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Physics (Forces (Resultant force and accelaeration (If the resultant force…
Physics
Forces
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Newtons laws
Newton’s First Law of Motion states that objects with balanced forces acting on them will stay at rest or stay in constant motion.
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Friction-When two surfaces slide past each other, the interaction between them produces a force of friction. Friction is a force that opposes motion.
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weight and mass
Weight is not the same as mass. Mass is a measure of how much matter is in an object. Weight is a force acting on that matter. Mass resists any change in the motion of objects.
In physics, the term weight has a specific meaning - which is the force that acts on a mass due to gravity. Weight is measured in newtons. Mass is measured in kilograms.
The mass of a given object is the same everywhere, but its weight can change. We use balances to measure weights and masses.
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Types of radiation
There are three main types of radiation emitted from radioactive atoms. These are alpha, beta and gamma radiation.
Alpha radiation
Alpha radiation consists of alpha particles. An alpha particle is identical to the nucleus of a helium atom, which comprises two protons and two neutrons.
Beta radiation
Beta radiation consists of high energy electrons emitted from the nucleus. These electrons have not come from the electron shells or energy levels around the nucleus.
Instead, they form when a neutron splits into a proton and an electron.
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Gamma radiation
Gamma radiation is very short wavelength - high frequency - electromagnetic radiation. This is similar to other types of electromagnetic radiation such as visible light and x-rays, which can travel long distances.
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Electrostatics
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Static electricity
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Gold leaf electroscope
Used to find the charge of an insulator, a metal rod connects a metal cap to a gold leaf
Bringing a negatively charged rod close to the cap will repel the electrons down the metal rod. The gold leaf moves away from the metal rod because they both have the same charge. The greater the charge the further away the leaf moves.
Bringing a positively charges rod close to the cap will attract the electrons towards the cap, leaving the gold leaf and the metal rod with a positive charge. Again, the gold leaf moves away from the metal rod because they both have the same charge.
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Background radiation
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Some sources of radioactive of background radiation from naturally occurring radioactive isotopes are
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Background radiation is all around us. Some of it comes from natural sources and some comes from artificial sources.
Half life
The nuclei of radioactive atoms are unstable. They break down and change into a completely different type of atom. This is called radioactive decay. For example, carbon-14 decays to nitrogen-14 when it emits beta radiation
It is not possible to predict when an individual atom might decay. But it is possible to measure how long it takes for half the nuclei of a piece of radioactive material to decay. This is called the half-life of the radioactive isotope.
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It is possible to find out the half-life of a radioactive substance from a graph of the count rate against time. The graph shows the decay curve for a radioactive substance.
Current, voltage and resistance
Charge and current
Electrical current is the rate of flow of charge. It is measured with an ammeter(connected in series and its unit is amperes or 'amps' (A).
A cell is a chemical device with its own positive and negative terminals which push electrons around a circuit. A battery is a collection of cells, often joined together in series.
A cell or a battery provides a direct current (d.c.). This means that the electrons travel in one direction.
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Resistance
Components have different resistances, and can be used to control the size and current in circuits
Series circuits
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The current will be larger when more cells are used, but the ammeters will still show the same current at all points around the circuit
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Current is conserved at a junction because the total number of electrons entering a junction must be equal to the total number of electrons leaving a junction.
Potential difference
A voltmeter in a circuit measures the potential difference (p.d.) V in volts (V) across a component. It is connected in parallel with the component
the resistance of the component can be determined from the ammeter and voltmeter readings. The resistance R in ohms of a component is given by the equation R=V/I
nuclear fission
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In a fission reaction
A slow moving neutron is absorbed by a Uranium nucleus, creating an unstable Uranium nucleus
The new nucleus splits into two smaller nuclei (daughter nuclei) and two or more fast-moving neutrons.
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