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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.

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1. ## paper cones investigation

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air C Displacement of fall C Time taken to fall D Prediction Since the theory suggests that So the square of time should be directly proportional to the inverse of mass. A straight line graph of t2 versus m-1 should give a straight line graph with a gradient of All of these values will be measurable or known, except for the drag coefficient, c. Method Preliminary experiments Determining a size of the paper cone: Three unweighted paper cones were constructed from A4 paper and selotape: w is the width (diameter)

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2. ## Determination of the acceleration due to gravity (g)

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this investigation, I am going to determine the acceleration due to gravity on the earth by using an electronic timer and varying its height of dropping. In this method, a steel ball is hold by a free fall adaptor (ball release mechanism) , when we release the ball, the current to the circuit is switched on and the ball begins to fall. At the same time an electronic timer starts. The ball falls through a receptor pad and this will break down the circuit to stop the electronic timer.

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3. ## Energy and its uses

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Elastic potential energy (EPE) is the energy stored in bodies such as springs, elastic and rubber bands. An archer drawing a bow applies EPE to the bow string. science.howstuffworks.com 4. Chemical energy is the stored energy possessed by foods, fuels and batteries. A human eating food is taking in chemical energy. http://en.wikipedia.org/wiki/Battery_ (electricity) 5. Thermal or heat energy is energy that flows by conduction, convection or radiation from hot areas to cold it can also be a by product of wasted energy during energy conversions http://www.oxfordreference.com/pages/VED_samples 6.

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4. ## Experiment to determine gravity from a spring using analogue techniques

The graph of period squared against mass can then be plotted. From this, the value for the spring constant, k, of each spring can be calculated by comparing the equation of the best fit line of the graph to the squared version of the equation above,. The second part of this experiment is concerned with Hooke's law, which states that the extension of a spring is directly proportional to the mass applied to it. Mathematically, this is stated as: Where x is the extension of the spring in metres, k is the spring constant of the spring measured in Nm-1 and F is the restoring force, measured in Newtons.

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5. ## Objective To find the acceleration due to gravity by means of a simple pendulum.

a = -g? = -g(x/l) (? ? radius=arc length) a=- (where g/l) Thus, the periodic time T of a simple pendulum of length l is given by T == 2? The period of oscillation of a simple pendulum depends on the length and is directly proportional to the square root of the length. Moreover, we know that the period of oscillation is independent of the amplitude when the amplitude is within small limits (length remaining constant). This means the amplitude can vary within small limits, but the period of oscillation will be the same.

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6. ## Practice A2 Investigation: Measuring the torsion of wire

attachment but hanging freely elsewhere * Attach a torsion bar to the bottom of the wire using a screw * Use a marker as a point from which the period of oscillation can be measured * Pull the torsion bar to any sensible angle, (far enough so the data is accurate but not so far that reaction time becomes a major uncertainty) and release it, allowing it to oscillate freely * Time the period of the oscillations over an accurate, logistically feasible length of time * Repeat this process at least three times for each measurement * Repeat the measurement for wires of same length, different thickness or same thickness, different length A diagram of this experiment is provided below.

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7. ## Physics of scuba diving

(this is also why it is important for submarines to be quiet to avoid detection). I have chosen to focus on the effects of the changes in pressure experienced by divers, as I feel this is the most important aspect of physics that needs to be appreciated for safe Scuba diving. A brief history of diving The first recorded incidence of diving comes from ancient Greece (1), divers jumped into the water carrying a 15kg stone, sank to around 30 metres and cut the sponges away from the sea bed.

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8. ## Measuring The Constant g; The Acceleration Due To Gravity

After measuring the time of 20 back and forth swings, I divided by that number to get the average duration of a single period. Then by that above formula I calculated g, to a high level of accuracy, having rearranged it to this form: g = 4?(L/P( Ultimately, I calculated it to be g ? 9.81 ms-2 with a percentage uncertainty of just ?1.3%. Introduction In this investigation I am going to be obtaining a measurement for the gravitational constant of acceleration 'g' using two main methods, in order to compare their accuracy, and hence determine the more precise value.

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9. ## Building a hovercraft with household objects.

* Razor knife * Staple gun * Duct tape * Spray Adhesive * Silicon Caulking * Marker * 2 Foot string * Hammer * Extension Cords * Stool * Measuring tape * Wrench * Ratchet * Drill Procedure 1. Tie a permanent marker to the end of a 2' long string, with a loop at the opposite end of the string. 2. Measure the exact center of the board, and drive a nail into it. 3. Loop the end of the string opposite of the marker around the nail.

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10. ## Elastictvy of Copper investigation

I think that the copper wire will have a young's modulus of about 130 Gpa(GigaPascals / Kn/mm), as the secondary source has worked this out The stretching force which extends material by equal steps is called Hooke's law. Hooke's law states that the force needed to stretch a spring is proportional to the extension of the spring from its natural length. The formula used for Hooke's law is Force, F=Ke. The K is the spring constant (measure in force by length)

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11. ## The experiment involves the determination, of the effective mass of a spring (ms) and the spring constant (k).

These measurements were then noted in a copy of the following table: Mass/Kg x number of oscillation's Time for 'x' oscillations (in seconds) xT av/s T/s T2/s2 ?xT/s % unc in xT % unc in T2 ?T2/s2 0.100 0.200 0.250 0.300 0.400 0.450 0.500 0.600 xT xT xT The quantities could then be derived in the following ways. To find the quantities first it was necessary to draw a graph of the results taken and to get the graph to be a straight line graph and so as to be of use the equation of T2 had to be rearranged as shown below: T= 2??(m+ms)

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12. ## Investigating the relationship of projectile range and projectile motion using a ski jump.

Hypothesis I predict that the higher ramp, the higher the velocity therefore an increase in range. Null Hypothesis There will be no relationship found between the height of the ramp, velocity and the range of the projectile. Rationale The displacement, velocity and acceleration of the projectile are all vectors. The forces of the projectile motion can be treated separately, so they can be resolved into horizontal and vertical components. They are independent of each other; that is, neither motion affects the other. We can label these components x and y. The horizontal component can be represented as Vx and the vertical component as Vy.

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13. ## Physics Coursework, Visit to Holly House

Only the part of the body that is to be scanned is scanned, and the patient can either enter head first or feet first, which is determined by the type of radiographic exam to be performed. Once the area of the body that is to be examined is in the exact centre of the magnetic field of the scanner then the examination may begin. The Examination Prior to allowing a patient to enter the scan room, he or she is thoroughly screened for metal objects.

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14. ## 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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15. ## 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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16. ## 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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17. ## 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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18. ## 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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19. ## How does the number of coils on an electromagnet affect its strength?

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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20. ## 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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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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22. ## Electricity and magnetism

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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23. ## Charge To Mass Ratio For An Electron

Comparing this experimental value to the theoretical value which is 1.76�1011 coulombs/kg makes a 7.38% experimental error. One of the reasons that this error can occur is related to earth's magnetic field and causing force on the electrons. In conclusion a charged particle will experience a force when moving through a magnetic field and also as the radius of the coil increases as electron flow the magnetic filed decrease. This can also prove that these two are inversely proportional. Introduction In 1897 J.J. Thomson made the first measurements of the charge to mass ratio of an electron (e/m), using cathode ray tub.

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