P4a - Electrostatic Sparks
Positively charged - missing electrons Like charges - repel
Negatively charged - extra electrons Opposite charges - attract
- When two insulators are rubbed, due to friction, electrons transfer off one and onto the other causing on to become positively charged and the other negatively charged
- Polythene rod and a duster = Polythene rod becomes negatively charged
- Acetate rod and duster = Acetate rod becomes positively charged
Electric shock - A flow of electrons though our bodies detected by our nerves
Earth connection - To discharge something, it can be connected to the floor with a thick metal wire connecting to a large metal plate on the ground. Objects with an earth connection are said to be 'earthed'
If you stand on a insulating mat you will become electrostatically charged easier. When you touch something which is earthed you will discharge.
P4a - Electrostatic Sparks Continued...
Anti-static sprays, liquids and cloths stop the build up of static charge
When an object discharges the electrons jump accross the gap just before the two objects touch. This is a spark and can cause explosions if
- the atrmosphere contains inflammable gases i.e. hydrogen and methane
- there are inflammable vapours i.e. petrol or methanol
- there is a high concentration of oxygen
P4b - Uses of Electrostatics
Defibrillators - Used to start the heart when it's stopped as they restores a regular heart rhythm by delivering an electric shock through the chest wall to the heart. This is done by two paddles being charged from a high voltage supply and placed firmly on the patients chest. They must make a good electrical contact so the charge can pas through the patient and make their heart contract.
Dust Precipitators - Remove smoke particles from chimneys before they pollute the air. This is done by metal plates, wires or grids being put into chimneys and given a charge from a high voltage supply. The dust particles then pass close to the wires and become charged. They then repel from the wire and become attracted to the oppositely charged plates and clump together. Eventually the become to heavy and fall back into the chimney.
Paint Sprayers - The object and the paint are given opposite charges. The paint particles repel each other and so give a fine spray. The object attracts an even coat on parts in shadow and underneath too.
P4c - Safe Electric Circuits
- Circuit - a flow of electric charge. Variable resistors can be used to change the current in a circuit. When the resistance increases the current decreases. When the pd across the resistor increases, the current increases.
- Current - The flow of electrons. The current only flows through wires or components.The electrons flow in the opposite direction to the direction of the current. Measured in amps (A) using an ammeter.
- Voltage - Potential difference (pd). The driving force which pushes the current round. Measured in volts (V) using a voltmeter.
- Resistance - Anything in the circuit which slows down the current. Measured in ohms (Ω) Resistance = V/A
- Live wire - Brown - High voltage connection - Right
- Neutral wire - Blue - Completes the circuit - Left
- Earth wire - Green and Yellow - Safety, stops wire becoming live - Middle
P4c - Safe Electric Circuits Continued...
Fuse - Thin piece of wire which melts if the current gets to large causing the circuit to break stopping the flow of current.
Circuit breakers - Switches which switch off when the current gets to high. They can be switched on again once the fault is corrected.
Double insulated appliances don't need earthing as the case isn't a conductor therefore it cant become live.
P4e - Ultrasound
Compression - Where the particles are closest together.
Rarefaction - Where the particles are furthest apart
Amplitude - The maximum distance a particle moves from its normal possition
Longitudinal waves - The wave vibrates back and forth, parallel to the direction of travel. Compression and Rarefaction occur.
Transverse waves - The wave vibrate at right angles to the direction of travel.
Both waves carry energy but not material. Particles vibrate moving up & down, side to side and back and forward but do not get carried along with the wave
Ultrasound are longitudinal waves with a higher frequency then that of the upper threshold of human hearing. It can be used to break down kidney stones due to the vibrations and energy and for body scans. The ultrasound beam is sent into the body and is reflected from different interfaces in the body which allow the layers to build up into a picture by a computer. It doesn't damage living cells like x-ray so is safer and is reflected from soft tissue so can detect things x-rays can't.
P4e - Treatment
X-rays are made by firing high-speed electrons at metal targets and the rate of production and energy can be controlled.
Gamma rays are produced from a nucleus emitting an alpha or beta particle. The surplus energy is then lost by emitting gamma rays. Gamma rays can be used as tracers and can sterilise equipment.
Gamma rays & X-rays have similar wavelengths and kill living cells. They also are both very penetrative and contain electromagnetic radiation.
Cancer treatment - Radiotherapy - Using a radioisotope
Three sources of radiation each containing 1/3 of the dose are arranged around the patient with the tumour at the centre. The tissue receives only 1/3 of the does whilst the tumour receives the full does. This can also be rotated so the tissue receives intermittent doses.
P4f - What is Radioactivity?
Radioactive substances decay naturally, emitting alpha, beta and/or gamma radiation. Radioisotopes have an unstable nuclei as their nuclear particles aren't held together strongly enough. The half-life of a radioisotope is the average time for the nuclei present to decay. This cannot be changed.
- Positively charged Negatively charged
- Has a large mass Has a very small mass
- Is a helium nucleus Travels very fast
- Has helium gas around it Is and electron
- consists of 2 protons & 2 neutrons
- Mass number decreases by 4 Mass number is unchanged
- Nucleus has 2 less neutrons Nucleus has 1 less neutron
- Nucleus has 2 less protons Nucleus has 1 more proton
- Atomic number decreases by 2 Atomic number increase by 1
P4g - Uses of Radioisotopes
Background radiation is in the environment 24/7 due to radioactive gases, rocks, soils, food, drink, cosmic rays, nuclear power, bomb tests, industries, etc.
- Tracers - Can be used to detect leaks or blockages in pipes
- The tracer is added to the fluid in the pipe. a gamma source is used so it can penetrate to the surface. An increase in activity on a detector shows where the leak is and little or no activity is detected after this.
- Smoke detectors - Alpha sources are used
- Alpha particles from the source ionise atoms in the air so the air conducts electricity. A small current flows and the sensor detects it. If smoke blocks the path there is no current and the alarm sounds.
- Radioactive dating
- Rocks contain radioactive isotopes of uranium. The older the rock, the more of the isotope would have decayed into lead. We can use the ratio of uranium to lead to date the rock
- Radiocarbon-dating - Carbon-14 is a radioactive isotope of carbon in all living things
- By measuring the amount of Carbon-14 present an approx. age can be found as when an object dies no more is produced but it still decays.
P4h - Fission
Nuclear power is generated in a nuclear power station. The nuclear reaction produces heat (nuclear fission) which is used to produce steam, and then the steam turns a turbine which turns the generator.
- A uranium nucleus is hit by a neutron and absorbs it becoming unstable
- The unstable nucleus then splits in 2 giving out energy which is used by a nuclear reactor and other neutrons
- The two smaller nuclei produced are radioactive waste whilst the neutrons go on to hit other uranium atoms and lead to a chain reaction.
Controlling Nuclear Reactions - Boron control rods - can be raised/lowered. They absorb neutrons so fewer are available to split uranium nuclei.