【备考10月A-level系列】WPH02物理第二单元考点分析_【A加学院】

今天下午就要考物理第二单元了，在考前让我们随着田老师把最后欧的知识点一起过一下，大家沉着冷静，迎接考试！--...

今天下午就要考物理第二单元了，在考前让我们随着田老师把最后欧的知识点一起过一下，大家沉着冷静，迎接考试！

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1.波的类型

横波纵波疏部密部

Electromagnetic waves are transverse, with oscillations perpendicular

to the direction of propagation.

Sound waves are longitudinal wave.

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2.波的重要参数

振幅amplitude 频率frequency 周期period 波速wave speed 波长wavelength

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3.同相反相 x⁰ out of phase

in antiphase

in phase 从波形图上辨识同相反相。

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4.波的叠加原则

1.two or more waves meeting

2.displacement is sum of individual displacements

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5.驻波（a standing/stationary wave）

`node antinode概念。

驻波的形成：

1，发出的与反弹的相遇

2，叠加

3，反相抵消成node，同相加强成antinode

1.Superposition between waves travelling in opposite directions (from open end and wave reflected at closed end)

2.At node the waves are in antiphase, so there is destructive interference .there is zero amplitude.

3. At the antinode they are in phase so there is constructive interference . there is maximum amplitude.

解释Vibration generator实验中绳子驻波的形成：

1.Waves from the generator are reflected at the end

2. When the two waves meet they superpose

3.points points of zero amplitude are produced where the waves are in phase.they are nodes

4. points of maximum amplitude where they are in antiphase. They are antinodes.

为何触碰绳子上的驻波节点，不会干扰它的驻波图案？

1.this point is a node, so amplitude is zero

2. Waves continue to move after superposition

弦乐器、管乐器的长度与驻波波长关系：

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6.折射

Refraction 概念：1.Change in direction of wave

2.Due to change of wave speed in two media

如何证明两种材料折射率相同？

1.There is no change in direction for the light passing between A and B

2.The light must have the same wave speed in A and B

解释折射的产生：

1.There is a change in light speed from water to air

2.This causes a change in direction of light (away from normal travelling from

water to air)

3.So light appears to come from a different point of origin

由某材料折射率refractive index = speed of light in air / speed of light in material计算材料中光速、折射率。

画入射、折射光路图。

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7.全反射

Total internal reflection解释：

1.light comes to a boundary from a denser medium to a less dense

medium

2.when angle of incidence is greater than the critical angle

3.All of the light is reflected

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8.干涉

双缝干涉的亮暗条纹如何产生？

1.at a certain point on the screen. When path difference is nλ，two waves are in phase， constructive interference occurs .Light band forms there

2.When path difference is (n + ½ ) λ ，two waves are in antiphase， destructive interference occurs .Dark band forms there.

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9.衍射

Diffraction概念：Waves spread out after passing around an obstacle

在孔或障碍物跟波长相近时，衍射现象明显。

晶体可以当作是X射线的三维衍射光栅,X射线波长,与固体中的原子间距大致相同。

电子束穿过薄的晶体材料射到荧光屏上，产生的什么现象揭示了电子的特性？

1.Electrons spread out and form a diffraction pattern

2.Electrons must behave as waves

3.Because diffraction is wave behaviour

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10.偏振

偏振片polarising filter

振动方向与偏正片方向一致的光才能通过。

When they pass through a polarising filter all the components of the oscillations

perpendicular to the plane of polarisation are blocked. When they pass through a polarising filter all the components of the oscillationsparallel to the plane of polarisation aretransmitted.

The oscillations of the polarised wave are all in the samedirection which is perpendicular to the direction of propogation.

什么是vertically polarised？

1.Unpolarised light has oscillations in all directions

2. Vertically polarised light has oscillation in only one vertical direction

3.this direction is perpendicular to the direction of propagation

为何偏振面互相垂直的two waves不能发生干涉？

1.Oscillations of two waves are perpendicular to each other

2.So there are no opposite components to cancel each other out

3.zero amplitude not possible ,so the waves do not interfere

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11.电磁波谱

频率由大到小：γ-ray，x-ray，ultraviolet，visible light，infrared，microwave，radio

微波microwave对人体危害：1.Human body contains water molecules.

2.cells would be heated.

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12.多普勒效应

Doppler effect

描述多普勒效应：

1. relative motion of source and observer causes change in frequency.

2.If the source is moving towards observer ，the frequency is increased.

3.If the source is moving away from observer, the frequency is decreased.

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13.脉冲回声

脉冲测距，距离d= vt/2，其中t为发出和接受脉冲的时间间隔。

探测距离时，超声为何以脉冲形式发出（emitted in pulse）？

So they can tell which received pulse matches which sent pulse.

一个脉冲能测量的最小距离distance=wave speed×pulse duration/2。

如果对坡面（sloping wall ）发脉冲，pulse will be reflected towards other direction and cannot be received，所以无法测距。