Improving Efficiency (HT only)
- The efficiency of a device can be improved by reducing wasted energy transfers
- Machines waste energy due to:
- Friction between their moving parts
- Air resistance
- Electrical resistance
- Sound
Reducing Friction
- In a mechanical system, for example, there is often friction between the moving parts of the machinery
- This results in unwanted energy transfers by heating to the machinery and the surroundings
- Friction can be reduced by:
- Adding bearings to prevent components from directly rubbing together
- Lubricating parts
Lubricating parts of a bicycle to reduce friction
Reducing Electrical Resistance
- In electric circuits, there is resistance as current flows through the wires and components
- This results in unwanted energy transfers by heating to the wires, components and the surroundings
- Resistance can be reduced by:
- Using components with lower resistance
- Reducing the current
Reducing Air Resistance
- Air resistance causes a frictional force between the moving object and the air that opposes its motion
- This results in unwanted energy transfers by heating to the object and the surroundings
- Air resistance can be reduced by:
- Streamlining the shapes of moving objects
- For example, a racing cyclist adopts a more streamlined posture to reduce the effects of air resistance
- Also, the bicycle, clothing and helmet are designed to allow them to go as fast as possible
Many factors such as posture, clothes and bicycle shape must be considered when trying to reduce air resistance
Reducing Noise
- Sound is often created by moving parts of machinery
- This results in unwanted energy transfers by heating to the surroundings as sound waves cause the particles in the air and nearby objects to vibrate
- Sound can be reduced by:
- Tightening loose parts to reduce vibration
- Lubricating parts
Exam Tip
When answering questions about improving efficiency, it is helpful to identify the useful energy transfers and the wasted energy transfers. Remember, the efficiency of a device is improved by increasing the useful energy transfers and reducing the wasted energy transfers.
In my experience of marking students' work, the most common error that students make is not reading the question properly. And by that I mean, reading the question, and then pausing to check that what you are about to write answers what the question is actually asking. I have done this myself as a student; you read in the question what you want it say, not what it actually says.
In improving efficiency questions, context is key. The methods required are different for different situations. There is no short cut to learning this, you just have to practice being able to recall the correct information for the given scenario. Vague terms like 'reducing the energy dissipated to the soundings' will not be enough to gain you the marks. Examiners are looking to see that you understand the context.
