9702-2020-F/M-42

[NaughtyChas]

解析

1(ii)

在场这一块，算变化量最好算出两个状态的量相减。 具体来说，就是不要直接把delta的值带入公式计算。

举个例子，一个卫星高度变化，让我们计算GPE的变化。

GPE=GMm/r，

ΔGPE=GMm/r1 - GMm/r2

而不是

ΔGPE=GMm/Δr。

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2(c)

Describe how movement of the gas molecules causes pressure in the container:

• Molecules collides with wall
• Momentum of molecule changes during cullision with wall
• Force on molecules so force on wall
• Many forces act over surface area of container exerting a pressure.

(d)

<c^2>是mean square speed，加个根号就是root mean square speed。这俩不要混掉了。

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4(a)

Describe why pulses of ultrasound is used in medical diagnosis:

• Allows the reflected signal to be distinguished from the emitted signal
• Cannot emit and detect at the same time so pulse is used.

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8(c)

Why the electrons follow a circular path when inside the region of the magnetic field:

• Force is always perpendicular to velocity
• Magnetic force provide centripetal force
• Magnitude of force is constant

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9(c)

${P}{avg}\ =\ {I}^{2}{r.m.s}R\ =\ (\frac {{I}{r.m.s}} {\sqrt {2}}{)}^{2}R\ =\ \frac {{I}^{2}{0}R} {2}=\frac {{P}_{0}} {2}$

同样也等于Vrms * Irms。

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11(a)

Ek = eV，这就是加速电压和Ek之间的计算式。

在X光产生的过程中，通过这个方式释放出来的能量，最后都会因为碰撞散失掉，所以eV=hf。