Review!

Exam Friday 10 questions Will cover Ch. 23-26 (no relativity) Multiple choice Only material discussed in lecture Bring student ID, pencil, calculator You are allowed one page handwritten formula sheet, no worked out problems on it, just formulas, and diagrams. Questions will be both conceptual and mathematical Similar to homework level of difficulty

Coherent Interference Intensity

Huygens’ Principle Section 25.4

Double Slit Analysis Constructive interference d sin θ = m λ Destructive interference d sin θ = (m + ½) λ Section 25.5

Single-Slit Analysis Destructive interference w sin θ = ±m λ Section 25.6

Diffraction Grating ΔL = d sin θ = m λ Section 25.7

Rayleigh Criterion Section 25.8

Applications of Optics Chapter 26 Applications of Optics

Applications of a Single Lens The eye can be modeled as a single lens with a focal length ƒeye Eyeglasses and contact lenses add a lens in front of the eye A magnifying glass is also a single lens Section 26.1

Normal Eye Light emanating from a point on the object is focused to a corresponding point on the retina The near-point distance, sN, is the closest distance an object can be that you can focus (~25 cm) Objects nearer than the near-point cannot be focused on the retina Section 26.1

Normal Eye, cont. The normal eye can also focus on objects that are very far away s ~ ∞ The eye must adjust its focal length to values between sN and ∞ Does this by using muscles that deform and change the shape of the eye’s lens Needs to change from about 2.3 cm to 2.5 cm Section 26.1

Glasses and Contact Lenses Glasses or contact lenses are lenses placed in front of the eye Along with the eye, these form a system of lenses One lens from the eye and one from the glasses or contact Section 26.1

Far-Sighted Vision The near-point distance is greater than for a normal eye Objects located closer than the near-point distance cannot be focused To compensate, a lens can be placed in front of the eye Section 26.1

Far-Sighted Correction The contact (or glasses) lens is the first lens in the system For example, if a person’s near-point distance is 75 cm, the corrective lens needs to be a converging lens with ƒlens = 38 cm If the person’s near-point distance is greater than 75 cm, the focal length of the corrective lens needs to be shorter Section 26.1

Far-Sighted Example A person’s near-point distance is 75 cm. Show that the corrective lens needs to be a converging lens with ƒlens = 38 cm. Section 26.1

Diopters The strength of a lens is sometimes measured in terms of its refractive power Units are m-1 which is called a diopter For example, the lens with ƒ = 38 cm will have a refractive power of 2.7 diopters Section 26.1

Near-Sighted Vision A nearsighted person is unable to focus light from distant objects on the retina The incoming rays from an object very far away are approximately parallel to the axis (at infinity) A nearsighted eye produces an image in front of the retina

Near-Sighted Correction The object at ∞ needs to focus on the retina For example, if the person can focus objects within 2.0 m, the corrective lens needs to be a diverging lens with ƒlens = -2.0 m

Near-Sighted Example If the person can focus objects within 2.0 m, show that the the corrective lens needs to be a diverging lens with ƒlens = -2.0 m.

Glasses The eyeglass lens is a short distance in front of the eye Instead of touching it as with the contact lens The distance must be taken into account This generally makes the focal length of the eyeglasses about 10% shorter than a contact lens Section 26.1

Glasses Example A farsighted person, with NPD=75cm need a pair of glasses. Assume the glasses are about 2cm in front of the eye. What diopter does person need?