured in hertz (Hz), frequency stays constant regardless of reflection or the medium that light travels through.

To calculate the frequency of light, you can use the speed of light, denoted as \( c = 3 \times 10^8 \text{ m/s} \), and the wavelength. The relationship between these quantities is given by the equation \( c = f \lambda \). Substituting known values, such as the wavelength \( \lambda = 5000 \times 10^{-10} \text{ m} \), allows us to solve for the frequency \( f \). Through this calculation, the frequency of light is determined to be \( 6 \times 10^{14} \text{ Hz} \).

Frequency remains unaltered because, during reflection, light's speed and wavelength stay the same, maintaining the uniformity of this parameter.

Understanding the angle of incidence is essential when analyzing light reflection. This angle is the measure between the incoming light ray and the normal—a line perpendicular to the reflecting surface. The law of reflection states that the angle of incidence \( i \) equals the angle of reflection \( r \).

A special case occurs when the reflected ray is perpendicular to the incident ray. Mathematically, this means that their angle forms a right angle (90°). Here, the angle of reflection can be expressed as \( r = 90^\circ - i \). Given that \( i = r \), it follows that \( i = 45^\circ \) when setting up the rays to be perpendicular.

In practical terms, this implies that, when you want the reflected ray to travel directly sideways in relation to the incident light, you should place the light source at a 45° angle relative to the normal of the mirror.