Year 9 Physics

• how can we improve efficiency in circuits

  use wires with little electrical resistance, like copper wires
• how can we improve efficiency for moving objects, like planes

  streamline the shape to reduce air resistance
• how can we improve efficiency for objects that create friction

  lubricate moving parts to reduce friction
• how can we improve efficiency for systems designed to transfer thermal energy

  thermal insulation to reduce the thermal energy that is transferred to the surroundings
• how can we improve the efficiency of a filament bulb

  use LED bulb instead
• define a renewable energy source


  a resource that can be replaced in our lifetime
• how can we improve the efficiency of objects that create sound

  cut out noise, tighten loose parts to reduce vibration
• how is work done to overcome friction transferred

  it is transferred as energy to the thermal energy stores of the objects rubbing together and to the surroundings
• define a non-renewable energy source


  a resource that cannot be replaced in our lifetime
• advantages of fossil fuels

  readily available therefore more reliable, easily transported and cheap
• disadvantages of fossil fuels

  nonrenewable, sulphur dioxide causes acid rain, produces co2 therefore greenhouse effect
• advantages of nuclear power

  no acid rain, no greenhouse effect as it is carbon neutral, cheap to run once built, high energy density
• disadvantages of nuclear power

  expensive to build, radioactive waste, large amounts of water required for cooling purposes which harms water life, nonrenewable, risk of disaster
• advantages of renewable energy sources


  renewable, no acid rain, no co2 so no greenhouse effect, no global warming, cheap to run once built
• disadvantages of renewable energy sources

  unreliable, few areas suitable, low power energy source, expensive to build
• Advantages of wind power


  renewable, no acid rain, no co2 so no greenhouse effect, cheap to run once built
• disadvantages of wind power

  unreliable as you need to turn them off when too windy or too icy, few areas suitable as lots of open space needed, low power energy source so a large amount of windmills needed to meet requirements, noisy, expensive to build
• biomass advantages


  carbon neutral, renewable
• biomass disadvantages


  need land to grow biomass crops, deforestation
• define fuel


  a source of chemical energy
• energy transfers in a bungee jumper

  gravitational potential to kinetic to elastic potential. energy dissipated as thermal energy to surroundings due to friction with air particles
• a panel of solar cells has an efficiency of 0.15

  the total power input to the panel of solar cells is 3.2 kW

  calculate the useful power output of this panel of solar cells

  0.48 kW
• a climber weighs 660 N

  calculate the work the climber must do against gravity to climb to the top of a 20m cliff

  13200 J
• a wind turbine has a power output of 388 kW

  the mass of air passing the wind turbine each second is 13,800 kg

  calculate the speed of the air passing the blades each second, and explain why

  (the process is 100% efficient)

  In a wind turbine, the kinetic energy of the wind passing through the air blades is converted into the energy stored in wind turbine (electrical energy) so using equation KE=0.5mv^2, 388,000 = 0.5 x 13,800 x v^2, v = 7.50 m/s
• calculate the period of time, in seconds, during which 600 J is provided to a 30 w light bulb

  20 s
• at the lowest point of the jump, the bungee cord is extended to 35 m

  the bungee cord behaves like a spring with a spring constant of 40 N/ m

  calculate the energy stored in the stretched bungee cord

  24500 J
• what are the 4 energy transfers

  mechanically, electrically, by heating, by light and sound
• factors that affect thermal insulation properties of a material

  mass of material, thickness of material
• what are the equations to work out elastic potential energy

  Ee = 1/2Fe, Ee = 1/2Ke^2
• what is the equation for force


  F = Ke, force = spring constant x extension
• what is the equation for gravitational potential energy


  GPE = mgh
• what is the equation for kinetic energy


  KE = 1/2mv^2
• what is the equation for efficiency

  Efficiency = useful energy output/total energy input
• what are the equations for power

  P = work done/ time, P = energy transferred/ time
• What is 1 joule equal to

  1 watt
• what is work done the same amount as

  energy transferred
• how much is giga

  10^9
• how much is mega

  10^6
• how much is kilo

  10^3
• how do you work out 20 KJ, show your working

  20 x 10^3 = 20,000