Topic5 ALEVEL物理知识点精讲 还有例题练习哟

ALEVEL物理考试的特点就是范围和海一样宽，因此大家复习的时候除了把力气花在力学、波等章节，核物理这样ALEVEL物理知识点也不能放过，今天我们就先来结合具体的题目整理一下核衰退相关概念。
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ALEVEL物理考查形式

AS的时候物理需要考Paper1、2、3，A2的时候需要考Paper 4、5。Paper 1是选择题，Paper2、4是大题，Paper 3、5是实验题。相对来说，paper2比较困难，因为题目的灵活性比较强，而且需要背的定义概念比较多。

整套卷子用时一个小时，满分是60分。每一道大题的问基本都是定义题，所以一定要背熟每一个定义。定义题之后一般是计算题或者是解释题。

ALEVEL物理知识点温习：核衰退

1.What is meant by a radioactive atom?

A radioactive isotope has an unstable nucleus which decays and emits α, β or γ radiation.

2.What is meant by Random?

We cannot know when an individual nucleus will decay and which will decay next.

In a given time interval each nucleus has a fixed probability of decay.

3.What is meant by Spontaneous?

The decay cannot be influenced by any external factors.

4.Atomic processes that produce emission spectra of X ray:

There are different energy levels for electron in atom. Electron jumps down to original state will release energy in the form of large photon energy.

5.What is the similarity and difference between popcorn kernels popping and radioactive atoms decaying?

Similarity: Both are random events. Both have decreasing rate of decay. Radioactive decay is an irreversible change, as is the corn popping.

Difference: Popping of corn depends on external factors and radioactive decay does not. The corn kernels do not emit standard fragments, while radioactive nucleus emit radiation.

6.What is half life?

The average time taken for the activity of the source to halve.

7.Why α radiation does not pose a health hazard?

α radiation only has a range of a few cm in air, and cannot penetrate wall of container or skin.

8.What are the characteristics of β radiation?

Beta particles can easily penetrate the body, since they are not very ionising.

Once inside the body beta radiation may damage DNA of cells.

Beta radiation can be absorbed by a few mm of aluminium.

9.What is binding energy?

Energy required to separate a nucleus into its component nucleons.

10.How is fusion able to release energy?

In a nuclear fusion small nuclei fuse to produce a larger nucleus. The mass of the fused nucleus is less than the total mass of initial nuclei.

Energy released ΔE = c^2 Δm

11.What are the conditions for fusion to occur and why the interiors of stars are ideal for this?

There must be a very high temperature so that protons have sufficient kinetic energy to overcome the electrostatic repulsion, and the protons can come close enough for fusion to take place.

There must be a very high density so that a sufficient collision rate is maintained.

The enormous gravitational forces acting in stars create a very high temperature and density, so it is ideal for fusion to occur.

12.What is Fission Process for nuclear power station?

A heavy nucleus absorbs a neutron,

And the nucleus becomes unstable and splits into two fragments.

A few neutrons are also emitted in the fission.

These neutrons can cause further fission.

接下来我们再结合题目理解一下核衰退ALEVEL物理知识点。

The isotope 209 84Po decays by emitting an alpha particle.

Which of the following correctly shows the nucleons in the isotope produced?
A 123 neutrons,82protons
B 129 neutrons80 protons
C205 neutrons,82 protons
D 207neutrons,80 protons

题干告诉我们Po这个核子排出了α粒子，也就是说它发生了α衰变。

那么它的质子数和中子数应该分别减少了2个，Po本来的中子数=209-84=125，所以现在新生成的核子质子数和中子数应该分别为82和123个。

综上，本题应该选A。有不少同学在过ALEVEL物理知识点的时候，普遍会感到复习时间不够。如果你也有同款疑惑，可以让专业的教学团队来点拨思路，欢迎点击预约试听【橡沐ALEVEL同步培训班】——

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