AM vs FM radio Frequency Modulated Amplitude Modulated
Both AM & FM radio signals have advantages and disadvantages. Generally, AM waves have much longer wavelengths than FM waves and can DIFFRACT better than FM waves and can travel greater distances before the signal fades. FM is more direct line of sight. However, because information is coded in the amplitude of an AM wave, power lines and lightning can influence the amplitude and are more likely to interfere with the AM wave. FM has a greater range of frequency which is better for music whereas AM is better for talk radio since there isn’t much fluctuation in a person’s voice.
Thermogram We radiate infrared light aka “heat”
Reflection and Refraction of Light
Rays instead of waves approximation A ray of light is an imaginary line drawn along the direction of travel of the light beams. We use this instead of a wave.A ray of light is an imaginary line drawn along the direction of travel of the light beams. We use this instead of a wave.
Law of Reflection θiθi θrθr
2 types of reflection:
With diffuse reflection, your eye sees reflected light at all angles. With specular reflection (from a mirror), your eye must be in the correct position.
Refraction of Light When a ray of light enters a different medium at an angle other than 0 o with the normal, it will bend or REFRACT due to a speed change due to material change.
θiθi θiθi θrθr θrθr θi>θrθi>θr θi<θrθi<θr
The Index of Refraction
Snell’s Law of Refraction
A ray of light is incident on the surface of a block of clear ice (1.309) at an angle of 40.0° with the normal. Part of the light is reflected and part is refracted. Find the angle between the reflected and refracted light. A ray of light is incident on the surface of a block of clear ice (1.309) at an angle of 40.0° with the normal. Part of the light is reflected and part is refracted. Find the angle between the reflected and refracted light.
Frequency Between Media
The light emitted by a helium–neon laser has a wavelength of 632.8nm in air. As the light travels from air into zircon (1.923), find a) its speed in zircon b) its frequency in zircon c) its wavelength in zircon.
Illusions from refraction
Sunset not really there?
Variation of Index of Refraction with Wavelength
Total Internal Reflection
TIR and ‘bling bling’
Fiber Optics and TIR Plastic or glass rods are used to “pipe” light from one place to anotherPlastic or glass rods are used to “pipe” light from one place to another This ‘light’ can be used to carry information at light speedThis ‘light’ can be used to carry information at light speed Fiber Optics, Medical EndoscopesFiber Optics, Medical Endoscopes
Observing the Rainbow If a raindrop high in the sky is observed, the red ray is seenIf a raindrop high in the sky is observed, the red ray is seen A drop lower in the sky would direct violet light to the observerA drop lower in the sky would direct violet light to the observer The other colors of the spectra lie in between the red and the violetThe other colors of the spectra lie in between the red and the violet
A bright underwater flood light at the bottom of a 2.75-m deep pool is positioned 1.85 m from one edge of the pool. At what angle will light emerge from the surface of the water at the edge of the pool. Assume the pool is filled to the brim with water.
Image Types for Mirrors
Image characteristics: A) TYPE – B) ORIENTATION C) MAGNIFICATION (M) D) Position & height of image and object
Reflection & Image Formation by a Plane Mirror What you see when you look into a plane (flat) mirror is an image, which appears to be behind the mirror.
Properties of the Image Formed by a Plane/Flat Mirror
Concave Mirror Converges light rays after reflection
Parallel light rays reflecting off of concave mirror Note how all 4 rays reflect and converge at common point. This is called FOCAL POINT.
Focal Length Incoming rays are parallel and all reflect through a common point called the FOCAL POINT, F.
Applications of concave mirror PARABOLIC REFLECTORS - Behind flashlight bulbs, headlights, searchlights. projects light out in a concentrated beam…bulb is placed at focal pt. SATELLITE DISH - Microwaves strike dish and reflect and collect at the receiver (at focal point) SOLAR COOKER MAKEUP MIRROR…provides an enlarged image of face when held close to face
Convex Mirror Diverges light rays after reflection
Object inside the focal point. Characteristics of image:
IMAGE IN CONVEX MIRROR
Example A concave makeup mirror is designed so that a person 25cm in front of it sees an upright image magnified by a factor of two. What is the radius of curvature of the mirror?
How far from a concave mirror with a focal length of 22.5 cm must an object be placed to produce an image with a magnification of +3.65? Example2
Thin Lenses Use same formulas as mirrors, except that f ≠ R/2…doesn’t apply
Converging or Convex Lenses The difference between mirrors and lenses is that mirrors reflect and lenses refract light.
Parallel rays refract through converging lens and then proceed through F on other side.
Diverging or Concave Lenses (THICKER AT EDGES)
Parallel rays refract through diverging lens and then diverge where rays can be traced backwards through F on incident side.
Sign convention for lenses Where you expect light to end up is assumed positive (opposite side of lens) Converging lenses have +f Diverging lenses have -f
Example Based on the picture shown, describe the type of lens and the type of image Based on the picture shown, describe the type of lens and the type of image If the magnifying glass was immersed in water, what effect (if any) would that have on parallel rays leaving the lens? If the magnifying glass was immersed in water, what effect (if any) would that have on parallel rays leaving the lens?
APPLICATIONS OF LENSES Overhead projector (lens + mirror), eyeglasses, contacts, magnifying glass, telescopes, microscopes, your eye, etc
Lenses and your EYE
The ability of the eye to instantly adjust its focal length is known as accommodation. Your ciliary muscles flex and manipulate the curvature and shape of your lens which changes the focal length of the lens.
Astigmatism means that the cornea is oval like a football instead of spherical like a basketball. This causes light to focus on more than one point in the eye, resulting in blurred vision at a distance or near.
Combinations of Lenses
Combination of Thin Lenses The image produced by the first lens is calculated as though the second lens were not present The light then approaches the second lens as if it had come from the image of the first lens The image of the first lens is treated as the object of the second lens The image formed by the second lens is the final image of the system
Example An object is located 4.75m from a simple optical system consisting of two converging lenses. The first lens of this system has a focal length of 100 mm and the second lens, which is 20.0 cm from the first lens, has a focal length of mm. What is the magnification of the system?
Example 2 An object is placed 20.0 cm to the left of a converging lens of focal length 25.0 cm. A diverging lens of focal length 10.0 cm is 25.0 cm to the right of the converging lens. Find the position and magnification of the final image.