Physics 6 Flashcards
What happens when two insulating materials are rubbed together ?
Electrons will be rubbed off one, on to the other
What is static electricity ?
Electricity that is not free to move
True or False - only electrons move
True - negative charges are formed when electrons move to the material. Positive charges are caused by electrons moving elsewhere
What is current ?
The flow of electric charge round a circuit
What is potential difference ?
The ‘driving force’ that pushes current round
What is resistance ?
Anything which slows the flow down in the circuit
The greater the resistance over a component, the …..
Smaller the current that will flow
What is current measured in ?
Amperes
How do you work out the current in a circuit ?
Charge divided by time
What is potential difference measured in and how do you find it ?
Volts, it is the amount of energy transferred (work done) per unit of charge. So…
Work done divided by charge
How do you measure the current flowing through the component ?
Using an ammeter. It can be placed anywhere in series
How do you measure the potential difference across a component ?
Using a voltmeter. It must be placed in parallel around a component
What is a standard test circuit ?
One of the simplest circuits you can make. It is use to test components and find V-I graphs
What does a variable resistor do ?
Alters the current flowing through a circuit
Why does a V-I graph of a filament bulb curve ?
As the temperature of the filament increases the resistance increases
Why does resistance increase with temperature ?
When an electrical charge flows through a resistor some of it is converted into heat energy. The ions vibrate more because they are heated, making it harder for charge- carrying electrons to get through
What does Current x Resistance =
Potential difference
What does a diode do ? How does it do this ?
It regulates potential difference in a circuit by only letting current through in one direction
What does a light emitting diode do ?
Emits light when a current flows through in a certain direction
What does an LDR do ?
It changes it’s resistance depending on the intensity of light. In bright light the resistance falls and in darkness the resistance is high
What does a thermistor do ?
It’s resistance depends on the temperature. In hot condition the resistance is low and vice versa
What is a series circuit ?
When all the components are connected in a line. If one component is disconnected the circuit breaks.
What is shared an what is the same in a series circuit ?
Potential difference is shared and current is the same
How is potential difference shared ?
If a component has more resistance it has a bigger share I the potential difference
What is a parallel circuit ?
When each component is separate. If one component is disconnected it will continue to work.
In a parallel circuit what is shared and what is the same ?
Potential difference is the same and current is shared
What is the UK mains supply ?
230 volts
What I the frequency of the AC mains supply ?
50Hz
What is the difference between mains supply (AC) and battery supply (DC) ?
Alternating current goes back and forward but direct current travels in the same direction
How do you work out the frequency of an electricity supply ?
1 divided by time period
What three wires are used in cables ? What do they do ?
Earth - for safety, carries electricity to earth should something go wrong
Live - alternates between positive and negative voltage
Neutral - always at 0v
What are the features of a plug ?
- Metal parts are made of copper or brass because they are good conductors
- The case and cable covers are made of insulating plastics
What do earthing and fuses prevent ?
Electrical overload
What do fuses do ?
When there is a surge in current, the fuse melts which breaks the circuit, preventing electric shocks
What does ‘doubly insulated’ mean ?
It is when an appliance has a plastic covering with no metal bits showing, as well as the wires being insulated. So it doesn’t need an earth wire.
What is a circuit breaker ?
They are an electrical safety device that protects the circuit from damage If there is an electrical overload
Why are circuit breakers better than fuses ?
- they almost instantly cut the circuit, faster than a fuse
- they an easily be reset by the flick of a switch rather than needing to be replaced like a fuse
How do you find an appliances power rating ?
Energy transferred = power rating x time
What was the plum pudding model ?
It was an early model of an atom in which negative electrons were dotted randomly inside a sphere of positive charge
What experiment did Rutherford use ?
He directed alpha particles at a gold sheet, it was expected that the particles would go through the sheet however some were deflected
How did Rutherford’s results back up the modern day model of the atom ?
It showed that most of the atom was empty space because they mainly passed through. If the plum pudding theory was correct none should be deflected because the positive charge would be thinly spread out and unable to deflect a fast moving alpha particle
What are isotopes ?
Different forms of the same element, they are atoms with the same number of protons and a different number of neutrons
When do radioactive substances decay ?
Randomly, they are unaffected by physical conditions and it is impossible to know when their nuclei will decay
What are the three forms of radiation ?
Alpha, Beta, Gamma
What is background radiation ?
Radiation that is present at all times. The radiation we receive is: - radioactivity of naturally occurring isotopes - radiation from space (cosmic rays) - man made sources, eg. Nuclear weapons
What is an alpha particle ?
Two neutrons and two protons. They are big and heavy and slow which means they don’t penetrate very far into materials.
What are beta particles ?
They are electrons, which means they are small and quick. They are moderately penetrating an have a long range in air.
What do gamma rays do ?
They penetrate far into materials, they easily pass through air. Eventually they hit something and do damage.
If the radiation dose is high what are you at risk of developing ?
Cancer
What is radiation dose ?
It is the amount of radiation you receive. It determines the damage done by the radiation and depends on the type of radiation and the amount of radiation
How can your location affect the radiation dose ?
Certain underground rocks emit higher levels of radiation. You could also live near a nuclear industry
Certain Professions can also increase your radiation dose, give examples
- Radiographers wear lead aprons to protect themselves from exposure
- Pilots have increased background radiation at high altitudes
- Miners are affected by the underground rocks
Why are alpha and beta particles deflected in a magnetic field ?
They are opposite charges.
Alpha = Positive
Beta = Negative
Beta particles spiral when deflected but alpha particles only move away slowly, why are beta particles more affected ?
Beta particles have a smaller mass
What is half life ?
The average time it takes for the number of nuclei in a radioactive isotope sample to halve
How are alpha particles used in smoke detectors ?
A weak source of the alpha particles is placed close to two electrodes. The ionisation from the source creates a current between the two electrodes. Smoke absorbs the radiation which cuts the flow and sounds an alarm
How are radioactive substances used in medicine ?
It can be used to measure whether parts of the body are functioning properly
Why are Gamma and Beta emitters used in medicine ? And why do they have to have a short half-life ?
So that the radiation passes out of the body, a short half-life is needed so that the substance isn’t in the body for too long
What is radiotherapy ?
Gamma rays can kill all living cells. Because of this they can be targeted at cancer cells at a specific dosage to kill them.
What is the down side to radiotherapy ?
The gamma rays kill some healthy cells which causes the patient to feel very ill.
How can gamma rays be helpful in the sterilisation of food ?
When exposed to a high dose of gamma rays, microbes inside the food will be killed. This keeps the food fresher for longer.
How does radiation harm cells ?
The radiation collides with molecules causing ionisation
How does radiation cause cancer ?
If it is a low dose, the radiation will cause minor damage to the cells without killing it. When the radiation hits the nucleus a mutated cell can form. These divide uncontrollably, this is cancer
Why are Beta and Gamma sources most dangerous outside the body ?
These sources can get inside organs, where as alpha particles cannot penetrate cells
Why is an alpha source the most dangerous form of radiation inside the body ?
Gamma and Beta can pass through your body if inside, where as Alpha particles cannot get out. As a result they do damage in a localised area
Which substance absorbs all forms of radiation ?
Lead
How do nuclear power plants currently generate electricity ?
Nuclear fission
What is nuclear fission ?
It is the splitting up of large atom nuclei, this releases lots of energy in the form of heat
How does the heat energy released in nuclear diffusion converted to electricity ?
In the same way coal, oil an gas does, it heats water which creates steam. This drives a turbine connected to an electrical generator
What radioactive substances are used for nuclear fission ?
Uranium-235
Plutonium-239
Describe the process of nuclear fission
A slow moving neutron is absorbed by a large nucleus forcing it to split into smaller nuclei. Along with the nucleus splitting neutron are also emitted. This causes a chain reaction as those neutrons are absorbed by another nucleus and the process begins again.
What is the biggest problem with nuclear fission ?
The waste product is highly radioactive so it is difficult and expensive to dispose of
Even though nuclear fuel is cheap the overall cost is high, why is this ?
The power plant is expensive to construct. As well as this the plants take decades to decommission
What is nuclear fusion ?
When two small nuclei are joint together to create a larger nucleus
Why is fusion better than fission ?
A lot more energy is released, not a lot of waste is left behind, fuel is readily available
What is the difficulty of nuclear fusion ?
It can only happen at very high temperatures - around 10,000,000 degrees Celsius
Why is nuclear fusion not currently a suitable source of electricity ?
More energy is used up getting to the high temperatures than is vein produced.
What is a protostar ?
Dust and gas that is spiralled together because of the force of gravity
How is a main sequence star formed ?
The gravitational energy is converted to heat energy which allows nuclear fusion to take place. This releases a lot of heat energy
What nucleus is used and what is produced in nuclear fusion ?
Two hydrogen atoms join to form a helium atom
What is the ‘stable period’
The time a star has where it’s heat output balances the force of gravity. This lasts for billions of years where the sun is ‘stable’
What happens at the end of the ‘stable period’ ?
The hydrogen begins to run out, so larger elements like iron are made. The outer layer cools, giving a red appearance, hence it being called ‘red giant’
What happens to a red giant about the size of the sun ?
It discards its outer layer leaving a hot, dense core. This ‘white dwarf’ cools to form a ‘black dwarf’ and eventually disappears.
A ‘Red super giant’ is just a larger ‘red giant’, how do they become supernovas ?
They undergo more fusion which causes them to expand and contract several times. Eventually they explode into a supernova. Supernova’s debris forms new planets and stars
A core is left over once the supernova explodes, what happens to it ?
The core, or a ‘neutron star’, becomes a black hole if big enough
