Core Practicals

RP 01 - Stationary Waves

Equipment: signal and vibration generators, pulley, string, masses, meter ruler, prism.

Safety:

• Cushion between the masses in case the string snaps.

• If using a metal wire, wear goggles to protect the eye.

Method:

• Measure the tension in the string using T = mg and an electronic balance to measure the mass.

• Measure the mass per unit length.

• Attach one end of the spring to the vibration generator, passing the other end over a prism.

• Hang this spring across a bench pulley with a mass hanger on the end.

• Adjust the length so that it is 1.00m and increase frequency until the spring oscillates at the first harmonic.

• Read and record frequency.

• Repeat from 1.00m to 0.50m intervals of 0.1m.

• Repeat the experiment twice more and find and record mean for each length.

RP 01 - Stationary Waves Improvements

Improvements:

• Use an oscilloscope to verify the signal generator’s readings.

• Signal generator should be left for about 20 minutes to stabilise.

• To avoid random error determining exact frequency of stationary wave, adjust frequency while looking at the node.

• Avoid zero error on the electronic balance when measuring mass.

• Place ruler directly beside string to reduce parallax error.

RP02 - Interference Effects

Equipment: diffraction grating, clamp, laser, meter ruler, screen.

Safety:

• Lasers: never turn on at eye level, point it away from people and reflexive surfaces.

Method:

• Ensure the laboratory is partially darkened, set up the diffraction grating and screen normally to the laser.

• Set the distance between the grating and screen to 1.0m using a metre ruler.

• Measure the distance from the zero-order to first maxima on either side using a vernier capiller, then take the mean of these values.

• Repeat this for increasing orders.

• Repeat with a different diffraction grating.

• Use trigonometry to calculate the angle to each order.

RP02 - Interference Effects Improvements

Improvements:

• Use a set-square and ruler to ensure the screen and double slit are aligned perfectly to the normal to the laser to avoid parallax error in measurement of fringe width.

• Use a grating with more lines per mm to increase diffraction and lower percentage uncertainty.

• Reduce uncertainty by measuring across all visible fringes and dividing by the number of fringes.

• Conduct the experiment in a darkened room.

RP03 - Determining g

Equipment: stand and clamp, light gates and datalogger, meter ruler, ball bearing, electromagnet

Safety:

• Use a counterweight or clamp to avoid the stand toppling.

Method:

• Set up the equipment with the light gates 0.5m apart, a counterweight to stop the clamp from tipping and an electromagnet.

• Turn on the electromagnet and add the ball bearing.

• Turn off the electromagnet and record the time taken to fall.

• Decrease the distance between the light gates between 0.50 to 0.25m in 0.05m intervals, taking readings for each value.

• Repeat twice and more and find and record the mean for each height.

RP03 - Determining g Improvements

Improvements:

• Use light gates and a datalogger to reduce human error in measurements of time.

• Use a timer with a high resolution.

• Distance between upper light gate and starting position must be kept constant.

• Ball bearing should be dense to mitigate effects of air resistance.

• To reduce parallax error, ruler can be clamped directly next to the light gates.

RP04 - Determining Young’s Modulus

Equipment: wire, micrometre, meter ruler, hanging masses, G-clamp and wooden blocks.

Safety:

• The wire is under tension because of extension, so wear safety glasses in case it snaps.

• Place a carpeted tray beneath the masses.

Method:

• Using a micrometre (resolution 0.001m), measure the diameter of the wire at five different points and find an average.

• Clamp the wire between two blocks and a G-clamp, then pass it over a pulley with hanging masses on the end.

• Measure the original length of the wire.

• Mark a reference point with tape and record the initial reading on the ruler of the reference point.

• Add a 0.1kg mass and record the new reading of the tape marker.

• Repeat this in increments of 0.1kg until the wire snaps.

• Repeat with a wire of the same material, taking averages for each mass.

• Find cross-sectional area.

• Calculate force applied for each new weight, W = mg.

• Plot a graph of stress against strain.

RP04 - Determining Young’s Modulus Improvements

Improvements:

• Use a vernier scale for more precise readings.

• Reduce parallax error from reading the marker on the ruler.

• Reduce uncertainty on cross-sectional area by taking repeat measurements of diameter.

• Reduce random error by repeating the experiment.

• Use a longer wire to decrease percentage uncertainty.

• Stretching the wire could cause diameter to decrease.

RP05 - Determining Resistivity

Equipment: constantan wire, voltmeter, ammeter, power supply, micrometre, meter ruler.

Safety: disconnect clips between readings to avoid wire heating up and causing burns if touched.

Method:

• Measure the diameter of the constantan wire at five points along it using a micrometre and find and record the mean diameter.

• Set up the equipment with the constantan wire connected to the power supply, with the voltmeter in parallel and the ammeter in series with it.

• Adjust the length between the crocodile clips to 0.1m using a meter ruler.

• Read and record current on ammeter and voltage on voltmeter, then calculate resistance from this.

• Repeat for values between 0.1m and 0.8m in 0.1m intervals.

• Repeat the experiment twice more and find and record the mean resistance for each length.

• Calculate the cross-sectional area.

RP05 - Determining Resistivity Improvements

Improvements:

• The wire heating up might cause change in resistance, so disconnect between measurements or use lower voltage supply.

• Only allow small currents to flow through the wire.

• Avoid parallax error when measuring length.

• Use a longer wire to reduce percentage uncertainty in length measurement.

RP06 - Internal Resistance and EMF

Equipment: battery, voltmeter, ammeter, variable resistor, switch

Safety: Another resistor could be included to avoid high currents.
Method:

• Set up the equipment with the voltmeter in parallel across the battery and the ammeter and variable resistor in series.

• With the switch open, record the reading on the voltmeter.

• Set the variable resistor to its maximum value, close the switch and record the voltage and current.

• Decrease the resistance of the variable resistor and repeat this over the widest possible range.

• Plot a graph of V against I.

RP06 - Internal Resistance and EMF Improvements

Improvements:

• Only close the switch for as long as it takes to take each pair of readings to avoid heating and change in internal resistance.

• Use fairly new batteries.

• Use voltmeter and ammeter with high resolutions to improve precision.

RP07 - Simple Harmonic Motion (Spring)

Equipment: spring, masses, stand and clamp, fiducial mark, meter ruler, stopwatch

Safety:

• To avoid injuring people with the masses, only pull the spring down by a few centimetres and don’t attach heavy masses.

Method:

• Clamp the spring onto the stand and place a 0.05kg mass on the end.

• Pull the mass hanger vertically downwards a few centimetres and release.

• Start the stopwatch when it passes the fiducial marker travelling downwards, and record the time taken for 10 complete oscillations.

• Divide this by 10 to find the time period of the system.

• Repeat from 0.05kg to 0.5kg in increments of 0.05kg.

• Repeat the experiment twice more and find a mean time period for each mass.

RP07 - Simple Harmonic Motion Improvements (Spring)

Improvements:

• Ensure the spring is not moving horizontally.

• Timing more oscillations for each mass reduces percentage uncertainty in the time period.

• The fiducial marker should be in the centre of the oscillation, where the mass is moving fastest and there is least uncertainty in starting and stopping.

• A motion tracker and data logger can be used to eliminate random error.

• Ensure the spring does not pass its elastic limit.

RP07 - Simple Harmonic Motion (Pendulum)

Equipment: pendulum bob on long string, stand and clamp, fiducial mark, stopwatch, wooden blocks.

Method:

• Clamp the string between the wooden blocks and place a fiducial mark at the centre of the oscillations.

• Using a ruler, adjust the distance between the centre of mass of the bob and the wooden blocks to 1.50m.

• Pull the pendulum to the side and release it so it has a small amplitude and travels in a straight line.

• Start the stopwatch when it passes the fiducial marker, then stop it after 10 complete oscillations.

• Divide this time by 10 to find the time period of the pendulum.

• Repeat from 1.50 to 0.50m, decreasing in increments of 0.10m.

• Repeat the experiment twice more and find and record a mean time period for each length.

RP07 - Simple Harmonic Motion Improvements (Pendulum)

Improvements:

• Ensure the oscillations are small so that the SHM equations apply.

• Timing more oscillations for each mass reduces percentage uncertainty in the time period.

• The fiducial marker should be in the centre of the oscillation, where the mass is moving fastest and there is least uncertainty in starting and stopping.

• Use a light string and dense pendulum so the centre of mass is within the pendulum.

• Reduce parallax error by viewing marker at eye level.

• A motion tracker and data logger can be used to eliminate random error.

RP08 Gas Laws (Boyle’s Law)

Equipment: stand, clamp, syringe, rubbing tubing, pinch clip, string, masses

Safety:

• The stand could topple over and cause injury so a counterweight should be used.

Method:

• Measure the internal diameter of the syringe using a vernier calliper, using this to find cross sectional area.

• Clamp the syringe to a stand with masses attached to the plunger.

• Replace the plunger and draw in roughly 4.0ml of air.

• Fit the rubber tubing over the nozzle and clamp it with the pinch clip as close to the nozzle as possible.

• Add 0.2kg onto the plunger and record the new volume on the syringe.

• Repeat this from 0.2kg to 1.0kg in increments of 0.2kg.

• Repeat the experiment twice more and find and record the mean volume for each mass.

• Calculate the force exerted by each mass F = mg, and the pressure exerted by this force, P = F / A. Subtract this from standard atmospheric pressure.

RP08 Gas Laws Improvements (Boyle’s Law)

Improvements:

• Taking repeat readings allows anomalies to be detected and removed.

• The clamp should be high enough that it does not distort the syringe barrel, making it more difficult for the plunger to move.

• The syringe can be lubricated to prevent the plunger from sticking.

• Read volume at eye level to avoid parallax error.

• Keep the room at constant temperature and add the weights gently to avoid sudden pressure changes.

• Use a barometer to measure the actual atmospheric pressure.

RP08 Gas Laws (Charles’ Law)

Equipment: capillary tube, sulfuric acid, 2 litre beaker, ruler, thermometer, kettle

Safety:

• Wear safety goggles as sulfuric acid can cause damage to the eyes.

• Boiling water could cause burns, so take care it does not spill.

• Set up the capillary tube with a drop of concentrated sulphuric acid. Place it in a beaker alongside a ruler and thermometer.

• Fill the beaker with hot water, stir the water and read and record the value of its temperature, as well as the length of the air sample.

• Repeat every 5 degrees down to room temperature.

• Repeat the entire experiment twice more and take averages for each reading.

RP08 Gas Laws Improvements (Charles’ Law)

Improvements:

• Use a travelling microscope or high precision ruler.

• Measure the air column at eye level to avoid parallax.

• Place the thermometer right next to the capillary tube.

RP09 - Capacitors

Equipment: capacitor, resistor, battery, voltmeter, switch.

Safety:

• Ensure the capacitor is connected with the correct polarity and that its voltage rating exceeds that of the battery to prevent it from exploding.

• Make sure there is no water or liquids near the electrical equipment.

• Use a flying lead to make sure the capacitor has fully discharged each time before it is charged again.

• Use a high resistance resistor to ensure capacitor does not discharge too quickly, as high current would cause the wires to heat up.

Method:

• Set up the equipment with a two pole switch, with one terminal leading to a battery and another to a known resistance resistor and a voltmeter in parallel across the capacitor.

• Allow the capacitor to fully charge.

• Move the switch to the discharge circuit and start the stopwatch.

• Observe and record the voltage reading initially and at 5s intervals as the capacitor discharges until 120s have passed.

• Repeat the experiment twice more and obtain average voltages for each time.

RP09 - Capacitors (Improvements)

Improvements:

• Use a large resistance and capacitance to decrease rate of discharge and hence percentage uncertainty.

• Use a digital voltmeter and data logger to accurately record voltage.

• Use low resistance wires to avoid systematic error in resistance readings.

• Short the capacitor using a flying lead before each discharge to avoid exceeding voltage limit.

RP10 - Magnetic Force on a Wire

Equipment: wire, metal cradle with magnets, weighing scales, ammeter, variable resistor, power supply, ruler.
Safety:

• High current flowing through the wire will cause it to heat up and could cause burn.

• Keep any water or fluids away from the electrical equipment.

Method:

• Clamp the wire, attached in series to an ammeter and variable resistor, between two magnets on an electronic balance and, with no current flowing, tare the balance.

• Adjust the resistance so the current measured by the ammeter is 0.5A. Read and record the mass displayed on the balance.

• Repeat for values of current between 0.5A and 6.0A in increments of 0.5A.

• Repeat the experiment twice more and find and record the mean mass for each length.

• Measure and record the length of wire within the magnetic field.

RP10 Magnetic Force on a Wire (Improvements)

Improvements:

• Use scales with high resolution because forces are generally very small.

• Use strong, uniform magnets.

• Wait a few seconds after increasing the current before taking readings to allow values to stabilise.

• Make sure the top-pan balance starts at zero to avoid zero error.

• Make sure no high currents pass through the wire, as this would cause the temperature and hence resistance to increase.

RP11 Magnetic Flux Linkage

Equipment: oscilloscope, large circular coil, stands, AC voltage supply, search coil, protractor

Safety:

• Keep any water or fluids away from electrical equipment.

• Don’t exceed the specified current rating for the coil in order not to damage it.

• The larger coil will heat up, so don’t touch the wire to avoid burns.

Method:

• Mount the circular coil vertically with the stand and position the search coil at the centre of the circular coil using another stand.

• The plane of the search coil should be parallel to the plane of the circular coil.

• Connect the AC power supply to the circular coil and the search coil to the oscilloscope.

• Adjust the time-base and y-gain settings on the oscilloscope and read and record peak to peak voltage, and half to find peak emf.

• Tilt the search coil so the angle between the two coils increases by 10 degrees and measure the oscilloscope reading.

• Repeat for angles from 0 to 90 degrees in increments of 10 degrees.

• Repeat the experiment twice and more and find and record mean values of induced emf for each angle.

RP11 Magnetic Flux Linkage Improvements

Improvements:

• The field lines are unlikely to be perfectly parallel and perpendicular to the area of the coil.

• Read the angle from the protractor far above and from the same point every time to reduce parallax error.

• Increase the reliability by repeating for a full turn.

• Use a calibrated motor to rotate the search coil by fixed increments.

• Turn off the power supply when not taking readings to avoid the coil heating up and its resistance increasing.

• Power supply must be AC to induce an emf.

• Turning off the time base allows more accurate readings on the oscilloscope.

• Measure peak to peak voltage to decrease percentage uncertainty.

RP12 - Inverse Square Law for Gamma Radiation

Equipment: gamma source, Geiger counter, metre ruler, stopwatch, long tongs, safety goggles, gloves, lab count

Safety:

• Exposure to radiation can destroy cells or cause mutations. It can also cause contamination, which would increase irradiation.

• Only keep the radioactive source out of the lead-lined container for as long as the experiment takes.

• Handle the source with tongs and kept at a long distance to avoid any contact with the skin.

• Do not point the source at anyone.

• Wear safety clothing including a lab coat, gloves and goggles.

Improvements:

• With the gamma source not present, start the stopwatch and Geiger counter and record the total count reading after 20 minutes. This is the background count.

• Bring the source into the laboratory and set the distance between the Geiger counter and gamma source to 0.600m, measuring using a meter ruler.

• Start the stopwatch and Geiger counter and take the count after 5 minutes.

• Repeat for values between 0.600m and 0.100m in increments of 0.050m.

• Repeat the experiment twice more and find and record the mean count rate for each distance.

• Find the corrected count rate by removing background count rate for each reading.

RP12 - Inverse Square Law for Gamma Radiation (Improvements)

Improvements:

• Graph may not pass directly through the origin because actual position of the gamma material inside the sealed source is not known.

• By plotting distance against the inverse of the square root of the count rate, this discrepancy can easily be determined from the y-intercept.

• Measure count rate over longer intervals to reduce random error due to random nature of radioactive decay.

• Geiger counter may suffer from an issue called ‘dead time'.

• A sheet of aluminium can be placed in front of the Geiger-Muller tube to prevent any alpha or beta radiation being measured.