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AS and A Level: Fields & Forces
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What are gravitational fields?
- 1 A gravitational field is a region where a mass experiences a force. The field strength, g, at any point in the field is given by g=F/m and the value of g on the Earth’s surface is taken to be 9.81Nkg-1.
- 2 Field lines point towards the centre of the Earth and are radial. Over small distances, near Earth's surface, g can be considered constant so field lines are parallel and the field is uniform.
- 3 G was calculated by Henry Cavendish by measuring the force of attraction between two lead spheres of known mass and separation. The force between two masses is given by F = Gm1m2/r2 and this is called Newton’s law of universal gravitation.
- 4 Inside the Earth, g falls from 9.81 to 0 Nkg-1 so we cannot use the inverse square law for r < RE.
- 5 Combining Newton’s law with circular motion can be used to calculate distance to geostationary satellites.
What are electric fields?
- 1 An electric field is a region where a charge experiences a force. The field strength E at any point in the field is given by E = F/Q. The force between two charges is given by Coulomb’s law.
- 2 For radial fields, E = 1/ Q/r2 and this is another inverse square law. For uniform fields, E = V/d.
- 3 Uniform electric fields can be set up to accelerate charges. The work done accelerating a charge through a p.d. V is given by W = QV. The unit of energy can be given in Joules (J) or electronvolts(eV).
- 4 When a charge enters a uniform electric field, such as between the deflection plates of an oscilloscope, there will constant acceleration and so suvat equations can be used.
For all electric fields, equipotential lines are drawn perpendicular to field lines. For radial fields, always show at least 3 equipotential lines as concentric circles with increased spacing.
The equipotential lines can be experimentally determined using conductive paper, metal electodes and a voltmeter to map out points of equal potential. You should be able to draw equipotential patterns for two point charges.
Similarities and differences between gravitational and electric fields.
- 1 Gravitational forces are always attractive but electric forces can be both attractive and repulsive. There are no negative masses but there are negative charges.
- 2 The ratio of the strength of the two forces is huge. For two electrons, FE/FG is approximately 1042. This demonstrates how much stronger the electric force is compared to the gravitational force over the same distance.
- 3 Both fields obey an inverse square law.
- 4 Over short ranges, electric forces dominate but over much larger distances, say between planets and their moons, gravitational forces dominate because the attractive and repulsive electric forces tend to cancel out.
Electromagnets are used to lift large masses of magnetic material such as scrap iron. Electromagnets are also found in electrical generators, electric motors, doorbells, circuit breakers, television receivers, loudspeakers, etc. The factors that increase the strength of an electromagnet are; * Increasing the number of coils, which adds more field lines and makes the electromagnet stronger. This is the magnetic field around a piece of wire, compared to a magnetic field on a loop or solenoid it is weak. Turning coils around and passing a current through them will make a much stronger electromagnet.
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The aim of this investigation to see the strength of an electromagnetic by varying many variable, and seeing how this affects the performance of the electromagnet.
Thickness of wire:- The thicker the wire is, the more electrons can travel through the wire simultanousely, and this will create more magnetic feilds, therefore increasing magnetism. Voltage:- As potential difference increases in the formula V=I x R, this means as voltage increases so will current and resistance, if current is increased this will alow more electrons to flow, causing the magnetism to increase. Resistance:- If the resistance of the variable resistor is increased, the voltage and current will drop as a result, therefore decreasing the amount of electrons passing through the wire, and also decreasing the magnetism.
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My aim is to investigate how to make electromagnets stronger to increase the amount of paperclips the iron bar magnet can pick up.
If the current flowing in the coil is reversed the direction of the magnetic field is also reversed. When I switch the current on the coil will pick up the paper clips. If I want to strengthen the magnetic effect of the coil, I will increase the number of coils. This will allow the iron bar to pick up more paper clips because the field around each of the coils contributes to the total magnetic effect. I will make sure that I keep the same variables because this could affect my experiment and give me different results that I should expect.
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To do a investigation in which to find out if increasing the number of turns on the coil will increase the magnetism.
If you put a compass on a field line then it points in the direction of the line. An electromagnet is a coil of wire with electricity flowing through it. This electric current turns the coil into a magnet with a magnetic field of exactly the same shape as a bar magnet. The good thing about an electromagnet is that you can turn it off if you switch off the current flowing through it, unlike a bar magnet. If you want to make the electromagnet stronger (in which we do)
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Variables * Input Voltage- This is the only variable being changed in this experiment. The voltage will be altered throughout the experiment * Number of turns on the primary coil- This variable will be kept constant. In my experiment the number of turns are 50. * Number of turns on the secondary coil- This variable will be kept constant. In my experiment the number of the turns will be 100. Therefore the 'turn ratio' will be 1:2. * The material used for the core- This variable will be kept constant. In my experiment the core is made out of Iron.
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the current varies, the strongest amps being (7.00A) and have the coils evenly spread across the iron rod. The 'soft' iron core means it changes easily between being magnetised and de-magnetised, it is perfect for electromagnets, which need to be turned on and off. From a previous experiment, using an electromagnet, I found out that the iron rod picked up many filings when turned on and dropped them all when switched off but the steel rod picked few filings up when switched on, yet held on to them even after the current was switched off.
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This will give me an idea of the strength of the magnet. To set up our experiment, first we'll attach one end of 2 wires to a power pack and the other ends to a wire wound into coils round a nail. The number of coils will be the changing variable. The power must be off until we are ready to use the circuit, or the nail will heat up and give us anomalous results, since the resistance changes with heat.
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The repulsive force between magnets with like poles facing explains how permanent magnets can be used to provide a levitating and thrust force to the train. Magnet Strength We know that magnets have a north and south pole and if we bring them together they will repel each other. We can see this effect in the picture below with the area between the two magnets having the iron filings being repelled away from the area in between the two magnets.
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The magnetic field around a wire is in the shape of circles. The magnetic effect can be strengthened by: -Using a larger current -Using more turns of wire on the core -Using a soft iron core -Bringing the poles together A circular magnetic field will develop around the wire. The field weakens as you move away from the wire, the field is perpendicular to the wire and the fields direction depends entirely on the direction of the current as it flows through the wire. The best way to amplify a magnetic field is to coil the wire.
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This experiment is designed to see if vertical height has anything to do with the speed of a moving vehicle as it rolls down a ramp.
We will also be careful when using the ramp, as it is heavy and has rigid edges. Prediction: I predict that the steeper our ramp is, the faster the trolley will travel. I think this because the higher the top of the ramp is, the greater the amount of Gravitational Potential Energy. (GPE). This will therefore result in more movement energy, or kinetic energy allowing the trolley to travel more quickly over a distance. The mass of our trolley will also be a dependant factor, as GPE=Mass X Gravity X Vertical height.
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In order for the test to be fair I am going to have to make sure that some aspects stay the same and some are changed. I plan to change the CURRENT (AMPS) and the amount of coils wrapped around the core of the magnet. The factors which will remain the same are the voltage which I will set at 12V and the size of the iron core of the magnet. The investigation will require me to increase the amount of coils surrounding the iron bar.
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The rules are issued under the authority of the hockey rules board on behalf of the International Hockey Federation.
As already mentioned, every team must have a goalkeeper. The other 10 players are referred to as 'field players', and are dispersed over the field of play. The field players can be put into three general categories - attackers, defenders and midfielders. While no player (other than the goalkeeper)
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All electromagnetic waves exhibit diffraction and interference as well as reflection and refraction. They also all obey the following equation: V = f.? (where v = velocity, f = frequency, ? = wavelength) Using this equation and because 'v' is a constant for a given medium, we discover that as the wavelength is decreased, the frequency is increased. *** There are seven main sections of the electromagnetic spectrum. They are, in ascending order of wavelength (where ? represents wavelength): * Gamma Rays ( ?
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Investigation into the factors affecting the strength of electromagnets - Planning Experimental Procedures.
The power pack will allow me to work with a safe voltage and to convert mains AC to DC. First I will connect the voltmeter to the power pack. From the voltmeter I will attach two connecting wires to the crocodile clips. I will then cut a large length of insulated wire and wrap the desired number of coils tightly around the soft iron bar, this is my electromagnet (EM). Then I will remove 3cm of the plastic coating around the copper wire using a wire stripper. I will then connect the ends of the exposed wire to the crocodile clips.
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It causes the circular motion of the moving electrons. Observe this phenomenon, and record the voltage applied to the accelerator and the radius of the circle along which these electrons are moving.
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Unlike refrigerator or bar magnets, electromagnets use electricity to generate a magnetic field. In addition, electromagnets give us the ability to turn the magnetic field on or off as we need. To make an electromagnet, you need electricity (usually supplied by a battery or a larger power source) and something for that electricity to flow through (wire coils, for example).
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3. Electromagnetic relay. A relay is something which changes a current form Big to Small, or Visa Versa 4. Doors in Banks/Jewellers Variables The different variables that can affect an Electromagnets field are: * Is the wire coiled (solenoid) * Number of coils in a wire * Different voltages * Is there an magnetic substance * Tightness (density) of the coils I will look at the number of coils and different voltages Hypotheses I think that an Electromagnet will be stronger if the wire is coiled round a magnetic substance tightly.
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The result of this is that the magnetised effect of the domains cancel each other out. In an unmagnetised piece of iron all the domains are lined up so that their magnetic effect reinforce each other. Flemming's left hand rule Using Flemming's left hand rule the direction of the force/motion can be predicted Electromagnet induction If a conductor such as a piece of wire is moved through a magnetic field cutting magnetic lines of force a voltage or emf will be induced across its ends. The process which produces the emf is called electromagnetic induction. If the wire is part of a complete circuit the induced emf will cause a current to flow.
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CURRENT - is the flow of electrons round the circuit. VOLTAGE - is the driving force that pushes the current round. RESISTANCE - is anything in the circuit that slows the flow down. There is a relationship between these three which is summarised as OHM'S LAW: V=IR voltage=Current x Resistance So if you increase the voltage - then more current will flow, if the resistance is constant. If you increase the resistance - then lass current will flow if voltage remains constant. Electromagnetic Induction This is the idea that magnetism can travel from one object to another even though they are insulated.
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First we have to use Pythagoras' theorem to work out the speed of the aircraft. Pythagoras' theorem is "the sum of the squares of the opposite and adjacent = hypotenuse" or a2 + b2 = x2 2002 = V2 + 502 2002 - 502 = v2 37500 = v2 v = ?37500 Resultant speed of aircraft = 193.6km h-1 (3s.f) We can now work out the time using the speed, distance, and time formula. V = S/T (speed = distance/time) T = S/V T = 50/193.6 T = 0.258 hours (3s.f) Time = 15 minutes 48 seconds This is the time just going to the base camp.
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I therefore predict that, the larger the ball bearing, the faster it will pass through the Glycerine. However, there is one slight drawback to this statement. The tube filled with the glycerine only has a circumference of about 24 or 25 cm. This means that after the diameter of the ball bearings become larger than about ten or eleven cm, then the time taken to pass through the Glycerine of seventy cm, will increase.
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In fact, NMR does not involve any form of radioactivity or ionising radiation. The word 'nuclear' was used to imply the manipulation of small atoms. Subsequently, the medical world has shed the term NMR, and has developed new techniques, which are based on the principles first established by Bloch. Most matter examined by NMR consists of molecules. Molecules are composed of atoms. For example, a water molecule contains two hydrogen atoms and one oxygen atom. A single hydrogen atom is made up of one proton.
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Physics Investigation Aim: To investigate the variables which effect the strength of an electromagnet and find the effect of a particular variable.
Prediction: I predict that in this investigation, the higher the number of turns, the stronger the magnetic field. This assures that the other variables are kept constant. Apparatus: 1) Insulated wire - wire to make the electromagnet. 2) Nail - to make the core. 3) Ammeter - to check if the current is constant. 4) Force meter - to check the Newtons. 5) Lead - to connect. 6) Crocodile clips - to join the leads together.
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An A.C current would demagnetise the core while a D.C. current would magnetise a core. This is because the D.C. current is direct and therefore all the electrons are arranged in the same order creating a magnetic field. When the current is A.C, the electrons are free to move where they want so there is no magnetic field. When an electromagnet has a current induced in it, it becomes magnetised and the greater the current induced the greater the strength.
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To change the angle of a ramp and place a trolley 70 cm away from its edge and release it and see how far the trolley travels off of the ramp.
I put the textbooks under the ramp at the same place each time * I make sure that the front of the trolley starts at the 70cm mark * I make sure that I let the trolley go rather then push it down the ramp * I do each test three times and average out the result * Our trolley isn't biased to one side when it rolls Measuring: To find out the distance travelled by the trolley from the end of the ramp I will use a metre stick and will measure from the base of the ramp to the front of the trolley where it has stopped on the desk/floor.
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