Module 6 Practicals

Question 1

Investigating the factors affecting capacitance
- Method (9)
- Graphs and Calculations (2)
- Validity (4)

Answer 1

• Attach an aluminium plate to a clamp stand so that it lays horizontal
• Place a second aluminium plate on a block directly below the first plate
• Measure the distance between the plates using a ruler
• Measure the length and width by which the plates overlap
• Use crocodile clips and leads to connect the plates to a multimeter
• Record the capacitance of the plates
• Disconnect the circuit and move the bottom plate over by 5cm
• Measure the new length overlapping, reconnect the circuit and measure the capacitance
• Repeat this moving the block over 5cm each tie
• Find the area of overlap using width x height
• Plot a graph of capacitance against area
• • C = AƐ0 /d
• Place wood blocks around the plates to insulate them
• Ensure the distance between the plates is kept constant
• Repeat the entire experiment to find mean values for the capacitance each time
• Ensure there is no zero error in the multimeter or the line of best fit may not pass through the origin

Question 2

Investigating Charging and Discharging Capacitors
- Method for Charging (4)
- Method for Discharging (6)
- Graphs and Calculations (3)

Answer 2

• Set up a circuit containing a power supply, a fixed resistor, a switch, an ammeter, a capacitor and a voltmeter across the capacitor
• Close the switch to charge the capacitor
• Record the voltage and current every 5s
• Repeat the experiment again and calculate mean values
• Set up a circuit containing a power supply and a capacitor and fixed resistor in parallel with each other with a switch over the join between the branches
• Connect a voltmeter in parallel
• Set the switch to the positon closest to the power supply and allow the capacitor to fully charge
• Move the switch over and start a stopwatch
• Record the voltage every 5s
• Repeat the experiment again and calculate mean values for voltage
• Plot a graph of voltage against time: V = V0(1-e-t/CR) (for charging)
• Plot a graph of current against time: I = I0e-t/CR
• • Area underneath = charge stored by capacitor
• Plot a graph of ln(V) against t: ln(V) = ln(V0) - t/CR

Question 3

Determining the uniform magnetic flux density between the poles of a magnet using a wire and a balance
- Method (7)
- Graphs and Calculations (3)

Answer 3

• Measure the length of a wire
• Set up the wire so it is between the faces of two bar magnets
• Place the magnets and wire set up on top of a balance
• Connect the wire to an ammeter and a power supply
• Zero the balance when there is no current flowing
• Let a current flow and record the reading on the balance
• Repeat the steps, increasing the current by 1A each time
• Repeat the entire experiment and calculate mean readings for the mass and current
• Calculate the force for each reading using F = mg
• Plot a graph of Force against current
• • F = BL I so gradient = BL

Question 3

Investigating Capacitors in Series and Parallel
- Circuit 1 (2)
- Circuit 2 (3)
- Circuit 3 (2)
- Method (4)
- Graphs and Calculations (2)
- Validity (3)

Answer 3

• Set up a circuit with a power supply, a variable resistor, a switch, a capacitor and an ammeter all in series
• Connect a voltmeter across the capacitor
• Set up a circuit with a power supply, a switch, a variable resistor and an ammeter in series
• Connect in to the loop two capacitors in parallel
• Connect a voltmeter across the capacitors
• Set up a circuit with a power supply, a variable resistor, a switch, an ammeter and two capacitors all in series
• Connect a voltmeter across the capacitors
• Set up the corresponding circuit
• Close the switch to allow current to flow and adjust the variable resistor to keep the current constant for as long as possible
• Record the value of the constant current
• Record the potential difference and time since the switch was closed at regular intervals
• Calculate the charge at each interval using Q = It
• Plot a graph of charge against voltage
• • Gradient = capacitance
• It will be impossible to keep the current constant once the capacitor is fully charged, only use the values for which current is approximately constant when drawing your graph
• Check before closing the switch that there is no systematic error in the voltmeter or ammeter.
• Using a large valued capacitor and resistor slows down the changes in the circuit so they can be observed more easily

Question 4

Investigate Transformers
- Method (6)
- Graphs and Calculations (1)
- Safety (1)
- Validity (3)

Answer 4

• Place two C shaped iron cores together
• Wrap 5 turns around the primary coil and 10 around the secondary coil
• Connect a voltmeter across both coils and connect the primary coil to a low voltage AC supply
• Add a variable resistor to the primary coil circuit and an ammeter to both circuits
• Turn on the AC supply and record the voltage across each coil
• Vary the variable resistor and record the voltages for a range of currents
• Find the efficiency of the transformer using E = IsVs/IpVp
• As transformers increase voltage use a low input voltage to keep it at a safe level
• Keep the number of turns constant
• Use a laminated soft core to reduce the energy loss by eddy currents
• Use low resistance thick copper wires for the coils

Question 5

Investigate Absorption of Radiation
- Method (6)
- Graphs and Calculations (1)
- Safety (4)

Answer 5

• Calculate the background count by turning on a geiger counter when there is no radioactive sources around
• Using tongs, place a radioactive source about 5cm away from the geiger counter
• Measure the count rate after 5 mins
• Place a few sheets of paper in front of the source and repeat the steps
• Repeat this using aluminium foil and lead
• Repat all this for the difference sources and identify the types of radiation each source emits based on how much radiation is emitted for each material between the source and counter
• Calculate the corrected count rates for each reading by subtracting the background rate from the measured rate
• Never handle sources directly, always use tongs
• Store the source in a lead lined container when no in use
• Never point the source at others
• Keep the source as far away as possible from yourself and others

Question 6

Determine half life using an ionisation chamber
- Method (4)
- Graphs and Calculations (2)
- Safety (4)
- Validity (1)

Answer 6

• Set up an the ionisation chamber (a gas filled chamber with a cathode and an anode), connecting it to a DC voltage source and an ammeter
• Place a radioactive source and place it in front of the chamber
• Immediately start a stopwatch and record the current every 10 seconds
• Repeat this twice more with a new source and find the average current for each reading
• Plot a graph of current against time
• Using the curve find the half life of the source by finding several and calculating a mean
• Never handle sources directly, always use tongs
• Store the source in a lead lined container when no in use
• Never point the source at others
• Keep the source as far away as possible from yourself and others
• Wait at least 5 mins between taking repeat readings

Question 7

Simulate radioactive decay using dice
- Method (3)
- Graphs and Calculations (2)

Answer 7

• Roll a large number of dice
• Note how many dice landed on a 6 and remove these dice
• Roll the remaining dice and repeat this process
• Plot a graph of number of dice remaining against number of rolls to see if there is an exponential decay
• Calculate the decay constant

Question 8

Investigate the Random Nature of Radioactive Decay
- Method (4)
- Graphs and Calculations (4)
- Safety (4)

Answer 8

• Calculate the background count by turning on a geiger counter when there is no radioactive sources around
• Using tongs, place a radioactive source about 10 cm away from the geiger counter
• Measure the count rate every 10 seconds for 5 mins
• Repeat this with new sources and find an average for each reading
• Calculate the corrected count rates for each reading by subtracting the background rate from the measured rate
• Plot a graph of count rate against time
• Using the graph, find the half life of the substance
• The curve won’t be a perfect exponential curve so it can be seen that the nature of radioactive decay is random
• Never handle sources directly, always use tongs
• Store the source in a lead lined container when not in use
• Never point the source at others
• Keep the source as far away as possible from yourself and others