Given :
The ball of a ballpoint pen is 0.5 mm in diameter and has an ASTM grain size of 12.
To Find :
How many grains are there in the ball?
Solution :
Volume of ball of the ballpoint is :

Now, grain size of 12 has about 520000 grains/mm³.
Therefore, number of grains are :

Battery based heaters use electric resistance heating, which uses a lot of current (electricity) to create the heat.
Exert force upward.
Like when you pick something up from the floor, or walk up the stairs.
Answer:
I'm pretty sure the answer you selected is correct.
Explanation: