AQA PHYSICS PAPER 1 (Higher Tier, Triple Science) - KEY POINTS FOR GCSE 2018
(A huge thanks for the amazing response to my key points posts for Biology and Chemistry!!)
* P = I x V
* P = I^2 x R
* V = I R
* P = E / t
* E = Q x V
* Q = I x t
* F = m x a
* F = K x e
* GE = mgh
* KE = 1/2 x m x v^2
* Nuclear fission is when a neutron is fired at a nucleus and it breaks into 2 (+ 3 neutrons) to make it unstable
* Nuclear fusion is when two small isotopes fuse (overcoming the Coulomb force which causes them to repel) to form a larger nuclei
* Circuit symbols are as follows:
* Resistance of an object is how much it resists the flow of charge
* An ohmic conductor is a resistor in which voltage is proportional to current with s constant temperature
* Moving electrons colliding with ions causes resistance
* The resistance of a thermistor decreases as temperature increases (useful in circuits where temperature control/response is required)
* Thermal conductivity is the rate of energy transfer by the material
* When heat is applied, atoms vibrate, and electrons collide, transferring kinetic energy to thermal energy
* Potential difference is the work done per unit
* Power is the rate at which an appliance uses electrical energy
* Live wire (brown) carries current to the appliance at a high voltage
* Neutral wire (blue) completes circuit and carries current away
* Earth wire is a safety wire which connects the metal case to earth allows a large current to live wire to melt fuse
* Plastic appliances don’t need this as plastic acts as an insulator so the case won’t become live
* Frequency in the UK is 50Hz and voltage is 230V
* Current increases at a faster rate with a higher voltage (current is inversely proportional to resistance)
* Energy stores = kinetic, thermal, light, chemical, electrical, elastic, and gravitational potential
* Internal energy is the total kinetic and potential energy of all the particles that make up a system
* Hearing increases energy of the particles
* Temperature increase depends on what the substance is, mass, and energy input
* Specific heat capacity is the amount of energy required to raise the temperature of 1 kg by 1 degree
* The current in a single, closed loop has nowhere to go so is the same in all points
* Potential difference tells us the difference in electrical potential from one point in a circuit to another
* The more collisions between electrons, the more resistance
* Ohmic conductors = V is proportional to I, goes through origins (resistance remains constant)
* Filament lamps = heat increase due to current increase means resistance increases (curved graph)
* Diode = only flows in one direction, has a high resistance in the reverse (line along x-axis where no current flows)
* The resistance of LDR decreases as light increasing
* Steep gradient indicates low resistance as a large current will flow for a low potential difference
* If the resistance is not constant, the graph will be non-linear
* In a series circuit, the current is the same, the total potential difference is shared between components, and the total resistance is the sum of all the resistances (current had to travel through each component in turn so adding resistors increases resistance)
* In parallel circuits, the potential difference is the same, the current is split up for each component as it has multiple paths to take, and the total of two resistors is less than the resistance of the smallest individual one because of the multiple paths for current (more resistors = less resistance)
* A device with a larger voltage or current will use more energy per second
* When insulating materials are rubbed against each other, they can become charged
* Friction moves electrons from one material to another and the charge remains (they are insulators, conductors would conduct charge to earth so it can’t build up)
* An object with no conducting path to earth is isolated
* As the charge of an isolated object increases, the voltage decreases
* When the charge becomes high enough, a spark jumps across the gap to any conductor near it (discharged as an electric shock)
* If a charged object is brought near an uncharged object, it will attract it - the same charges repel
* Charged objects create electric fields which increase with charge and closer distances
* Cells and batteries have direct current (potential difference is positive or negative)
* Mains electricity has alternating current (alternates between positive and negative)
* Touching a live wire creates a large potential difference and current in the body
* If someone touches the wire through a break, they complete the circuits and create a P.D. from the live wire to earth, thus a current flows through them (enough to be fatal) in the form of an electric shock
* When a charge flows, it has to overcome the resistance of a circuit (needs energy)
* Power stations transfer energy supply to electrical energy (larger power stations are more efficient because they use large steam turbines meaning a higher temperature)
* Step up transformers increase voltage to transmission cables to reduce current (less heat lost)
* Step down transformers reduce voltage to a safe value
* Latent Heat is the amount of energy needed to change the state of an object (horizontal points on the graphs are where energy is being used to change the state)
* When particles collide with the walls of a container, they exert a force
* When work is done on a gas (for example bicycle pumps), energy is given to the particles, and the internal energy of the gas increases
* EM radiation is emitted when an electron drops to a lower energy level
* Absorbing EM radiation moves electrons to a higher energy level
* Rutherford and Marsden bombarded gold foil with alpha particles - some were deflected meaning they must have a concentration of mass (repelled by the same charge alpha particles carried)
* When electrons undergo a reaction they move from ground state to excited state (gain energy)
* This causes electrons to orbit the nucleus in shells further from the nucleus
* CHADWICK PROVIDED EVIDENCE FOR NEUTRONS IN THE NUCLEUS!!! (it might come up!!)
* Unstable nuclei give out radiation to become stable
* Activity of a radioactive source is the rate at which it decays (1 Becquerel = 1 decay per second)
* Alpha radiation is stopped by paper, has strong ionising power, is basically a helium nucleus, most likely to be absorbed
* Beta radiation is stopped by aluminium (reasonably penetrating), is a high speed electron, is likely to cause damage to cells/organs
* Gamma is an EM wave, is not absorbed by will ionise, very penetrating and needs thick lead/concrete to weaken it
* Contamination is the unwanted presence of radioactive materials
* Irradiation is the accidental/deliberate exposure to radioactive material, or the decay of contaminating atoms
* Safety includes only using for short times, wearing protection, and wearing gloves
* Food contaminated with an alpha source would be most ionising, however an area of gamma source is most dangerous because it is the most penetrating
* Radioactive decay is spontaneous and random
* The half life is the average time it takes for half the nuclei to decay/the time it takes for the activity to fall to 50% of its original value
* Isotopes with a short half life are unstable and emit radiation fast, but are not radioactive for long
* Medical teachers include isotopes entering the body and being detecting outside it
* In kidney tracers, isotopes pass through kidneys or build up elsewhere (radioactivity not being detected implied blockage)
* Thyroid cancer can be treated with radioactive iodine building up in the gland, or with gamma rays to destroy rumours
* Gamma is best to use as it is most penetrating, can be detected from outside the body, and is the least ionising
* The half life, activity and type of radiation needs to be considered when investigating medical uses of radiation
(Remember to get plenty of rest tonight!! Best of luck!)
