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PHYSICS ASSESSMENT - Coggle Diagram
PHYSICS ASSESSMENT
ELECTRICITY
CIRCUITS
SERIES CIRCUITS.
In a series circuit, the different components are connected in a line (end to end) between +ve and -ve of the power supply.
If you remove one component, the circuit becomes broken and all the different components stop working. This is why not many things are connected it series.
The total potential difference of supply is SHARED between the various components. The pd round a series circuit always equals up to the source of pd.
Vtotal = V1+V2+...
The current is the same everywhere in a series circuit: I1 = I2 =....
The size of the current is determined by the total pd of the cells and the total resistance of the circuit:I = V/R
The total resistance of two components is just the sum of their resistance: Rtotal = R1 + R2. This is because by adding a resistor in series the two resistors have to share the same pd.
There is a bigger pd when more cells are in series, if they are all connected the same way.
For example when two cells with a potential differnence of 1.5v are connected in series the supply 3v between them.
PARALLEL CIRCUITS
In parallel circuits each component is connected to the power supply separately.
If you remove or disconnect one of the components it hardly affects the other ones at all. this is how many things are connected in cars and household electrics.
The total current flowing the circuit is equal to the total amount of currents through the seperate components: Itotal = I1 + I2 The current is shared into the branches.
There are junctions where the current either splits or rejoins. The total current the junction will be the total current leaving the junction too.
If you have resistors in parallel, their total resistance is less than the smallest of the two two resistors.
In parallel circuits all the components get the full source of potential difference, it is the same the whole way around the circuit: V1 = V2 = ... . This means that the identical bulbs in the circuit will have the exact same brightness.
CURRENT
Current is the flow of electrical charge. The unit for it is ampere, A.
Electrical current will only flow around a complete circuit (closed circuit), if there is a potential difference a current can only flow if there is a source of potential difference (voltage).
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Potential difference (or voltage) is the driving force that pushes the charge around the ciricuit. It is a V for volt.
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Resistance and V = IR
The formula linking potential difference and current is: potential difference (V) = current (I) x resistance (R)
example: A 4.0Ω resistor in a circuit has a potential difference of 6.0V across it. What is the current through the resistor?
V = I x R --> pd = current x resistance.
6.0V = 4.0Ω x ?
rearrange!!!
so, I = V/R
? = 6.0 / 4.0
I = 1.5A
STATIC ELECTRICITY
When two objects are rubbed together, electrons are transferred from one object to the other. One object becomes more postivley charged and the other negative.
A non-contact force exists between charges objects.
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MOVING CHARGES
When you rub two different materials against each other, they become electrically charged. This only works for electrically insulated objects and not with materials like metals, which conduct.
For example... if you rub an acetate plastic rod with a duster.
- Electrons move form the rod to the duster.
- The duster becomes negatively charged and the rod becomes positively charged.
The opposite happens with a polythene rod:
- electrons move from the duster to the rod.
- the rod becomes negatively charged and the duster becomes positively charged.
In both examples, the materials gain an equal amount or charge but the charges are opposite (one material becomes negative while the other becomes positive).
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RADIOACTIVITY
NUCLEAR RADIATION
There are three main types of ionising radiation emitted from the unstable nuclei of 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 come from the 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 electron. The electron then shoots out of the nucleus at high speed, leaving the new proton behind.
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.
PROPERTIES OF RADIATION
Radiation can be absorbed by substances in their path. For example, alpha radiation travels tens of centimetres in air and gamma radiation travels very large distances.
All types of radiation become less intense as they travel further away from the radioactive material this is because the particles or rays become more spread out.
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Gamma radiation is the most penetrating. Even smalll levels can penetrate air, paper or thin metal. Higher levels can only be stopped by many centimetres of lead or many metres of concrete.
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HALF-LIFE
The nuclei of radioactive atoms are unstable. They breakdown and change into a compleltely differnent type of atom. This is called radioactive decay.
For example... carbon-14 decays to nitrogen-14 when it emits beta radiation. As this breakdown occurs the activity of any radioactive source becomes less. This activity is measured in becquerels.
There are two definitions of half-life: 1) the time it takes for the number of nuclei of the isotope in a sample to halve. 2) the time it takes for the count rate from a sample containing the isotope to fall to half its starting level.
GRAPHS
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.
The count rate drops from 80 to 40 counts a minute in two days, it drops from 40 to 20 - it halves. In the two days after that, it drops from 20 to 10 - it halves again and so on.
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