Where is the magnetic field of point p pointed

What do we mean by the event horizon of a black hole?

How is an electron dot structure used to represent a covalent bond?

12. ritu obtained a distinct image of a distant tree on the screen with the of a concave mirror.to find the focal length of the mirror she has to measure the distance between: (a) mirror and the tree. (b) screen and the tree.(c) mirror and the screen. (d) mirror and tree as well as between screen and the tree.