An electric field mill measures
Answer: C
A rotating shutter modulates the field at a sensing plate to give a measurable signal. Field mills are used to warn of imminent lightning risk at launch sites and airfields. They report conditions rather than completed flashes.
Please log in or register to report this question.
Assertion (A): Field mills are used to issue lightning warnings before any flash occurs.
Reason (R): They detect the rising surface field as charge accumulates overhead.
Answer: D
Both are true and the reason gives the anticipation, and this is why they are installed at rocket launch facilities. Detection networks by contrast report only flashes that have already happened. Anticipation is what makes the field mill valuable.
Please log in or register to report this question.
The potential of the electrosphere (ionosphere) is positive with respect the Earth and its magnitude is about :
MH SET - 2018, SET Exam - 2018,
Answer: C
The ionosphere's potential relative to the earth is about 300 kV.
In the global atmospheric electric circuit, thunderstorms act as generators that charge the upper atmosphere (the electrosphere) positively with respect to the ground. The resulting potential difference is about 250-300 kV, which drives a small fair-weather current downwards and produces the surface electric field of about 100 V/m.
1000 kV and 2000 kV are several times too large, and 10 kV is far too small for this ionospheric potential.
Please log in or register to report this question.
