Auroras are frequently seen : B. After solar flares
The Aurora is created by an ongoing influx of particles into the Earth's existing magnetic field,
This particles originated from the Sun as part of Solar wind
hope this helps
Answer:
A. Sulfur _________ group 16 chalcogens
B. Sodium _________ group 1 alkali metals
C. Argon _________ group 18 noble gases
D. Silicon _________ group 14 carbon family
E. Chlorine _________ group 17 halogens
F. Phosphorus_________ group 15 pnicogens
Answer: E = 
Explanation: The formulae for intensity of an electric field of a solid metal sphere relative to a point is given below
r
where
,
, r = 0.1m r = is the position vector of the charge.
it has been stated in the question that the charge is placed at the center thus it has no position vector.

Explanation:
It is given that,
Length of the helicopter, l = 3.1 m
The helicopter rotates, the length of helicopter will become the radius of circular path, r = 3.1 m
Angular speed of the helicopter, 
(a) The centripetal acceleration in terms of angular velocity is given by :



(b) Let v is the linear speed of the tip. The relation between the linear and angular speed is given by :


v = 90.89 m/s

Hence, this is the required solution.