Required practicals Flashcards
Investigation of stationary waves on a string
Set up string attached to an oscillator and a bridge
String goes over bridge onto a pulley with masses attached
Adjust the oscillator to produce a first harmonic standing wave
Investigate how the frequency of this wave changes with length and tension
Rearrange equations to for a graph of 1/f against l, to find v = gradient = root T/u
Young’s double slit experiment
Investigate changing D, lambda and s and the impact on w
Use a laser with a double slit and a board
Mark out the fringe spacing on the board with a pencil and measure using vernier calipers
Sources of uncertainty and problems:
Difficult to know the centre of each fringe
Uncertainty in measuring s, D and w
Laser risk assessment
Risk of laser damaging the eyes:
- Turn off the laser when not in use
- Don’t stare at the laser
- Wear eye protection if working closely with powerful lasers
- Put up a safety sign to indicate a laser is in use
Diffraction grating experiment
Set up a laser to shine through a diffraction grating onto a screen
Record w, d and D
Calculate theta for first order using tan^-1 (w/D)
Sub this value into nLambda = d sin theta to find the wavelength of light used
Can investigate the effect changing D, d and wavelength has on the angle between the first order and the central maxima and the number of orders
Investigation of g: trap door method
Electromagnet releases a metal ball, starting the timer
Metal ball hits trap door stopping the timer
Distance fallen is recorded
s = 1/2 at^2, graph of s and t^2, gradient = 1/2 g
Investigation of g: light gates
Metal ball is released to fall between two light gates
The distance between light gates is measured
Each of the light gates attached to a data logger, calculate time difference between second and first light gate
Graph of s against t^2, gradient is 1/2 g
Determining Young modulus
Clamp copper wire in place at one end and then over pulley with masses attached at the other end
Measure the initial length of the wire
Use an initial mass to remove any kinks from the wire
stress = F/A and strain = dL/L
Calculate stress and strain for each value of force from masses - measure A using micrometers and dL using a marker and metre rule
Plot a graph of stress against strain, gradient is Young modulus
Uncertainties and issues with determining Young modulus
Measuring dL, L, A and F
Difficult to know when all the kinks have been removed
Determining resistivity
R = p/A L
Calculate cross sectional area using a micrometer to find radius
Change length using crocodile clips along a wire attached to a metre rule
Measure resistance using an ammeter and a voltmeter, R = V/I
Plot a graph of R against L and the gradient is p/A
Uncertainties and issues with determining resistivity
Measuring R, A and L
May be kinks in the wire impacting length
Crocodile clips provide poor connections
Fluctuations in ammeter and voltmeter readings
Investigating internal resistance and emf
Set up a circuit with an ammeter, voltmeter and variable resistor
Record values of I for each value of V, using the variable resistor to change V and I
Plot a graph of V against I, should be a straight line with a negative gradient
m = -r and y-intercept = emf
Uncertainties and issues with investigating emf and internal resistance
Uncertainties in V, I and variable resistor
Heating effect of current will skew results - include a switch and open it after every reading
Investigating SHM using a mass-spring system
T = 2pi root m/k
Attach a spring to a clamp and stand and hang the spring over the bench
Attach masses to the end of the spring and place a position sensor beneath the spring
Pull the spring a set distance from equilibrium this is the amplitude
Set up computer software to plot a graph of displacement against time and use this to calculate the period
Investigate the effect of changing mass, spring constant and amplitude on time period
Uncertainties and issues with investigating SHM using a mass-spring system
Uncertainties in m, k and displacement
Spring and mass may also experience side-to-side oscillation - suspend the spring from a string to eliminate this
Investigating SHM using a simple pendulum
T = 2pi root L/g
Attach pendulum to an angle sensor connected to a computer
Measure the length of the pendulum
Displace the pendulum from rest position at an angle less than 10 degrees
Angle sensor will record the bob’s displacement with time , use the computer to plot a graph and from this T can be found
Change the mass, the amplitude of displacement and the length independently to see how they affect T
Uncertainties and issues with investigating SHM using a simple pendulum
String may not remain vertical and may have unwanted horizontal and rotational oscillations - use a stiff lightweight rod instead
Uncertainties in displacement, mass, length and time
Angle of swing decreases over time - measure time for a single swing accurately using a data logger
Investigating Boyle’s law
PV = constant p cx 1/V
Use an oil well a pump and a pressure gauge to measure the impact of increasing pressure on volume of gas
Increasing the pressure forces more oil into the tube compressing the air and decreasing its volume
Calculate volume using pi r^2 l
Plot a graph of P against 1/V - should be straight line through the origin
Investigating Boyle’s law uncertainties and issues
Friction will cause less oil to flow into the tube resulting in smaller changes in volume
Uncertainties in measuring volume and pressure
Temperature must remain constant - gas must be compressed very slowly
Investigating Charles’ law
V cx T
Use a glass capillary tube with a small drop of concentrated sulphuric acid trapping a column of air beneath it
Connect this to a 30 cm rule and put this setup in a beaker along with a thermometer
Boil water in a kettle and pour this in the beaker
Record the height of the air column for each value of temperature
Plot a graph of V against T - should be straight line through the origin
Investigating Charles’ law uncertainties and issues
Some of the thermal energy will be dissipated to the surroundings
Parallax error - difficult to read the length of air column
Length reading may be impacted by diffraction through the water
Uncertainties in temperature and length
Investigating charging and discharging capacitors
Setup a circuit with a dc power supply, a resistor, a capacitor, voltmeter and an ammeter
The ammeter and voltmeter need to be connected to a data logger and a computer
Use log linear graph of current and the gradient will be -t/RC
or for voltage and charge it will be t/RC
Same method for discharging except no need for the power supply
Investigating F=BIL
Place two magnets producing a uniform magnetic field on a top pan balance and zero it
Clamp a wire passing through the magnets perpendicular to the field
Use Fleming’s left hand rule to ensure the current direction will result in a downwards force
Record different values of current through the wire and the force produced using 9.81 x mass on top pan balance
Plot a graph of F against I and the gradient will be BL
Investigating F=BIL issues and uncertainties
Uncertainties in the I and F
Wire must be exactly perpendicular
Wire may have kinks
Investigating magnetic flux linkage
Search coil is placed inside a solenoid which is connected to an alternating current so the magnetic flux through the search coil is constantly changing
Search coil is attached to an oscilloscope and should have a known area and a set number of coils
Oscilloscope is setup to show emf as a vertical line (turn off time base)
Search coil is originally positioned perpendicular to the field direction and then rotated 10 degrees at a time recording the emf for each angle
When the normal of the coil relative to the field lines is:
At zero degrees the induced emf will be a maximum
At 90 degrees the induced emf will be zero
Investigating the inverse square law
Record background count 3 times and take an average
Set up a Geiger counter positioned with a metre rule and a gamma source
Record the count rate for each distance 3 tiems and take an average
Correct the data for background radiation
Plot a graph of count rate against 1/distance squared
Should be a straight line
Investigating the inverse square law issues and uncertainties
The half life of the source may impact count rate - select a source with a long enough half life
Uncertainty in count rate and distance
Investigating stationary waves on a string uncertainties and issues
Measuring mass
Measuring length
Measuring frequency
Difficult to tell if the string has settled and if the amplitude is the same for each of the lengths
Investigation of g: trap door method uncertainties and issues
Measuring s
Electromagnet may take time to demagnetise without releasing the ball whilst the timer has started
May be a delay for trap door to open and stop the timer
Doesn’t account for air resistance
Investigation of g using light gates issues and uncertainties
Uncertainty in measuring s
Ball may not fall directly through centre of the light gates, causing time delays at each gate
Difficult to drop the ball through each light gate
Safety when using radioactive sources
Store source in a lead lined box when not in use - reduce exposure time
Handle the source using long handling tongs - increase the distance
Stand behind lead shielding - reduces exposure
Wear a film badge to monitor your radiation exposure
Data loggers/light gates advantages and disadvantages compared to a stopwatch
Fewer errors
No need to account for reaction time
High precision - e.g. readings to the nearest millisecond
Graph can be drawn automatically and displayed in real time
Difficult to set up
Requires a power supply
Not readily available and expensive
Stopwatch advantages and disadvantages and disadvantages compared to data loggers/light gates
Readily available
Cheap
Easy to set up
More errors - random, systematic or parallax
Reaction time adversley impacts results
Graph would have to be drawn manually
Insufficient precision for shortest times
