Optics

• What is a lens?

  A lens is a piece of equipment that forms an image by refracting light.
• What are the two types of lenses?

  • Convex
  • Concave

  
• What happens to parallel rays of light in a convex lens?

  They are brought to a focus at a point called the principal focus.

  
• What is another name for a convex lens?

  A convex lens is sometimes referred to as a converging lens.
• What is the focal length of a lens?

  The focal length is the distance from the lens to the principal focus.

  
• How does the curvature of a lens affect its focal length?

  The more curved the lens, the shorter the focal length.
• What happens to parallel rays of light in a concave lens?

  They are made to diverge from a point.

  
• What is another name for a concave lens?

  A concave lens is sometimes referred to as a diverging lens.
• Where do parallel rays from a concave lens appear to come from?

  They appear to come from the principal focus.

  
• What symbols are used to represent concave and convex lenses in diagrams?

  • Convex lens: converging symbol
  • Concave lens: diverging symbol

  
• Why is it important to remember the symbols for each type of lens?

  You will be expected to draw these for ray diagrams in your exam.
• What is the relationship between a convex lens and convergence?

  A convex lens is a converging lens.
• What are the steps to draw a ray diagram for a convex lens forming a real image?

  1. Draw a ray from the top of the object through the center of the lens.
  2. Draw a ray from the top of the object parallel to the axis to the lens.
  3. The image is where the two rays meet.

  
• What characteristics define a real image formed by a convex lens?

  A real image is inverted, can be projected onto a screen, and is formed by the convergence of light rays.

  
• What is a virtual image?

  A virtual image is formed when light rays do not meet but appear to meet behind the lens.

  
• What is a characteristic of virtual images?

  Virtual images are always upright.
• How can you identify a virtual image in ray diagrams?

  Virtual images are where two dashed lines or one dashed and one solid line cross.

  
• What are the steps to draw a ray diagram for a concave lens?

  1. Draw a ray from the top of the object through the center of the lens.
  2. Draw a ray from the top of the object parallel to the axis to the lens.
  3. Draw a dashed line continuing this ray downwards to the focal point.
  4. The image is where the two rays meet.

  
• What characteristics define the image produced by a concave lens?

  The image is always virtual, diminished, and upright.

  
• How do the images produced by convex and concave lenses differ?

  • Convex lens: can produce real or virtual images (inverted or upright)
  • Concave lens: always produces virtual images (upright)

  
• What is the formula for magnification of a lens?

  The magnification is equal to the ratio of the image height to the object height.

  
• How can you rearrange the magnification formula?

  Using a formula triangle.

  
• What is a real image defined as?

  A real image is formed when the light rays from an object converge and meet each other and can be projected onto a screen.

  
• What is a virtual image defined as?

  A virtual image is formed when the light rays from an object do not meet but appear to meet behind the lens and cannot be projected onto a screen.

  
• What are the characteristics of real images?

  Real images are always inverted and can be projected onto pieces of paper or screens.
• What are the characteristics of virtual images?

  Virtual images are always upright and cannot be projected onto a piece of paper or a screen.
• What are the steps to draw a ray diagram for a convex lens forming a virtual image?

  1. Draw a ray from the top of the object through the center of the lens.
  2. Draw a dashed line continuing this ray upwards.
  3. Draw a ray from the top of the object parallel to the axis to the lens.
  4. The image is where the two dashed lines meet.

  
• What is the importance of using a ruler and straight edge in ray diagrams?

  • Ensures accurate drawings
  • Helps gain full marks in exams
• What is the first step in drawing a ray diagram for an object?

  Draw a line from the top of the object through the middle of the lens
• What does the top of the image in a ray diagram represent?

  The top of the image lies somewhere along the line drawn from the top of the object
• How do you find the top of the image in a ray diagram?

  By drawing a line from the focal point through the top of the lens and finding where it crosses the first line

  
• What is the best way to remember ray diagrams?

  • Draw them and see the results for yourself
  • Use a ruler or straight edge for accuracy
• What is the formula for magnification of a lens?

  Magnification = image height / object height

  
• What factors does magnification depend on?

  The distance of an object from the lens and the power of the lens

  
• What are the units for height when calculating magnification?

  The units are unimportant as long as both object and image are measured in the same units
• What does a magnification greater than 1 indicate?

  That the image is magnified

  
• What does a magnification equal to 1 indicate?

  That the object and image are the same size

  
• What does a magnification less than 1 indicate?

  That the image is diminished

  
• How do you calculate magnification using a magnifying glass?

  By measuring the height of the object and the height of the image, then substituting into the magnification equation

  
• What does each color in the visible light spectrum correspond to?

  A narrow band of wavelength and frequency