Physics P2 Flashcards
Structure of the atom
Nucleus in the middle- contains protons and neutrons, positive charge
Electrons whizz round nucleus with a negative charge
Proton
Mass- 1
Charge- positive
Neutron
Mass- 1
Charge- 0
Electron
Mass- 1/2000
Charge- Negative
How is the build up of static caused?
When two insulating materials are rubbed together, electrons will be scraped off one and dumped on the other
This will leave a positive charge on one and a negative charge on the other
Only electrons can move not protons, the way they transfer depends on the materials involved
When polythene rods are rubbed with a cloth duster what happens?
Electrons move from the duster to the rod. The rod becomes negatively charged and the duster is left with an equal positive charge
When an acetate rod is rubbed with a cloth what happens?
Electrons move from the rod to the cloth. The duster becomes negatively charged and the rod is left with an equal positive charge.
Like charges repel…
Unlike charges attract
Examples of static electricity sparks
- Clothing crackles
- Car shocks
- Shocks from door handles
Clothing crackles
When synthetic clothes are dragged over each other, electrons get scraped off. This leads to attraction and little sparks as the charges rearrange themselves
Car shocks
Static charge can also build up between your clothes and a synthetic car seat. Some cars have conducting strips which hang down behind the car, giving a safe discharge to earth
Shocks from door handles
If you walk on a nylon carpet wearing shoes with insulating soles, there will be a transfer of electrons from the carpet to you and and charge will build up on your body. Then if u touch a metal door handle the charge flows to the conductor and you get a shock
Give examples of electrically charged objects attracting other objects
- Balloons can stick to walls
- A charged comb can pick up small pieces of paper
Balloons sticking to walls
Rubbing a balloon against your hair or clothes causes electrons to be transferred to the balloon, leaving it with a negative charge. If you hold it up to a wall it will stick even if the wall isn’t charged. That’s because the charges on the surface of the wall move- the negative charges on the balloon repel the negative charges on the wall, leaving positive charges on the surface of the wall.
What is induction?
The method of using a charged object to force charges in an uncharged object to move
A charged comb picking up pieces of paper
If you run the comb through your hair, electrons will be transferred to the comb and it will become negatively charged. It can then be used to pick up little bits of paper even though they have no charge, the comb near the paper causes induction
How is lightning caused?
Rain drops and ice bump together inside storm clouds knocking off electrons and leaving the top of the cloud positively charged and the bottom of the cloud negative. This creates a huge voltage and a big spark
Uses of static electricity
-Paint sprayers use electrostatic charges to get an even coat
Dangers of static electricity
Can cause problems filling fuel
Earthing
Dangerous sparks can be prevented by connecting a charged object to the ground using a conductor. Earthing provides an easy route for static charges to travel to the ground. This means no charge and build up and create a shock or spark.
Electrons flow down the conductor to the ground if….
…the charge is negative
The electrons flow up the conductor from the ground if…
…the charge is positive
How do paint sprayers work?
The spray gun is charged, which charges up the small drops of paint. Each paint drop repels all the others since they all have the same charge so you get a very fine spray. The object being painted has an opposite charge to the gun so attracts the fine spray. There are no paint shadows
Electrostatic charges and fuel filling
As fuel flows out of the filler pipe, static can build up. This can easily lead to a spark which may cause an explosion in dusty or fumey places like when filling up a car with fuel. This can be fixed with earthing
Current
Rate of flow of charge around a circuit
What is current carried by?
Electrons
Why are metals good conductors?
They have free electrons which are able to move
Charge formula
Current x time
When a bigger current flows…
More charge passes round the circuit
What current to cells and batteries supply?
Direct current
What is direct current?
Current that keeps flowing in the same direction
A direct current source is always at the same voltage so you get a straight line
How does charge move in a direct current
In one direction only
Voltage (potential difference)
Voltage is the driving force that pushes the current round. Kind of like “electrical pressure”
Resistance
Anything in the circuit which slows the flow down (ohms)
The voltage is trying to push the current round the circuit and the resistance is opposing it
Increase the voltage…
…increase the current
Increase the resistance…
…then less current will flow
When an electrical charge goes through a change in voltage what happens?
Energy is transferred
Potential difference is the energy transferred per unit charge passed
Energy is supplied to the charge at the power source to ‘raise’ it through the voltage
The charge gives up this energy when it ‘falls’ through any voltage drop in components elsewhere in the circuit.
The bigger the change in voltage…
…the more energy is transferred for a given amount of charge passing through a circuit
A battery with a bigger voltage will supply more energy to the circuit for every coulomb of charge which flows round it. Why is this?
The charged is raised up “higher” at the start and more energy will be dissipated in the circuit too
What happens to current at a junction?
Current is conserved, this means the total current entering a junction is equal to the total current leaving a junction
Ammeter
Measures the current flowing through the component
Must be placed in series (connected in a line with the component)
Voltmeter
Measures the voltage (potential difference) across the component
Must be placed in parallel around the component under test- not around the variable resister or the cell
Static electricity
Charges are not free to move
This causes them to build up in one place and it often ends with a spark or shock when they finally do move
Fixed resister V-I graph
The current through a resistor (at constant temperature) is proportional to voltage. Different resistors have different resistances hence the different slopes
Filament lamp V-I graph
As the temperature of the filament increases, the resistance increases, hence the curve.
Diode V-I graph
Current will only flow through a diode in one direction as shown.
Light dependent resistor and resistance
1) In bright light, the resistance falls
2) In darkness, the resistance is highest
Light dependant resistor
In bright light the resistance falls
In darkness the resistance is highest
Thermistor
In hot conditions the resistance drops
In cool conditions the resistance goes up
Why do resistors get hot when a current passes through?
Electrons collide with ions in the lattice that makes up the resistor
This gives the ions energy which is emitted as heat
Electrical power
The rate in which an appliance transfers energy
When are all forces in balance?
When an object is stationary
When there’s a steady velocity any direction
When are there unbalanced forces on an object?
When there is acceleration
Why do falling objects in a vacuum accelerate at the same rate?
Because there is no air resistance to slow the falling objects down
Newtons 3rd law
For every action there is an equal and opposite reaction
Newton’s 1st law
If there are no forces on an object, or all the forces are balanced, the object will remain at rest or carry on moving at a constant velocity
Newtons 2nd law
If the forces acting on an object are unbalanced it will either accelerate or decelerate
Things that affect thinking distance
Reaction time
How fast you’re going
What affects braking distance
How fast you’re going
The mass of the vehicle
How good your brakes are
How good the grip is
Thinking distance
The distance the car travels in the time between the driver noticing the hazard and applying the brakes
Braking distance
The distance the car travels during its deceleration whilst the brakes are being applied
How are cars designed to reduce momentum change?
Crumple zones
Seat belts
Air bags
How is ionisation caused by the 3 types of radiation?
Alpha pulls electrons out of orbit because it’s positive
Beta pushes electrons out of orbit because it’s negative
Gamma transfers enough energy to the electrons to break free from the atom
Alpha
Helium nuclei- 2 protons 2 neutrons Big, heavy, slow moving Strong positive charge Strongly ionising Stopped by paper
Beta
Electrons Fast and small Negative charge Moderately ionising Stopped by aluminium When one is released a neutron turns into a proton in the nucleus
Gamma rays
Weakly ionising
Stopped by thick lead
Nuclear fission
Slow moving neutron is fired at an isotope of uranium
The neutron is absorbed making it unstable and causing it to split
When it splits it forms two lighter elements, 2 or 3 neutrons and thermal energy
How is nuclear fission controlled?
Uranium fuel rods placed in a moderator to slow down the fast moving neutrons
Control rods made of boron are raised and lowered between the fuel rods to limit the rate of fission by absorbing excess neutrons
Nuclear fusion
Two light nuclei (hydrogen) collide at high speed and fuse to create a larger nucleus (helium) and energy
Nuclear fusion advantages and disadvantages
- Releases a lot of energy- more than fission
- Doesn’t leave behind a lot of radioactive waste
- Plenty of hydrogen for fuel
- Requires high pressures and temperatures due to electrostatic repulsion of protons
- Fusion reactors really expensive and hard to build
Cold fusion
- Scientists Stanley pons and Martin Fleischmann reported cold fusion
- Many tried to repeat their work but few could do it reliably
- Many people discredited it
Where does background radiation come from
- Naturally occurring unstable isotopes
- Space
- Human activity
Uses of alpha
Fire alarms
A weak alpha source is placed close to two electrodes, the source causes ionisation and a current flows
Smoke will absorb the radiation so the current stops and the alarm sounds
Uses of gamma rays
Sterilising food and medical equipment
Doesn’t involve high temperatures
Treat cancer
Tracers
Uses of beta
Tracers
Thickness gauges
Dangers of radioactivity
Ionising
Can cause cancer
Radiation sickness
How to protect yourself from radioactivity
Use tongs
Arms length
Pointing it away and avoid looking directly at it
Keep it in a labelled lead box
How do protect yourself by working with nuclear radiation
- Wear full protective suits
- Lead lined suits/ lead barriers
- Remote controlled robot arms
Nuclear power advantages
- Releases a lot of energy
- Pretty safe
- Very reliable
- Doesn’t release CO2 or sulphur dioxide
- Fuel is cheap and readily available
Nuclear power disadvantages
- Reactive waste products
- Public perception is negative
- Danger of polluting land and rivers
- Carries the risk of leaks or major catastrophes
- Cost is high
Nuclear waste
- Cannot be recycled
- Long half lives
- Dangerous
- Can be dealt with using vitrification
- Packing into thick metal containers and burying the waste into a deep hole and filling it with concrete
Vitrification
Melting nuclear waste with other materials to form a type of glass
The liquid glass is sealed inside steel canisters and buried deep under ground
