An airplane black box contains a bunch of unknown resistances and batteries con- nected in unknown way such that (1) a 9 Ohm resistor across the terminals of the circuit box draws 0.80 A, and (2) an 17 Ohm resistor draws 0.50 A. What resistance will draw 0.12 A

The unknown resistance which will draw a current of 0.12 A is 84.5 ohm

Explanation:

Let say the emf of the cell is E and internal resistance of the system is "r"

now we will have

here we have 9 ohm resistance draw current of 0.80 A

also we know that 17 ohm resistance will draw current of 0.50 A

so we will have

also we have

now when 0.12 A current is drawn across unknown resistance then we have

so we have

if the person is shown to have +90n, then ans is -10n.

if the person is shown to have -90n, then ans is +10n.

answer: the metamorphic rocks are formed when they are exposed to high pressure and high temperatures. this happens when one of the earth's plates comes in contact with the other plate by traveling in opposite directions, straight into each other or slipping under one another. the friction that is caused by this activity results in   melting of rocks and when it cools they are known as metamorphic rocks. this process needs a controlled amount of pressure and temperature otherwise it may turn into magma.