Paper 1

• System - An object or group of objects that you are interested in

  Closed system - no energy in or out

  Energy is transferred when a system changes:

  • mechanically
  • electrically
  • heating
  • radiation
• Specific heat capacity - the amount of energy required to raise the temperature of 1kg of a substance by 1°C

  Investigating:

  1. Block of material with hole for thermometer and hole for heater
  2. Measure mass of block, wrap in insulation, insert heater/thermometer
  3. Measure initial temp, set power supply potential difference to 10V and start stopwatch
  4. Record temperature and current (using ammeter) every 10 mins. Current shouldn't change
• Electricity units

  Power (P) - Watt (W) = joules/second

  Potential difference (V) - Volt (V)

  Current (I) - amp (A)

  Resistance (R) = Ohm (Ω)

  Energy (E) - joule (J)

  Charge (Q) - coulomb (C)
• Investigating insulators

  1. Place boiling water into a sealable container
  2. measure mass and initial temp
  3. seal container and cover in insulator
  4. leave for 5 mins then remove lid and measure final temp
  5. Reset container temp and repeat for different insulator
• Energy is dissipated when friction occurs - lubricant reduce friction of two surfaces rubbing against each other
• Resistance:

  
  

  • set up a circuit with a wire along a ruler, a voltmeter in parallel and a ammeter in series
  • Secure one crocodile clip to 0cm
  • move the other crocodile clip along recording distance, voltage and current
  • plot a graph of resistance (V/I) against length of the wire
• I-V characteristics

  • set up circuit with tested component in parallel with a voltmeter and in series with an ammeter and a variable resistor
  • alter the resistance and record potential difference and current (repeat each measurement twice)
  • Swap positive and negative battery terminals and repeat with negative values
  • eg. ohmic conductor (constant resistance) - straight line
  • eg filament lamp - resistance increases with °C
  • eg diode - one-way current - exponential graph
• Series vs Parallel circuit

  In series:

  • Potential difference at cell is sum of potential difference at each component. Shared amongst components
  • Total resistance is the sum of the resistance of every component
  • Current is equal everywhere

  In parallel:

  • Potential difference is equal at each branch
  • Total resistance decreases with number of components with resistance added (1/total-resistance = 1/R1 + 1/R2 + 1/R3 + ...)
  • Current is shared between each branch
• Investigating resistance

  Series:

  1. set up a circuit with a voltmeter, ammeter and a resistor
  2. record the potential difference and current
  3. add another identical resistor in series
  4. repeat steps 2 and 3 twice more
  5. Use R=V/I to calculate the resistance
  6. Plot the resistance against the number of resistors. should be a straight line
• Investigating resistance

  Parallel:

  1. set up a circuit with a voltmeter, ammeter and a resistor
  2. record the potential difference and current
  3. add another identical resistor in parallel, ie. on a new branch
  4. Repeat steps 2 and 3 twice more
  5. Use R=V/I to calculate the resistance
  6. Plot the resistance against the number of resistors, should be the positive side of 1/x graph
• LDR - resistance decreases with light

  Thermistor - resistance decreases with temperature
• Electricity in the home

  230V DC at 50Hz

  LIVE - brown

  NEUTRAL - blue

  EARTH - green and yellow
• National grid

  Power lines 400000V down to 230V in the home
• Change of state

  Sublimation is the change from a solid straight to a gas

  Deposition is the change from a gas straight to a solid
• Specific latent heat

  of FUSION - solid <-> gas

  of VAPOURISATION - liquid <-> gas

  Amount of energy needed to change the state of 1 Kg of a substance without changing the temperature
• Increasing the temperature of a gas causes particles to have more kinetic energy and therefore pressure exerted on walls of a container increases
• History of the atom

  JJ Thompson's plum pudding model was disproved by firing positive alpha particles:

  • most went through - atom mostly empty space
  • some deflected straight back - must be a small positive centre
  • same charges repel
• Radiation definitions:

  • Ionising - knocking an electron off an atom creating an ion
  • alpha particle ₂⁴​ α = ₂⁴​ He - heavy particle therefore doesn't penetrate or move much - stopped by paper
  • beta particle ⁰₋₁​ β = ⁰₋₁ ​e - stopped by 5mm of aluminium
  • Gamma particle ⁰₀​ ϒ - short wavelength EM wave - stopped by thick lead or concrete
• Activity and half-life

  Geiger-Muller tube and counter used

  1 becquerels (Bq) = 1 decay/second
• Irradiation and Contamination

  • Irradiated - affected by a source of radiation
  • Contaminated - radioactive material physically on or into something

  Body:

  • outside - gamma and beta most dangerous - penetrating
  • inside - alpha most dangerous - highly ionising
• • Even low-level radiation doses can cause cell mutations
  • Alpha particles should never be used within the body
  • Radiation within the body should have short half-life
• • Fission - unstable nucleus split using neutron producing energy and another neutron, starting a chain reaction. Used to heat water in power stations or for bombs
  • Fusion - two atoms fused, some mass lost as energy. Currently impossible as pressure and temperature needed is too high