Efficiency and powerIB MYP Sciences: Mind map

Exam questions on Efficiency and power

1. A student in Lagos compares a filament lamp with an LED lamp. Both are connected to the mains. After a few minutes the filament lamp is too hot to touch, but the LED lamp is only warm.
   Explain why the filament lamp is less efficient than the LED lamp.2 marks
2. A construction company in Mumbai uses a crane powered by an electric motor to lift steel beams to the top of a tall building.
   In one lift the motor takes in 6000 J of electrical energy and transfers 4200 J as gravitational potential energy of the beam. Calculate the efficiency of the motor.2 marks
3. Students in Cape Town compare two electric kettles, P and Q. Each kettle heats 1.0 kg of water through 20 °C. Kettle P has a thick plastic body and kettle Q has a thin plastic body. Kettle P took in 100 kJ of electrical energy and kettle Q took in 120 kJ. In both cases the water gained 84 kJ of energy.
   State a hypothesis that the students could test about the two kettles, giving a scientific reason.3 marks