Experiments

Question 1

A2: Determining the value of the specific heat capacity of a material

Answer 1

p19

• Graphs:
  Plot temp change against time.
• Equations:
  Use E = Vit and substitute into E =mctheta.
• Assumptions:
  All of energy transferred electrically is used to heat material
• Uncertainties:
  Thermal energy lost to surroundings (insulation).
  Temp rise needs to be higher than 20K to reduce uncertainty.

Question 2

A2: determining the specific latent heat of vaporisation

Answer 2

p22

• Setup:
  Spherical beaker filled with mass m of water.
  Heating element in water
  Holes in beaker to allow water vapour a path to attached condenser.
  Beaker below condenser to catch condensed liquid.
• Method:
  Liquid heated to boiling point by heating element with supplied voltage and current.
  Vapour passes through holes into condenser.
  Vapour is collected over time t and mass is found.
  This is repeated for different values of voltage and current.
• Equations:
  For initial V1 and I1, the mass of condensed water m1 is found over time t.
  By equating electrical energy to thermal energy we get V1 I1 t = m1 Lv + Q
  Q is thermal energy transferred to surroundings in time t, it is constant.
  Voltage and current are changed to V2 and I2.
  Mass of condensed water in the same time t is m2.
  Leading to equation V2 I2 t = m2 Lv + Q

Subtracting the two equations we can cancel Q and get (V2 I2 - V1 I1)t = (m2 - m1)Lv
Rearrange to find Lv.

Question 3

A2: investigating pV = constant (Boyle’s law)

Answer 3

p29

(pressure exerted by oil on the air is recorded on pressure gauge)

• Graphs:
  pressure against volume (inversely proportional)
  pressure against 1/volume (directly proportional)
• Assumptions
  Constant temperature
• Uncertainties
  p against v graph hard to verify relationship, need p against 1/v

Question 4

A2: Investigating pressure and temperature of a gas at constant volume

Answer 4

p30

(fixed mass of gas attached to pressure gauge placed in water bath and heated)

• Graphs:
  Pressure against temperature (linear)
  Extrapolate the line back to x axis will give estimated absolute zero.
  Plotting pressure against absolute temperature would result in a straight line through the origin.

Assumptions:
- Temp of water matches temp of gas

Uncertainties:

• Stirrer needed to distribute heat evenly
• Flask cannot touch sides of beaker and must be fully submerged.

Question 5

A2: Investigating circular motion using a whirling bung

Answer 5

p47

(centripetal force can be investigated using rubber bung whirled in a horizontal circle)

• Method:
  Tie one end of thread to rubber bung and hold thread at 0.3m from the bung.
  Attach weight at other end of string and whirl it.
  If the weight is 1N then the centripetal force is 1N.
  Measure time t for 10 revolutions in a horizontal circle.
  Determine v using s = d/t.
  since bung makes 10 rev and the circumference of a circle is given by 2pier, v = 10 x 2pier/t.
  Repeat for different values of centripetal force.
  Plot graph of F against v^2 (F = mv^2/r) and draw line of best fit.
  Gradient will = m/r.
  Determine mass of bung from gradient.

Uncertainties:

• ensure bung moves in horizontal circle.
• due to speed of bung can be hard to count revolutions.

Question 6

A2: Investigating factors affecting period of simple harmonic oscillator

Answer 6

p62

• Oscillations of a second or less can be times using a stopwatch however it is best to time a large number of oscillations and divide the time.
• The period is impacted by the length of the spring/string, mass and spring constant.

To reduce uncertainties:

• a motion sensor could be used to show x against t graph.
• Aim to minimise parallax error and percentage uncertainty in time.

Question 7

A2: Measuring capacitance 3 methods

Answer 7

p131

• Plotting graph of charge against voltage and drawing line of best fit can be more accurate than using a digital multimeter.
• There are 2 ways to find charge:
  1. Setup circuit with switch and a Capacitor with a voltmeter in parallel and ammeter in series. A variable resistor is needed to keep current constant until fully charged. Once switch is closed start stopwatch and record value for I and V at intervals until current falls to zero. Use Q = I x t.
  2. Can use a coulomb meter to measure charge. Charge capacitor to different voltages and measure charge stored for each value. Find % difference between the actual and experimental values.

Question 8

A2: Investigating the way pd and current changes as a capacitor charges and discharges

Answer 8

p137

• Circuit with capacitor and switch able to connect to circuit 1 and 2 individually. Resistor, voltmeter, ammeter and filament lamp in circuit 2.
• Close switch to circuit 1 to begin charging. Record current and pd every 15 seconds.
• Then close switch to circuit 2 and monitor current and pd as capacitor discharges through the lamp.
• Plot graphs of current through and voltage across the capacitor as it charges/discharges.

Charging:

• current decreases
• pd increases
• Charge increases

Discharging:

• current decreases
• charge decreases
• pd decreases

Question 9

A2: Investigating the magnetic flux density between the poles of a magnet

Answer 9

p174

(Measuring force experienced by a current carrying wire in the uniform magnetic field)

• Force experienced by wire when perpendicular to field is F = BIL.
• Measure force on the mass balance for different values of I.
• Plot graph of F against I, the gradient = BL.

Question 10

A2: Measuring magnetic field strength using a search coil

Answer 10

p183

• Faraday’s law enables us to measure B using a search coil.
• Coil with turns N is placed in magnetic field, perpendicular.
• if coil is rotated quarter turn or removed from field the flux decreases from BAN to zero meaning an emf is induced in the coil.
• Induced emf = BAN/change in t
• B can be found if emf and t are recorded using data logger.
• We can also find B in terms of charge that flows in circuit, If coil is connected in series with a galvanometer.
• Max deflection of galvanometer is proportional to charge in short time.
• average current = emf/resistance.
• So if resistance is R then average induced current I = emf/R = BAN/Rt.
• Total charge Q = it therefore Q = BAN/R.
• If Q is measured then B can be found.

Question 11

A2: Investigating the action of a transformer

Answer 11

p190

• Transformer can be made through 2 coils of copper wire and an iron rod.
• Connect primary coil to cell 1.5v in series with a switch.
• Connect secondary coil to 2.5v lamp and open and close the switch to light the lamp.
• To investigate output voltage, make transformer using 2 coils and an iron core.
• Connect wires from primary coil to low v AC and connect a multimeter to secondary coil.
• Plot change in voltage as number of turns on secondary coil changes.

Question 12

A2: Investigating the absorption of alpha particles, beta particles and gamma rays

Answer 12

p209

• Investigate pen entreating power of alpha, beta and gamma using geiger muller tube and counter to detect radiation.
• Background radiation count must be measured first and subtracted from recorded count rates.
• Use aluminium and paper foils and pieces of lead of different thickness to investigate absorption.

Question 13

A2: Determining the half life of protactinium

Answer 13

p215

• Protactinium has a half life of 1 minute. Its half life can be monitored using a GM tube.
• Protactinium is generated by alpha decay of uranium, followed by beta decay to protactinium.
• Sealed plastic bottle contains solution of a uranium salt, some of the daughter products.
• Bottle also contains solvent immiscible with water, only the protactinium is soluble.
• When shaken most of protactinium dissolves into the solvent but it will separate over time.
• We can monitor decay of protactinium in oily layer from beta radiation it emits.
• Alpha particles are absorbed by the bottle.
• Remember to subtract background from all counts.

Question 14

A2: Simulation of radioactive decay using dice

Answer 14

p216

• Models the probability of decay.
• Have a large number of dice, each one represents a radioactive atom.
• throwing a 6 models a nucleus that has decayed.
• For each roll note how many land on 6.
• All the sixes are removed. Remaining dice are rolled again.
• Each roll represents the same time interval, repeat until no dice remain.
• Carry out test to see if pattern of decrease is exponential and calculate the decay constant.

Question 15

investigating the specific latent heat of fusion

Answer 15

p.22

(immersion heater in ice funnel)

• Graphs:
  No graph - measure mass of melted water in beaker A and B.
  Use Lt = E/change in m
• Assumptions:
  All of heat energy transferred to ice.
• Uncertainties:
  The immersion heater not fully submerged as it ice melts so power supplied to ice is inaccurate.