P1 Revision Particles State the size of atoms and molecules Explain Rutherford’s model Explain Bohr’s model Rutherford fired alpha particles at a piece of gold Structure of the Atom 1926 1911 1803 Ernest Rutherford showed atoms have a nucleus, with electrons orbiting it Erwin Schrodinger stated that electrons do not move in set path, but in waves John Dalton proposed that all matter was made up of atoms – the smallest thing possible 1913 1904 AD 300 J.J Thomson discovered electrons, proposes the plum-pudding model Neils Bohr showed that electrons orbit at specific distances from the nucleus Why change ideas? New evidence emerge More experiments are done Technology improves Density Density is the ratio of the mass to the volume 𝒎𝒂𝒔𝒔 𝑫𝒆𝒏𝒔𝒊𝒕𝒚 = 𝑽𝒐𝒍𝒖𝒎𝒆 Practice how you would determine the density of a pebble using measuring cylinder, eureka can, electronic scale Solids have more particles in the same volume Pressure at the top As water freezes the volume expands, same mass or particles, so density reduces Oil is less dense than water So it floats on top of water Pressure at the bottom Pressure at bottom is greater so pushes upward (upthrust) Revision techniques: Physics Mathematical equations form the foundations of the Concepts in Physics. 30% of the questions students get in their exams are based on mathematical principles In the course of your studies, you would learn to apply the following equations, which are given to you in the datasheet … while you would need to recall these ones and apply them How marks are awarded: Physics Any equation you are able to recall gets you one mark. Rearranging the equation gets a second mark. Higher tier candidates however are encouraged to transfer what they would have learned from Maths in ‘change of subject of formula’. They thus benefit from applying this in Maths and in Physics Foundation tier candidates learn to use the formula triangle. We reinforce to them to be able to do rearranging with this. An example 𝑫𝒆𝒏𝒔𝒊𝒕𝒚 = 𝒎𝒂𝒔𝒔 𝑽𝒐𝒍𝒖𝒎𝒆 All students are trained to recognize how to work out mathematical problems by looking at the units in the answer lines. Please see example with the excerpt below. To rearrange to work out the volume of a substance, you ‘cover’ the ‘v’, and write out the formula for this as it appears in the formula triangle. Thus, you write out the formula as below and substitute the numbers 𝒗𝒐𝒍𝒖𝒎𝒆 = 𝒎𝒂𝒔𝒔 𝒅𝒆𝒏𝒔𝒊𝒕𝒚 Students know to recognize that this means to divide the ‘g’ by the ‘cm3’ Icebergs Icebergs Why do you think the ice floats on water? 10% 90% 06/03/2024 Estimate the fraction of the iceberg that is above water 𝒎𝒂𝒔𝒔 𝑫𝒆𝒏𝒔𝒊𝒕𝒚 = 𝑽𝒐𝒍𝒖𝒎𝒆 Conservation of mass Conservation of mass, states that the mass of an object or collection of objects never changes, no matter how the particles rearrange themselves Conservation of mass, the mass remains the same even when the block of ice melts into water Why? Heat, Temperature & State rate of cooling energy flow 3J 3J 3J 3J 12J thermogram Energy = mass × specific latent heat temperature same temp & mass 3J Low High vs ‘normal’ heat latent heat cooling graph raises temperature breaks bonds loss heat temperature arbitrary scale total KE of particles particles Celsius (°C) tiny building blocks direction force matter energy supplied absolute scale Joules (J) kinetic energy vs movement form energy distance time more heat higher temp rate of cooling 1a : Energy : Heat, Temperature & State energy flow 3J 3J 3J 3J 12J thermogram Energy = mass × specific latent heat temperature same temp & mass 3J Low High vs ‘normal’ heat latent heat cooling graph raises temperature breaks bonds loss heat temperature arbitrary scale total KE of particles particles Celsius (°C) tiny building blocks direction force matter energy supplied absolute scale Joules (J) kinetic energy vs movement form energy distance time more heat higher temp 5d : Motion : PV PV volume temperature energy / particle Gas and Pressure more collisions harder direction forces P T P T matter momentum change energy distance force = pressure area time Separate Science ONLY(Slides 17 – 19) The atmosphere Atmospheric pressure The atmosphere is the layer of air around the Earth. Key features of the atmosphere: •it is thin compared to the size of the Earth •it becomes less dense as the altitude increases Pressure Air molecules colliding with a surface cause atmospheric pressure. Atmospheric pressure at sea level is about 101,000 Pa (101 kPa) but just 27,000 Pa (27 kPa) at the cruising altitude of a passenger plane. Atmospheric pressure decreases as the height of a surface above ground level increases. This is because, as the altitude increases: the number of air molecules decreases the weight of the air decreases there is less air above a surface This is why aircraft that fly at high altitudes must be pressurised. If the air pressure is too low, humans cannot take in oxygen quickly enough to meet their bodies’ needs. Calculating pressure Atmospheric pressure To calculate atmospheric pressure between two points Separate Science ONLY Pressure difference = density x gravitational field strength x difference in height Pressure difference = ρgΔh Separate Science ONLY Upthrust Remember Upthrust force from fluids is due to pressure difference P1 – Matter (Broadsheet)
