Physics

• What is the smallest value of efficiency?

  0 (0%)
• What is the largest possible value of efficiency?

  1 (100%)
• What is the equation for efficiency?

  Efficiency = \frac{\text{Useful energy}}{\text{Total energy}}
• Why is it impossible to have an efficiency of 1 for an energy transfer?

  Because some energy is dissipated to other non-useful stores
• If an appliance wastes 15 J of energy and is supplied with 200 J of energy, what is its efficiency?

  Efficiency = \frac{200 J - 15 J}{200 J} = \frac{185 J}{200 J} = 0.925
• How can energy dissipation be reduced for objects moving through air or water?

  By making them more streamlined to reduce drag/air resistance
• How can energy dissipation be reduced for surfaces moving against each other?

  By lubricating the surfaces with oil to reduce friction
• How can energy dissipation be reduced in a house?

  By using loft insulation, cavity wall insulation, double glazing, and materials with low thermal conductivity
• Why do materials with high thermal conductivity have a high rate of cooling?

  Because they have a higher rate of energy transfer across the material
• What is gravitational potential energy?

  The energy store of an object due to its height from the ground
• What is the equation for calculating gravitational potential energy?


  Ep = mgh
• What is kinetic energy?


  The energy store of a moving object
• What is the equation for kinetic energy?


  Ek = 0.5 \times m \times v^2
• When will all the energy in the gravitational store be shifted to the kinetic store for a falling object?

  When the object hits the ground
• At which point does a ball have the highest gravitational potential energy when rolled down a ramp?

  At the highest point on the ramp
• At which point does a ball have the highest kinetic energy when rolled down a ramp?

  At the lowest point on the ramp
• How do the energy stores change as a ball rolls from position A to position D?

  The gravitational store of the ball decreases while the kinetic store increases
• What is meant by a non-renewable energy resource?

  Energy resources that will run out and cannot be replenished
• Give an example of a non-renewable energy resource.

  Fossil fuels: oil, coal, gas
• What is meant by a renewable energy resource?

  Energy resources that will never run out or can be replenished as they are used
• State 5 examples of renewable energy resources.

  Solar power, wind turbines, tidal power, hydroelectric power, geothermal energy, biomass
• What is the environmental impact of using fossil fuels?

  Burning fossil fuels releases carbon dioxide, which contributes to global warming
• What is the environmental impact of using nuclear fuels?

  Nuclear power produces dangerous radioactive waste, which must be stored securely for a long time
• Explain why tidal power can be used to produce electricity reliably.

  Because the tides rise and fall every day, so large amounts of water always move in and out of river estuaries
• Give one advantage of hydroelectric power.

  Energy can be stored as gravitational potential of the water and released at times of high demand for electricity
• Explain why wind power may be considered an unreliable energy resource.

  Because if the wind is too light, little power is produced