1. 1
   A factory conveyor belt motor is supplied with 500 J of electrical energy every second. Of this, 350 J is usefully transferred to the kinetic energy store of the products on the belt, and the rest is transferred to the thermal energy store of the motor and surroundings.

   (a)

   What is this wasted 150 J commonly called?

   [1 mark]

   • AUseful energy transfer
   • BWasted energy transfer
   • CInput energy transfer
   • DEfficiency

   (b)

   Which equation correctly calculates the efficiency of the conveyor belt motor?

   [1 mark]

   • Aefficiency = useful output energy transfer / total input energy transfer
   • Befficiency = total input energy transfer / useful output energy transfer
   • Cefficiency = wasted energy transfer / total input energy transfer
   • Defficiency = useful output energy transfer x total input energy transfer

   (c)

   Calculate the efficiency of the conveyor belt motor, giving your answer as a decimal and as a percentage.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A cyclist oils the chain of their bicycle before a race, because an unoiled chain wastes energy to the thermal energy store of the chain and surroundings.

   (a)

   What is the main cause of this wasted energy in an unoiled chain?

   [1 mark]

   • AAir resistance between the wheels and the road
   • BElectrical resistance in the chain
   • CFriction between the moving metal links of the chain
   • DSound energy released by the chain

   (b)

   After oiling the chain, the cyclist finds that a larger fraction of the energy they supply through pedalling is usefully transferred to the kinetic energy store of the bicycle. What has happened to the efficiency of the chain system?

   [1 mark]

   • AThe efficiency has decreased
   • BEfficiency cannot be determined without knowing the cyclist's mass
   • CThe efficiency has stayed the same but total input energy has changed
   • DThe efficiency has increased

   (c)

   Before oiling, the cyclist supplies 200 J of energy per pedal stroke, of which 140 J is usefully transferred to the kinetic energy store of the bicycle. After oiling, the same 200 J input results in 170 J of useful transfer. Calculate the efficiency of the chain system before and after oiling, and state the increase in efficiency as a percentage.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   An old diesel generator on a remote farm has an efficiency of 35%, meaning that for every 100 J of chemical energy stored in the diesel fuel supplied to it, only 35 J is usefully transferred to electrical energy. The farm owner is considering replacing it with a new generator with an efficiency of 42%.

   (a)

   Explain, in terms of energy stores, what happens to the remaining 65 J, and suggest one reason why this wasted energy transfer cannot be reduced to zero.

   [3 marks]

   (b)

   The farm owner is considering replacing the old generator with a new one that has an efficiency of 42%. If both generators are supplied with fuel storing 2000 J of chemical energy per second, calculate the useful electrical energy output per second of each generator, and calculate how much less energy per second is wasted by the new generator compared with the old one.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A school with a fixed budget is comparing two classroom heater designs: Heater X, a simple electric bar heater with an efficiency of 100%, and Heater Y, a heat pump with a stated 'efficiency' of 300%. The school is also considering improving the thermal insulation of the classroom walls.

   (a)

   A school is comparing two designs of classroom heater. Heater X is a simple electric bar heater with an efficiency of 100%, meaning all input electrical energy is transferred to the thermal energy store of the room. Heater Y is a heat pump with a stated 'efficiency' of 300%, which some students find confusing since efficiency cannot normally exceed 100%. Explain how a heat pump can appear to have an efficiency greater than 100%, and explain why, in terms of the definition of efficiency used in physics, this apparent value does not break the principle of conservation of energy.

   [6 marks]

   (b)

   The school has a fixed budget and must choose between installing Heater X (the bar heater) or Heater Y (the heat pump) in a classroom, alongside also considering improving the thermal insulation of the classroom walls. Evaluate the overall energy and cost implications of these options, discussing how the choice of heater efficiency interacts with the building's thermal insulation in determining the total energy wasted from the classroom.

   [6 marks]

   Total for question 4: 12 marks

End of questions