Physics Y8 Light Flashcards
How do we see things?
We see any object because light from that object reaches the retina at the back of our eyes where an electrical signal is then sent to our brain. Some objects are luminous and produce their own light, other objects reflect light from other sources.
What is the normal line?
The normal line is a dashed line drawn at 90 degrees to the surface of an object.
What is the law of reflection?
The angle of incidence equals the angle or reflection.
What is the difference between diffuse and specular reflection?
Specular reflection happens when light is incident on smooth surfaces. Parallel rays of incident
light are reflected in a predictable manner and remain parallel to each other upon reflection. Diffuse reflection happens on rough surfaces.
Parallel rays of light do not remain parallel to each other on reflection and are scattered in different directions.
What is a virtual image? Why is it different to a real image?
A virtual image is one from which the light rays appear to come but don’t actually come from the image e.g. the image seen in a mirror. A real image is one where the light rays do come from.
What is refraction and why does it
happen?
Refraction is the change in speed of a wave when it reaches the boundary between two different materials. It happens because materials have different densities. It causes the wave to change direction.
What effects does the refraction of light
lead to?
Refraction of light at water/air boundaries causes objects to appear closer to the water than they actually are. Refraction is the reason why a straw in a glass of water looks “bent”.
What happens to parallel rays of light
when they enter a convex lens?
In a convex lens parallel rays of light are made to converge at a point known as the focal point.
What happens to parallel rays of light
when they enter a concave lens?
In a concave lens parallel rays of light are made to diverge away
from the lens.
How are lenses used to correct eye
defects?
Eye defects occur when the eye cannot focus light onto the retina. In shortsighted people the incoming light is focused to a point before the retina. This can be corrected using a concave lens. In longsighted people the light would be focused on a point beyond the retina and this can be corrected using a convex lens.
What happens to white light when it is
shone through a prism?
When white light is shone through a prism the separate colours of the spectrum are seen. This is called dispersion and happens because different colour (wavelength) light changes speed by different amounts.
What is the electromagnetic spectrum?
The electromagnetic spectrum is a family of transverse waves to which light belongs. They are
made when charged particles (e.g. electrons) are made to vibrate. The order of the electromagnetic spectrum from long wavelength to short wavelength is: Radio waves, Microwaves, Infrared, visible
light, Ultra Violet, X-rays, and Gamma rays.
What are electromagnetic waves used
for?
Radio waves: Communication. Microwaves: Communication and cooking. Infrared: Heating and communication. Ultra violet: security and fluorescent lights. X-rays: medical imaging and cancer treatment. Gamma rays: medical imaging and sterilization.
Why are UV, X rays, and gamma rays
dangerous?
UV, x-rays and gamma rays can damage the structure of DNA within cells. This prevents the cell
from replicating correctly and can lead to mutations and possible cancerous tissue.
