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# AS and A Level: Fields & Forces

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## What are gravitational fields?

1. 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. 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. 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. 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. 5 Combining Newton’s law with circular motion can be used to calculate distance to geostationary satellites.

## What are electric fields?

1. 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. 2 For radial fields, E = 1/ Q/r2 and this is another inverse square law. For uniform fields, E = V/d.
3. 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. 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.
5. 5 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. 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. 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. 3 Both fields obey an inverse square law.
4. 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.

1. ## Investigate ways of inducing a current in a coiled conductor and ways of affecting the size of the induced current.

withdrawn from the solenoid. 5. The magnet was plunged into the solenoid at a: a. slow speed b. medium speed c. rapid speed. 6. Two magnets were plunged into the solenoid with constant speed. 7. The second solenoid (with additional turns) was used in place of the first solenoid and the magnet plunged: a. Into the solenoid with constant speed b. out of the solenoid with constant speed. 8. All qualitative results were recoded in Table 1. DIAGRAM 1: Set up for Experiment 1. RESULTS: Table 1-Qualitative Observations of Experiment 1. Step Action Observation of galvanometer's needle. 2A Plunge N into Needle flicks positive 2B Hold N still inside Needle remains on 0 2C Move N in circulatory

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2. ## Electromagnet Interference.

They are inherent, natural and man made! I will now talk through how each one of these work! * Inherit: This produces noise but with any electronic equipment! A good example would be your television set making funny sounds when say a mobile phone is ring! The technical explanation for this is the thermal agitations of electrons that are flowing through the circuit resistance! * Man Made: A number of different classes of electronic and electrical equipment produce man-made EMI! They include power generators transmitters, power lines, motors, lighting, engines and electrical controllers. People might think these equipment help us live better in life but they do have downsides!

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3. ## About Hurling.

The object of the game is to score as often as possible into the opposing team's goal. * The Playing Field The playing area is a rectangular grass field approximately 137 meters in length (130m minimum & 145m maximum) by 82merers in width (80m minimum & 90meters maximum). These dimensions are often reduced in European games depending on what playing facilities are available. There is a goal area at either end of the pitch. The goals are comprised of two high circular posts 6.5m apart and at a height of not less than 7m. There is a crossbar spanning the distance between these posts at a uniform height of 2.5m over the ground.

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4. ## Investigating a factor affecting the voltage output of a transformer.

of turns on the secondary coil Increasing number of secondary coil turns increases the number of times the magnetic field lines are cut, increasing the secondary voltage * Primary voltage Increasing primary voltage increases the current, increasing the speed at which the magnetic field alternates, increasing the number of times the magnetic field lines are cut by the secondary coil in a given time, increasing the secondary voltage * Cross-sectional area of secondary coils Increasing cross-sectional area of secondary coils increases the number of magnetic field lines cut in a given time, increasing secondary voltage * Distance of separation between

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5. ## Cricket - The Rules of Play.

The cricket ball weighs from about 5.5 to 5.75 ounces which is about 156 to 163 grams. It is made of twine, which is wound around a cork core, which is surrounded in hard leather. The bat is a piece of willow 96 cm long and 11cm wide, with a handle at the top of the bat. The field or ground on which you play on may range in size from about 137-160 meters by 152-168 meters. In the center of the field, there is a pitch, which contains two wickets, 20 m apart. Each wicket consists of three wooden stumps.

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6. ## The Agricultural Revolution.

Therefore, farmers had allowed one of the villager's fields to rest or lie "fallow" each year. To help the fallow field to recover further, the villagers grazed their sheep and cattle there. The animal's manure put the goodness back into the soil. That field would be called a "fallow field". Also, every year they would vary where each crop would be grown in each field.

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7. ## A Comparison of Methods for History Matching.

This allows for the modification of grid blocks as required. As of the step required in the traditional method; identifying parameters that need change and implementing those changes, the AHM method is based on that assumption. The history matching algorithm used in AHM enables the method to thoroughly be in control of parameters. The method recognises that the permeability is the most frequently changed parameter and also that there are no in-situ measurements of it. Therefore it assigns effective Kv/Kh ratio on a well-by-well basis.

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8. ## EMF Investigation - electricity and magnetic fields.

So in reverse, if more coil of wire is passed through the field, more electricity should be consequentially generated. Strength of electromagnet is also one of the three factors in the Left-Hand rule. Thus if the strength of the magnetic field is increased, more electricity should be generated. In the same way, more movement of the wire in the field should generate more EMF. The proof of this has also been acquired through the preliminary experiment. However, it was found out that the result in moving the wire in the field is too insignificant to record, so this factor could be undoubtedly omitted.

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9. ## Einstein's theory of relativity.

A book may be jarred from a seat and fall without being dropped. A ball will travel differently. One way of stating the principle of this theory is to say that the laws of mechanics are the same for an observer in a smoothly moving train as for the observer at a fixed position on the ground. Physicists would say: if two systems move uniformly relative to each other, then all the laws of mechanics are the same in both systems. This principle may be called the classical relativity principle. This principle is as old as the ideas of mechanics and physics.

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10. ## Magnetic Resonance Imaging.

Basic idea Hydrogen nuclei are subjected to a pulse of radio waves, which causes them to briefly emit low-intensity radio waves. These are detected by the MRI scanner, which measures the signal as the patient is scanned by a changing magnetic field. The signal is processed, producing an image of where the hydrogen atoms in water molecules and lipids are located. Nuclei used in NMR contain an odd number of protons or neutrons and so possess intrinsic spin. (Spin is an inherently quantum property.

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11. ## My Autobiographical Essay.

Out of nowhere I suddenly had a sinking sensation of impending doom as I realised what an enormous task I was faced with. I walked out onto the field. The weather was picture perfect for a memorable day, with the clouds sparse and the sky as blue as the ocean. Many birds were chirping in the sun lit afternoon and the grass was as smooth and velvety as baize on a snooker table. As the game got underway, the balls seemed to be rocketing past at the speed of light, destroying my already low confidence.

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12. ## Investigate the factors affecting the induced e.m.f. in a coil due to the changing magnetic field in a neighbouring coil.

Rate of Change Suppose the normal of the coil is parallel to the field, the flux linkage is given by The induced e.m.f. can be increased by increasing the frequency of the primary current. From the equation (*), suppose the magnetic field strength and the area of surface are kept constant, it would become 2. Field It is easily found that 3. Number of Turns It is clear that 4. Area It is also true that 5. Orientation of Coil and Field The relation of induced e.m.f. and the orientation of coil and field is as follows: EXPERIMENTS Fig.

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13. ## Investigation of the plants on the school field.

* The person/people estimating the amount of plants. * The conditions on the school field e.g. wet/dry, cut/uncut etc. We will keep the distance between each quadrat a constant 1 metre, and the quadrat itself will always be 1 metre squared. We will do the whole experiment on the same day to ensure the conditions on the field are the same, and the same people will estimate the amount of plants on the field. Prediction: I predict that grass will be the most dominant species in each of our quadrats. Results: We gathered our results in a table, shown below.

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14. ## Stopping distance Investigation.

As the trolley goes down the ramp, it will pass through the light gate, registering a time as it does. Be recording this time, I will be able to draw graphs, and I will also be able to find out if the mass of the vehicle affects the speed at which the trolley goes down the ramp. In order for the trolley to break the light beam, a piece of paper will have to be positioned on top of it.

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15. ## Electromagnetic compatibility (EMC).

Optical engine lab An optical engine lab basic purpose is to measure the flow of liquid. It does this by using the following techniques. 1) Particles image velocimetry (PIV)- measure of the flow of liquid. Particle image velocimetry offers many advantages for the study of fluid flows. Lots of PIV techniques and PIV systems had been developed. However there are no standard evaluation tools for the effeteness and accuracy of PIV systems 2) Laser- induced fluorescence (LIF)- is the optical emission from molecules that have been excited to higher energy level by absorption of electromagnetic radiation Semi anechoic chamber The

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16. ## Electro-magnetic Induction.

For this investigation I shall pose the question 'how does the amount of turns in a coil affect the voltage induced?' This means that the input variable I am going to change will be the number of turns in my coil and I shall measure the change by the voltage induced. To make sure my experiment is a fair test, I shall keep the following variables the same: * Strength of the magnet * Speed the magnet is moving * Area of the cross-section of the coil These variables have to remain the same as, if any of them were changed then it would have an affect on the results I achieve.

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17. ## Find how varying the current in an electrical circuit affects the strength of an electromagnet.

I also suggest that there is a relationship of direct proportion between the two variables. For instance, if the current doubles, the strength of the electromagnet will also double. This is possible to be demonstrated when analysing the following equation: Power = Voltage Current � (P=VI) This shows that if the current increases, so does the power, subsequently increasing the strength of the electromagnetic field. This means that as the electromagnetic field is stronger, a larger amount of iron filings will be attracted to the magnetised core. I know that magnetic effects are produced by a moving electrical charge (current).

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18. ## A Personal Experience.

field with the wheelbarrow before taking Emily and Fuse to their weekly riding lesson at the local stables I took hold of the Fuse, as usual and began to lead him up the field, a mundane journey both he and I had travelled numerous times before. He seemed unwilling at first, but this adolescent behaviour was far from unusual so I gave a tug on the lead rope and told him firmly to 'walk on'. That seemed to do the trick as he stubbornly moved into walk.

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19. ## Rules, Regulations and Scoring Systems of boxing.

Drug usage The use of drugs or stimulants before or after the fight is forbidden. Scoring Practice Scoring from a strike 1. Points will be awarded for a correct Muay Thai strike, combined with a hard and accurate delivery. 2. Points will be awarded for aggressive and dominating Muay Thai skill. 3. Points will be awarded for the use of a traditional Muay Thai style of defence and counter attack. 4. Points will be deducted from an athlete who fouls or breaks the rules.

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20. ## To investigate the effect of current on the strength of an electromagnet field.

This is called the north-seeking pole of the magnet and the other end is the south seeking pole. The region around a magnet where a force is experienced is called the magnetic field of the magnet. If a magnet is snapped in half, both halves will have north and south seeking poles, this can be explained by the Domain theory. This describes some metals as being full of domains, or tiny patches of magnetism. In unmagnetised steel these domains are jumbled up, so there is no overall magnetism. In a magnet the domains are lined up so that at one end are the north seeking poles of domains, and at the other end are the south seeking poles: Some metals, such as copper and aluminium cannot be magnetised.

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21. ## Aurora- Light of Mystery.

This is not absolutely true because vacuum is a space with nothing, no even air, but there are actually particles existing in the interstellar space. At sea level the density of air molecules is 1 quintillion per cm3; at 100km roughly where aurora occurs, density is 1 trillion per cm3; in the interstellar space the density is merely 1 per cm3. Therefore as a result, most of outer space is filled with electrically conductive plasma. Besides of particles, there are magnetic field, electric current, electromagnetic force, gravitational forces...

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22. ## Making electricity.

The current stops if the magnet stops moving - even if it is inside the coil. The current goes the other way if the magnet moves in the opposite direction To make the current greater: * use more coils * move the magnet faster * use a stronger magnet The magnetic field goes around each loop of wire in the coil, so if you increase the number of coils there are more places where the magnetism changes. The faster the magnet moves, the faster the magnetism changes. If you keep the magnet still and move the wire, you induce a current in exactly the same way.

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23. ## The origins of mathematics come from the classical Greeks and then those scholars prior to Augustus in Rome.

Math is a science in which you are not solving; but rather proving that something is always true under certain circumstances and, that there is only one set of true solutions to an equation, which extraordinarily resembles basic criteria. The job of a mathematician is to discover sets of criteria that can prove or disprove a theory that has been made. As far as preparation to be a mathematician goes there are a couple of majors that work: either Applied Mathematics -OR- Mathematics.

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24. ## Find out what kind of effect the strength of an electromagnet has if the number of turns on the coil and the current going through the coil are increased.

The greater amount of turns causes constructive interference, which increases the size and strength of the magnetic field. The type of wire also affects the strength of the electromagnet. If a wire is thicker then current can flow more easily and the current will increase so the strength of the electromagnet will increase. In addition, the length of wire may also affect the strength of the electromagnet because as the wire becomes longer there is a greater amount of resistance so current may decrease. Diagram Variables * Voltage * Current * Number of coils around the core * Size of wire used for coils * Size of magnet I chose to use the number of coils around the core as my variable.

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25. ## Varying the current in an electrical circuit affects the strength of an electromagnet.

In addition, if the solenoid receives greater current then the field it generates will be stronger. . On the power pack, which I will be, using there is an option to change the voltage, which could be altered to change current with the aid of an ammeter. The main implication of the domains is that there is already a high degree of magnetization in ferromagnetic materials within individual domains, but that in the absence of external magnetic fields those domains are randomly oriented.

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