Answer:
the focal length of the mirror is : 
Explanation:
Use the formula for the formation of image using a divergent mirror and recalling that the image (s') that this mirror formed is virtual, so it is entered as a negative number in the formula. Use the object position (s) as 10, the image position (s') as -2, and derive the value of the focal length:

Answer:
Option E
Explanation:
In the presence of two point charges at the two vertices of an equilateral triangle, the resultant electric field at the third vertex due to these charges can not be zero whether the charges are identical or not.
The reason being that only of the x or y component of the field can be cancelled out in either case still the total field can't be reduced to zero.
This can only be achieved if another charge is present.
I guess it is a: seismic waves
J.J. Thompson is the scientist who recieved credit for discovering them.