AQA A LEVEL PHYSICS -REQUIRED PRACTICALS| 2022 UPDATE |

Number 1: Frequency of a stationary wave Equipment  Signal generator  Vibration generator  Stand  2kg mass  1.5m length of string (eg 1.5mm thick)  Pulley which can be clamped to the bench  Wooden bridge slightly higher than the pulley  100g masses on a holder  Metre ruler  An electronic top pan balance with precision 0.1g or better Method 1. Set up the apparatus as shown in the diagram. 2. Adjust the position of the bridge so that l is 1.000m measured using the metre ruler. 3. Increase the frequency of the signal generator from zero until the string resonates at its fundamental frequency (as indicated in the diagram with a node at each end and a central antinode). 4. Read the frequency f, on the signal generator dial. 5. Repeat the procedure with l = 0.900, 0.800, 0.700, 0.600 and 0.500m. 6. Obtain a second set of results by repeating the experiment and find the mean value of f for each value of l. 7. Plot a graph of mean 1/f against l. 8. Draw the best straight line of fit though the points and find the gradient (the graph should be a straight line through the origin). 9. The speed of the travelling waves on the string is c = fλ where λ is the wavelength. When the string is vibrating in its fundamental mode, λ = 2l. Hence c = 2fl. The gradient is 1/ fl so c is given by 2/gradient in ms-1. 10. The speed is also given by c = √(T/m) where T is the tension in the string in N and m is the mass per unit length of the string in kgm-1 11. With a 100g mass hanging from the string, T = 0.981N. m can be found by weighing the 1.5m length of string on an electronic balance, converting this into kg, and dividing by 1.5. These values can then be substituted into the above equation to find another value for c, which can be compared to the value obtained from the graph. 12. The experiment can be repeated with different masses hanging from the string, and different thicknesses of string to investigate the effect of changing T and m. 13. Doubling the fundamental frequency while keeping l, T and m constant will cause the string to resonate in its second harmonic (or first overtone, with nodes at either end, a central node, and two antinodes). Tripling the frequency will give the third harmonic, and so on 2 Technical information  The signal generator should be operated for about 20 minutes in order for the frequency to stabilise.  The power output (eg 20V peak-to-peak) should be used. The output level should be turned up to a value which gives steady vibrations of the vibration generator.  The string should be tied to the stand and passed through the hole in the vibration generator.  The bridge should be at the same height as the hole.  The 2kg mass is used as a counterweight to ensure the stand does not topple over (an alternative would be to clamp the stand to the bench using a G-clamp) Risk assessment String snapping – wear safety googles, weights falling – stand back from equipment Results analysis – investigating changing length The shorter the length, higher the frequency Mean value for μ = 6.4x10-3 Evaluation μ didn’t stay constant showing that there is some error within our experiment Systematic: mass of masses, mass per unit length Random errors: reading of frequency, length of string especially, human errors Graph Uncertainty Frequency 4Hz +- 0.1Hz Mass 0.3kg +- 0.003kg Length 3.43m +- 0.0005m Tension 2.9439N +- 0.029N 3 Number 2: Young’s slit experiment Equipment  laser – class II optical laser with output 1mW or less  darkened slight with double slit ‘rulings’ (usually 1mm slit separation)  Vernier callipers to measure slit separation  Adjustable single slit (might be unnecessary with the laser)  white screen (wall covered with white paper may be suitable but paper must be matt finish or non-reflective to reduce chances of reflected beams)  metre ruler Method 1. A partially darkened laboratory is required ensuring lasers are used safely. 2. Set up the apparatus as shown in the diagram, with the laser illuminating the double slit and the screen a distance D of initially about 1 metre. (With the laser the single slit might not be required, provided the laser beam is wide enough to illuminate across the double slit). 3. Carefully adjust the position of the laser until the light spreads evenly over the two slits. An interference pattern should be visible on the screen. 4. The fringe width (or fringe spacing), w, can be measured by measuring across a large number of visible fringes. (Take care when counting – counting from the first bright fringe to the tenth bright fringe would represent nine fringe widths!). 5. Use the metre ruler to measure D. 6. A measurement of the slit separation, s, is required. The value could be measured with Vernier callipers or travelling microscope. If a travelling microscope is used it must only be used to measure slit separation and not the fringe width. Alternatively the manufacture may quote the value on the slide. 7. Use the equation λ = w s D 8. Alternatively, the value of D could be changed from approximately 0.5 m to 1.5m and the fringe width, w, measured for each value of D. 9. A graph of w on the y-axis against D should be a straight line through the origin, with gradient = λ /s 4 Technical information  Using a laser for this this experiment makes it possible to produce visible interference fringes in a partially darkened laboratory. Ensure lasers are used safely and set up so they are not pointed directly into anyone’s eyes Risk assessment Laser shining into eyes – turn off when not in use/don’t point at people, reflection off screen – use plain surface e.g. matt balck Results analysis As the distance increased, so did the slit separation Wavelength found = 5.9x10-7 m, real wavelength of laser = 6.5x10-7 m Evaluation Wavelength was similar but not the same showing some error Systematic: screen wasn’t flat, diffraction grating reading, wavelength reading Random: place of which dots were measured from, size/shape of dots, distance between diffraction grating and screen, position of diffraction grating against screen Graph Can’t do with results, only graph possible is looking at the pattern Uncertainty Ruler 1m +- 0.5mm Diffraction grating 3 lin/mm +- 0.5 lin/mm Laser wavelength 650 nm +- 10nm 5 Number 3: g by free fall Equipment  Stand and clamp  Electromagnet  Low voltage variable DC supply (to power the electromagnet)  2kg mass  Steel ball bearing  Two light gates with bosses to attach them to the stand  An electronic clock or data logger with precision 1ms or better.  A pad (e.g. of felt) to protect the bench when the ball bearing lands.  Metre ruler Method 1. Set up the apparatus as shown in the diagram. The height between the starting position of the ball bearing and the upper light gate should be kept constant, so that the velocity, u, with which the ball bearing reaches this light gate is also constant 2. Adjust the position of the lower light gate so that h is 0.500m measured using the metre ruler. (If a taller stand is available, h could be set at a higher starting value.) 3. Switch on the supply to the electromagnet, and hang the ball bearing from it (or fit the ball bearing into the clamp if a mechanical release mechanism is being used). 4. Reset the clock or data logger to zero and switch off the electromagnet (or open the clamp). 5. Read the time on the clock or data logger once the ball bearing has passed through the light gates. 6. Take repeat readings to find the mean time, t. 7. Reduce h by 0.050m and repeat the procedure down to a value of 0.250m (lower values than this make it difficult to obtain accurate timings). 8. Plot a graph of 2h/t against t. 9. Draw the best straight line of fit though the points and find the gradient Technical information 6  The electromagnet is a convenient way of releasing the ball bearing.  The low voltage supply should be set at the voltage specified by the manufacturer for the electromagnet.  The supply is switched on and the ball bearing hung from the electromagnet. It will then be released when the supply is switched off.  Several trials and adjustments will be required to ensure the ball bearing falls directly through the light gates.  A mechanical release mechanism could be used (e.g. holding the ball bearing in the clamp which is opened to release the ball bearing, but this is not as quick to reset, and won’t give as clean a release).  The upper light gate should be connected to the clock or data logger to start the timing. The lower gate should be connected to stop the timing.  The 2kg mass is used as a counterweight to ensure the stand does not topple over (an alternative would be to clamp the stand to the bench using a G-clamp) Risk assessment Rebounding of ball – wear safety googles, electric shock – check apparatus before use Results analysis Finding a mean time of all the attempts Put into formula s=gt2/2 Rearrange/solve to g Our value of g = 9.99ms-2 , real value of g = 9.81ms-2 Evaluation Value is close, due to errors Systematic: height of apparatus, timing of machine, length Random: non, all equipment checked before use Graph  Plot a graph of 2h/t against t.  Draw the best straight line of fit though the points and find the gradient (the graph should be a straight line with intercept 2u).  h = ut + gt2/2  Re-arranging 2h/t = gt + 2u  Hence the gradient of the graph gives g in ms-2  The intercept will be 2u. Uncertainty Ruler 1m +- 0.5mm Counter 0.447sec +- 0.000sec Number 4: Young modulus Equipment 7  Ceiling beam or suitably strong fixing to attach loaded wires  2 x 1.5m lengths of copper wire  scale and Vernier arrangement with integral clamps for the wires  micrometer screw gauge  metre ruler  2 x slotted kg mass holders  selection of 0.5kg and 1kg slotted masses  safety goggles (in case wire breaks)  sand tray (to catch masses if wire breaks) Method 1. Set up the apparatus as shown in the diagram. Ensure all the wire clamps are fully tightened. 2. Measure the initial length of the test wire, l, with the metre ruler. 3. A 1 kg mass hanger is initially attached to each wire, to ensure both wires are initially stretched taught. 4. Take the initial scale reading, using the Vernier scale to read to 0.1mm 5. Add an additional 1 kg (or 0.5kg) mass to the test wire and take the new scale reading using the Vernier. The extension of the wire can be calculated by subtracting the two scale readings. 6. Repeat the process, adding an extra 1 kg mass (or 0.5 kg) mass each time, take the new scale reading and calculate the corresponding extension. A total mass of up to 8kg should be adequate. 7. With the wire full loaded remove a1kg mass and take the scale reading. 8. Continue to unload the wire, 1kg at a time, taking the scale reading each time. 9. The extension of the wire for each mass during the unloading process can then be calculated. If the extension during unloading is greater than during loading, the elastic limit for the wire might have been exceeded. If the extension values are similar a mean extension for loading /unloading can be calculated for each mass. 10. Measure the diameter of the wire at several places using a micrometer screw gauge. Technical information  It is important that the steel wire used is completely free from kinks – otherwise any measured ‘extension’ will partly be due to the straightening out of the kinks. Scientific equipment suppliers produce suitable wires for this experiment. They also supply suitable clamps to attach the wires to the ceiling beam, Vernier- scale arrangement and mass holder.  A 1 kg mass will produce an extension of 0.47mm for a 1.5m steel wire of diameter 0.45mm. Consequently, an accurate measurement of extension requires specialised apparatus. The mm scale and Vernier arrangement is one designed specifically for this experiment – the Vernier is attached to, and slides alongside the main scale. The main mm scale is usually clamped to the comparison wire and the Vernier section clamped to the test wire.  The main safety consideration is the possibility of the wire breaking. Goggles should be worn and a sand tray placed underneath the arrangement to catch the falling masses.  The comparison wire compensates for sagging of the beam and thermal expansion effects, and provides a reference point against which to measure the extension of the loaded test wire 8 Risk assessment Masses falling – stand back/sand tray, wire snaps – wear safety googles, cutting wire – wear gloves to avoid cuts Results analysis As weight increased, so did extension until ultimate tensile stress (UTS) Young’s modulus = tensile stress/tensile strain Our equipment YM = 1.87x107 Pa, real value YM = 1.1x1011 Pa Original length, 1.374m, diameter 0.55mm Evaluation The value for young modulus is different to the real value. This is down to errors Systematic: length of wire measurement before/after setting up apparatus, length of control to experimental wire 9 Random: readings, uncertainty in equipment Graph  Plot a graph of mean extension, e, on the y-axis against load, mg. (where g = 9.81 N/kg)  The Young Modulus for the material of the wire (steel) can be calculated using the gradient of the graph.  Estimate the uncertainty in your values of l, A, e and m. Use the values to estimate the overall uncertainty in the value obtained for Youngs Modulus.  Young modulus E = tensile stress tensile strain= mg/A e/L = mgL Ae = L A x gradient  A = cross sectional area of wire  L = initial length of wire Uncertainty Mass 8.5kg +- 0.25kg Vernier scale 25mm +- 0.5mm Micrometer 0.245mm +- 0.0005mm Ruler 1.374m +- 0.0005m 10 Number 5: Resistivity of a wire Equipment  1 metre length of constantan wire of thickness 0.25mm, for example  Low voltage variable DC supply (e.g. 0-6V)  Ammeter (e.g. 0-1A with 0.02A precision or better)  Voltmeter (e.g. 0-5V with 0.1V precision or better)  Two crocodile clips  Five connecting leads  Metre ruler  Micrometer Method 1. Measure the thickness of the constantan wire using the micrometer in at least 3 places and find the mean diameter d. Convert this to metres. 2. Set up the apparatus as shown in the diagram. 3. Attach the crocodile clips so that l = 0.100m measured on the meter ruler. 4. Set the voltage, V, to 0.5V and measure the current, I in A. 5. Calculate the resistance R = V/I in Ω 6. Repeat the procedure for l = 0.200, 0.300, 0.400, 0.500, 0.600, 0.700 and 0.800m, increasing V by 0.5V each time to maintain the current at about 0.5A. (This will allow a reasonably accurate measurement of the current, without it being so large that the wire is warmed, which may change its resistance. Switching off the power supply between readings will also keep any heating to a minimum.) 7. Obtain a second set of results by repeating the experiment and find the mean value of R for each value of l Technical information  The constantan wire should be free from kinks and held as straight as possible when measuring the length.  The thickness of 0.25mm has been suggested as this is sufficiently large to measure accurately with the micrometer.  A 10cm length of it will have a resistance of around 1Ω, which will allow a reasonably accurate determination of its resistance 11 Risk assessment Hot wires – turn power off when not in use, electricity – check equipment before use/low voltage Results analysis As length increases, so does voltage and current decreases Aluminium wire, diameter 4.4x10-4 Resistivity value = 7.9x10-5 Ωm, real value = 2.65x10-8 Ωm Evaluation Different resistivity values mean errors Systematic: variable DC supply, voltmeters Random: length of wire, position of crocodile clip, temperature Graph  Plot a graph of the mean R against l.  Draw the best straight line of fit though the points and find the gradient (the graph should be a straight line through the origin).  Calculate the cross-sectional area of the wire A = πd2/4 in m2.  The resistivity of constantan is then ρ= RA/ L  The gradient of the graph gives R/l  so ρ = gradient x A in Ωm (the accepted value is 4.9 x 10-7 Ωm.) Uncertainty Ruler 0.9m +- 0.005m Voltmeter 0.82v +- 0.005v Ammeter 5.35A +- 0.005A 12 Number 6: emf and internal resistance Equipment  cell or battery whose internal emf and internal resistance is being investigated. Avoid using rechargeable cells or batteries as these have a very low internal resistance, making it difficult to measure and they can deliver high currents on short circuit.  Cell holder (or suitable connectors for cell/battery used)  variable resistor (e.g. A large wire wound rheostat is suitable)  digital voltmeter (eg 0 - 10V)  digital ammeter (eg 0 – 1A)  switch  connecting leads Method 1. Set up the circuit as shown in the diagram. Set the variable resistor at its maximum value. 2. With the switch open record the reading, V, on the voltmeter. 3. Close the switch and take the readings of pd, V, on the voltmeter and current, I, on the ammeter. 4. Adjust the variable resistor to obtain pairs of readings of V and I, over the widest possible range. 5. Open the switch after each pair of readings. Only close it for sufficient time to take each pair of readings. Technical information  Ideally the cells and/or batteries used should be fairly new. The emf and internal resistance of older, ‘run down’, cells will vary during the experiment. It is advisable to switch off the circuit between readings to avoid the cells/batteries running down.  Ensure that the power rating of the variable resistor is adequate for the maximum current used. Risk assessment 13 Electric shock – remove power when changing length, blowing multimeter – use unfused holes, heat – remove power source when not in use Results analysis As the voltage decreased, the current increased With our results internal resistance = 2/3Ω, emf = 2.5v Evaluation Systematic: voltmeters, variable resistor, ammeter Random: reading Graph  Plot a graph of V on the y-axis against I.  Using ε = I (R+r) and V = I R  Gives ε = V+I r  Rearranging V = ε–I r  A graph of V against I will have: o Gradient = - internal resistance o Intercept = emf Uncertainty Voltmeter 1.6v +- 0.1v Ammeter 3.2A +- 0.01A 14 Number 7A: Simple harmonic motion, mass spring system Equipment  helical spring  100g slotted mass hanger  100 g slotted masses  stand , boss and clamp  pin and blu tack to use as fiducial mark  metre ruler  stopclock (reading to 0,01 s) Method 1. Hang the spring from a clamp and attach the 100 g mass hanger. Ensure the spring is securely attached from it’s support. 2. Position the blu tack and pin, acting as a fiducial marker, at the bottom of the mass as a reference point. This will represent the centre of the subsequent oscillations. 3. Pull the mass hanger vertically downwards a few centimetres and release. The spring should oscillate vertically up and down. 4. Determine the time period of the mass-spring system by timing 10 complete oscillations. 5. Take repeat readings of the time for 10 oscillations, T10. Use the values of T10 to find the time period for one oscillation, T. 6. Add a 100g mass to the mass hanger and repeat the timing process to enable the time period of the oscillations to be found. 7. Repeat the experiment with a range of different masses, m, and for each mass determine the corresponding time period, T. Technical information  Expendable springs (with k approximately 25 Nm-1) are suitable for this experiment, together with a range of slotted masses from 0 – 800g Risk assessment Masses - Stand to side in case they fall, place sand tray on the floor underneath it Spring – wear eye protection in case they snap 15 Results analysis As the mass increases, the time period increases Spring constant = 29.09Nm-1, real value approx. 25Nm-1 Evaluation Systemic errors: masses, stopclock Random: readings: Reaction time Graph  Plot a graph of T2 on the y-axis against m.  A straight line through the origin will confirm the relationship between T and m predicted by SHM theory i.e. � 2 = 4� 2 � / � where k is the spring constant or stiffness of the spring.  The gradient of the graph can be used to determine k  T 2 = 4π2 m / k hence k= 4π2 / gradient Uncertainty Ruler 1m +- 0.5mm Stopclock 4.53 +- 0.005sec Mass 100g +- 0.5g 16 Number 7B: Simple harmonic motion, simple pendulum Equipment  pendulum bob  approximately 1.5 m string or thread  two small wooden blocks to clamp the string  stand , boss and clamp  pin and blu tack to use as fiducial mark  metre ruler  stopclock (reading to 0,01 s) Method 1. Attach the pendulum bob to the string and clamp it between two small wooden blocks. 2. Measure the length, L, of the pendulum from the point of suspension to the centre of mass of the pendulum bob. (It might be easier to measure to the top of the pendulum bob and then add on the radius of the bob to give L). 3. The pendulum should be suspended from the stand as shown, with a pin and blu tack acting as a fiducial marker, placed immediately below the pendulum bob. This will be at the centre of the oscillation when the pendulum oscillates. 4. Carefully pull the pendulum bob to the side and release it. The pendulum should oscillate with small amplitude and in a straight line. Check that it continues in a straight line by viewing the oscillation from the side – if not stop it and start the oscillation again. 5. Determine the time period of the simple pendulum by timing 10 complete oscillations. 6. Take repeat readings of the time for 10 oscillations, T10. 7. Change the length of the pendulum and repeat the process to determine the time period. 8. Determine the time period of the pendulum for at least seven different lengths, L. Technical information This is a standard laboratory experiment which can be used to give an accur