Flashcards in Physics 2 Deck (50):
Most alpha particles went straight through the gold foil but a few were deflected. This is because...
Most of the atom is empty space as they passed through the foil.
Nucleus must have large positive charge as positively charged alpha part lies were deflected at a large angle.
Nucleus must be small as few particles were deflected back.
What did Rutherford and Marsden come up with?
What are radioactive substances?
Give out radiation from their nucleus of atoms all the time. This is known as radioactive decay.
Is radioactive decay random?
What happens to unstable isotopes of elements during radioactive decay?
They turn into stable ones.
Two neutrons, two protons, same as helium nucleus. When an atom decays by emitting an alpha particle, two protons and two neutrons are lost from the nucleus. They are slow and big so the don't penetrate far into materials. But as they are large, they are ionising as they knock into atoms and cause electrons to go off, this creates many ions.
Has no mass and a charge of -1. In beta decay a neutron turns into a proton in the nucleus, this releases a beta particle. They are small and fast so the penetrate a bit and are a little ionising.
Short wavelength electromagnetic waves. No mass and no charge. Penetrate far but weakly ionising as they don't collide with atoms.
What happens to alpha and beta particles when traveling through a magnetic field?
They are deflected as they are charged. Alpha are deflected less as they have a larger mass. They also have a greater charge so feel more force in a magnetic field.
What is a half-life?
Average time in which it takes for the number of nuclei of a radioactive isotope to halve.
Where does background radiation come from?
Space, nuclear waste, rocks, air.
What are the safety precautions to reduce exposure to radiation?
Keep exposure to minimum.
Don't point towards body.
Don't make contact with source.
Keep it far from the body.
Lead absorbs the radiation, so keep in lead box, wear lead aprons, stand behind lead screens, only expose the part of the body that needs to be
Use alpha radiation. A weak source is positioned in the detector, close to two electrodes. A current can flow between the two electrodes as the alpha causes ionisation of the molecules in the air by knocking electrons. If there is a fire, smoke absorbs the radiation and the current stops.
Beta or gamma used. They are placed into people and their progress around the body is followed by an external detector.
The treatment of cancer. This uses ionising radiation. The radiation such as gamma is aimed at the right area with the correct dosage. This ensures that cancer cells are killed but other cells aren't however, they will get slightly damaged.
High doses of gamma rays kill microbes.
What is nuclear fission?
When an atomic nucleus splits up. This creates two nuclei which are smaller.
Nuclear fission releases a lot of energy.
Uranium 235 and Plutonium 239 are used in nuclear power stations.
In order for nuclear fission to occur, a neutron which a moving slowly must be absorbed into the nucleus. This makes the nucleus unstable so it splits to form to smaller nuclei which are radioactive as they don't have the right amount of neutrons.
Nuclear power stations.
Use nuclear reactors. Inside this, there is chain reaction which is controlled. Uranium 235 or Plutonium 239 nuclei split up and release energy as heat. This can be used to heat a coolant which is then pumped into a boiler. The heat is then transferred to water to produce steam which drives a turbine which is connected to a generator. The coolant can then be pumped into the reactor and the process proceeds.
What are the disadvantages of nuclear power?
Difficult and costly so dispose radioactive waste.
Expensive to build and decommission.
What are the advantages of nuclear power?
What is nuclear fusion?
When two nuclei join such as hydrogen nuclei. It releases more energy than fission.
Don't leave much radioactive waste.
A lot of hydrogen about.
It can only occur at high temperatures which requires a strong magnetic field.
What is the life cycle of a star?
1) Stars form from clouds of dust and gas.
2) Force from gravity makes gas and dust to spiral together and form a protostar.
3) In a protester, gravitational energy in converted into heat energy which makes the temperature rise.
4) Once the temperature is high enough, the hydrogen nuclei undergo under go nuclear fusion to form helium nuclei. At this point a star is born.
5) Now, it enters a long stable stage known as a main sequence star. The heat provided by nuclear fusion gives an outward pressure which balances the force of gravity which pulls everything inwards.
6) Eventually hydrogen begins to run out and the star begins to fuse helium and other heavy elements up to iron.
What happens to a star larger than the sun?
1) Becomes a super red giant as it expands.
2) It expands and contracts multiple times which forms elements as heavy as iron.
3) It explodes into a supernova which forms elements heavier than iron. They are ejected into space which will create planets and stars.
4) The exploding supernova throws the outer layers of dust and gas into space which leaves behind a dense solid core, neutron star. If it is large enough it will become a black hole.
What happens to a star the same size as the sun?
1) Expand to red giant. It becomes red as the surface cools.
2) As it is unstable it ejects its outer layer of dust and gas as a planetary nebula.
3) This leaves a dense and solid core, a white dwarf. It then cools to a black dwarf.
Crumple on impact. Increase the impact time, decreasing the force produced by a change in momentum.
Side impact bars.
Direct kinetic energy away from passengers.
Stretch to increase the time taken for the wearer to stop. Absorb some kinetic energy. Stops person going through windscreen.
Slow you down more gradually. Prevent you hitting surfaces.
What is a static charge?
An electrical charge which cannot move.
Longer life time than filament bulbs.
More energy efficient.
Use smaller current to operate.
They are more expensive.
You need serval to provide the same amount to light.
Allows current to flow freely through it in one direction. This is because it has a high resistance in the other direction.
A resistor which is dependent on light intensity.
In bright light, the resistance falls.
In darkness, the resistance is highest.
Type of resistor whose resistance depends on temperature. A negative temperature coefficient (NTC) thermistors resistance decades as the temperature increases.
In hot conditions, the resistance drops.
In cold conditions, the resistance increases.
Most appliances are connected by three-core cables. This means they have three wires inside of them, they are copper and surrounded by a plastic.
Green and yellow. (Works with fuse)
Don't have earth wire. Used for electrical appliances that have a casing which doesn't conduct electricity.
Three-pin plugs and cables- Wiring
There should be no bare wires showing.
The cables must be tightly fastened to the outer layer of a cable.
The right colour wire must be connected each pin and screwed in.
Three-pin plugs and cables- Materials.
Metal parts use copper or brass as they are good conductors of electricity.
The case, insulation and grip are made from plastic or rubber as they are not only flexible but are also good insulators.
In a three-pin plug, current flows through the fuse to the live wire. If the current is too high, the fuse will melt and the circuit will break.
If they detect a surge in current they will brake the circuit by opening a switch to the live wire. These are faster and safer as you don't have to wait for a fuse to melt. It can also be reset easily where as a fuse has to be replaced. But, they are more expensive.
Works with a fuse or a circuit breaker to prevent damage to an appliance.
If a fault occurs in which the live wire happens to touch the metal casing, because it is earthed, too big a current will flow through the live wire, through the case and down the earth wire. This surge in current melts the fuse which causes the live supply to be cut off and the circuit is broken. This then makes it impossible to receive an electric shock.
The larger the current, the thicker the cable needed.
Residual current circuit breakers (RCCB)
Protects users from electrocution.
RCCB detects differences in currents and rapidly cuts off the power by opening a switch.