Practicals Flashcards
Determine the terminal velocity of a ball bearing - describe
Use a clear viscous fluid in a long plastic tube. Then, measure the speed of a ball bearing travelling through it at regular intervals. Plot this to gain a better understanding of where the terminal velocity could be.
Determine the terminal velocity of a ball bearing - method
Wrap elastic bands around the tube of viscous fluid at set regular intervals (measured out using a rules)
Drop the ball into the tube and record the time it takes to travel between each band.
Repeat 4 times to reduce the effect of random error.
Determine the terminal velocity of a ball bearing - calculations
Calculate the time it takes to travel between intervals and then calculate the speed for each distance (using speed= distance/ time)
Plot a graph of velocity against time. The velocity to which the graph tends to is the terminal velocity.l
Determine the terminal velocity of a ball bearing - sources of error or improvements
- Use a taller tube that allows the ball bearing to travel at its terminal velocity for longer.
- use larger intervals for the bands, to reduce the % uncertainty in both the distance and time between bands.
- Use a viscous liquid that doesn’t cause skin irritation.
Investigating initial speed and stopping distance - describe
Have a piece of wood go down a surface, and it interrupts a beam of light in light gates at different distances. It is also allowed to stop by itself (due to friction on the surface)
Investigating initial speed and stopping distance - Method
Glue a 10cm x 10cm card to the side of a block.
Place the light gates such that it records the average starting velocity and then place the second set of light gates about 2cm after.
The average speed to= 0.1/ time for card to move through.
Push the block and record the position where it stops.
Record the velocity and the distance between the light gate and the stopping distance.
Investigating initial speed and stopping distance - calculation
Find the stopping distance.
Plot a graph of stopping distance against velocity squared.
This should be a straight line because:
KE = 0.5 mv2. = F x stopping distance.
Mass and 1/2 are constants, and you should assume that the friction stays constant as well, so that the v^2 = k stopping distance.
(use a surface with a constant friction so that the frictional force doesn’t vary too much.)
Investigating the property of a plastic
Get a piece of plastic and attach a 100g mass to the strip and measure the length.
Repeat at least 10 times, measuring the extension caused.
If they haven’t broken, then measure the extension when you remove each mass as well.
Then, plot a loading-unloading curve.
Investigating the resistivity of a wire using a micrometer, ammeter and a voltmeter- method
- Measure the diameter of the wire at 3 points along its length using a micrometer and calculate the mean.
- Attach a voltmeter in parallel and an ammeter in series.
- Adjust the length of the wire attached to 10cm (measure using a metre ruler) using crocodile clips
- Read and record the voltage and current. Calculate resistance using V=IR.
- Switch the circuit off in between readings.
- Increase the length and repeat.
- Repeat entire experiment and calculate the mean resistance for each length.
Investigating the resistivity of a wire using a micrometer, ammeter and a voltmeter- Calculations
Calculate the cross sectional area using the radius.
Plot a graph of mean resistance against length and draw a line of best fir.
Gradient = resistivity x cross sectional area, so divide it to get the resistivity of the wire.
Investigating the resistivity of a wire using a micrometer, ammeter and a voltmeter-Safety/ notes
Disconnect the crocodile clips in between measurements to reduce the heating elements from over heating.
This could also change the value of the resistance.
Make sure the wire is held straight and free of any kinks to ensure the length is accurate.
Determining the internal resistance
Set up a circuit with a voltmeter in parallel with a cell, an ammeter in series and a variable resistor.
- Set the variable resistor to its maximum value.
- Record the voltage from the voltmeter and the current from the ammeter, open the switch between readings to prevent heating of the variable resistor.
- Decrease the resistance of the variable resistor and repeat, obtaining values for V and I.
Plot a graph of v against I and draw a line of best fit. The y-intercept will be the emf and the gradient will be the negative internal resistance.
Safety for determining the internal resistance
Another resistor can be included in series with the other to avoid high currents which could be dangerous and make the wires and variable resistor get hot.
Close the switch when not taking readings, so that the wires don’t get too hot.
Calibrate the voltmeter and the ammeter to avoid any systematic errors.
Determining the maximum power of a cell
Set up a circuit with a voltmeter in parallel with a cell, an ammeter in series and a variable resistor.
Record the terminal voltage for at least 8 different current values determined by altering the variable resistor, make sure that the values for the current are in a wide range to ensure you can see a trend well.
P=VI, and you can calculate the resistance at each current by using R=V/I.
Plot a graph of power against resistance, it should have an arches shape in which the peak of the arch is the max power of the cell.
This should occur when the variable resistor’s resistance is equal to the internal resistance of the cell.
Determining the speed of sound (by forming stationary waves in a resonance tube)- Description
- Fill a resonance tube halfway with water.
- Hit the tuning fork above the resonance tube and lower the water level until the intensity of sound is amplified, and when resonance (the highest sound) is reached, mark this level of water using a rubber band.
- Keep lowering the water until the next resonance is heard and mark it.
Resonance occurs in an open tube every λ/4, 5λ/4 etc
Determining the speed of sound (by forming stationary waves in a resonance tube)- Maths/ calculations
If the first maximum is 15cm down the tube, then the wavelength is 4 x 15 = 60cm.
Repeat this step for each maxima and calculate the mean wavelength.
Multiple this by the known frequency to get the speed of sound.
Using an oscilloscope to determining the frequency and amplitude of a wave
Generally, put the microphone near the device that you need to read a signal from.
To find the time period, count the number of divisions and multiply by the time base. Then, you can figure out the frequency because the frequency=1/time period.
To get the amplitude, count the number of divisions and multiply this by the volts per division.
What does an oscilloscope tell you
Y axis is the volts per division, and the x axis is the time base.
For a direct current, it will show a straight, horizontal line. Without the time base, it will only show a dot at the height of the output voltage.
For an alternating current, there will be a sinusoidal wave, and a straight vertical line without the time base. This vertical line shows all the possible voltages.
Determining the Planck Constant using LEDs
Set up this circuit.
A battery with a resistor in series. Across the resistor (an arrow pointing to it connected like. a potentiometer) have an LED, in series with an ammeter and a voltmeter in parallel.
2. Find the wavelength of light the LED is emitting.
3. Find the threshold voltage, which is the p.d when the light turns on, or the current starts to flow.
4. Find the threshold voltage for a range of LEDs with different wavelengths and record these against their threshold voltage.
Determining Planck’s Constant- calculations.
Plot a graph of 1/ wavelength against threshold voltage. Calculate the gradient. Energy of photons = eV = hc/ λ. So the gradient = Vλ = hc/e.
And now, you can calculate Plank’s constant.
Estimate a value for absolute zero using gas volume- method
- Attach the 30 cm ruler to the capillary tubes using 2 elastic bands so that the 0 cm mark is at the very start of the length of the air sample.
- Boil water using the kettle, leaving it to cool slightly before pouring it into the large beaker.
- Place the capillary tube (attached to the ruler) into the beaker, with the open end facing
upwards. - Measure the temperature of the water using the thermometer, making sure to stir the water
with the thermometer beforehand, and record this value. - Measure the length of the air sample without removing the capillary tube from the beaker.
- Decrease the temperature of the water by 5 °C by adding a small amount of cold water/ice
to the beaker, and again measure the temperature and length of the air sample. - Repeat the above step until the water reaches room temperature
Estimate a value for absolute zero using gas volume- calculations
Draw a graph of length against temperature and draw a line of best fit.
At absolute zero, the volume will be zero, so the length will be zero. Create an equation of this graph, in the form y=mx +c and calculate the x-intercept.
Estimate a value for absolute zero using gas pressure- method
1.Place the bung into the neck of the flask making sure that it sits in the flask tightly so that it does not fall out. Attach the connective tubing to the bourdon gauge, again making sure it fits the gauge tightly.
2. Place the flask into the large beaker.
3. Boil water using the kettle, leaving it to cool slightly before pouring it into the large beaker
until it reaches the bung in the flask.
4. Measure the temperature of the water using the thermometer, making sure to stir the water
with the thermometer beforehand, and record this value.
5. Record the value of pressure on the bourdon gauge.
6. Decrease the temperature of the water by 5 °C by adding a small amount of cold water/ice
to the beaker, and again measure the temperature and pressure of the air in the flask.
7. Repeat the above step until the water reaches room temperature.
Estimate a value for absolute zero using gas pressure- calculations
Draw a graph of pressure (y) against temperature (x).
Draw a line of best fit and determine an equation for the graph. At absolute 0, the pressure will be 0, so calculate the x intercept.
Investigating the relationship between pressure and volume- Description of the experiment
You use a syringe and attach different masses onto the end of the syringe and see how the volume inside the syringe changes.
Investigating the relationship between pressure and volume- Calculations
Measure the diameter of the syringe and then calculate the cross-sectional area.
The force applied is equal to the F=mg
Pressure at each volume is equal to P=F/A.
Plot a graph of 1/v against pressure and draw a line of best fit.
You should get a straight line that goes through the origin.
What is the total pressure in any gas
The pressure of the gas + the atmospheric pressure.
Estimating the work done by a gas as its temperature increases- method description
You place a capillary tube attached to a ruler in a large beaker. Then add some boiling water.
Measure the length of the air sample without removing the capillary tube from the beaker.
Decrease the temperature of the water by 5 °C by adding a small amount of cold water/ice to the beaker, and again measure the temperature and length of the air sample.
Repeat the above step until the water reaches room temperature.
Estimating the work done by a gas as its temperature increases- Calculations
Measure the internal diameter of the capillary tube using vernier callipers.
Make sure to stir the thermometer in the water so that the temperature remains uniform in the water.
Calculate the cross sectional area.
Calculate the volume of the air sample at each length by multiplying each length by the cross-sectional area.
Plot a graph of volume against temperature and draw a line of best fit (should be a straight line through the origin).
As the pressure of the air sample is constant, you can use the following equation to calculate the work done:
Workdone = pΔV
P= atm pressure and the volume is the change in volume.
As temperature and volume are proportional, you can see that as the temperature increases, the work done also increases.
Investigating the charging up of a capacitor- description
Set up a circuit with a voltmeter in parallel with a capacitor and in series, an ammeter and a resistor.
Close the switch and charge up the capacitor . Record the voltage and current in intervals of 5s.
Then, repeat the experiment twice.
Investigating charging up a capacitor
Calculate the mean voltage and mean current for each time.
Plot a graph of voltage against time, this graph will show you an exponential growth curve that obeys the V= V0 (1-e ^-t/RC) relationship.
Then, plot a graph of the current against the time, this should show you a exponential decrease. The area under the I-t graph is the charge stored by the capacitor.
Investigating discharging a capacitor- description
Set up a switch and a capacitor in parallel with a voltmeter, and in another branch, a resistor.
Allow the capacitor to fully charge.
Then, let it discharge across the resistor. Observe the voltage at 5s intervals and repeat the experiment.
Obtain the average V at each t.
Investigating discharging a capacitor- calculations
Calculate the natural log of V at each t and tabulate this. Plot a graph of ln(V) against t and draw a line of best fit forming a straight line graphs with a negative gradient equal to -1/RC.
The equation of the graph becomes V= -1/RC t +ln V0.
Investigating capacitors in series- description
Set up a circuit with a voltmeter in parallel with a capacitor, and a variable resistor in series, with an ammeter and a switch as well.
Record the value of the current and p.d sand the time since closing the switch.
Investigating capacitors in series- calculations
Calculate charge (Q=It) for each current. Draw a graph of charge against voltage, and draw a line of best fit. Find the gradient, this is the capacitance.
Investigating capacitors in parallel- Method/ description
Set up a circuit with a variable resistor, an ammeter, a switch and 2 capacitors in parallel with each other, and a voltmeter in parallel with both.
Get values for the current, p.d and the time since closing the switch.
Investigating capacitors in parallel- Calculations
Calculate charge (Q=It) for each current. Draw a graph of charge against voltage, and draw a line of best fit. Find the gradient, this is the combined capacitance.
Investigating the factors affecting simple harmonic motion - describe
- Attach the ball bearing to the string and attach this to the clamp stand.
- Adjust the length of the string, until it is 1m in length.
- Wait until the pendulum stops moving and then place a fiducial marker directly underneath the bob.
- Pull the bob slightly to the left and let it go so it oscillates.
- As the pendulum passes the marker, start the stopwatch and count the time taken for it to complete 10 full oscillations.
- Take more readings for 10s and calculate a mean.
- Reduce the length by 10cm and repeat.
Investigating the factors affecting simple harmonic motion - calculations
- Divide the lengths of time by 10 to get the Time period of one oscillation.
- Draw a table of T^2 against l.
Plot a graph of T^2 against L. Draw a line of best fit. - Should be a straight line through the origin, showing that l is directly proportional to T^2.
- Y= mx : T^2 = 4π^2/g x L.
Investigating the factors affecting simple harmonic motion - notes/ Uncertainties
- To reduce uncertainties further, you could use light gates attached to a data logger to record the period of 10 oscillations.
Investigating the factors affecting simple harmonic motion using a mass-spring system - Description
- Attach a spring to the clamp and attach a mass holder to the spring.
- Wait until the spring stays completely still and then place the marker on the clamp stand at the very bottom of the mass.
- Pull the spring down slightly and let it go so that it s oscillating with a small amplitude in a straight line.
- As the bottom of the mass holder passes the marker, start the stopwatch and count for it to pass 10 oscillations.
- Take more readings and calculate a mean.
- Add 100g mass to the bottom and repeat.
Investigating the factors affecting simple harmonic motion using a mass-spring system Calculations
- Divide the time by 10, to get the time period.
- Draw a table of t^2 against m. Plot a graph and draw a line of best fit.
- Your line of best fit should be a straight line through the origin..
- Graph is y = mx
T^2 = 4pi^2/k x m.
Observing damped oscillations
- Attach the spring to a clamp stand and attach the 500g mass holder to the spring.
- Wait until the spring stops moving completely and then place the marker at the very bottom of the mass holder.
- Attach the 15cm ruler to the marker.
4 Pull the spring down with a small amplitude and allow it to oscillate in a straight line. - As the bottom passes the marker, start the stopwatch and count the time taken for it to complete 10 oscillations- and record the amplitude to which the spring is pulled down to.
- Measure the maximum amplitude of the spring at the start of the 10 oscillations. Repeat twice and calculate a mean value.
- Repeat all, but use a 400g mass holder and add a damping card wedged between the mass holder and a 100g mass.
Observing damped oscillations - calculations
Calculate the time period.
Calculate the frequency as well.
Plot a graph of the max amplitude against the number of oscillations for both systems and draw a line of best fit.
The frequency of the system with the card will be less than that without using the damping card.
Observing forced oscillations
- Set up a spring and a mass holder and a vibrator generator attached to the spring. Then, add a position sensor beneath the mass.
- Turn on the signal generator (and connect it to an oscilloscope and read the time period, to calculate the frequency) and set it to a frequency much lower than the natural frequency.
- Wait until it stops moving completely, then measure the distance of the bottom of the mass holder to the sensor.
- Using the position sensor connected to a computer with a data-logging software, record the max amplitude.
- Increase the frequency above by 10Hz.
- Repeat until the frequency is above the natural frequency.
Observing forced oscillations- Calculations
Plot a graph of maximum amplitude against frequency. You should get a graph that peaks at the natural frequency.
There is a non-zero intercept.
At higher frequencies, there is not enough freedom to react to the driver, so the amplitude simply tends to 0.
Comparison of static and dynamic methods of determining spring stiffness.
The static method is easier to carry out and more likely to give more accurate results, however the dynamic method is also accurate, when using light gates and a data logger.
Techniques and procedures used to investigate transformers- main notes
The formulaes may not work fully, because the transformers aren’t 100 efficient.
- Use a laminated core to reduce the energy loss by eddy currents
- Use a low resistance thick copper wire for the coils
- Use a magnetically soft materials so less energy is needed to magnetise and demagnetise the core.
- To increase the amount of magnetic flux generated by the primary coil that cuts through the secondary, put the coils together.
Transformers equations
Ns/Np = Vs/Vp = Ip=Is
Investigating the magnetic field of a magnet - method
- Set up the wire so it is between the faces of the magnets and both the wire and
magnets are on top of the balance, the ammeter and power pack should be part of
the complete circuit. - With no current flowing, zero the balance.
- Change the supply voltage so that the current, measured on the ammeter, flowing
through the wire is 6.0 A. - Record the reading on the mass balance.
- Repeat the steps and readings for I = 5.0 A, 4.0 A, 3.0 A, 2.0 A and 1.0 .
- Find a second set of results by repeating the experiment.
- Using a ruler measure the length of the magnadur magnets, L, in meters. (This is the
length of wire in the magnetic field)
Investigating the magnetic field of a magnet - calculations
- Find the mean reading on the mass balance for each current.
- Plot a graph of mean m against l.
- Draw a line of best fit, should form a straight line through the origin.
F=BIL.
This is equal to the force from the mass balance. F= mg. (convert to kg)
Hence, the gradient of the graph is m/l, so B = gradient x g(1000L)
Define uncertainty
Interval within which the true value can be considered to lie.
Define error
The difference between a measurement or results from the true value.
How to reduce percentage uncertainty
Make the resolution or the scale divisions smaller.
Make the value larger.
Apparatus that can increase accuracy of the measurements
Timing over multiple oscillations, using a fiducial marker or a set square
Examples of random error
Timing, fluctuations in readings.
Non- uniform diameters
Examples of systematic errors
Parallax, zero, energy dissipation or friction.
Safety for ionising radiation PAGs
Maximise distance from it, and limit time of usage.
How to increase accuracy in the SHM
- Time over multiple oscillations
- Use a fiducial marker
- Set Square
