f5phy 解答 wave motion 題目

Remember, speed of a wave depends on the material travelling.
All the waves, no matter EM wave, transverse wave, longitudinal follow this theory.
For example, speed of light is always 3*10^8 ms-1 in vacuum
in other material, such as water or diamond is slower.
Speed of sound in air is always about 333ms-1 and faster in some solid, such as iron 5000ms-1

so
Q1 velocity no change, u flick faster will only increase the frequency. And so the wavelength will decrease.
your v=f*lambda is correct, however, u assumed wavelength has no change. but the fact is the speed no change.

Q2 as mentioned above. speed no change
frequency increase and wavelength decrease.

Q3 Basically frequency depends on how you produce the wave. For example, atomic vibration to produce EM wave, your hand's vibration produce transverse wave. And your vocal chord's vibration determines ur sound's frequency.
And speed determined by many factors. in general, the speed of mechanical wave can be calculated by v=sqrt(elastic property/inertial property). This formula is excellent for a transverse wave travelling on a rope v=sqrt(tension/material density). For other waves, such as sound wave, also obey similar expression v=sqrt(Young's modulus/air density) and also it vary when temperature changes.
Furthermore, transverse wave and longitudinal wave may travel in different speed even in same matter. such as the P wave and S wave of earthquake wave.
For EM wave, it depends of the permeability of electric field and magnetic field. Also, the frequency of light also affects the speed, otherwise rainbows would not appear.
Wavelength is determined by the combination of speed and frequency


2011-04-25 23:00:57 補充：
The wavespeed formula's proof requires some mathematical skill. But u can find it in almost every university textbook. you can borrow them in public library if interest

1. The speed of a transverse wave on a spring dpeneds on the spring tension and linear density (i.e. mass per unit length) of the spring.

The frequency of flicking the spring doesn't alter either one of them. Hence, the speed of the wave remains unchanged.

The increase in frequency leads to the decrease of wavelength of the transverse wave, which you could have observed on the spring.

2. As explained above, flicking the spring in a faster rate would generate a wave with higher frequency, with a corresponding reduction in wavelength. The wave speed is unaltered.

Therefore, the only physical quantity to be increased is frequency.

3. The wave speed v on a spring under tension T is given by the following relation:

v = square-root[T/p]
where p is the linear density of the spring

Hence, the wave speed will increase by increasing the tension and vice versa