Images Formed by Mirrors
Đã giới thiệuYour reflection stands behind the glass — but nothing is there
- Look in a bathroom mirror and "you" appear to stand an equal distance behind it.
- Reach behind the mirror and there's nothing — the image is virtual.
- Mirrors form images by bouncing rays according to the law of reflection.
- Curved mirrors can shrink, enlarge or even flip the image.
Plane (flat) mirror images
- A plane mirror makes a virtual, upright image the same size as the object.
- The image sits as far behind the mirror as the object is in front.
- It appears left-right reversed, but is otherwise identical.
- "Virtual" means the rays only appear to come from behind — no light is really there.
Trace the image rays
Move the object and focal length and watch how the image position and size change.
You stand $0.5\ \text{m}$ in front of a flat mirror. How far behind the mirror is your image, in metres?
Độ khó 2/5 · 140 xu + một phần thưởng nhỏ cho lần hoàn thành đầu tiên trong ngày
A plane mirror puts the image as far behind as the object is in front: $0.5\ \text{m}$.
A plane mirror image is:
Độ khó 1/5 · 100 xu + một phần thưởng nhỏ cho lần hoàn thành đầu tiên trong ngày
It is virtual, upright and the same size as the object.
Curved mirrors
- A concave (curved-in) mirror can focus rays to a point — it can magnify or flip.
- Close up it gives an enlarged upright image (a shaving/make-up mirror); far off, a small inverted one.
- A convex (curved-out) mirror always gives a small, upright, virtual image with a wide view.
- That is why convex mirrors are used as car and shop security mirrors.
A ____ mirror gives a small, upright image with a wide view, used for security mirrors.
Độ khó 1/5 · 100 xu + một phần thưởng nhỏ cho lần hoàn thành đầu tiên trong ngày
Convex mirrors always give a small, wide-view virtual image.
Select all correct statements about mirrors.
Độ khó 2/5 · 140 xu + một phần thưởng nhỏ cho lần hoàn thành đầu tiên trong ngày
Plane = virtual same-size; concave can make real inverted images; convex widens the view. Plane mirrors do not magnify.
Real vs virtual images
- A real image forms where rays actually cross — you can catch it on a screen.
- A virtual image forms where rays only appear to come from — it can't be projected.
- Plane and convex mirrors make only virtual images.
- Concave mirrors make a real image when the object is beyond the focal point.
Which type of image can be projected onto a screen?
Độ khó 1/5 · 100 xu + một phần thưởng nhỏ cho lần hoàn thành đầu tiên trong ngày
A real image forms where rays actually cross, so it can be caught on a screen.
A plane mirror image is virtual — there is no light behind the mirror. It is not magnified: the image is exactly the same size as the object, just reversed left-to-right and placed an equal distance behind.
A plane mirror magnifies the image, making it larger than the object.
Độ khó 1/5 · 100 xu + một phần thưởng nhỏ cho lần hoàn thành đầu tiên trong ngày
A plane mirror image is exactly the same size as the object.
You stand $0.5\ \text{m}$ in front of a flat mirror. Where is your image, and how big?
- The image is $0.5\ \text{m}$ behind the mirror — so it looks $1.0\ \text{m}$ away from you.
- It is upright and the same size as you.
A plane mirror forms a virtual, upright image the same size as the object, as far behind as the object is in front. Concave mirrors can make magnified or real (inverted) images; convex mirrors always give a small, wide-view virtual image. Real images can be projected; virtual ones cannot.
Write from an image 1.2 m behind the mirror
- You stand 1.2 m in front of a flat mirror.
- Find how far behind the mirror the image is, and how far the image is from you.
You stand 1.2 m in front of a plane mirror. How far behind the mirror is the image, and how far is that image from you?
A plane mirror matches the distances, so the round trip is 2.4 m.
How far is the image from you?
Độ khó 1/5 · 100 xu + một phần thưởng nhỏ cho lần hoàn thành đầu tiên trong ngày
Object distance plus image distance is 2.4 m. Other options — 1.2 m (the distance behind the mirror only); 0.5 m (the lesson object distance).