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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. ## Flexural strength measurement of a concrete beam.

The beam was visually inspected for faults and damages. 4. Length and cross-sectional dimensions were measured accurately with a caliper. 5. Test device was wiped with a dry cloth. 6. The beam was put centrally in flexural loading device with the rough as-cast top surface vertical. 7. All rolling and supports were in evenly contact with the beam before applying the load. 8. Appropriate loading was chosen for the test. The load was increased at a rate between 0.03 to 0.06N/mm2 per second.

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2. ## Objective of Experiment. To use a search coil and CRO to investigate the magnetic field due to a straight wire carrying an alternating current

the wire is long). The proportionality constant is written as ?o/2? , thus, The value of the constant ?o, which is called the permeability of free space, is 4? ? 10-7 H m-1. Procedure The circuit was set up as shown below. The signal generator was set to 5 kHz. The CRO was adjusted such that a trace was displayed. The frequency was changed to find out how the trace on the CRO was affected. The output of the signal generator was adjusted to produce a current. The time base was switched off and the length of the vertical trace on the CRO was measured.

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3. ## Using a search coil and CRO to investigate the magnetic fields generated by alternating currents (A.C.) through a straight wire and a slinky solenoid.

Induced E.M.F. (?) / V 0.5 0.6 0.7 0.8 0.9 1.0 1.1 1.2 1.3 1.4 1.5 Current (I) / A 0.8 1.0 1.12 1.28 1.40 1.56 1.80 2.0 2.1 2.3 2.5 Relationship between the potential different across the capacitor and the time From the above V-t graph, the curve is a straight line passes through origin. Hence, the potential difference across the capacitor is directly proportional to the time for the CRO trace to rise in steps of 1V and the slope () which represented the charging rate, is constant. Relationship between the charge stored in the capacitor and the potential different across it when the charging current is constant The area of the graph (Vt)

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4. ## Centripetal Force Experiment. Measure the centripetal force and compare it with the theorectical value Fc=mr&#969;2

3.1 Electronic balance was used to measure the mass of bung, metal weights and hanger. 3.2 Meter ruler was used to measure the length of string. 3.3 Stop watch was used to record the time for 20 revolutions. 3.4 It was not easy to keep L unchanged when whirling the bung, so we had to practise for a while before taking the data. 4. Data Analysis Mass of rubber bung (m) is 0.0192 � 5�10-5 kg. L / m (�5�10-4) M / kg (�5�10-5) Mg / N Time for 20 revolutions (t)/ s (�0.005) ?

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5. ## Determination of Force Constant k from Spring-mass System

We can see that the mass will accelerate upward. As the mass is moving in SHM, (by SHM equation) So by measuring the oscillation period and the mass of mass, we can calculate the spring constant (or say the force constant). Apparatus: Slotted mass (10g, 20g, and 50g), hanger, spring, retort stand and clamp, stop watch. Procedure: 1. Fix the spring to the clamp with the help of an eraser. Hook the spring to the eraser and place the eraser in the clamp and screw up the clamp.

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6. ## Centripetal Motion

In the other part of this experiment the radius was varied while keeping the weight the same. Measurements of the period were calculated by measuring the time taken for ten rotations, and this proved easier to measure than one rotation, and then divided by ten. Glass was chosen as a material for the cylinder to reduce the energy lost due to friction between the top of the cylinder and the string; this will help increase the reliability of the final results.

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7. ## Measurement of Young modulus of iron

the unstretched original length (?) of the copper wire. Unstretched original length (?) = ___2.42m_____________________________________ 4. Add 500c.c. of water as load (m) to the water bucker holding with iron wire. Measure the extension of the iron wire (e) from the ruler. 5. Repeat step 4 until the iron wire breaks. Tabulate the results. Mass of load (m) / kg 0 4 6 8 9 10 11 13 13.5 Extension (e) / m 0 0.01 0.012 0.016 0.018 0.02 0.024 0.115 0.143 6. Plot a graph of the extension (e) of the iron wire against the mass of the load (m).

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8. ## Lift

The higher the L/D ratio, the higher the efficiency of the aircraft. The angle at which the front of the wing is inclined affects the amount of lift produced, as well. The 'angle of attack' is directly proportional to lift. This is because the surface area hitting the air is greater, meaning more air molecules act to create a force, which means that lift is greater. Nevertheless, this only works up to an angle of about ~10o. If the angle gets too high, then air molecules start sticking to the wing, which means that there is no constant flow of fluid, which is essential for lift.

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10. ## The Law of Electromagnetic Induction

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11. ## Flame probe experiment

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12. ## Centripetal motion experiment. Objective To study the relationship between the angular speed and the centripetal force and verify the expression of centripetal force.

* Use nylon spread, which is inextensible to lower the error. Theory To keep the body moving in a circle, the centripetal force is required. It is provided by the external resultant force towards the centre. To keep the radius unchange, the cantripetal force should alter the angular speed of the object. However, it does no work on the body and the kinetic energy of the body remains unchanged. By comparing the horizontal and vertical component of the tension, the expression of tthe centripetal force can be deduced. We can find out that the centripetal force=Tsin?=m?(lsin?), so T=ml?2.

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13. ## Scalars and Vectors

Ice shut airport runways, roads were gridlocked and trains broke down. If the average, young or middle-aged citizen finds it difficult to survive in conditions like this, imagine how the elderly must find the conditions of this year's winter. This brings me to talk about how elderly people must suffer from the freezing cold in their homes, vulnerable to many kinds of hazards, right from their front door step. Icy conditions have led to hundreds, even thousands more hospital admissions this year in the United Kingdom - most of these admissions have been elderly people.

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14. ## Determining the force constant

Also, we assumed that the effect of air resistance acting on the mass and the spring is negligible . Difficulties encountered When conducting the experiment, we initially used a spring which cannot be extended significantly. As a result, we cannot conduct the experiment efficiently as we couldn't see the tiny change in period.

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15. ## Measuring Young modulus of copper

The wire is loaded in steps and be recorded the extension e produced. Data Analysis and Results 1. Measurements of the diameter of wire 1st measurement 2nd measurement 3rd measurement Diameter d/m 0.0003 0.0003 0.0003 Mean diameter of wire d = 0.0003m 2. Measurements of the original length of wire 1st measurement 2nd measurement 3rd measurement Length l/m 2.9960 2.6400 3.7730 3. Measurements of the extension of the wire with load and hanger(0.0996kg) Load m/+0.0996kg Extension e/m 1st measurement 2nd measurement 3rd measurement 0.0000 Failure 0.0000 0.0000 0.1000 Failure 0.0010 0.0015 0.2000 Failure 0.0020 0.0020 0.3000 Failure 0.0025 0.0030

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16. ## Callibrate a Hall Probe: Planning

n = no. of electrons per unit volume (e/m3) e = electron charge (1.6 x 10-19 C) d = thickness of film in Hall probe (m) Formula 2 Diagram of Apparatus for calibration Draw diagram here Method of calibration 1. Place the Hall probe in an area with no magnets and zero it. 2. Set up Helmholtz coils as above. The current going through each coil should be 0.5A. 3. Use a wooden ruler, held by wooden clamps, positioned behind and beside the coils to find the centre of the magnetic field. 4. Position the Hall probe in the centre so that it is perpendicular to the direction of the field.

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17. ## Investigating the Damping of Motion in a Simple Pendulum through Induced Eddy Currents

I will start recording, and then release the pendulum. Using frame by frame analysis of the video I will determine the frame when the pendulum was released, and the first swing in which the pendulum achieves strictly less than 15 degrees of deflection. By working out the number of frames this takes, and dividing by the frame rate of the camera, I can calculate the time taken. The equipment will be set up as in the diagram on the next page, although the camera is not shown in the diagram.

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18. ## Power Lab Report

I made a table with columns name, Fg(N), Vertical Height (m), Work done, Power, Ranking 2. We measured the height of a one step, and then multiplied it to 14 since the stairs has 14 steps. 3. Then I used the stopwatch to measure how fast Xerxes made it to the top. Then record it on the time column of the table. Then Xerxes timed how long I took to reach the top. 4. Then other partners did just like what we did, they timed each other. 5. After that, we share the data we got.

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19. ## Simple Harmonic Motion

Put a cross one the tape at the position just beneath the pin of the ticker-timer to indicate the equilibrium position of the mass. 6. Pull the mass towards the ticker-timer through different distance. 7. Switch on the timer and at the same time release the mass. Stop the timer when the mass reaches the opposite side. Question Answering: 8a) A motion which said to be S.H.M. if the acceleration of the motion is always directed toward a fixed point and the magnitudes of the acceleration is directly proportional to the displacement to the fixed point.

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20. ## As Fast As you can

Thinking Distance Thinking distance is calculated by the general equation: Thinking distance is the distance covered in the time it takes for a reaction to occur. In what can be a fraction of a second, a substantial amount of ground can be covered. Human reaction time is usually between 0.2 and 1 second. However, there can be various conditions and factors that can dramatically affect this. Smoking whilst driving or in general causes a stimulus affect which can speed up reaction times or create a neurotic result.

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21. ## Does the mass of a block of wood effect the size of a frictional force?

Extra mass placed on block (g) Total Mass (g) Force exerted on block on the smooth surface (N) Force exerted on block on the wooden surface (N) Force exerted on block on the rough surface (N) 105 50 155 0 0.1 0.2 105 100 205 0.1 0.3 0.4 Prediction I predict that the mass of the block will have an effect on the amount of frictional force. My preliminary experiment results prove this as when we put more weight on the block the frictional force became greater. When the block is pushed down onto the surface of the floor, this causes the two surfaces to lock.

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22. ## Investigate how the static force exerted on the front axle varies with the vertical load applied to the rear end

A hook represents the towing mechanism of the recovery truck. Diagram of apparatus: The rear axle consists of a metal bar, placed through the drilled hole R, which is suspended from an elastic band on either side of the wooden block. The elastic bands hang of another metal bar which is held horizontally by a clamp stand. The front axle consists of a metal bar, placed through the drilled hole F, which is balanced on small wooden blocks placed on either side of the wooden block.

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23. ## Electromagnetic Induction

If an electric effect can produce a magnetic effect, maybe the reverse may also be true, i.e. a magnetic effect may produce an electric current. APPARATUS * Ballistic galvanometer * Horseshoe magnet * Bar magnets * Leads * Wired metal rod * Induction coils * 60 microamp galvanometer METHOD 1. The coil was connected to a Microammeter. The N pole of the magnet was inserted into the solenoid and a description was recorded.

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24. ## Physics Spring Coursework

To do this different arrangements of springs (each with spring constant k) were used to form spring systems of different spring constants. To work out the spring constant of each arrangements, ktot-1=k1-1+k2-1 (for springs in parallel) and ktot=k1+k2 (for springs in series) were used. The laws of logs can be used to change the formula lnT= ln(pkqmr ) into a straight line graph, in the form y=mx+c. Using Law 1, ln(pkqmr) = lnCHNKWKS -�"TEXTTEXTVZFDPPFDPP^FDPPFDPP`FDPPFDPPbFDPPFDPPdFDPPFDPPfFDPPFDPPhFDPCFDPCjFDPCFDPClFDPCFDPCnFDPCFDPCpFDPCFDPCrFDPCFDPCtFDPCFDPCvFDPC FDPCxFDPCFDPCzFDPC FDPC|FDPC FDPC~STSHSTSH�h B This expIntroduction The aim of this experiment was to find out if the time period of a vertical mass oscillating system is dependant on the spring constant (k)

25. ## Sliding & Friction Lab Report

Your car can move faster because less force is needed for the car to move. On the hand, when you are driving on a gravel road, you need greater force to cause motion because the surface is not smooth as asphalt paved road, which is flat. There are three different types of variables in this experiment. The independent variables in this experiment are the surface area, the block material, the sliding surface, and the mass of the block. The controlled variables in the experiment are the sliding surface, the block mass, and the surface area.

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