Colour and Light
Firstly, one of the key misunderstandings in relation to this investigation is what colour really is. What we perceive as colour, is merely certain frequencies of visible light, with certain wavelengths. The wavelength of a wave is inversely proportional to its frequency, given the equation:
Speed of Light = Frequency x WavelengthVisible Part of the Electromagnetic Spectrum
And so, visible light ranges in wavelength from 380nm (nanometres) to 740nm. Violet exhibits the highest frequency (most energy) and thus shortest wavelength, while red has the lowest frequency and longest wavelength.
White light contains all colours of the spectrum, whilst black light is the absence of any colours in the spectrum.
White light contains all colours of the spectrum, whilst black light is the absence of any colours in the spectrum.
Colour of an Object
Colour PerceptionThe colour of an object is determined by what frequency light, the object reflects, and what it absorbs. By way of example, let’s use an apple in the sunlight.
When sunlight (which we perceive to be colourless- when in fact, it contains all ‘colours’) shines on the apple, the surface of the red apple absorbs all the different frequency light (i.e. colour). Except for those corresponding to red light, in which case, it reflects this colour to the human eye, making the apple appear as if it is red.
When sunlight (which we perceive to be colourless- when in fact, it contains all ‘colours’) shines on the apple, the surface of the red apple absorbs all the different frequency light (i.e. colour). Except for those corresponding to red light, in which case, it reflects this colour to the human eye, making the apple appear as if it is red.
Light is Energy!
One of the most important things to understand about light is that it essentially is a form of energy. It can be thought of as nature’s way of transferring energy through space. And so when colour is absorbed by a certain object, it is in essence absorbing energy. As we know, because of the first law of thermodynamics – Law of Conservation of Energy, energy cannot be created or destroyed. And so, the energy absorbed by the object has to go somewhere.
First Law of Thermodynamics - Law of Conservation of Energy: Energy cannot be created nor destroyed.
The result of this is that the energy absorbed by the object is turned into heat. Emissivity refers to the ability of a material’s surface to emit heat or energy by radiation. And so, materials with high emissivity emit a lot of heat.
Colour and Heat
The more reflective an object is, the less emissivity it has. On the contrary, dull objects with darker colours tend to have higher values of emissivity. This is because darker shades of colours such as black tend to absorb more colours, and thus, absorb more energy, which is then in turn, used to emit radiation. The effect is even increased to the extent to which black often absorbs infrared radiation (which is essentially heat).
Although, the actual frequencies of light present within the light source could potentially cause some discrepancy, it is a general rule of thumb there is a direct relationship between the darkness of a material, and its ability to absorb and emit heat. But just how big of a difference does it make? Follow through to the experiment to find out…
Although, the actual frequencies of light present within the light source could potentially cause some discrepancy, it is a general rule of thumb there is a direct relationship between the darkness of a material, and its ability to absorb and emit heat. But just how big of a difference does it make? Follow through to the experiment to find out…