P5 - Images & Converging Lens Flashcards
What is a real image?
- A real image is where the light from an object comes together to form an image on a “screen”, like the the image formed on an eye’s retina ( the “screen” at the back of an eye. )
- Real images can be projected onto screens.
What is a virtual image?
- A virtual image is when the rays are diverging, so the light from the object appears to be coming from a completely different places.
- Virtual images cannot be projected onto screen.
What happens when you look into a mirror?
• When you look into a mirror you see a virtual image of your face, the object ( your face ) appears to be behind the mirror.
How can you get a virtual image?
You can get a virtual image when looking at an object through a magnifying lens, the virtual image looks bigger and further away than the object actually is.
What are the 4 things you need to say to describe an image properly?
- How big it is compared to the object.
- Whether it is real or virtual.
- Whether it is upright or inverted.
- Where it is ( in relation to the lens and focal points.
What is a converging lens?
A converging lens is convex, it bulges outwards.
What does a converging(convex) lens do?
• It causes rays of light to converge ( move together) to a focus.
What happens if the rays entering a converging lens are parallel?
If the rays entering the lens are parallel to each other and to the principal axis, it focuses them at a point called a focal point.
What is the focal length?
• The distance between the centre of the lens and the focal point is called the focal length of the lens.
What happens if a blue ray parallel to the principal xis passes through a convex lens?
- A ray travelling parallel to the principal axis slows down as it enters and bends towards the normal.
- When it hits the glass to air boundary on the other-side it speeds up and bends away from the normal.
- The curvature of the lens means all the parallel rays hitting different parts of the lens are bent towards the same focal point, where an image is formed.
What happens if a red ray passes through the optical centre?
- A ray passing through the optical centre of the lens appears to pass straight through.
- It exits the lens at the same angle it entered at, but on the opposite side of the principal axis, so it is bent the same amount but in the opposite direction upon entering and exiting the lens.
What happens if the diverging light enters the convex lens?
They can turn diverging light rays into parallel light.
What can the image produced depend upon?
• Convex lenses can make real or virtual images depending on how close the object is to the lens.
