Physics Website Review
Working principle of Radar
Source: http://science.howstuffworks.com/radar2.htm
Sonar and radar systems are actually quite similar. Both of them use the theory that waves will reflect when they hit on an obstacle. However, sonar system requires sound waves while radar system requires radio waves.
The working principle of radar is that, a transmitter will emit high-frequency radio waves at first. Afterwards, antenna will receive the echo to be received and the Doppler shift can be measured. The distance between the antenna and the obstacle which causes the reflection of the waves can thus be calculated.
When radar is ground-based, there are many obstacles which will give out the echo, but not the target objects. Thus, the unwanted echo needs to be filtered by recognizing that it is not Doppler-shifted. Therefore, radar has many important applications in our daily lives.
By Ginny
Spinning neutron star
Source: http://physicsweb.org/articles/news
This news reported astronomers found the fastest spinning neutron star recently. Spinning neutron star calls pulser and most of them rotate slower than a few times a second. They are extremely dense stars that are heavier than the Sun. But neutron stars in binary systems can spin several hundreds of times a second. It is because their companion stars transfer angular momentum to them.
It is difficult to find this neutron star since it is eclipsed by its companion star for over 40% of the time.
By finding the sizes of the of neutron stars, scientist can constrain the equation of state of matter at supranuclear densities. This can help us understand the behaviour of matter at these extreme conditions. I hope the astronomers can find a even more faster neutron star, so that we can understand more clear of matter in our universe.
By Vicky