Edexcel Physics A Level Core Practicals

A comprehensive set of vocabulary flashcards covering the key concepts, formulas, and experimental evaluation points for Edexcel Physics A Level Core Practicals 1 through 16.

Practical 1 Aim

Determining the acceleration of a free-falling object

Practical 1 method

Using an electromagnet:

1. Open the switch to break connections between battery and electromagnet in the primary circuit and turn on the timer in the secondary circuit

2. Electromagnet demagnetises causing steel ball to fall distance, h (measured using a ruler), from the bottom of the ball to the top of the trap door

3. When the ball falls through the trap door it breaks the connection of the timer to the battery hence the timer stops

4. Record time taken to fall h metres, t, repeat 3 times and discard anomalies and find mean t

5. Vary h and record t

6. Use $s=ut+\frac12at^2$ given s=h u=0 a=g t=t to get $t^2=\frac{2}{g}h$

7. Plot $t^2$ against h and draw line of best fit, gradient (m) will be $\frac{2}{g}$

   So $g=\frac{2}{m}$

Practical 1 risk assessment

1. If dropping off a table, clamp electromagnet stand to table to prevent toppling over

2. Be aware of falling ball - try to capture at the bottom

3. Small currents should be used in the circuit to prevent danger of electrical shock

Practical 1: Evaluation

1. Small t values: use larger distances to reduce uncertainty

2. Time delay between timer starting and ball being released due to residual magnetism in the ball: use Lowe current so electromagnet has a weaker magnetic field

3. No air resistance: not fast enough

Practical 2 Aim

Determine electrical resistivity of a material

Practical 2 Method

1. At various points along the wire measure the diameter, d, repeat at 90 degree angles at the same point, get about 6 readings and find average - check for zero error on micrometer

2. Find cross-sectional area, A, of wire as: $A=\frac{\pi d^2}{4}$

3. Connect circuit with battery, variable resistor, ammeter, switch and volt meter in series and potentiometer in parallel to voltmeter

4. At 10cm intervals from crocodile clip, touch wire with probe, record voltage, v, and current, I, readings on voltmeter and ammeter respectively

5. Calculate Resistance R, as $\frac{V}{I}$

6. Measure length of wire, L, from one crocodile clip to the other, using a ruler

7. Vary L by changing position of the crocodile clips along the wire, and record corresponding values of R

8. Plot R (y-axis) against L and draw line of best fit with equation: $R=\frac{\rho}{A}L$

9. Calculate resistivity as gradient x A

Practical 2 risk assessment

1. Small voltage used so little danger of electric shock

2. Wire may get warm so don’t touch unless with probe

Practical 2 evaluation

1. High varying voltage/current readings: remove power supply, voltmeter, ammeter and replace with ohm-meter (connect crocodile clip/probe directly to it)

2. Uncertainty from micrometer is doubled as radius gets squared

3. Crocodile clip is not directly in contact with the exact end of the wire due to windings on the end of the ruler

4. Poor connection between crocodile clips and wire/dirty crocodile clips creates will mean a higher resistance is measured

5. Constant does not change resistivity at high temps - this is not a source of error

6. Use ohm-meter to achieve resistance directly, reduce the wire heating (uses a very low current)

7. Avoid pressure hard on wire, as deformation affects cross sectional area, and resistance

8. Ensure wire straight so length measurement accurate

Practical 3 aim

Determine the EMF (electromotive force) and internal resistance of an electrical cell

Practical 3 method

1. Set up apparatus with cell and resistor and ammeter and voltmeter in parallel to cell.

2. Measure potential difference across the terminals, $V_{T}$ , using voltmeter

3. Vary current in circuit by changing value of load resistance, R using variable resistor, measure pd (V) for several values of I

4. Repeat several times and find average $V_{T}$ (y-axis) and current I (x-axis) and draw line of bestfit with equation: $V_{T}=\epsilon-Ir$ where gradient is the negative internal resistance (-r) and y-intercept is emf

Practical 3 risk assessment

Low potential difference so no danger of shock but variable resistor may get hot so handle with care

Practical 3 evaluation

1. For small voltage/current values use new cell or one with a higher emf

2. The terminal potential difference can be measured across the terminals of the power supply, or across the component (provided there is only one component)

3. Keep temperature constant by opening switch between readings to prevent current flow in between each trial

4. Check for zero errors on voltmeters and ammeters

5. Could use a multimeter as it is difficult to read meters simultaneously when there are fluctuating readings on the meters

Practical 4 aim

Determine the viscosity of a liquid

Practical 4 method

1. Zero a mass balance with a 250$\operatorname{cm}^3$ measuring cylinder on top

2. Pour washing up liquid up to the 200$\operatorname{cm}^3$ mark, record the mass and determine the density of the liquid using $density=\frac{Mass}{Volume}$

3. Measure the mass of the ball bearing. Using a top pan balance

4. Measure diameter of the ball bearing with micrometer (at several positions and find average). Halve the diameter to get radius. Find volume of the ball: $Volume=\frac43\pi r^3$

5. Calculate density of the ball bearing

6. Place elastic bands along the measuring cylinder 10cm apart, measured with a ruler

7. Drop the ball into the cylinder (use forceps to hold it securely)

8. Start the stopwatch when the ball touches the top of the washing up liquid, lap when the bottom of the ball just passes a rubber band

9. Record these 2 times ($t_1$ and $t_2$ )

10. Repeat 2 more times with the same radius sphere

11. Repeat procedure for ball bearing with the same mass but varying radii

12. For each radius, find average $t_1$ and $t_2$, calculate velocities, $v_1$ and $v_2$ And average to find average velocity for each radius

13. For each radius (where $\rho_{s}$ is the density of the ball bearing and $\rho_1$ is the density of liquid) find the viscosity $\eta$ ; $\eta=\frac{2(\rho_{s}-\rho_{l})}{9v_{avg}}r^2$

14. Average the viscosity values to find mean viscosity

Practical 4 risk assessment

1. Spilled liquid can make it easier to slip on floors so mop up any spills

2. Use gloves if allergic to liquid

3. Wear goggles to avoid splashes in eye

Practical 4 evaluation

1. Keep temp roughly the same as it may change the viscosity of oil

2. Ensure the lap timer is hit for constant parts of the ball

3. Larger distance between elastic bands will lower percentage uncertainty, but there will still be a high uncertainty in time due to human reaction time

4. Light gates and data loggers can be used to eliminate uncertainty due to reaction time

5. Strong magnet could be used to remove ball bearings from the tube

6. If ball falls close to wall, repeat reading since the flow will no longer be laminar

7. If velocity at second band higher than first band, ball bearings might not have reached terminal velocity when you started timing, so move bands further down the tube and try again

Practical 5 aim

Determine Young Modulus of a material

Practical 5 method

1. Using the micrometer screw gauge, measure the diameter of the wire (various points at 90 degree angles make an average) - hence find the radius, r, in mm and convert to metres

2. Find cross sectional area, A, of wire in $m^2$ : $A=\pi r^2$

3. Set up equipment; clamp wire so that its taut

4. Measure the distance between the two strips of paper tape (original length, L)

5. Add 100g masses at a time, each time measuring the new distance between the paper tape: Calculate force applies, F as F=mass added x g, calculate the extension, x, as x= new length - original length

6. Repeat until wire snaps

7. Calculate stress and strain for each value of F and x: $Stress=\frac{F}{A}$ Strain = $\frac{x}{L}$

8. Plot stress (y-axis) against strain (x-axis) find gradient of straight line section to find Young Modulus

Practical 5 risk assessment

1. Wire snaps and can recoil due to large amount of energy stored due to extension - wear safety glasses whenever wire is under tension

2. Paper prevents wire from recoiling too much

3. Place tray with carpet under the masses to catch the masses when the wire snaps and absorb energy upon impact with the floor

4. Do not stand directly under the masses

Practical 5 evaluation

1. Use large distance between the paper tape at the start, to reduce uncertainty

2. Use a thick enough wire to ensure that a wide range of values is given before the wire fails

3. Wait for necking to finish before taking final length measurements

4. Area of the wire may not be constant so take several measures and find mean

5. For more precise reading, use smaller masses

6. Small extension hard to measure accurately; gives large percentage uncertainty

7. Use a reference marker to avoid parallax when measuring extension

Practical 6 aim

Determine the speed of sound in air

Practical 6 method

1. Set time base on oscilloscope to 100ms//cm and y-gain 0.1V/cm

2. Connect microphone to input on oscilloscope, activate second beam mode

3. Place microphone in front of the speaker and set signal generator to 1000Hz

4. Place metre ruler between the signal generator and microphone

5. Move the microphone away from the loudspeaker, until the microphones wave has moved one full wavelength along the signal generators wave so the peaks and troughs line up

6. Measure the distance using the metre ruler as one wavelength

7. Keep moving microphone back and recording the distances at which the traces line up until 1 metre is reached

8. Convert the measured distances so as to record the length of one complete wavelength: for the 2nd result divide length by 2 for one wavelength, for the 3rd result divide length by 3 for one wavelength etc.

9. Find the mean wavelength

10. On the oscilloscope find the time period (number of squares for 1 wavelength x time base) then invert (1/time period) to find actual frequency being produced

11. Vary the frequency on the signal generator to 2000Hz and 3000Hz and repeat procedure as above

12. Calculate the speed of sound at each frequency using $v=f\lambda$ and determine the mean speed of sound.

Practical 6 risk assessment

1. Hearing protection used as high frequency sound can be painful to listen to for long periods of time

2. Sound not too loud to avoid ear damage

Practical 6 evaluation

1. Changing the time base until only 1 wavelength is shown reduces uncertainty in measurements

2. Finding the frequency from the oscilloscope overcomes uncertainties in the signal generator

3. Make sure oscilloscope dial is in calibrate position

4. The time interval is very small, so maximise the distance between microphones

Practical 7 aim

Factors affecting the frequency of a vibrating string

Practical 7 method

1. Attach 10g of mass to the end of the pulley and calculated tension as tension = mass added x g

2. Switch on transducer and increase frequency until first harmonic is formed

3. First harmonic is observed when there is a standing wave on the string with 2 nodes and 1 antinode (wavelength = twice the length of the string)

4. Using time base on oscilloscope, find frequency of first harmonic (1/T) - record the frequency

5. Increase the amount of mass up to 100g in 10g increments finding the first harmonic frequency and tension each time

6. Plot frequency against tension and frequency against square root tension to investigate the relationship between the two variables

Practical 7 risk assessment

No major hazards - string is elastic so wont snap easily low masses used pulley firmly attached to bench

Practical 7 evaluation

1. Using oscilloscope overcomes uncertainty in signal generator

2. To measure one variable (Tension, Length, Mass/length) keep the other two constants

3. Don’t use heavier masses in order to keep low frequencies required to form the first harmonic

4. Set time base on oscilloscope so one wavelength is on display to reduce uncertainty in measuring the distance across time base

5. Uncertainty at nodes measuring wavelength due to blur

6. For graphs the following relationship applies $v=f\lambda=\sqrt{\frac{T}{\mu}}$ where wavelength is 2x length of string T is tension and f is fundamental frequency

Practical 8 aim

Determine the wavelength of light

Practical 8 method

1. Set up equipment with diffraction grating at right angle to the light from the laser parallel to the screen

2. Find the slit width which is (1/slits per metre value)

3. Measure the distance, D, between grating and the screen with a metre rule

4. Measure the distance, x, by measuring the distance between the first orders and dividing by 2 (to get the mean x between the 1st orders and 0th order)

5. Using small angle approximations find $\theta$ ($\theta=xD$ )

6. Ensuring your calculator is in radians - find wavelength using $\lambda=\frac{d\sin\theta}{n}$ , lambda is the wavelength of light (m), d is the slit width, theta is the beam angle, n is the order used

7. Repeat for more order lines to get an average of wavelength

8. Repeat for a diffraction grating with a different number of slits per metre and average

Practical 8 risk assessment

Do not look into the laser can cause eye damage

Practical 8 evaluation

1. If slit width is bigger (less slits/metre) the pattern will not spread out as much (if d is larger, sine theta is smaller so individual maxima are sharper)

2. Place laser far enough from diffraction grating that a good spread of diffraction patterns can be seen

3. Conduct experiment in a dark room

4. Use Vernier scale to record x in order to reduce percentage uncertainty

5. Larger grating to screen distance makes all x values greater so reduces uncertainty

6. Measure from nth order on one side to other nth order on the other side so distance measured larger so lower percentage uncertainty in x

7. Use grating with more lines per mm so values of x greater so lower percentage uncertainty

Practical 9 aim

Investigating change in momentum

Practical 9 method

1. Set up apparatus with pulley fixed to the edge of the desk and a string

2. Masses and a card are placed inside the trolley

3. Measure the mass of the system, M, of masses both in the trolley and hanging off the string using a mass balance and the mass within the trolly only, m

4. Measure the length of the card, L, using a ruler

5. Release the trolley such that the hanging masses will fall vertically pulling the trolley along the ramp

6. The initial and final velocity, u and v, of the trolley are calculated: $velocity=\frac{L}{t}$ Where t is the time recorded by the first light gate (for initial velocity) and second light gate (for final velocity)

7. Calculate the change in momentum $\Delta p=M\cdot\Delta v$ where $\Delta v=v-u$

8. Calculate the force acting: $FORCE=\frac{\Delta p}{\Delta t}$ where change in time is the time taken for the card to travel between the two light gates

9. Repeat 3 times and calculate mean force

10. Repeat procedure moving the masses from the trolley to the hanger recording $\frac{\Delta p}{\Delta t}$ And F (where F=mg m is the mass in the trolley )

11. Plot F against $\frac{\Delta p}{\Delta t}$ which should give a straight line supporting the relationship: $F\Delta t=\Delta P$Impulse= Change in momentum

Practical 9 risk assessment

No major hazards light masses are used so impact to feet etc do not pose any major risks

Practical 9 evaluation

1. Assume mass of string negligible in the calculation of the mass of the entire system

2. Assume the string is in extensible so that the change in velocity of the hanging masses is the same as the change in velocity of the trolley

3. Tilt ramp until trolley is just on the point of moving - to account for friction (friction changes the gradient as it makes the x axis variable smaller due to a larger t and a smaller velocity over the same distance)

4. Using an air track negates the need for tilting the ramp

5. Moving the masses from the trolley to the mass and the hangar makes sure the system is of constant mass

6. Light gates can find acceleration also - use this to find a and plot essentially F=ma

7. Considering energy of the trolleys and energy of the falling mass - conservation of energy can also be investigated

Practical 10 aim

Use ICT to analyse collisions between small spheres

Practical 10 method

1. Record the masses, m, of the two spheres using a mass balance then place them on a level table top

2. Position two metre rulers perpendicular to each other using a set square

3. Position a video camera above the table top (birds eye view) and start camera recording

4. Roll one sphere towards stationary sphere and allow them to collide and roll

5. Stop recording when both spheres come to rest

6. Import video to tracking software and calibrate distance and a 90 degree angle using the metre rulers

7. Go through each frame of the video use the rulers to calculate the distance travelled and calculate the time between each frame

8. Calculate the initial and final velocity of the spheres using Pythagoras Theorem

9. Angle of travel of the two speeds calculated using trigonometry our calculated by the software

10. Use velocities to find the initial and final momentum in both the horizontal and vertical plane and show if momentum is conserved in the two collisions

Practical 10 risk assessment

Low energy collisions used no major hazard

Practical 10 evaluation

1. Uncertainty in velocity comes from half the range of repeat readings

2. Friction cannot be accounted for in 2D

Practical 11 aim

Analyse the potential difference across a charging and discharging capacitor

Practical 11 method

1. Set up circuit with DC power supply, high resistance resistor, switch, capacitor, ammeter and a voltmeter around the (initially discharged) capacitor

2. Close the switch to charging position and start the timer

3. Record pd and current every 10s

4. Repeat process 3 times and calculate mean V and I

5. Plot graph of current against time and pd against time

Practical 11 risk assessment

1. Ensure that the capacitor is connected the right way in the circuit as to prevent it exploding

2. Use low (sub 40V) voltages for open circuit work

Practical 11 evaluation

Increasing the circuit resistance causes the capacitor to discharge slower; measuring a larger value for time reduces percentage uncertainty (and effect of reaction time)

Practical 12 aim

Calibrate a thermistor in a potential divider circuit as a thermostat

Practical 12 method

1. Set up circuit it’s a power source, a fixed resistor, a thermistor and an ohmmeter (around the NTC thermistor)

2. Set up a Bunsen burner, tripod, gauze, breaker with ice, stirring rod, mercury thermometer to 0.5 C and waterproof thermistor

3. The temperature of water in the beaker changes in 2-5C increments from 0-100C (using crushed melting ice to get close to 0C and placing the thermistor in the interface of the steam and water to get close to 100C)

4. Allow time for the temperature to reach equilibrium, stir the water, and ensure the thermometer bulb is completely submerged in the water and level with the thermistor

5. Measure the resistance using the ohmmeter

6. Vary the temperature and record resistance

7. Plot calibration curve of resistance against temperature

8. Use the temperature graph to find the resistance at a given temperature and use to set up potential divider circuit using $V_{out}=V_{IN}\cdot\frac{R_1}{R_1+R_2}$

Practical 12 risk assessment

1. Boiling water/bunsen burner includes a risk of scalds and burns so, do not handle the beaker when hot

2. Do not exceed the voltage limit of the thermistor

3. Keep leads away from hot things to prevent melting the plastic coating

4. Support the thermistor to prevent it tipping the beaker over

Practical 12 evaluation

1. Alternative to using the ohmmeter: measure current and pd with voltmeter and ammeter with adequate ranges

2. Fixed points with linear change of a property in temperature are a requirement to form a temperature scale

3. Heating slowly allows the semiconductor to adjust to the temperature of the water and the thermometer

4. Improvement: Heat very slowly over long periods of time using data logger with temperature and resistance probes for the water and thermistor respectively

5. Read temperature off thermometer at eye level to avoid parallax errors

6. If fixed resistors resistance is too high $V_{Out}$ wont vary enough with temperature and if its too low $V_{Out}$May vary across a bigger range than the voltmeter can handle

7. Simultaneous reading of two variables (temperature and resistance) may result in systematic error

8. Check meter for zero error by connecting a lead across terminals so no systematic error in resistance measurements

9. Use a small current and switch off circuit between readings so no heating effect in addition to hope water which would make results inaccurate

Practical 13 aim

Determine the Specific Latent Heat of a Phase Change

Practical 13 method

1. Set up apparatus as shown in diagram

2. Weigh each of the beakers and record their initial mass

3. Crush the ice and put it into the funnel, packed closely

4. Fully submerge the immersion heater into the funnels of ice; one of the heaters are switched on while the other is not as a control, start the stopwatch

5. Record the voltage and current across the heater

6. After 5 minutes, switch off the heater and record the final mass of water in each of the beakers

7. Calculate the total mass of water melted in the given time of 5 minutes, by finding the difference between the initial and final mass in each of the beakers

8. Mass of ice melted by heater (Δm) = Total mass melted – Mass melted due to heat from surroundings (Therefore, Δm = Mass melted in beaker – Mass melted in control)

9. Find the s: $L_{f}=\frac{VIt}{\Delta m}$

Where t = 300s, Lf is specific latent heat of fusion, v is voltage and I is current

Practical 13 risk assessment

Melted ice may drip onto the floor creating a slipping hazard, ensure that there is a beaker to catch the melted ice

Practical 13 evaluation

1. Uncertainty is ±1C (uncertainty in each temperature measurement is ±0.5C but the measurements are both used to calculate the change in temperature)

2. The ice must be melting so that it is at 0C as the method does not account for heating the ice up to 0C

3. Ice must be crushed so that it cools the water down quickly, meaning less heat is absorbed from the room as the mixture is below room temperature - insulate the container

4. If heat from the room enters, L is too small as temperature doesn’t get as low as it should be

Practical 14 aim

Investigate the relationship between Pressure and Volume of a Gas

Practical 14 method

1. A fixed mass of gas is trapped by oil in a sealed tube with fixed dimensions

2. Increase the pressure of gas slowly by using the tyre pump to increase the pressure on the oil (so that level of oil rises and the air will compress)

3. Measure pressure on the gauge and the volume of the gas from the column

4. Wait 30 seconds for the temperature of the liquid to return to room temperature (keep the temperature constant)

5. Find at least 7 data values for pressure and corresponding volume

6. Obtain at least 3 repeated reading and find mean volume for each pressure value

7. Plot pressure against 1/volume to find the relationship (should be straight line, with gradient nRT following the equation PV=nRT)

Practical 14 risk assessment

1. Apparatus could fall over so, clamp it to the desk

2. Pressure pump could be unstable under high pressure so press vertically downwards

3. Tubing/joints unstable at high pressure so wear safety goggles to avoid eye damage

Practical 14 evaluation

1. Pressurise slowly to keep a constant temperature on the liquid, Boyle’s law only applies at a constant temperature

2. The gauge measures excess pressure - so add atmospheric pressure if needed

Practical 15 aim

Investigate the Absorption of Gamma Radiation by Lead

Practical 15 method

1. Set up a Geiger counter and radioactive source, with a clamp and sheet of lead between them

2. Before the radioactive source is removed from the box, record the background radiation count on the GM tube over a long period of time (5-10 minutes)

3. Place the source in the source holder and point at the GM Tube

4. Measure the thickness of each lead sheet at various points around the lead sheet using a micrometer, and find an average thickness of one sheet

5. Add each sheet one by one, recording the count over a much shorter amount of time than for the background count

6. Repeat process three times, and find the average count for each thickness

7. Calculate the count rate as: Count rate= Number of Counts/Time elapsed

8. Calculate the corrected count rate by subtracting background radiation count from each reading

9. Plot corrected count rate (y axis) against thickness, and use to find several half thickness values and calculate the mean half thickness

Practical 15 risk assessments

1. Gamma source: reduce exposure time by keeping in lead lined box when not in use, handle with tongs, do not point at anyone else and keep distance (as activity reduces by an inverse square law)

2. Wash hands after handling lead

Practical 15 evaluation

1. Aluminium removes ɑ and β radiation from the counts, so only gamma is recorded on the 0 count

2. Repeats required as decay is random

3. Less time required for counts with a source as the activity is so much higher than background

4. For more clear results, plot ln A (y axis) against thickness for a straight-line graph, straight line with gradient of λ (the decay constant), A being the activity or corrected count rate

Practical 16 aim

Determine the value of an unknown mass using the Resonant Frequencies of the Oscillation of known masses

Practical 16 method

1. Hang a number of masses to the end of the spring

2. Extend the spring up to the position of the fiducial marker, release it and start the stopwatch

3. Measure time for 10 oscillations; use fiducial mark on clamp stand to improve accuracy

4. Find time period for the oscillation of a given mass by dividing time by 10

5. Repeat process several times and find mean time period

6. Vary the number of masses and record the time period for each condition

7. Plot $T^2$ (y axis) against mass and draw line of best fit with equation $\omega=\sqrt{\frac{k}{m}}$ As $\frac{\omega}{2\pi}=f$ and $f=\frac{1}{t}$ Substituting the latter two equations into the former gives relationship between $t^2$ and m $t^2=m\left(\frac{k}{4\pi^2}\right)$.

8. Attach an unknown mass to the end of the spring and record the time period for this oscillating mass

9. Use the $T^2$ against mass graph to calculate the value of mass

Practical 16 risk assessment

1. Clamp stand to the desk to prevent it falling

2. Do not overload spring so it does not break and cause harm

3. Energies involved are low due to low masses - but falling masses can still cause harm

Practical 16 evaluation

1. Finding time for 10 oscillations then dividing by 10 reduces the percentage uncertainty on each time

2. Make the fiducial mark at the equilibrium position as the mass has the lowest acceleration at this point so it is the easiest to see

3. Double uncertainty in time period due to $T^2$

4. Springs in series: add spring constants

5. Improvements: use Vernier motion tracker and data logger to find a more accurate value for time period - removes human error altogether and parallax error from fiducial mark

Corrected Count Rate

The radiation count rate obtained by subtracting the background radiation count from the measured count rate of a radioactive source.

Fiducial Marker

A reference point placed at the equilibrium position of an oscillation to improve the accuracy of timing measurements.