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Physics. Topic 1: energy transfers Kinetic energy = ½ mass x velocity2. KE = ½ mv2 GPE = mass x height x field strength. GPE = mgh Power = energy/time. P=E/t Power = work done/time. P=W/t Efficiency = useful energy output/total energy input Efficiency = useful power output/total power input Force on a spring = spring constant x extension. F=ke Pressure = force/area. P=f/a Specific heat capacity: Specific heat capacity is the amount of energy required to raise the temperature of 1kg by 1°. The amount of energy transferred from the thermal energy store is linked to specific heat capacity. Δenergy = mass x specific heat capacity x ΔƟ. Δe = mcΔƟ. Core practical: investigating specific heat capacity. 1) Start by assembling the apparatus, placing the heater into the top of the block 2) Measure the initial temperature of the aluminium block from the thermometer 3) Turn on the power supply and start the stopwatch 4) Whilst the power supply is on, the heater will heat up the block. Take several periodic measurements to calculate an average for each at the end of the experiment up to 10 minutes 5) Switch off the power supply, stop the stopwatch and leave the apparatus for about a minute. The temperature will still rise before it cools. Monitor the thermometer and record the final temperature reached for the block Topic 2: circuits. Voltage = current x resistance. V=IR Core practical: factors affecting resistance. 1) Connect the crocodile clips to the resistance wire, 100cm apart. 2) Record the reading on the ammeter and on the voltmeter. 3) Move one of the crocodile clips closer until they are 90 cm apart. 4) Record the new readings on the ammeter and the voltmeter. 5) Repeat the previous steps reducing the length of the wire by 10 cm each time down to a minimum length of 10 cm. 6) Use the results to calculate the resistance of each length of wire. Core practical: I-V characteristics. 1)Vary the voltage across the component by changing the resistance of the variable resistor, using a wide range of voltages. Check the appropriate voltage reading on the voltmeter 2)For each voltage, record the value of the current from the ammeter 3 times and calculate the average current 3)Make sure to switch off the circuit in between readings to prevent heating of the component and wires 4) Reverse the terminals of the power supply and take readings for the negative voltage 5) Replace the fixed resistor with the filament lamp, then the diode, repeating the experiment for each Topic 3: particle states of matter. Density = mass/volume. P=m/v. Core practical: measuring density of a solid. 1)Use a ruler to measure the length, width and height of a steel cube. 2) Place the metal cube on the top pan balance and measure its mass. 3) Calculate the volume of the cube. 4)Use the measurements to calculate the density of the metal. Core practical: measuring density of a liquid. 1) Place the measuring cylinder on the top pan balance and measure its mass. 2) Pour 30 cm3 of liquid into the measuring cylinder and measure its new mass. 3)Subtract the mass in step 1 from the mass in step 2. This is the mass of 30 cm3 of liquid. 4)Use the measurements to calculate the density of the water. Specific latent heat: Specific latent heat is the energy required to change and object’s state of matter. Specific latent heat of melting is SLH of fusion and specific latent heat of evaporation is SLH of vaporisation. Topic 3: forces and motion. Weight = mass x field strength. W=mg Acceleration = Δvelocity/time. A=Δv/t. Elastic potential energy = ½ constant x extension2. Ee=1/2ke2 Core practical: investigating springs. 1) Align the marker to a value on the ruler, record this initial length of the spring 2)Add the 100 mass hanger onto the spring 3)Record the mass and position from the ruler now that the spring has extended 4)Add another 100 g to the mass hanger 5) Record the new mass and position from the ruler now that the spring has extended further 6) Repeat this process until all masses have been added 7) The masses are then removed, and the entire process repeated again, until it has been carried out a total of three times, and an average length is calculated Moments: A moment is the turning effect of the force. A moment is given by the force multiplied by the distance from the pivot. Moment = force x distance. M=Fd. If the total anticlockwise moment equals the total clockwise moment about a pivot, then the object is balanced and won’t turn. Levers make it easier for us to do work as it increases distance from the pivot. This allows for less force to applied which increases turning force. Gears are circular discs with teeth which interlock with other gears so that when they turn one gear goes clockwise and the other goes anticlockwise. Different sized gears can be used to change the moment of a force because a force transmitted to a larger gear will cause a bigger moment as distance from pivot is greater, also a larger gear will turn slower than a smaller gear. Newton’s laws: 1) If the resultant force on a stationary object is 0, then it will remain still. If the resultant force on a moving object is 0, then it will remain moving. If there is a non-zero resultant force on an object, the velocity will change in the direction of the force. 2) The larger the resultant force acting on an object, the more it accelerates. Force and acceleration are directly proportional. Acceleration is also inversely proportional to mass, so a heavier object accelerates less. Force = mass x acceleration. F=ma. Inertia is the tendency to continue in the same state of motion. An objects inertial mass measures how difficult it is to change the velocity of an object. M=F/a. 3)When 2 objects interact, they produce an equal and opposite force onto each other. Core practical: investigating motion. 1) Use the metre ruler to measure out intervals on the bench. Draw straight lines with pencil or chalk across the table at these intervals 2) Attach the bench pulley to the end of the bench 3) Tie some string to the toy car or trolley. Pass the string over the pulley and attach the mass hanger to the other end of the string 4) Make sure the string is horizontal and is in line with the toy car or trolley. Hold the toy car or trolley at the start point. Attach the full set of weights to the end of the string 5)Release the toy car or trolley at the same time as you or a partner starts the stopwatch. Press the stopwatch at each measured interval on the bench and for the final time at 1.0 m 6)Record the results in the table and repeat step 5 to calculate an average time for each interval 7) Repeat steps 4-5 for decreasing weights on the weight hanger. Make sure you place the masses that you remove from the weight stack onto the top of the car, using the Blu-tac, each time you decrease the weight Momentum: Momentum is a property of moving objects. The greater the mass and velocity, the greater momentum it carries. Momentum = mass x velocity. p=mv. Ina closed system, the conservation of momentum states that after an event, momentum is the same as before the event. Force = change in momentum/change in time. F=mΔv/Δt.