A copper transmission cable 140 {\rm km} long and 12.5 {\rm cm} in diameter carries a current of 115 {\rm A}.

1.What is the potential drop across the cable?
2.How much electrical energy is dissipated as thermal energy every hour?

1.

2.

Explanation:

Given:

length of copper cable,

diameter of copper cable,

current through the copper wire,

We have the resistivity of copper,

We know that the resistance of a wire is given as:

where:

cross sectional area of the wire

1.

Now from the  Ohm's law:

2.

From the Joules law the thermal energy generated as an effect of electrical energy is mathematically given as:

where:

time duration for which the current flows

(∵ we have 3600 seconds in 1 hour)

work: w = fd (given)

work done by chet   =50*1 = 50 j

work done by mika =40*2 = 80 j

work done by sara =30*1.5 = 45 j

work done by bill =60*0.5 = 30 j

students in order from the greatest amount of work done to the least is mika> chet> sara> bill

hence option (b) is correct.

the amount of current in the coil