What must be present in any population before selection, either artifical or natural that can bring about changes?

A charged particle moving with a uniform velocity vecv enters a region where uniform electric and magnetic fields vecE and vecB are present. It passes through the region without any change in its velocity. What can we conclude about the magnitude of vecE and vecB ?

Write what do you know about Natural Selection or Survival of the fittest.

A charged particle moving with a uniform velocity vecv enters a region where uniform electric and magnetic fields vecE and vecB are present. It passes through the region without any change in its velocity. What can we conclude about the relative direction of vecE , vecv and vecB?

Three students X,Y and Z performed an experiment for studying the variation of alternating currents with angular frequency in a series LCR-circuit and obtained the graphs shown in the figure They all used a.c sources of the same r.m.s. value and inductances of the same value. What can we conclude about the capacitance value. What can we conclude about nature of the impedance of the set up at frequency omega_0 ?

Give the technical terms used for the following: The chemicals which can be sprayed on the leaves to either bring about closure of stomata or to form aflim on their surface to check transpiration.

What is population density ? Explain any three different ways the population density can be measured with the of an example of each.

The population of a village increases continuously at the rate proportional to the number of its inhabitants present at any time. If the population of the village was 20, 000 in 1999 and 25000 in the year 2004, what will be the population of the village in 2009?