1 Working as a physicist

• Δp = F.Δt

  
  

  P = F/A
• Meter ruler has a resolution of 0.1cm or 1mm

  Accuracy is how close the measured value is to its true value

  Precision refers to a small spread of values
• Uncertainty

  Range in which the true value can be considered to lie or be at
• Error

  Difference between the measured value and true value
• Resolution

  Smallest measuring interval and the source of uncertainty in a single reading
• Explain how the student could reduce the uncertainty in the measurement of the diameter

  • Measure the diameter in multiple places and find mean
  • Calculating mean reduces random error
• Desribed how to determine the corrected count rate from the source

  • Record background count for time and subtract from the equivalent quanitity
  • divide by time to give a count rate
• Explain another modification to the experimental method which would improve the accuracy of the data

  • Record the count rate at least three times and find an averaget count rate
  • The reduces the effect of (random) errors in the measurement of the count rate
• Explain what is meant by the particle nature of light

  Light consists of photons

  Photons are discrete packets of energy
• Systematic error

  Any measurement where you are measuring from zero

  Zero error
• Parallax error


  Not eye level
• Reducing %U

  Use set squares to line them up against metre rulers
• Reducing Uncertainty

  Use a higher resolution instrument

  • Metre ruler - 1mm
  • Digital calipers - 0.1mm
  • Micrometer - 0.01mm

  Higher resolution doesnt always increase accuracy but does reduce uncertainty
• SHM procedure for spring

  • Use a stopwatch to record the time and to record the ‘N’ oscillations where n is greater than 5. Divide the time by N
  • Increase the time recorded in order to reduce uncertainty
  • Repeat times and calculate a mean
  • Use a fiducial marker to indicate the reference point
  • Use equilibrium as reference position
  • Trolley is moving fastest at this point so the uncertainty in starting the stopwatch is least
• Amplitude of oscillation increase, how does max KE change

  • Vmax = ωA where ω is constant
  • If A doubles, Vmax doubles
  • 1/2mv^2 so kinetic energy will quadruple
• Increase accuracy of measurements

  Stir water in the beaker

  Use digital thermometer

  Take reading in line with scale

  Use a higher electrical power heater

  So short time is needed to boil liquid
• Explain how radium releases a significant amount of energy

  • Rate of decay depends on number of unstable nuclei A = λN
  • Radium has a long half life so unstable nuclei are present for longer
  • When a nucleus decays there is a decrease in mass
  • Energy released according to E=mc^2 as E decrease m decrease
  • m is small as c^2 is very large so significant amount of energy released
  • Energy released by decay becomes kinetic energy of the atoms in the sample
• Alternating p.d is applied to the coil, cone oscillates

  At certain frequencies, box vibrates with large amplitudes

  • Alternating p.d causes an alternating current in the coil
  • Current carrying conductor in a magnetic field experiences a force
  • Current is alternating, so force changes direction with current
  • Loudspeaker forces the box into oscillations
  • Frequency of oscillations equals the natural frequency of the air in the box
  • Maximum energy is transferred and the amplitude of vibration in the box increases
• High resolution may not guarantee high accuracy or precision
• Why there is a exponential decrease in the rate of decay

  • Fixed probability of an individual nucleus undergoing decay
  • For a large sample of unstable nuclei there will be a predictable pattern
  • Fraction of nuclei decaying in the next second is equal to the decay constant
  • Hence no. Of nuclei decaying in the next second depends on no. Of nuclei according to A = N
  • The number of unstable nuclei decrease exponentially
  • So rate of decay decreases exponentially
• Rider moves from bottom to top of the circular path

  • Rider experiences a resultant force acting towards the centre
  • The resultant force is constant, as the rider has a constant angular velocity
  • At the bottom, P and W act in opposite directions so P > W
  • At the top, P and W act in the same direction so P is less
  • P is the weight the rider has at the top
  • Rider would then feel lighter at the top
• Determine T for pendulum or spring

  • Time a number of oscillations and divide this time by the number of oscillations
  • This reduces the effect of reaction time
  • Time from the mid-point of the oscillation
  • Use a marker to identify the mid-point of the oscillation
  • Each method reduces the uncertainty
• How shaker torch is able to light the LED

  • As magnet moves through coil there is a change in magnetic flux linkage
  • An e.m.f. is induced across the coil
  • This generates a current in the circuit
  • The diode only allows current in one direction
  • So capacitor is charged
  • When switch is closed capacitor discharges through the LED
• "Value for the mass of glass slides was precise, i measured using a mass balance which was accurate to the nearest 0.01g. I reduced the random error by repeating the measurement several times" Comment dawg

  • Precision refers to the spread of values
  • Accuracy refers to how close the value is to the true value
  • The resolution (of the balance) is 0.01 g
  • Repeating the measurement and calculating a mean reduces the effect of random error
• Determine the extension of the spring as ACCURATELY


  • calculate mean value by taking repeat readings (for each mass)
  • Take readings at eye level
  • Check that metre rule is vertical
• More accurate using a data logger instead of stop watch. Assess students suggestion

  Data has to be collected in a short time

  • difficult to read stopwatch and voltmeter
  • Suggestion is correct
• Student used a half metre ruler. Comment on student's choice of measuring instrument

  Use digital calipers

  • Ruler has a resolution of 1mm
  • Digital caliper has a resolution of 0.1mm
• Why pressure exerted by a gas increases as the temperature of the gas increases

  As temperature increases kinetic energy of the gas increase

  • Momentum and speed of the gas particles increases
  • Rate of collisions with the container walls increase
  • Rate of change of momentum increase
  • Due to p=F.t force increases with momentum
  • and P = F/A so force increases with pressure
  • pressure exerted by gases will then increase