Electrostatics Video

Uses of Electrostatics  Defibrillators – restarts a heart  Paint Spraying  Dust Precipitators  Photocopiers & Laser Printers

Paint Spraying  Spray Gun is charged – all of the paint gets the same charge  Like charges repel – paint particles spread out giving a fine spray  Object being painted is given the opposite charge – paint is attracted to object and sticks to it.  Advantages : less wasted paint; even coat of paint; awkward places are painted.

Electrostatic Dust Precipitators  Removes harmful smoke particles from a chimney. 1. Metal grid/wires placed in chimney 2. Grid connected to high voltage supply 3. Dust particles attracted to metal grid 4. Dust particles stick together 5. Large particles fall down chimney 6. Soot used to make building blocks

Electrostatics & Uses of Electrostatics Tests!

Mains Electricity Video

Current Electricity  Electric Circuits – must be COMPLETE to allow electricity to flow from + to – terminals on a cell/battery.  A Cell provides POTENTIAL DIFFERENCE (Voltage) in VOLTS. This provides the FORCE to move the charge carriers (in wires – electrons; in electrolysis – ions)  The resulting flow of charge is called CURRENT measured in AMPS.  Current always flows from + to – (even though the electrons flow from – to +!)

A Circuit to measure resistance A V A variable resistor varies the current in the circuit The component which is having its resistance measured A voltmeter measures Potential Difference in Volts An ammeter measures Current in Amps Resistance = Potential difference ÷ Current R = V ÷ I

Ohm’s Law  “For a metallic conductor at constant temperature, the ration of Potential difference (V) to Current (I) is constant”.  The constant is called Resistance, R measured in ohms, symbol Ω.  So R = V ÷ I, also V = I x R and I = V ÷ R RI V x ÷÷ Cover up what you want to find

Mains Electricity  Live (brown) brings supply to house  Neutral (blue) is return path to power station  Earth (green and yellow) carries current to 0V if the casing becomes live. This blows the FUSE which cuts off the supply.  Fuse is in series with the Live wire. Fuses come in various values; 2A,3A,5A,13A. A 13Amp fuse blows when current through it exceeds 13Amps A circuit-breaker is a re-settable fuse which can be re-set at the flick of a switch These have replaced fuse wire in the main fuse box.

Electrical Circuits Test!

Ultrasound - sound waves beyond the human hearing range  Range of human hearing is 20 – 20,000Hz so beyond that is Ultrasound Sound waves are LONGITUDINAL – the vibrations of the particles are in the same direction as the wave Compression – particles in wave squashed together Rarefaction – particles in wave spread out. Wavelength – distance occupied by one complete wave (unit – metres) Frequency – number of complete waves per second (unit – hertz) Amplitude – maximum distance a particle moves from its normal position.

Uses of Ultrasound  Check the condition of a foetus  Investigate heart and liver problems  Look for tumours in the body  Break down kidney stones and stones elsewhere in the body  Measure the speed of blood flow in vessels when a blockage of a vein or artery is suspected  Cataract surgery Non – medical uses : dentists shake plaque and dirt off teeth; jewellers clean delicate pieces of jewellery and watches

Ultrasound Test

Radioactivity Video

Radiotherapy and Diagnosis  Gamma rays γ  High frequency/energy electromagnetic waves emitted from the nucleus of a radioactive isotope  Very penetrating – can pass into the body to treat internal organs  Can damage living cells – over exposure should be avoided  X rays  High frequency/energy electromagnetic waves emitted when high speed electrons are decelerated  Very penetrating  Can damage living cells  An X-ray machine can produce and control X-rays of different energies – so some X-rays can have higher energy than γ rays

Alpha, Beta and Gamma emissions RadiationAlphaBetaGamma Ionising PowerVery strongMediumWeak Range in airAbout 5cmAbout 1mVery large, its intensity decreases with distance What stops it?paperA few mm of Aluminium Reduced by lead and concrete Ionisation – the ability to remove an electron from an atom, causing the atom to become charged. Alpha has 2 + charges so has a great ionising effect, beta has 1 – charge so a lesser ionising effect. Alpha and Beta particles are not good inside the body – they cannot escape from inside – so don’t swallow any – remember Mr Litvinienko? – killed with Polonium 210, an alpha emitter!

Using Gamma radiation  Treating cancer – large doses can kill and destroy cancer cells. A ‘gamma knife’ is rotated around a cancer to give the cancer a high dose but the healthy tissue a low dose. Side effects of this kind of therapy can be unpleasant but slows down the growth of the cancer.  Sterilising hospital equipment – Gamma kills bacteria and prevents the spread of disease. Tracers – some radioactive isotopes (in very low doses!) can be injected into the body to highlight places where a cancer may be growing. Common isotopes are Technetium – 99 and Iodine Radiographers – carry out procedures using X-rays and nuclear radiation. Lead prevents tissue absorbing radiation.

Radioactivity - discovered by Becquerel and researched by Pierre & Marie Curie (among others)  Some atoms naturally break up because the nuclear forces holding them together are not strong enough.  Radioactive substances decay naturally and give out Alpha (α), Beta (β) and Gamma (γ) radiation.  Radioactivity is a random process that cannot be controlled by external conditions such as temperature, pressure etc. Neither can the decay be predicted.  Radioactivity is detected usually with a Geiger-Müller (GM) tube and a ratemeter.  Activity is measured by counting the average number of nuclei that decay every second, unit – Becquerels (Bq).

Half Life  The time taken for the activity of a sample to fall to one half of its original activity, OR  The time for half of the atoms in a radioactive isotope to have decayed.  It is different for every radioisotope A Typical Decay curve

Alpha Decay  An alpha particle (or helium nucleus) contains 4 nucleons (2p + 2n)  When α is emitted, A decreases by 4, Z decreases by 2  The new element formed is two places lower in the Periodic table than the original radioisotope.  92 U 2 α + 90 Th Remember : A is the mass number = protons + neutrons Z is the proton number = number of protons OR electrons

Beta Decay - 1 β  A beta particle is a high energy electron emitted from the nucleus (!) [This is because a neutron decays to a proton, an electron and a bit of antimatter]  When β - is emitted, A does not change Z increases by 1 ( because it has an extra proton). 6 C -1 β + 7 N  A new element is formed that is one place higher in the periodic table than the original radioisotope

Background Radiation  This is ionising radiation that is always present in the environment.  The level of background radiation is low and does not cause harm.  E.g. Granite contains small amounts of Uranium which decays to Radon, a radioactive gas.  Sources (7): radioactivity in the air; radiation from Space (cosmic rays); rocks; food; medical uses; nuclear power; nuclear weapons testing (these last two make up just 1%).

Uses of Radioactivity  Alpha is used in Smoke detectors Americium-241  Beta is used to monitor the thickness of paper – Strontium-90  Gamma is used to treat cancer; to search for leaks from pipes; to check welds in castings. Dating: Uranium/Lead levels are used to date rocks – VERY OLD! Potassium/Argon levels date rocks up to about 100,000 years old Carbon 14/Carbon12 levels are used to check organic material up to 60,000 years old

What is radioactivity? Uses of radioisotopes & Radiation treatment tests!

Nuclear Fission U 235 can become unstable when bombarded with neutrons. It accepts a neutron, becomes U 236, which decays readily to Kr 92, Ba 141 and extra neutrons. (These may go on to strike the nuclei of other atoms causing further fission reactions – a CHAIN REACTION). It also releases massive amounts of energy!!!

A Nuclear Power Station The output of a Nuclear Reactor is controlled by: A graphite moderator between the fuel rods slows down fast-moving neutrons Boron control rods absorb neutrons and so control the rate of fission. Control Rods in a reactor core

Nuclear Fission Test!