What are AC and DC in terms of mains electricity?
Mains supply is AC (alternating current) which means that the current is constantly changing direction. The frequency of AC is 50Hz. Cells and batteries supply DC (direct current) which means that the current is always flowing in the same direction.
Approximately how many volts is the UK mains supply?
In a cable what are do the brown, blue, green&yellow wires mean?
Brown= live wire, alternates between +ve and -ve high voltage Blue= neutral wire is always at OV Green&yellow= protects wiring and for safety, works with fuse
How do fuses work?
If a fault develops in which the live wire touches the metal case, because the case is earthed, too great a current flows in through the live wire, through the case and out down the earth wire. This surge in current melts the fuse when the amount of current is greater than the fuse rating. The cuts off the live supply and breaks the circuit.
What is earthing?
When the case in a cable is connected to an earth wire
What is double insulation?
If an appliance has a plastic casing and no metal parts showing. Doesn't need an earth wire, known as two-core cables
Name one advantage and one disadvantage about Circuit Breakers compared to Fuses
Can be reset whereas fuses have to be replaced, however circuit breakers are more expensive
Are u enjoying revising?
YES I LOVLOVLOV REVISING!!!!
What is the equation to work out how much energy is transferred in an appliance?
Energy Transferred= Power x Time
What is the formula for Electrical Power?
Power= Current x P.D.
What is the formula for Energy transformed?
Energy Transformed= Charge x P.D.
Atoms with the same number of protons but a different number of neutrons, same atomic number but different mass numbers.
Name some sources of Background Radiation
Air, food, building materials, space, dumped nuclear waste
Alpha Particles are the nuclei of what?
Helium Nuclei, two neutrons and two protons
Describe Alpha particles e.g fast and the outcome of this e.g penetration into materials
Big, slow moving and heavy and therefore don't penetrate very far into materials and are stopped quickly even when travelling through air.
Are alpha particles ionising?
Yes, strongly. They bash into a lot of atoms and know electrons off, creates lots on ions.
What are Beta particles?
Describe Beta particles e.g fast and the outcome of this e.g penetration into materials
Quite fast and quite small, virtually no mass and a charge of -1. Penetrate moderately into materials before colliding, have a long range in air and are moderately ionising.
For every Beta particle that is emitted, what happens?
A neutron turns into a proton in the nucleus
What are Gamma rays?
Very short wavelength EM waves
Describe Gamma rays e.g fast and the outcome of this e.g penetration into materials
Opposite of alpha, no mass or charge, penetrate far into materials without being stopped and pass straight through air, weakly ionising because they tend to pass through rather than colliding with atoms.
What happens to Alpha, Beta and Gamma in Electirc and Magnetic Fields.
Gamma has no charge and is therefore not deflected. Alpha is positive and Beta is negative and therefore are deflected in opposite directions. Alpha has a larger charge and will therefore feel a greater force however it is deflected less because it has a greater mass.
The average time it takes for the no. of nuclei in a radioactive isotope sample to halve.
What is the unit for measuring Radioactivity?
Becquerel (Bq), 1Bq means one nucleus decaying per second.
The radioactivity of a sample always ... over time
A short Half-life means the activity falls how and why
Quickly because lots of the nuclei decay quickly
Name four uses of radiation
Smoke detectors, Tracers in medicine, Radiotherapy and sterilisation of food and surgical instruments.
Name five safety precautions taken when dealing with radiation
Use for as short a time as possible, never allow skin contact, far away from body as possible, keep source pointing away, lead absorbs all so store in lead box wear lead aprons and stand behind lead screen
The extent of the harmful effects of radiation depends on two things, what are they?
How much exposure you have to the radiation, the energy and penetration of the radiation (some sources are more hazardous than others)
Define Nuclear Fission
The splitting up of big atoms nuclei