P2 FGF

• To construct electrical circuits to investigate the effect of factors on a filament lamp and resistor, set up a series circuit with the resistor, the power supply and the ammeter, with a voltmeter in parallel across the resistor. Starting on a low voltage, turn the power supply on and record the values for potential difference and current, taking them straight away so that the resistor doesn’t get too hot and reduce the accuracy of the results. Some time should also be left after for the resistor to cool down. Repeat, increasing the voltage in the circuit each time and recording voltage and current, then plot these values on a graph of current against potential difference. The reciprocal of the gradient will give the resistance of the fixed resistor as R = V / T, the gradient remains constant which shows the resistance of the fixed resistor does not change as the potential difference increases.
• Replace the resistor with a filament lamp and repeat the experiment, the new I-V graph should show a curve that plateaus. As the gradient decreases, resistance increases, showing that the resistance of a filament lamp increases as the potential difference increases. Do not put the voltage of the power supply too high when using a filament lamp as it may blow the bulb and do not touch the bulb whilst hot.
• To construct electrical circuits to test series and parallel circuits set up a series circuit with a voltmeter attached in parallel across the cell and around each filament lamp, alongside an ammeter. Then start the power supply on 0V where all values will be 0, then increase the voltage in intervals and record the values of all voltmeters and the ammeter each time up to 6V. 
• Then repeat this process with a parallel circuit with a separate branch for each filament lamp, each with ammeters, and it will show that the amps in each branch are half the current in the main circuit - whereas all the voltages will be the same.
• To investigate the density of a solid or liquid, first either use  a balance to determine the mass of the solid, ensuring the balance is zeroed and converting any measurements in grams to kilograms or for a liquid place an empty beaker on a balance and zero it then add the liquid to determine its mass. Then use a ruler to measure a regular shape and work out its volume, but for an irregular shape start with a known volume of water in a measuring cylinder and add the solid - the increase in volume is equal to the volume of the solid. Ensure no water splashes out of the cylinder. Then use the formula density = mass / volume to calculate the densities of the solid or liquid.
• Take all measurements for the liquid from the meniscus. When using a measuring cylinder, take readings from eye level to avoid parallax error. For solids that float either push the volume down until it is just completely submerged or weight it down with a known volume of another substance. Take care no water gets onto the electronic balance.
• To investigate the properties of water, fill the beaker with boiling water and keep it warm using a bunsen burner. The water should remain at a constant temperature – you can ensure this by using a second thermometer in the water bath. Fill a boiling tube with crushed ice and take the initial temperature. Place the boiling tube in the beaker and start the stopwatch. Record the temperature of the ice every 30 seconds until all of the ice has melted. Continue taking readings until three minutes after all of the ice has visibly melted. Take note of the state of the ice (solid or liquid) for every recorded temperature. Plot a graph of temperature against time for the results. The graph should show a plateau when the ice is melting. The energy is going towards breaking the bonds between the water atoms rather than increasing the temperature.
• Place the empty beaker on the balance and zero it. Fill the beaker with water and record its mass. Place the thermometer and the immersion heater in the water and then insulate the beaker with cladding (ensure the top is also covered with a lid). The immersion heater should also be connected to a joulemeter to measure the energy transferred during heating. Record the initial temperature of the water and turn on the immersion heater. Let the heater heat the water for an hour, or until there is a significant change in temperature, and then take the final temperature, as well as recording the value on the joulemeter. The water should be continually stirred so that the heat is evenly distributed (this can be done using an electric stirrer). Rearranging the formula Q = mcΔT to c = Q , you can input the values for mass, change mΔT in temperature, and energy transferred to obtain the specific heat capacity of water.
• Using the ruler, measure the initial length of the first spring when no force is applied. Set up the spring so it is hanging securely from the clamp stand. You can also secure the ruler to the clamp stand to ensure it does not move at all during the experiment. Add one of the masses to the end of the spring and record the extension of the spring. The extension is the difference between the new length and the initial length. Continue adding masses and recording the extension each time. Plot a graph of force against extension for the spring. Force can be calculated from mass x gravitational field strength (i.e. 10 x the mass hanging on the spring). The gradient of the line of best fit will be the spring constant as F = kx. Using this value, you can calculate the work done each time the spring extends. Use the formula W = 1/2 k x^2.
• Ensure all measurements are taken from eye level in order to avoid parallax error. After every measurement, remove all weights and ensure that the spring has not undergone plastic deformation. It should always return to the same initial length. All lengths should be measured in metres. Ensure goggles are worn during this experiment in case the spring snaps and use heavy objects or a G clamp to secure the clamp stand to the desk.
• Free body diagrams show the direction of forces that are present in a situation. The reaction force always acts at the normal to the line of contact, from the point of contact. Friction acts in the opposite direction to movement, along line of contact. Weight always acts downwards, acting from Centre of Mass.
• Sublimation is solid to gas.

  Deposition is gas to solid.
• On a scale drawing the length of each arrow represents its size in relation to the other forces acting on the object so the direction with larger arrows shows the resultant force. If arrows are in opposite directions with equal length they are equal in magnitude so cancel eachother out, meaning the object is in equilibrium at a constant velocity.
• Rotation occurs if an object is an attached to a pivot point, which it can rotate about but not move away from. If the force is applied perpendicular to the object the object will move about the pivot in this direction. The moment of a force (newton metres) = force x distance perpendicular to the direction of the force.
• Gears can change speed, force or direction by rotation. The second gear will always turn in the opposite direction, to increase power use a larger secondary gear as the force is. Further distance from its pivot so has a greater momentum. Lubrication of the gears reduces friction so increases efficiency.
• In a series circuit components are connected end to end and all the current flows through all the components which can all be switched off at once. The potential difference is shared across the whole circuit and the current is the same, the total resistance is the sum of the resistance in each component meaning the resistance of two components is bigger than just one of them as charge has to flow through both.
• In a parallel circuit components are connected separately to the power supply a current flows through each one separately, so components can be switched off individually. Potential difference is the same across all branches and current splits between them. The total resistance is less than the branch with the smallest resistance because two resistors in parallel will have a smaller overall resistance than just one as charge can flow through more than one branch so only some flows along each branch.
• As current increases electrons have more energy, when electrons flow through a resistor the collide with ions in the resistor and the current does work against the resistance. This transfers energy to the ions, causing them to vibrate more which makes it more difficult for them to flow through the resistor, therefore as resistance increases, current decreases. This may be a benefit as appliances like toasters use heating filaments that have a high resistance to get hot easily. In normal wires as temperature increases so does resistance however for thermistors the higher the temperatures, the lower the resistance.
• The greater the length of a wire, the more resistance and the lower the current as electrons make their way through more resistor atoms, so it is harder to get through than a shorter wire. With cross sectional area, thinner wires give greater resistance because there is less overall room for electrons to pass through between atoms.
• Light dependent resistors lower resistance with greater light intensity so resistance is greatest when dark, used in automatic street lights. Diodes allow current to flow freely in one direction, in the opposite direction there is very high resistance so no current can flow. Low resistance wires are more efficient as less energy is lost as current flows through the circuit.
• Power is the energy transferred per second and is directly proportional to current and voltage, power loss is proportional to resistance and to current squared. Energy is transferred from chemical potential in batteries to electrical energy in wires to any form of useful energy in the devices they power.
• The live wire is brown and it carries voltage from mains to appliance. This may be dangerous even if mains circuit is off, as current may still be flowing through it. The neutral wire is blue and completes the circuit. The earth wire is green and yellow striped and it is a safety wire to stop the appliance becoming live, it is attached to the earth and to the casing in case the live wire touches the metal casing and causes it to become live. Its low resistance means the current will go through it. A fuse is connected to the live wire so if a current surge occurs it will melt and break the circuit. The greater the power rating, the greater the energy consumption per second.
• When two insulators are rubbed together it an be charged by friction, electrons are transferred from one object to the other forming a positive charge on one and a negative charge on the other. If conductors were rubbed, electrons will flow in an out of them so they stay neutral. Insulators become charged because the electrons cannot flow, which object loses/gains electrons depends on the materials involved.
• Sparking occurs when enough charge builds up and the objects are close but not touching. The spark is when the charge jumps through the air from the highly negative object to the highly positive object to balance out the charge. A positively charged balloon next to wall attracts electrons in the wall, this induction causes the balloon to stick to the wall.
• Insecticide sprays are sprayed from aircraft and given a charge, this means the spray droplets repel eachother so the droplets spread evenly and are attracted to the earth. If charge builds up and a spark forms when fuelling cars, it could ignite and cause an explosion. As fuel passes through a hose to the vehicle, a static charge can build up and when it is too large a spark might form and ignite the fuel - the hoses are earthed to stop this from occurring.
• Induced magnets are magnetic but do not have fixed poles because magnetism is induced, these can be made into temporary magnets by ‘stroking’ them with a permanent magnet, which aligns all domains in the material in the same direction so a temporary magnet is created. Electromagnets use temporary magnetic material in their core. After time the domains move back into random positons so magnetism is lost.
• The Earth’s core is magnetic and created a large magnetic field around the Earth. A freely suspended magnetic compass will align itself with the Earth’s field lines and point North, a compass is effectively a suspended Bar Magnet, with its own north pole line up with the Earth’s one. This contradicts like poles repelling so, in fact, Earth’s magnetic pole in the north is a magnetic south pole and vice versa.
• The motor effect refers to the phenomena that a motor experiences a force when an electric current carries it through a magnetic field. It is caused by the interaction between the magnetic field and the electric current. The size of the force that acts on the conductor is directly proportional to the strength of the magnetic field and the amount of current flowing through the conductor. The direction of the force is at right angles to the direction of the current and the magnetic field. The direction of the force can be determined using Fleming’s left-hand rule.
• Current is induced if a wire is moved in a magnetic field, the conductor (wire) forms a potential difference as electrons move to one side of the conductor when the field changes. If the conductor is connected in a circuit, a current will flow which will produce its own magnetic field, the direction of this new field is in the opposite direction to the first field so opposes the original change.
• Spinning a coil of wire in between two permanent magnets will cause a current to flow in the wire, which can be shown by a sensitive ammeter as only milliamps will be generated. Passing a wire through the field will also show a deflection in an ammeter. In a thermal power station, water heats up and evaporates to form steam which could be caused by combustion of fossil fuels or nuclear fission. The steam is put under pressure and forced into a turbine which causes the turbine to rotate, which is connected to a massive coil of wire in a strong magnetic field (the generator). Current is generated in the coil by the spinning motion of the coil through the field.
• In an alternator the current switches every half-turn, as the wire will be in the opposite orientation compared to its starting positon, this produced alternating current. Dynamos have the same set up as an alternator but at the end of the coil there is a commutator, a metal ring that reverses the sign of the current that flows from the coil, ensuring current output remains positive. Every half-turn the commutator switches the sign of the current so this produces direct current.
• Microphones produce a current which is proportional to the sound signal with a fixed magnet at the centre and a coil of wire around it that is free to move. Pressure variations in the sound waves cause the coil to move, and as it moves current is induced in the coil because it passes through the magnetic field. This current is then sent to a loudspeaker with an identical setup, where current flows into the coil and interacts with the magnetic field, causing the coil to move and produce pressure variations that produce sound waves.
• Transformers have AC in the first coil which creates a changing magnetic field which cuts through the secondary coil. This induces a current in the secondary coil which is also AC, if the primary current was DC the magnetic field would be constant so no current would be induced in the secondary coil. If there are more coils on the secondary coil voltage will be increased because the changing field will cut through more of the secondary wire to induce a larger potential difference, so it is a step up transformer.
• Electrical energy is transferred at high voltages from power stations, in domestic uses electrical energy is transformed to lower voltages. This is done to improve the efficiency of the transmission as the larger the current, the greater the heating effect occurs in wires so a larger current causes more energy loss. So because power is current multiplied by voltage, increasing the voltage reduces the current through the use of step up transformers. However high voltages are dangerous so near domestic areas voltage is decreased and current increases so it s safer to use, this is only for a short time so has little affect on overall efficiency.
• Doing work on a gas means compressing or expanding it to change the volume, pumping more gas into the same volume means more particles are present, so more collisions occur per unit time with the walls, so pressure increases and energy is transferred to the particles which heats the gas. As volume decreases particles collide with a moving wall so gain momentum as the rebound velocity is greater than the approaching velocity. This increases the pressure in the volume.
• Atmospheric Pressure is the total weight of the air above a unit area at a certain altitude so decreases with increasing height above the Earth’s surface. The weight of the air is the force which causes the pressure. So with higher elevation there are fewer air molecules above the unit area so less weight and less pressure.
• An object floats if its weight is less than the weight of the water it displaces. Pressure in a liquid varies with depth and density, which leads to a upwards forces on a partially submerged object as the buoyancy force, the upwards force counteracting the weight of the floating object, is equal to the weight of the fluid displaced by the object. Increasing the depth increases the weight of fluid above an object so a greater force is felt, and a greater pressure.
• The applied force must be resolved horizontally to determine the force that separates the magnets. Since the size of the resolved force is always less than the actual force then a larger force is required when applying the force at an angle.
• A semiconductor diode only allows current to flow in one direction. If the potential difference is arranged to try and push the current the wrong way (reverse-bias) no current will flow as the diode's resistance remains very large. Current will only flow if the diode is forward-biased. When forward-biased, the diode's resistance is very large at low potential differences but at higher potential differences, the resistance quickly drops and current begins to flow.
• Light-dependent resistor (LDR) is a type of sensory resistor. The resistance of an LDR changes depending on the light intensity on it. As the light intensity increases the resistance of an LDR decreases and vice versa. LDRs can be used as light sensors, so, they are useful in circuits which automatically switch on lights when it gets dark, for example, street lighting and garden lights. A thermistor is a type of sensory resistor. The resistance of a thermistor changes depending on its temperature, as the temperature increases the resistance of a thermistor decreases and vice versa.