Required practicals Flashcards
Methods, safety, sources of error
Method for stationary wave on a string
-Set up apparatus with stand, vibration generator, string, moveable bridge, pulley, masses, counterweight, metre ruler
-Measure mass of string with balance
-Start at length 1m and change frequency until first harmonic, record f
-Change length by 0.1m and repeat
-Repeat and find mean f for each l, plot f against 1/l
Safety measure for stationary wave on a string
Stand could topple and cause injury so put counterweight on it
Sources of error for stationary wave on a string
Vibration may not be at right f, use oscilloscope to verify
Signal generator may not be at right f, leave for 20 mins to stabilise
Method for Young’s double slit
-Set up apparatus with laser, double slit and screen in darkened room
-Measure D to be 0.5m, measure multiple fringes’ width and divide to find mean w
-Increase D by 0.1m and repeat
-Repeat and plot mean w against D
Safety measure for Young’s double slit and diffraction grating
Lasers could shine in someone’s eye, so tilt reflective surface’s down, don’t do at eye level, don’t point at people
Sources of error for Young’s double slit and diffraction grating
Screen and double slit could be misaligned so use set square
Fringe width could be uneven so find mean
Method for diffraction grating
-Set up apparatus with laser, diffraction grating and screen in darkened room
-Measure D to be 1.0m and measure distance from 0th order to other orders and find mean
-Calculate d by doing 1/ number of slits on grating
-Find angles, calculate λ and find mean
Method for g by freefall
-Set up apparatus with stand, clamp, electromagnet, steel ball, light gates, counterweight
-Make h, distance between light gates, 0.5m
-Set stopwatch to zero, turn off magnet and record time t for fall
-Reduce h by 0.05m by moving lower light gate up, repeat and find mean
-Plot graph of 2h/t against t, gradient is g
Safety measure for g by freefall
Stand could topple and cause injury so use counterweight
Ball could bounce onto someone so cushion it
Sources of error for g by freefall
Distance between first light gate and start could change so keep measuring
Air resistance so use a dense ball
Use set square or clamp to reduce parallax error in measuring h
Method for Young’s modulus
-Set up apparatus with 2 long steel wires, the main and Vernier scale, metre ruler, masses
-Measure initial length of test wire
-Add 1kg mass so wires are taut and record l
-Add 1kg more and calculate e each time, find mean e for each l
-Use micrometer to calculate A of wires
-Plot F against E
Safety for Young’s modulus
Wire will stretch and could break and go in someone’s eye so wear safety goggles
Masses could fall if wire break so cushion below them
Sources of error for Young’s modulus
Comparison wire compensates for other sagging and thermal expansion
Percentage uncertainty could be large so have large initial length
Method for resistivity of a wire
-Set up apparatus with power supply, ammeter in series, voltmeter in parallel, a constantan wire and two crocodile clips
-Use a micrometer to calculate A of wire
-Measure l as 1.00m with clips and metre ruler and calculate R using R=V/I
-Increase l by 0.1m and repeat, find mean R for each l
-Plot mean R against l
Safety for resistivity of a wire
Wire could heat up and cause burns if touched, disconnect crocodile clips between readings
If wire is tight it could snap so wear goggles
Sources of error for resistivity of a wire
Wire could heat up and resistance could increase so disconnect clips between readings
Wire should be kept as straight as possible and without kinks so l is as accurate as possible
Method for internal resistance and emf
-Set up apparatus with cell, voltmeter in parallel to it, switch, ammeter and variable resistor
-With switch open record initial V
-Set variable resistor to max value, close switch and record V and I
-Decrease resistance and record V and I for each over widest possible range
-Plot V against I
Safety for internal resistance and emf
Wires could get hot and cause burns so another resistor could be used
Sources of error for internal resistance and emf
Wires could get hot and increases resistance in circuit so open switch between readings
Old cell’s emf could change in experiment so use a new cell
Method for mass spring and simple pendulum SHM
-Set up apparatus with spring or string, masses or bob, stand and clamp, pin and blue tack (marker) at equ point
-Add a mass or increase length, pulland release
-Time the time taken for 10 complete oscillations and find mean
-Increase mass or length and repeat, find a mean T for each mass or length
-Plot T^2 against m or T^2 against l
Safety for mass spring SHM
Suspended masses could fall and hurt someone so don’t pull too far and use light weight
Sources of error for mass spring SHM
Make sure oscillates only downwards
Place fiducial marker at centre of oscillation to give a clear point to time from
Time many oscillations to get more accurate mean
Sources of error for simple pendulum SHM
Have to measure to centre of mass so use a small bob
Don’t release from a large angle
Method for Boyle’s law
-Set up apparatus with syringe, stand and clamp, masses, valve at top, counterweight
-Without plunger, measure d of valve to calculate area
-Start with 100g and allow 4ml of air in, increase and measure V for each mass
-Calculate F using mg and calculate A, so find pressure and subtract from 101kPa to get P at each V
-Plot 1/V against P and should get straight line through origin
Safety measures for Boyle’s law
Stand could topple so use counterweight
Sources of error for Boyle’s law
Plunger could stick so could lubricate
Don’t prevent movement with clamp
Method for Charles’ law
-Set up apparatus with large beaker, hot water, capillary tube, thermometer, elastic bands, 30cm ruler
-Stir water with thermometer and record temp and length
-Repeat once it cools every 5 degrees until room temp, could use ice to go further
-Plot l against temp and find absolute zero
Sources of error for Charles’ law
Tube needs to be clean to keep bead intact
Tube needs to be submerged in the water
Safety for Charles’ law
Conc H2SO4 could damage eyes so wear goggles
Boiling water could cause burns so don’t spill
Method for discharging capacitor
-Set up apparatus with capacitor with flying lead, in series on one side with cell, other with resistor and with voltmeter in parallel
-Set switch to cell side and allow to fully charge
-Put switch to other side and record V for t=0 and every 5 seconds
-Repeat twice and find mean V for each t
-Plot lnV against t and find RC
Safety measures for discharging capacitor
Make sure capacitor’s voltage rating is above that of the cell to prevent it from exploding
Method for charging capacitor
-Set up apparatus with capacitor in series with switch, cell and resistor and with voltmeter in parallel to it
-Close switch and record V for t=0 and every 5s, repeat and find a mean V for each t
-Plot V or lnV against t
Method for magnetic force on a wire
-Set up apparatus with wire, magnets, ruler, scales, stands and clamps, ammeter, power supply
-Tare balance and increase power until 0.5A and record mass m on balance
-Increase voltage and record m for each I, find mean m for each I
-Measure length of the two magnets
-Calculate F and plot against I
Sources of error for magnetic force on wire
Can be hard to achieve the desired currents so could use variable resistor
Scales with high resolution needed as force will be small
Safety for magnetic force on wire
Large currents in wire will cause increase in temp so do not touch
Method for magnetic flux linkage
-Set up apparatus with search coil, oscilloscope, protractor, stands, ac supply, circular coil
-Connect search coil to oscilloscope and circular coil to ac supply
-Choose good time-base and voltage sensitivity settings, turn on ac and find the emf
-Tilt search coil by 10 degrees and repeat, find mean emf for each angle
-Plot emf against cosθ, should be a straight line
Sources of error for magnetic flux linkage
Could be parallax error when recording angle so read from far above to reduce this
Safety measures for inverse square law
Gamma can cause damage to cells and DNA, keep as big a distance as possible, don’t point at people, handle with tongs, keep out as short as possible, if dropped report it
Method for inverse square law
-Set up apparatus with metre ruler, GM tube, counter, gamma source, stopwatch
-Record background count for long period of time, find mean background count
-Place gamma source close to GM tube, record counts over time and find mean activity
-Increase distance and repeat, finding a mean count rate for each distance
-Find corrected count rate for each distance, plot distance against 1/ √ new C, should be straight line
Sources of error for inverse square law
Gamma source will be slightly back from the front of the source so this will show on the graph plotted
How can you reduce random error?
Take repeats and mean
Use computer, datalogger, camera
Use appropriate equipment (eg higher resolution)
How can you reduce systematic error?
Calibrate correctly, tare balances
Find background count rate
Read at right level to reduce parallax error
