i] Heating elements of electrical heating devices is made up of an alloy rather than a pure metal. Give two reasons.
ii] Four resistors of `2Omega` each are joined end to end to form a square. Calculate the equivalent resistance of the combination between two adjacent corners?

Explanation

i] Heating elements of electrical heating devices are made up of an alloy rather than a pure metal because
a] The resistivity of an alloy is more than the resistivity of a pure metal.
b] Alloy does not burn [or oxidize] easily even at higher temperature.
ii]
Resistors, `R_(1),R_(2)andR_(3)` are in series, therefore their equivalent resistance is
`R_(s)=R_(1)+R_(2)+R_(3)=2+2+2=6`ohm
Now, `R_(s)andR_(4)` are in parallel, therefore equivalent resistance of the combination between two adjacent corners A and D is
`1/R_(p)=1/R_(s)+1/R_(4)=1/6+1/2=2/3`
Therefore, `R_(p)=1.5` ohm