paper 2

• Energy is always conserved - it can't be created or destroyed. it ix measured in joules (j)
• energy stores:

  • kinetic energy
  • gravitational potential energy (gpe)
  • elastic potential energy
  • thermal energy
• specific heat capacity is the amount of energy needed to raise the temp of 1kg of as a substance by 1 degree
• sound / vibrational energy is the same as kinetic energy
• fuels, food & cells/ batteries have chemical potential energy
• specific heat capacity practical:

  1. measure mass of metal block or water in beaker, using top-pan balance
  2. place electrical heater in metal block/water
  3. measure initial temperature of substance using thermometer
  4. turn heater on, start timer and measure p.d. and current supplied to heater using voltmeter and ammeter
  5. after set time, measure final temperature and calculate change in temperature (final T- initial T)
• SPECIFIC HEAT CAPACITY PRACTICAL:

  • Power supplied to the block= P=VI (voltage x current)
  • energy supplied to block using E=Pt (power x time)
  • specific heat capacity- change in thermal energy (J) = mass (kg) x SHC (J/kg'c) x change in temperature ('c)
• Power is the rate of energy transferred. measured in Watts (W)
• Efficiency is the ratio of the total input energy/ power that is converted to useful output energy.

  efficiency = (useful e or p out/ total e or p in) x100
• thermal energy is usually lost from buildings through CONDUCTION transferring energy to the surroundings.
• Energy sources are where we harness energy from in the world, there are either renewable sources or non-renewable resources
• non-renewable:

  • fossil fuels
  • nuclear fuels
• renewable:

  • wind power
  • solar power
  • hydroelectric
  • biofuels
• FORCES:

  • contact force: when objects physically touching
  • non-contact force: when objects not touching
• • Vector: magnitude and direction
  • Scalar: only has magnitude

  the resultant vector can be found by adding them (maybe negative). If at right angles, make a triangle and use pythagoras or use trig to find and angle.
• SCALARS:

  • distance
  • speed
  • mass
  • energy
  • temperature
• VECTORS:

  • displacement
  • velocity
  • a cceleration
  • force
  • momentum
• weight (N) = mass (kg) x gravitational field strength (N/kg)
• work done is the energy transferred by a force:

  work done (J)= Force (N) x distance (M)
• any object that deforms elastically obeys Hooke's law (force and extension are directly proportional)

  force (N) = spring constant (N/m) x extension (m)
• SPRINGS PRACTICAL:

  1. add masses onto spring to change force
  2. measure extension with ruler at each weight, plot F against e.
  3. gradient of graph = spring constant
  4. avoid systematic error by lining up 0cm with the bottom of spring
  5. avoid parallax error by getting on eye level when measuring
• energy is supplied to electrons by a cell/ battery or mains electricity, which then move through the wires to transfer energy. Cells/ batteries have a store of chemical potential energy.
• current always flows from + to - around a circuit
• potential difference is the measure of how much energy is transferred to/by each coulomb of electrons/charge.
• voltmeters are always connected in parallel to components.
• potential difference (V) = energy transferred (J) / charge (C)

  $V=$$E/Q$
• current is the rate of flow of charge (how many coulombs pass every second).

  current (A) = charge (C)/ time (s)

  $I=$$Q/t$
• we measure current with an ammeter. ammeters are connected in series with components.
• resistance: the measure of how much a component/ object resists the flow of current. (Ohms)
• ohms law: voltage= current x resistance
• if the gradient on a graph is a curve this means the resistance is not constant
• diodes only let current flow in one direction: low resistance in a forward direction, high resistance in reverse direction.
• SERIES CIRCUITS:

  • total potential difference is shared between all components
  • current is the same for all components
  • total resistance = sum of resistances
• if the temperature of the thermistor increases the resistance decreases.
• an LDR is similar to the thermistor but for light. if the light intensity increases resistance decreases.
• DC current:

  • a direct potential difference (a p.d. that only acts in one direction) results in D.C. (direct current) e.g. from a battery
• AC:

  • mains electricity is A.C. (alternating current) resulting from an alternating potential difference. (both of these reverse direction at a frequency of 50Hz, at least in the UK)
• PLUGS:

  • the neutral wire stays at 0V, whilst the live wire changes between positive + negative potentials, which average out to a p.d. of 230V- this is UK mains voltage
  • the earth wire is a safety feature: it acts as an 'escape route' for currents that would otherwise cause a shock if the appliance is touched. Not needed for double insulated appliances
  • every plug has a fuse connected to the live wire. It's a thin metal wire in a tube that's designed to melt or blow if there is a fault that causes a high current, usually 3A, 5A or 13A
• the national grid:

  • power stations produce a relatively high current. If this went straight into the grid, a huge amount of energy/ power would be lost as heat due to the resistance of the cables (as power lost)
  • a step up transformer increases the voltage to ~132kV, which decreases the current, reducing the power lost due to heating in the cables. P=VI, if V&I are inversely proportional.
  • a step-down transformer reduces the voltage down to a safer and usable 230v for homes and businesses
• permanent magnets always produce a magnetic field, whereas induced magnets become magnetised when in another magnetic field