Medical physics
Physics
Basic concepts of medical physics.
Sample Data
| Front | Topic 27 & 28 |
| Back | Electric circuits, Ohm's law:Circuits consist of circuit elements connected by wires (eks. resistor, capacitor). Electric circuit is a path or line through which an electrical current flows.Any device that supplies energy to cause charges to separate = electromotive force (EMF), ε = V + IrOhm's law : V=IR V=voltage, I=current, R=resistance Electric potential energy = ΔEp=VΔq Δq = charge The electric power (P)= V2/R = I2RElectric instruments: Galvanometer: current measuring device. I and V are connected as of Ohm's law. Living cell as an electric capacitor: The membrane can maintain a potential difference between inside and outside of the cell - comparable to a capacitor. An RC circuit is a circuit containing resistance and capacitance - said to be reactive. Skin has three layers: The epidermis, the outermost layer of skin, provides a waterproof barrier and creates our skin tone. The dermis, beneath the epidermis, contains tough connective tissue, hair follicles, and sweat glands. The deeper subcutaneous tissue (subcutis) is made of fat and connective tissue.Electrical impedance of the skin: Outer layer of the skin is a big part, 99% of the body's resistance to electric current is at the skin. Medical applications of electrical properties of the skin:- pain relief- muscle stimulation- differentiation of skin cancer- essential in pharmacy- drug delivery through skin |
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| Front | Evaporation and vapor pressure |
| Back | Evaporation (liquid to gas) occurs at T>0oC, process of a substance in a liquid state changing to a gaseous state due to an increase in temperature and/or pressure.Saturation vapor pressure: If the container is closed, an equilibrium will be reached when the number of molecules bouncing back into the surface is equal to the number leaving. Gaseous particles in the space above the liquid will hit the walls of the container, and exert a pressure called saturated vapor pressure. The mass of water vapor per unit volume under saturation condition is the saturation vapor density.Boiling point of any liquid is the temperature at which the vapor pressure equals atmospheric pressure. |
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| Front | Physics of vision |
| Back | Refraction and lenses: Light when entering a transparent medium (feks. glass/air) it travels at a slower speedRefraction; "bending" of light rays at interfaces where speed of light changes.
 n ≥ 1Index of refraction (n) is used instead of v.
 Lens power (P) = 1/fLens equation;
 u = object distancev = image distancef = focal lengthMagnification of lens;
 Image formation by the eye: When light from an object strikes the eye, it passes through the cornea; the crystalline lens and the transparent vitreous humor to form an image on the retina.Common vision defects;Myopia/nearsightedness; If the focal length of the eye's lens is too short, the light rays will focus before they reach the retina, resulting in a blurred image on the retina. Can be corrected by inserting a diverging or "negative" lens in front of the eye to cause the rays to diverge slightly before entering the eye.Hyperopia/farsightedness; If the focal length of the eye is too long then the light would focus at a distance greater than the distance to the retina. A converging lens will correct this defect.Astigmatism; the lens has different focal lengths for light rays striking it in different planes.
 Converging lens - produces a magnified virtual image of an object located within the focal length of the lens.
 Used to view small samples that can not be identified with the naked eye. THE OPHTHALMOSCOPE - an instrument for viewing the retina of the eye. In its simplest form it consists of a light source and a mirror with an aperture.Fiber optics - the medium and the technology associated with the transmission of information as light pulses along a glass or plastic strand or fiber.Color vision:The retina of the eye contains two types of light - sensitive nerve endings commonly referred to as "rods" and "cones."Rods are good for night vision, peripheral vision, and motion changes.The cones are responsible for the ability to discriminate between colors.Color is associated with frequency. |
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