Required practicals

Question 1

Investigation of stationary waves on a string

Answer 1

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

Question 2

Young’s double slit experiment

Answer 2

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

Question 3

Laser risk assessment

Answer 3

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

Question 4

Diffraction grating experiment

Answer 4

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

Question 5

Investigation of g: trap door method

Answer 5

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

Question 6

Investigation of g: light gates

Answer 6

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

Question 7

Determining Young modulus

Answer 7

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

Question 8

Uncertainties and issues with determining Young modulus

Answer 8

Measuring dL, L, A and F

Difficult to know when all the kinks have been removed

Question 9

Determining resistivity

Answer 9

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

Question 10

Uncertainties and issues with determining resistivity

Answer 10

Measuring R, A and L
May be kinks in the wire impacting length
Crocodile clips provide poor connections
Fluctuations in ammeter and voltmeter readings

Question 11

Investigating internal resistance and emf

Answer 11

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

Question 12

Uncertainties and issues with investigating emf and internal resistance

Answer 12

Uncertainties in V, I and variable resistor

Heating effect of current will skew results - include a switch and open it after every reading

Question 13

Investigating SHM using a mass-spring system

Answer 13

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

Question 14

Uncertainties and issues with investigating SHM using a mass-spring system

Answer 14

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

Question 15

Investigating SHM using a simple pendulum

Answer 15

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

Question 16

Uncertainties and issues with investigating SHM using a simple pendulum

Answer 16

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

Question 17

Investigating Boyle’s law

Answer 17

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

Question 18

Investigating Boyle’s law uncertainties and issues

Answer 18

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

Question 19

Investigating Charles’ law

Answer 19

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

Question 20

Investigating Charles’ law uncertainties and issues

Answer 20

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

Question 21

Investigating charging and discharging capacitors

Answer 21

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

Question 22

Investigating F=BIL

Answer 22

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

Question 23

Investigating F=BIL issues and uncertainties

Answer 23

Uncertainties in the I and F
Wire must be exactly perpendicular
Wire may have kinks

Question 24

Investigating magnetic flux linkage

Answer 24

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

Question 25

Investigating the inverse square law

Answer 25

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

Question 26

Investigating the inverse square law issues and uncertainties

Answer 26

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

Question 27

Investigating stationary waves on a string uncertainties and issues

Answer 27

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

Question 28

Investigation of g: trap door method uncertainties and issues

Answer 28

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

Question 29

Investigation of g using light gates issues and uncertainties

Answer 29

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

Question 30

Safety when using radioactive sources

Answer 30

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

Question 31

Data loggers/light gates advantages and disadvantages compared to a stopwatch

Answer 31

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

Question 32

Stopwatch advantages and disadvantages and disadvantages compared to data loggers/light gates

Answer 32

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