Physics Notes 28.8.20

1 Physics Notes

2 Contents Chapter: Page: 1 Measurements 3 2 Kinematics 5 3 Forces 6 4 Mass, Weight and Density 8 5 Turning Effect of Forces 9 6 Energy, Work and Power 10 7 Pressure 11 8 Temperature 12 9 Kinetic Model of Matter 14 10 Transfer of Thermal Energy 15 11 Thermal Properties of Matter 17 12 Light 20 13 Waves 23 14 Electromagnetic Waves 25 15 Sound 27 16 Static Electricity 28 17 Current Electricity 31 18 D.C Circuits 33 19 Practical Electricity 35 20 Magnetism 40 21 Electromagnetism 43 22 Electromagnetic Induction 45

3 Chapter 1: Measurements Physical Quantities - Quantities that can be measured, consists of a numerical magnitude and a unit. Prefixes Prefix Symbol Standard Form Tera T 1012 Giga G 109 Mega M 106 Kilo k 103 Deci d 10-1 Centi c 10-2 Milli m 10-3 Micro μ 10-6 Nano n 10-9 Conversion of km/h to m/s - 𝑘𝑘𝑘𝑘/ℎ ÷ 3.6 = 𝑘𝑘/𝑠𝑠 Sizes of well-known objects: - Radius of Earth: 6378000m (6.378 × 106) - Size of atom: 0.0000000001m (10−10)

4 Instruments Vernier Calipers - Precision: 0.01cm - Read the main scale until the immediate left of the zero mark on the vernier scale, then add the marking which coincides with the marking on the main scale. - Zero Errors: - Positive - Zero mark of Vernier is slightly to the right of the main scale. - Negative - Zero mark of Vernier is slightly to the left. Micrometre Screw Gauge - Precision: 0.01mm - Read main scale, then read thimble reading - Zero Errors - Positive - Zero marking on thimble scale is below datum (centre) line. - Negative - Zero marking on thimble scale is above datum line. Pendulums - Oscillation - One complete to-and-fro motion (A->C->A)/(B->C->B->A->B) - Period - Time taken for one complete oscillation

5 Chapter 2: Kinematics Scalar Quantities - Quantities with only magnitude - Distance, Speed, Mass, Energy, Time Vector Quantities - Quantities with both magnitude and direction - Displacement, Velocity, Acceleration, Force Distance - Total distance travelled. Displacement - Total distance travelled in a straight line. Speed - The distance moved per unit time (m/s). Velocity - The rate of change of displacement (m/s). Acceleration - The rate of change of velocity (m/s2). - 𝑎𝑎 = 𝑣𝑣−𝑢𝑢 𝑡𝑡 Important Information - The gradient of a displacement-time graph of an object is its velocity. - The gradient of a velocity-time graph of an object is its acceleration. - The area under a velocity-time graph of an object is its displacement. - Acceleration due to Gravity = 10 m/s2

6 Chapter 3: Forces - Newton (N) Vector Diagrams - In a vector diagram, if all 3 arrows form a complete loop, the forces are in - equilibrium. - Parallelogram method - Tip-to-tail method

7 Newton’s Laws of Motion First Law - Every object will continue in its state of rest or uniform motion in a straight line unless a resultant force acts on it. Second Law - When a resultant force acts on an object of constant mass, the object will accelerate in the direction of the resultant force. The product of the mass and acceleration of the object gives the resultant force. Third Law - If body A exerts a force FAB on body B, then body B will exert an equal and opposite force FBA on body A. Friction - The contact force that opposes or tends to oppose motion between surfaces in contact. Reducing friction - Wheels, Ball bearings, Lubricants, Air Cushions Increasing friction - Treads, Parachute, Chalk

8 Chapter 4: Mass, Weight and Density Mass - The amount of matter in a body. - Measured with a beam balanced. - Kilograms (kg). Weight - The gravitational force, or gravity, acting on an object. - Measured with spring balance. - Newton (N). Gravitational field - A region in which a mass experiences a force due to gravitational attraction. Gravitational field strength - The gravitational force acting per unit mass. Relation Between Mass and Weight 𝑤𝑤 = 𝑘𝑘𝑚𝑚 Inertia - The reluctance of the object to change its state of motion due to its mass. Density (kg/m3): 𝑝𝑝 = 𝑚𝑚 𝑣𝑣

9 Chapter 5: Turning Effect of Forces Moments - Moment of a force (torque, Nm): the product of the force F and the perpendicular distance from the pivot to the line of action of the force. 𝑀𝑀𝑀𝑀𝑘𝑘𝑀𝑀𝑀𝑀𝑡𝑡 𝑀𝑀𝑜𝑜 𝑎𝑎 𝑜𝑜𝑀𝑀𝑓𝑓𝑓𝑓𝑀𝑀 = 𝐹𝐹 × 𝑑𝑑 (𝑝𝑝𝑀𝑀𝑓𝑓𝑝𝑝𝑀𝑀𝑀𝑀𝑑𝑑𝑝𝑝𝑓𝑓𝑝𝑝𝑝𝑝𝑎𝑎𝑓𝑓 𝑑𝑑𝑝𝑝𝑠𝑠𝑡𝑡𝑎𝑎𝑀𝑀𝑓𝑓𝑀𝑀) - Moments are vector quantities, thus must specify both magnitude and direction. - Principle of Moments: when a body is in equilibrium, the sum of clockwise moments about a pivot is equal to the sum of anticlockwise moments about the same pivot. Centre of Gravity - The point through which its whole weight seems to act. Stability - The measure of an object’s ability to return to its original position after it is slightly displaced. Equilibrium - Stable, unstable, neutral

10 Chapter 6: Energy, Work and Power Energy - Energy is the capacity to do work. Principle of Conservation of Energy - Energy cannot be created or destroyed, but can be converted from one form to another. The total amount of energy in an isolated system is constant. - Efficiency is calculated by: 𝑈𝑈𝑠𝑠𝑀𝑀𝑜𝑜𝑝𝑝𝑝𝑝 𝐸𝐸𝑀𝑀𝑀𝑀𝑓𝑓𝑚𝑚𝐸𝐸 𝑇𝑇𝑀𝑀𝑡𝑡𝑎𝑎𝑝𝑝 𝐸𝐸𝑀𝑀𝑀𝑀𝑓𝑓𝑚𝑚𝐸𝐸 × 100% Work done - Work done by a constant force on an object is the product of the force and the distance moved by the object in the direction of the force. - Work Done = Energy Transformed - Work done is calculated by: 𝑊𝑊 = 𝐹𝐹 × 𝑠𝑠 Kinetic Energy - Kinetic energy is the energy an object possesses due to its motion. - Kinetic energy is calculated by: 𝐸𝐸𝑘𝑘 = 1 2 𝑘𝑘𝑚𝑚 Gravitational Potential Energy - Gravitational potential energy is the energy an object possesses due to gravity. - Gravitational potential energy is calculated by: 𝐸𝐸𝑝𝑝 = 𝑘𝑘𝑚𝑚ℎ Power - Power is the rate of work done or energy conversion. - Power is calculated by: 𝑃𝑃 = 𝑊𝑊𝑊𝑊 𝑡𝑡 = 𝐸𝐸 𝑡𝑡