1.   This questions is based on the Doppler effect, for which the following thumb rule would be useful.

Associate the words TOWARDS with a frequency increase and the words AWAY FROM with a frequency increase. In this case as the train is moving towards the stationary observer the APPARENT frequency will increase and as the train moves away from the stationary observer the apparent frequency would decrease.

2.   This notion of extended source is more common in the formation of shadows. For example, a lamp can act as an extended source and doesn't always produce a sharp shadow, whereas a point source usually produces a sharp shadow.

    In the case of observing colours in thin films, the physics is due to what's popularly called 'thin film interference'. To observe interference one must have TWO COHERENT sources. The sources when extended produce what's called a PLANE wavefront. The pattern of colours would become difficult to study with a point source which which would produce a spherical wavefront. A wavefront is simply the locus of all points that are in the same state of vibration, say all crests or all troughs.

    Even with a plane wavefront, the physics is quite involved. Interference takes place between the wavefronts reflected off the top surface and the wavefront that has been refracted and then reflected at the bottom surface and finally refracted again. It can be shown mathematically that this causes a difference in path the two wavefronts have travelled that results in a difference of 2(mu)(t)cos(r). Don't worry about the formula and its subsequent modifications but what you need to know is the two coherent plane wavefronts from the top AND bottom of the thin film such as a soap bubble, small oil slick, air wedge and so on.

3.   Ultraviolet rays as you know cannot be detected directly by the human eye. However they can be converted to visible light throught the process called fluorescence, similar to what happens in the popular fluorescent lighting.

We had this problem a few years ago of studying Solar Radiation for our Grade 12 student Group 4 Project. For a while the students were struggling about how to measure that from the sun but once told them about this techniuque using fluorescence, they did scores of experiments in physics, chemistry and biology. We used the fluorescene sodium that was available in the lab as one of the basic components of a model eye kit. We used this to suit our convenience without resorting to buying expensive equipment when we coupled them with our light sensors.

The other method you could use to detect UV is to use its capacity to cause photoelectric effect in several material including zinc which is widely used for laboratory demonstrations.

4.   "Light" travels very fast almost a million times faster than sound. However even its speed is limited and it is for the same reason why when you're seeing the sun now, it's actually how is was EIGHT minutes and twenty seconds ago!

The television interviews are transmitted using one kind of "light" waves called MICROWAVES. They belong to the same family but have a much longer space between the waves (physicists call that WAVELENGTH).

The microwaves are usually sent into space and reflect of satellites carrying the information CODED in them. Obviously the distance they have to travel being larger, the pause you observe appears longer.

Have you made international calls or used a telephone to call your mobile placed next to you. You'll find the same long pause you're observed. Even if your mobile phone is next to your telephone, the signal has to be sent into space and then comes back to find your mobile a while later. Try it.

5.   I'll suggest a websites where you can find interesting information.

    http://www.howstuffworks.com/radar.htm