Unit 2: Lesson 14 - Thin Lens & Magnification Equations

practice

practice

Focal Point? (symbol?)

Focal Point (F) - point where reflected rays from parallel incident

rays meet

2F - ?

2F - point that is 2x the F distance

Focal Length? (symbol?) - ?

Focal Length (f) - distance from point F to the lens centre

Image Distance? (symbol?) -

Image Distance (di) - distance from the lens centre to the image

Object Distance? (symbol?) -

Object Distance (do) - distance from the lens centre to the object

Image Height? (symbol?)

Image Height (hi) - height of the image

Object Height? (symbol?)

Object Height (ho) - height of the object

Thin Lens & Magnification Equations

Q: What is the thin lens equation?

and what do each symbol mean?

Thin Lens & Magnification Equations

A: 1 / f = 1 / di + 1 / do

- f = focal length of the lens

- do = object distance from lens

- di = image distance from lens

Q: What is the magnification equation?

and what do each symbol mean?

A: M = hi / ho = - di / do

- hi = image height

- ho = object height

di/do ratio also gives the size and orientation of the image

Sign Conventions for Lenses

Q: What are the signs for focal length (f)

A:

+f → converging lens

-f → diverging lens

Q: What are the signs for image distance (di)?

A:

+di → real image (opposite side of lens)

-di → virtual image (same side as object)

Quick Study Tip

Thin lens equation → tells you?

Magnification equation → tells you?

Quick Study Tip

Thin lens equation → tells you location & type of image

Magnification equation → tells you size & orientation

Magnification tells you two things about the image:

Size - ?

Orientation - ?

Magnification tells you two things about the image:

Size - How big or small the image is compared to the object

Orientation - Whether the image is upright or inverted

hi / ho → ratio of?

di / do → ratio of?

Both formulas do what?

hi / ho → ratio of image height to object height

di / do → ratio of image distance to object distance

- Both formulas give the same value, just different ways to measure magnification.

Examples:

M = 2 → image is ?

M = -0.5 → image ?

4️⃣ Quick tip to remember

Sign (+/-) → ?

Magnitude (absolute value) → ?

- So if you ever calculate M, look at the sign for?

- and the number for?

Examples:

- M = 2 → image is 2× bigger, upright

- M = -0.5 → image is 1/2 the size, inverted

4️⃣ Quick tip to remember

- Sign (+/-) → orientation

- Magnitude (absolute value) → size

- So if you ever calculate M, look at the sign for orientation

- and the number for size.