Lenses & Mirrors Review | Show Me The Physics

Fill in the Blank Notes Ray Diagram Practice (handout)

The Big Picture

	Shape	Light	Sign of f	Images It Can Make
Plane mirror	Flat	—	—	Virtual upright, same size
Concave mirror	Caves in	Converges	+	Real inverted (object outside F) Virtual upright, larger (object inside F)
Convex mirror	Bulges out	Diverges	−	Virtual upright, smaller — always
Converging lens	Thick middle	Converges	+	Real inverted (object outside F) Virtual upright, larger (object inside F)
Diverging lens	Thin middle	Diverges	−	Virtual upright, smaller — always

Principal Rays

Ray	Mirrors	Lenses
1. Parallel	Parallel in → out through F (or as if from F)	Parallel in → out through F (or as if from F)
2. Focal	Through (toward) F → out parallel	Through (toward) F → out parallel
3. Center	Through (toward) C → back on itself	Through the center → straight, no bending

1f = 1d_o + 1d_i M = h_ih_o = −d_id_o

Explore Any Mirror or Lens

Drag the orange object. Turn rays on and off with the check boxes.

Mixed Practice

1. Name That Diagram

What kind of mirror or lens is this, and where is the object? Describe the image with L-O-S-T.

↓

Converging lens, object between 2F and F. Image: beyond 2F on the other side, inverted, larger, real. This is how a projector works.

2. Name That Diagram

What kind of mirror or lens is this? Describe the image.

↓

Concave mirror, object between F and the mirror. Image: behind the mirror, upright, larger, virtual. This is a makeup mirror.

3. Calculate

A 4.0-cm-tall object is 30. cm from a converging lens with f = 10. cm. Find the image distance and image height.

↓

d_i = +15 cm, M = −0.50, h_i = −2.0 cm (real, inverted, 2.0 cm tall)

4. Calculate

An object is 10. cm from a concave mirror with f = 25 cm. Find d_i and M, and describe the image.

↓

d_i = −17 cm, M = +1.7 — virtual, upright, larger (the object is inside F).

5. Calculate

A convex security mirror has a focal length of magnitude 30. cm. A shopper is 60. cm away. Find d_i and M.

↓

d_i = −20. cm, M = +0.33 — virtual, upright, one-third the size.

6. Design

You need a lens that makes a real image 3 times larger than the object on a screen 60. cm from the lens. How far from the lens is the object, and what focal length do you need?

↓

M = −3 → d_o = 60/3 = 20. cm. 1/f = 1/20 + 1/60 = 4/60 → f = 15 cm (converging).

Check Your Understanding

6 quick questions — pick an answer to see if you’re right.

1. Which two devices can form a real image?

2. An image that is upright and smaller than the object could be made by

3. An object is at the focal point of a converging lens. The image

4. A real image is 12 cm from a concave mirror when the object is 12 cm away. The focal length is

5. Which statement about virtual images is true?

6. A 2.0-cm object makes an image with M = −1.5. The image is

Refraction →