CIE A Level Physics复习笔记5.1.3 Efficiency
Efficiency of a System
- The efficiency of a system is the ratio of the useful energy output from the system to the total energy input
- If a system has high efficiency, this means most of the energy transferred is useful
- If a system has low efficiency, this means most of the energy transferred is wasted
- Multiplying this ratio by 100 gives the efficiency as a percentage
- The efficiency is calculated using the equation:
Efficiency equation in terms of energy
- Efficiency can also be written in terms of power (the energy per second):
Efficiency equation in terms of power
Worked Example
Exam Tip
Efficiency can be in a ratio or percentage format. If the question asks for an efficiency as a ratio, give your answer as a fraction or decimal. If the answer is required as a percentage, remember to multiply the ratio by 100 to convert it, e.g. Ratio = 0.25, Percentage = 0.25 × 100 = 25 %
Solving Problems Involving Efficiency
- Recall the two equations for calculating efficiency are:
- Which to use will depend on whether you’re given a system calculating energies or power as shown in the examples below
Worked Example
The diagram shows a pump called a hydraulic ram.
In one such pump, the long approach pipe holds 700 kg of water. A valve shuts when the speed of this water reaches 3.5 m s-1 and the kinetic energy of this water is used to lift a small quantity of water by a height of 12m.The efficiency of the pump is 20%.Which mass of water could be lifted 12 m?
A. 6.2 kg B. 4.6 kg C. 7.3 kg D. 0.24 kg
- The pump is what converts the water’s kinetic energy into gravitational potential energy
- Since its efficiency is 20%, you would multiply the kinetic energy by 0.2 since only 20% of the kinetic energy will be converted (not 20% of the gravitational potential energy)
Exam Tip
Equations for kinetic and potential energies are important for these types of questions. Also, familiarise yourself with the different equations for power depending on what quantities are given.
转载自savemyexam
以上就是关于【CIE A Level Physics复习笔记5.1.3 Efficiency】的解答，如需了解学校/赛事/课程动态，可至翰林教育官网获取更多信息。
往期文章阅读推荐：
生物竞赛金牌教练的实战书单！生物学/生物化学/病理学...电子版免费领！
哈佛商学院2026暑期书单曝光！十余位教授私藏书单，本本是“商科天花板”
翰林AMC8视频课重磅上线！
国际竞赛真题资源免费领取
