The Effect of Light (GCSE Chemistry)
The Effect of Light
Light Intensity
- The intensity of light can influence the rate of a photochemical reaction. Light is made up of photons, which contain enough chemical energy to break chemical bonds and lower the activation energy.
- Increased light intensity increases the rate of a reaction. An increased intensity of light means more reactant molecules will have the necessary activation energy in order for a reaction to occur. Therefore the rate of the reaction increases.
Examples
Silver Salts
- Silver salts are used in photography. Silver salts are used to produce photographic film and detect visible light and radiation.
- Silver salts are photosensitive. Photosensitive means something is sensitive to light. Silver halide salts are photosensitive.
- Silver ions are reduced. When light hits the photographic film, the silver ions gains electrons to become silver. We can say the silver ions have been reduced.
Ag+ + e– ⟶ Ag
- Halide ions are oxidised. When light hits the photographic film, the halide ions lose electrons to become halogen molecules. We can say the halide ions have been oxidised.
2X– ⟶ X2 + 2e–
Photosynthesis in Plants
- Photosynthesis requires light energy. In order for a reaction to occur, green pigments in plants called chlorophyll, need to absorb light energy.
- Chlorophyll absorbs light energy. By absorbing light energy, energy is provided for the reaction of photosynthesis to occur. The greater the intensity of light, the more energy provided for photosynthesis.
6H2O(l) + 6CO2(g) ⟶ C6H12O6(aq) + 6O2(g)
Light is a form of electromagnetic radiation that travels in straight lines and is visible to the human eye. It is responsible for allowing us to see objects and is a vital source of energy for living things.
The electromagnetic spectrum is the range of all types of electromagnetic radiation. It includes radio waves, microwaves, infrared radiation, visible light, ultraviolet radiation, X-rays, and gamma rays.
The speed of light is 299,792,458 meters per second (m/s) in a vacuum, and it is the fastest speed at which anything can travel in the universe.
Frequency and wavelength are inversely proportional, meaning that as one increases, the other decreases. The frequency of light is the number of waves that pass a given point in one second, and wavelength is the distance between two consecutive peaks of a wave.
The color of light depends on its wavelength. Different colors of light have different wavelengths, and when all the colors are combined, we perceive this as white light.
Refraction is the bending of light as it passes from one medium to another of different density. This causes the light to change direction and can result in the creation of optical illusions, such as mirages.
Total internal reflection is a phenomenon that occurs when light passes from a medium of higher refractive index to a medium of lower refractive index, and is reflected back into the original medium. This type of reflection can be seen in optical fibers, where light is guided along the fiber by repeated internal reflections.
The effect of light on pigments depends on the color of the pigment. Pigments absorb certain wavelengths of light and reflect others, which determines the color we see. For example, a red pigment absorbs all colors except red, which it reflects, resulting in it appearing red to the eye.
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