MedPhysics PPTs 2024-25 PDF

Introduction – Units and Measurements Physical quantity: The property that can be measured and describe the state of the system. i) Fundamental quantity and ii) derived quantity The measurement of every quantity has two parts- number and unit Ex: 50 m ; 5 s ; 10 kg System of Units: CGS FPS MKS S...

Introduction – Units and Measurements Physical quantity: The property that can be measured and describe the state of the system. i) Fundamental quantity and ii) derived quantity The measurement of every quantity has two parts- number and unit Ex: 50 m ; 5 s ; 10 kg System of Units: CGS FPS MKS SI unit- System of International Dr. Syed Ismail Ahmad  Phases of Matter The matter is composed of atoms and molecules (Light is NOT matter) Matter exists in 2 types - Solids and Fluids i) Solid are rigid have definite size and shape. They are highly dense, have strong inter molecular forces, so can’t be compressed. ii) Fluids→ a)Liquid: No definite shape, but have defnite size or Volume (defnite volume at only constant pressure) →low density, Not easily compressible- have weak or moderate intermolecular forces b) Gases: No definite size and shape →Very 7 low density, very easily compressible, very weak intermolecular forces  Mechanical Properties - Solids 1. Elasticity: Elasticity is a property by virtue of which original shape is regained once the external force is removed. (Mechanical properties does NOT change) 2. Plasticity: Plasticity is opposite of elasticity. Property means permanent deformation, does NOT regain original shape after removing external force. (Many mechanical properties change) 3. Ductility (malleablity): Property of being drawn into thin wires or sheets. 4. Strength: Ability to withstand applied stress without failure.  Stress Stress is internal restoring force (in response to external force) per unit area acting on the material. If an external or deforming force is applied on a body to change its shape, then there is a restoring force develops in the body in the opposite direction. The restoring force per unit area is called stress. Force F Stress = = Area A Where F= Restoring force (which is proportinal to force we 2 apply) and A= area. 9 S.I. Unit :- N/m or Pascal(Pa)  Strain Strain is a measure of deformation representing to a reference length. It indicates how and what changes takes place when a body is subjected to stress. Strain deformation in the direction of applied force = original dimention In terms of length where ΔL = change in length and Lo= original length  It is dimensionless quantity – no units  Strain occurs as a result of stress. 10 Elasticity; Stress and Strain The stress and strain are proportional to each other. Until proportional limit called Elastic limit, the object will still return to its original shape. Beyond the elastic limit, the material is permanently deformed, and it breaks at the breaking point.  Modulus of elasticity Stress and strain are proportional to each other. The constant of proportionality is called modulus of elasticity Stress ∝ strain Stress = Modulus × Strain Stress Modulus = Strain There are three types of modulus depending on the above stress and strain 1. Young’s modulus 2. Shear modulus 3. Bulk modulus  Type of Stress and Strain a)Tensile stress (Longitudinal)- b) Shearing stress- Area Stretching or C) Hydraulic Stress or Surface compression – Volume  Force is parallel to  Force is along the  Force from all cross-section area axis sides DR. S I AHMAD Image courtesy- Principles of Physics – 10th Edn- Walker, Hallady, Resnick  Three types of Stress (= F/A) i) Longitudinal iii) Hydraulic stress stress-Tensile ii) Shear stress (Stretch) and compressive stress Three types of strain Tensile strain Shear strain Volume strain (ΔL/L) (Δx/L) (ΔV/V) Three types of modulus Bulksmodulus(𝑩) F F F HydraulicStress ( A ) Longitudinal Stress ( ) Shear Stress ( ) = Young′s modulus(𝐘)= A Shear′s modulus(𝐆)= A 𝜟𝑽 𝚫𝐋 𝚫𝐱 Volume Strain ( 𝑽 Longitudinal Strain ( Shear Strain ( 𝐋 𝐋  Young’s Modulus ( Y ) It is the ratio of longitudinal stress to longitudinal strain. It is denoted by Y. It is also called ‘Elastic modulus’ Y = (F/A)/ (ΔL/L) Y= FL/AΔL Y = σ/ ε, Larger the Young’s modulus of a material, more stress is required to produce a small change in DR. S I AHMAD length. S.I. Unit is N m–2 or Pascal (Pa). 15 Dr. Syed Ismail Ahmad Problem: A bone of length 0.26 m and area A= 10-6 m2 elongates by ΔL = 3 mm (0.003 m) under a tension of 2500 N. What is the Young’s modulus of the bone? Extra Problem: A femur bone of length 0.4m has Young’s modulus Y= 16×109 Pa or N/m2 and under compression it withstand a maximum stress 150×106 Pa before it break. Calculate the amount of compression before it break? Solution:- Given, L = 0.4 m ; Y = 16×109 Pa ; Maximum stress (F/A) = 150×106 16 then find compression, ΔL =? Answer: 3.75 mm check?