Alevel物理真题答案解析-热力学简答题

接触到Alevel物理热力学（Thermal physics），会从微观粒子（particles或molecules）的角度来解释物质的温度、压强、动能、势能等问题。学生们会觉得微观的部分不太好理解，上课的时候知识点可以理解，落实到练习题，仍然会有下不了手的感觉。

今天我们整理并讲解一下ideal gas（理想气体）相关的几道真题及答案。通过这几题辅助大家思考一下理论知识点和考题的联系。

试题来源：CAIE A Level物理（9702）近年真题

问题1：What is meant by an ideal gas.

解析：这是一道基础的定义题，解释什么是ideal gas。简单来说只要符合ideal gas equation，pV / T = constant的，就叫理想气体。不过要同时解释清楚p、V和T分别代表哪些物理量。

答案：
gas obeys formula pV / T = constant
p is pressure
V is volume
T is kelvin temperature

问题2：An ideal gas is said to consist of molecules that are hard elastic identical spheres. State two further assumptions of the kinetic theory of gases.

解析：问题要求写两点关于kinetic theory of gas的假设。假设一共有好多条，大致可以整理成6条，这几条是后面理解kinetic theory equation的推导和有关理想气体internal energy相关问题的重要前提。

答案：6选2，优先选择前面几条答案。
total volume of molecules negligible compared to that of container
no intermolecular forces/ no forces between molecules (except during collisions)
molecules in random motion
all collisions involving molecules of the gas are elastic
time of collision small compared with the time between collisions
large number of molecules

问题3：One of the assumptions of the kinetic theory of gases is related to the volume of the atoms.

解析：本题是由上述6条假设延伸出的问题，要求我们写有关粒子体积的那一条假设。

答案：assumption: volume of atoms negligible compared to volume of container

问题4：ΔU = (+q) + (+w)  热力学第一定律这几个字母所代表的含义。

解析：ΔU指的是内能（internal energy）的变化，如果internal energy增加，那ΔU是正的；如果internal energy减少，那ΔU是负的。q代表这个系统吸收thermal energy或者释放thermal energy。w代表work done，做功，是对系统做功还是系统对外做功。

答案：
+ΔU ： the increase or decrease in internal energy of the system
-ΔU ： decrease in internal energy of the system
+q：thermal energy transfer to system
+ w：work done on system

问题5：State what is meant by the internal energy of a system.

解析：Internal energy的定义，指的是组成物质的particles所具有的动能和势能的总和。U=Σk.e.+Σp.e.

答案：
sum of potential energy and kinetic energy (of particles)
(total) energy of random motion of particles

需要针对A-level考试辅导提升的同学可以扫码添加翰林顾问老师咨询~

还能【免费领取】相关真题及解析！