Question

Value of H on Earth’s surface is
A. 0.32G
B. 0.32T
C. $0.32\times {{10}^{-4}}G$
D. $0.32\times {{10}^{-5}}T$

Answer 1

Hint: As a first step find out what quantity is represented by letter H. You could also get help from the units of the given options in finding out the quantity. When you realize what quantity it is, recall the value or at least the range of values that is measured on the surface of earth for this quantity. H represents the value of magnetic intensity with respect to the earth’s surface

Complete answer:
We know that H is the magnitude of earth’s magnetic field. Earth’s magnetic field is the field from the interior of earth to space. In outer space it gets to interact with the solar wind (charge particles from the sun). The creation of these fields is due to the flow of convection currents in the outer core of Earth.
Now let us come back to the discussion on the magnitude of these fields. The strength of the magnetic field lines on the earth’s surface is found to range from less than 30microteslas (as measured in areas of South America and South Africa) to over 60microteslas (as measured around the magnetic poles in Canada, south of Australia and also some parts of Siberia).
We know that one tesla is given by${{10}^{4}}$ gauss. So, 30microteslas can be given by,
$1T={{10}^{4}}G$
$\Rightarrow 30\times {{10}^{-6}}T=30\times {{10}^{-6}}\times {{10}^{4}}G$
$\Rightarrow 30\times {{10}^{-6}}T=30\times {{10}^{-2}}G=0.3G$
Similarly, 60 microteslas can be given by,
$1T={{10}^{4}}G$
$\Rightarrow 60\times {{10}^{-6}}T=60\times {{10}^{-6}}\times {{10}^{4}}G$
$\Rightarrow 60\times {{10}^{-6}}T=60\times {{10}^{-2}}G=0.6G$
 Now that we have converted the given range of values in microteslas to gauss we get that the field strength H varies from less than 0.3G to over 0.6G. So, among the given values we see that 0.32 G falls in this range.

So, the correct answer is “Option A”.

Note:
If you wish to understand how strong this field intensity is, we could compare this value with some magnet that we come across in our daily life. A strong refrigerator magnet is expected to have a field of intensity of 100G. Also the value of H tends to decrease from the poles to the equator.