Conservation of energy and efficiencyIB MYP Physics: Mind map

Exam questions on Conservation of energy and efficiency

1. A school in Seoul is replacing its filament lamps with LED lamps. Each second a filament lamp takes in 60 J of electrical energy and gives out 3 J as light. An LED lamp takes in 8 J each second and gives out 6 J as light.
   Show that the LED lamp is more efficient than the filament lamp.2 marks
2. A motor in a warehouse in Lagos lifts boxes. Each second the motor takes in 500 J of electrical energy and the boxes gain 350 J of gravitational potential energy. The rest of the energy is wasted because of friction in the bearings.
   Suggest one way to improve the efficiency of the motor and explain how it works.2 marks
3. A student investigates which material is the best insulator for a beaker of hot water. For each test she starts with water at 80 °C, wraps the beaker in a different material and measures the water temperature after 10 minutes. The results are: no insulation 62 °C, bubble wrap 71 °C, cotton wool 73 °C and aluminium foil 66 °C.
   Identify the independent variable and the dependent variable, and state one control variable.3 marks