Physics Module 4 Flashcards
How is static caused?
2 insulating materials rub together, electrons are scraped off leaving one positive (lack of electrons) and one negative (gained electrons)
What is static electricity?
Build up of static caused by friction
What happens if enough charge builds up?
Sparks/shocks
How can you discharge a charged conductor?
Connect it to an earth wire with a metal strap. Electrons flow down the strap if negative, up if the charge is positive. This is earthing.
What are ions?
Charged atoms/molecules
Explain paper rollers
As paper drags over rollers, static builds up, spark, which can cause explosions
What does earthing do?
Provide easy route for charges to travel to the ground so no charge builds up which can cause shocks
What do anti-static sprays/cloths do?
Make the surface of a charged object conductive so they can carry the charge away
What is a current?
A flow of electrical charge around a circuit
What is voltage?
Driving force that pushes current round
What does resistance do?
Slow down the flow
What happens if you increase the voltage?
More current flows
What happens if you increase the resistance?
Less current flows
What is the purpose of the wire and the circuit breakers?
They break a circuit if there’s a fault
Give a use of static electricity
Paint sprayers-charged gun, charged paint, drops repel, object attracts, fine spray,even,no waste.
Defibrillators, dust precipitators-smoke particles reach grid with high voltage and negative charge, particles attracted to metal plates, when heavy enough, fall to bottom.
What is a variable resistor?
A resistor where the resistance can be changed.
What happens when you turn the resistance up?
The current drops
What happens when you turn the resistance down?
Current increases
What does a longer wire do to the resistance?
More resistance, less current
What happens to the resistance if the wire is thinner?
More resistance, less current
What is the equation for resistance?
Resistance= voltage/current
What is potential difference?
Same as voltage
What does ammeter measure?
Current
What does the brown wire do in a plug?
It’s a live wire that carries voltage
What does the blue wire in a plug do?
It’s a neutral wire, electricity flows out through it
What does the earth wire do?
For safety
What is double insulation?
A plastic casing over the plug
What fuse rate do you need?
Slightly higher than the current, too high and won’t blow the current if a fault develops
What wave is ultrasound?
Longitudinal
Give a use of ultrasound
Breaking down kidney stones- high energy waves turn it into particles/ body scanning, waves pass through body, some reflected, detected at different depths
What’s better, X-ray or ultrasound?
Ultrasound safer, can see soft tissue
What is radioactivity made of?
Atoms with unstable nuclei
What does decay give out?
Alpha, beta, gamma
Explain alpha
Helium nucleus, mass 4, charge +2, 2 protons, 2 neutrons
Explain beta particles
Fast moving electron, no mass, charge of -1
What happens to an equation when a nucleus emits alpha?
Top number -4, bottom number -2
What happens to an equation when a nucleus emits beta?
Top number 0, bottom number +1
When does ionisation occur?
When particles gain/lose electrons
Why do alpha particles make good ionizers?
Large and easy to collide with, highly charged to remove electrons from atoms
What does radiation cause?
Cause cells to multiply cancer
What is the most dangerous radiation outside the body?
Beta and gamma
What kind of Waves are X-rays and gamma rays?
Electromagnetic waves
How are gamma rays released?
Released from unstable atomic nuclei when they decay
How are X-rays produced?
Firing high speed electrons at a heavy metal
What are some uses of radiation and background radiation?
Tracers in industry to find leaks- gamma, short half life, detectable
How do smoke detectors work?
Weak alpha source placed in, causes ionisation of air particles, which cues a flow of current, if a fires smoke particles hit by alpha particles, less ionisation of air particles, reduced current, alarm
Where does background radiation come from?
Unstable isotopes (air, rocks) space (cosmic rays) human activity, waste
Why does radioactivity decrease over time?
More unstable nuclei decay
What is half life?
Time taken for half of the radioactive nuclei to decay
What does a short half life mean?
Radioactivity falls quickly, lots of nuclei decay in a short time
Give a medical use of radiation
Radiotherapy-treatment of cancer using gamma rays, focused on tumour with wide beam rotated around patient so less exposure to normal cells.
Tracers in medicine-beta/gamma, short half life
Sterilisation of tools- gamma, better than heat, won’t melt plastic
What is a use of radioactive dating?
Can date rocks, measure amount of radioactive isotope, and knowing half life, you can find the age
Where is carbon 14 found?
In living things, when they die they stop exchanging gases with the air outside, carbon 14 is trapped inside, and decays with a half life is 5730 years
Explain uranium isotopes
They have long half lives, when they decay they produce stable isotopes of lead
What is nuclear fission?
Splitting of uranium atoms
How does nuclear fission work?
A nuclear reactor, causes a chain reaction or uranium and plutonium atoms split and release heat energy
How does uranium 235 work?
Used in some reactors, it’s stable but needs to be unstable to split, so slow moving electrons are fired at the atom. A neutron joins to create u236 which is unstable and splits to form 2 smaller nuclei, which release energy and fast moving neutrons, which cause a chain reaction
What are nuclear bombs?
Out of control chain reactions
How do control rods control chain reactions?
Free neutrons start a fission reaction, neutrons collide with uranium, split which raises the temperature. They limit the rate of fission by absorbing excess neutrons and keep the reaction in control.
What is nuclear fusion?
Joining of small atomic nuclei, 2 small nuclei combine to make a large nucleus
What are the conditions needed for fusion?
High temperatures and pressures
Why are fusion reactors hard to build?
Materials can’t take the heat needed
Give am example of am experimental reactor
JET- Joint European Torus
What bombs do fusion reactions happen in?
Hydrogen/H bombs
What is cold fusion?
Nuclear fusion at room temperature
