A food blender is used in a kitchen to blend ingredients. The blender transfers electrical energy, but not all of this energy is a useful energy transfer. Explain how energy is wasted in the blender and describe two ways in which the efficiency of the blender could be improved.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
A food blender transfers electrical energy. Its motor spins at high speed, but the blender becomes warm and noisy during use.
Model answer (4 marks)
Energy is wasted as heat because the motor and its wiring have resistance, so electrical energy is converted to thermal energy (I²R losses). It is also wasted as sound – the spinning blades and motor produce noise, which is acoustic energy that does not help blending.
The efficiency can be improved by:
1. Reducing friction – better lubrication of the moving parts lowers resistance to motion, so less electrical energy is lost as heat.
2. Reducing current – using a motor that draws less current (or a lower voltage supply) decreases I²R losses in the wires, so more of the electrical energy is converted to useful mechanical work.
The efficiency can be improved by:
1. Reducing friction – better lubrication of the moving parts lowers resistance to motion, so less electrical energy is lost as heat.
2. Reducing current – using a motor that draws less current (or a lower voltage supply) decreases I²R losses in the wires, so more of the electrical energy is converted to useful mechanical work.
Examiner tips
- Use the term "I²R losses" when explaining heat waste. Mention "acoustic energy" for noise. Show two specific improvements: lubrication and lower current. Keep answer concise and use correct terminology.
Common mistakes
- Confusing heat loss with sound loss. Failing to mention I²R or friction. Using vague terms like "more efficient" without explaining how.
Mark scheme (4 marks)
- Energy is wasted as heat (thermal energy) due to the resistance of the wires / motor heating up
- Energy is also wasted as sound (noise produced by the spinning blades/motor)
- Lubrication of the moving parts reduces friction, reducing heat loss and improving efficiency
- Reducing the current through the motor decreases power loss in the wires (since power loss = I²R), reducing waste heat and improving efficiency
Key terms in this question
useful energy transfer · efficiency
Related
- All OCR GCSE Physics A: Gateway Science (J249) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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