Physics Questions

Electrical discharge machining (EDM), also known as spark machining, spark eroding, burning, die sinking, wire burning or wire erosion, is a manufacturing process whereby a desired shape is obtained by using electrical discharges.

Resistivity :

Resistivity is a measure of the resistance to the flow of electrons. 

Conductivity :

Conductivity is just the inverse of resistivity, σ = 1/ρ, where σ is conductivity and ρ is resistivity.

Example:

Think of a pipe and water, the bigger the pipe, the easier water can flow and thus the lower the resistance. 

Cast iron is a group of iron-carbon alloys with a carbon content greater than 2% and is a brittle material.

Its usefulness derives from its relatively low melting temperature.

From the given circuit,

The resistors R1 and R2 are in parallel connection and R3 is in series with R1 & R2

The equivalent resistance of R1 and R2 is

Req = (12 × 4)/(12 + 4) = 3 Ω.

Adding R3 in series with the pair gives

R = Req + 9

R = 3 + 9

R = 12 Ω.