Light Physics Typed Version

MR.DERYK NG PHYSICS NOTES LIGHT www.youtube.com/thephysicsidiot REFLECTION 2 Laws • Incident ray, reflected ray & normal line lies on the same plane • Incident angle, i = Reflected angle, r Caution : Make sure the angle is measured from normal! Example

Curved Mirrors u = object distance Concave

v = image distance

f = focal length Convex

Rules for Ray Diagram • Parallel with principal axis, comes out strikes f • Strikes f, comes out parallel with principal axis • Passes through C = 2f = R, reflected along normal line and comes back along the same incident path

Very Ugly Monkey u=f AND u
MIDDLE GUY Object placed btw 2f & f is considered in the middle. Middle is spelt with M

PAGE 260 SUCCESS PHYSICS OXFORD FAJAR

CONCAVE MIRROR AND CONVEX LENS PAGE 290 SUCCESS PHYSICS OXFORD FAJAR

FAR.RID u = INFINITY AND u >2f

SAME SIZE GUY u = 2f, v = 2f RI=

RIM But the M in RIM is Magnified ONE METHOD OF MEMORISATION ASSISTS YOU TO UNDERSTAND BOTH CONCAVE MIRROR AND CONVEX LENS! Linear Magnification, m Linear magnification, m = v / u We are always interested in the final image and its relationship with the original object. Therefore the formula above is a ratio of image distance from the lens to object distance Looking at the diagram below

m > 1, object is magnified (it becomes a bigger image) m = 1, the image is having the same size / height as the object m < 1, object is diminished (it becomes a smaller image)

Example: An object’s height, 6 cm, is placed at u cm to the left from the convex lens. The hI cm tall image is found to be 6u cm away to the right of the lens. Find : i) The linear magnification, m ii) hI, height of the final image iii) Draw the corresponding diagram if u = 1 cm

LENS FORMULA

Convex Lens, f = +ve [but why positive?]

Rays strike f on the other side, converge on the RIGHT HAND SIDE of the lens A real image can be formed if a white screen is placed along the dotted line. REAL IMAGE FOR LENS ALWAYS ON RIGHT HAND SIDE & IMAGE DISTANCE ALWAYS POSITIVE! Concave Lens, f = -ve [but why negative?] QUESTION: Ray A & B seem to be diverging away from a starting point, but where?

ANSWER: At Q, virtual focal point from the “optical centre” (it’s not a place where they sell specs!) VIRTUAL FOCAL POINT HAS NEGATIVE VALUE! For CONVEX LENS, regardless of object distance, it always end up as an image of Very Ugly Donkey – Virtual, Upright & Magnified VIRTUAL IMAGE FOR LENS ALWAYS LEFT HAND SIDE & IMAGE DISTANCE ALWAYS NEGATIVE! REPEAT REAL IMAGE FOR LENS ALWAYS ON RIGHT HAND SIDE & IMAGE DISTANCE ALWAYS POSITIVE! VIRTUAL IMAGE FOR LENS ALWAYS LEFT HAND SIDE & IMAGE DISTANCE ALWAYS NEGATIVE! RULE #1

RULE #2

RULE #3

f = +ve CONVEX f = - ve CONCAVE

No matter what, u (object distance) always positive!

v = -ve if on LEFT [VIRTUAL] v = +ve if on RIGHT [REAL]

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